Advanced Science, Engineering and Medicine, Volume 12, Number 3, pp. 289-313(25), March, 2020
Mirror symmetry is found to be the only fundamental symmetry in crystalline solids because all ot... more Mirror symmetry is found to be the only fundamental symmetry in crystalline solids because all other symmetries, such as rotation, inversion, rotoreflection, rotoinversion and translational periodicity can be easily derived from suitable combinations of mirrors. Similarly, the point group symmetries can also be derived from the same. The mirror combination scheme is found to work in accordance with the principle of Wigner-Seitz cells and Brillouin Zones (and not with the conventional unit cells as proposed by Bravais), where the zone boundaries of a Brillouin zone represent different sets of Bragg planes obtained from diffraction pattern of the given crystal, while the diffraction of given crystal takes place in terms of decreasing interplanar spacing in reciprocal space. Because the Wigner Seitz cells, the Brillouin zones and the diffraction patterns possess defined origin and exhibit spherical symmetry, they cannot have translational symmetry of any kind (microscopic or macroscopic). Results obtained on the basis of this concept help us to remove the existing ambiguities in crystallography and make the crystal structure determination simple. Further, prima facie the diffraction patterns are found to take care of the proposed 'systematic absences' arising due to the so called lattice centering, glide planes and screw axes without actually taking them into consideration. This newly and first discovered concept is expected to explain all other complicated or less understood issues related to crystallography.
Advanced Science, Engineering and Medicine, Volume 11, Number 12, pp. 1179-1186(8), December, 2019
An ab-initio calculation of angles has been made between various directions on close packed basal... more An ab-initio calculation of angles has been made between various directions on close packed basal plane with the tilted axis obtained by placing identical atoms on voids. Results obtained from simple calculations provide a lot of important information related to Rhombohedral Close Packed and Hexagonal Close Packed structures, effectively leading to their discovery as independent and genuine space lattices from close packed category of materials. En-route, we also propose a separate equation to calculate the angles between two given directions in the above mentioned close packed crystal systems. Modes of polytype formation in close packing of identical atoms is also briefly discussed.
Materials Focus, Volume 7, Number 3, pp. 321-332(12), June, 2018
For the first time, a large number of geometrically possible rhombohedral modifications (polytype... more For the first time, a large number of geometrically possible rhombohedral modifications (polytypes) have been found to exist in close packing of identical atoms (spheres). The stacking sequence ABC : A... is found to be common to all rhombohedral unit cells. The unit cell volumes of increasing cell height corresponding to this sequence exhibit an interesting geometric series. Polytypic transformations in both hexagonal close packed (HCP) and rhombohedral close packed (RCP) structures have been studied using the ab-initio process. The results obtained from the same are interesting and will be extremely useful in explaining the transformations occurring in the real structures of close packed elements and MX compounds.
Materials Focus, Volume 7, Number 2, pp. 223-231(9), April, 2018
In this paper, genesis and formation of hexagonal close packed (HCP) polytypes from the packing o... more In this paper, genesis and formation of hexagonal close packed (HCP) polytypes from the packing of identical spheres (atoms) have been investigated using a step by step process. The detailed theoretical analysis of the results suggest that both HCP and RCP (rhombohedral close packed) are inherently related to each other and suitable orientations of these units take part in the formation of higher order HCP polytypes. The results shown by the arrangements of three layer sequences (viz. ABA and ABC) have lead to modify the very old Jagodjinski's criteria.
Based on identical sphere (atom) models, a comprehensive study of SH and HCP has been carried out... more Based on identical sphere (atom) models, a comprehensive study of SH and HCP has been carried out for the first time by constructing the unit cells (e.g. the conventional, primitive, Wigner–Seitz, reciprocal and Brillouin zone) of HCP and comparing them with their SH counterparts to resolve the existing ambiguities between them. This has been further supported by a comprehensive crystallographic calculation. Similarly, a thorough study of symmetry of the two unit cells has been carried out to decide their positions in the final crystal system table. The geometrical study suggests the existence of rhombohedral close packing (RCP) and its inherent structural connection with HCP throughout (i.e. as its primitive cell, etc.). Similarly, the study of symmetry suggests the existence of a Trigonal unit cell and its inherent association with SH throughout as a symmetry derivative. The present study resolves clearly that SH, Trigon, HCP and RCP are exclusive and independent lattices where HCP and RCP are exclusively associated with the close packing of identical atoms and hence proposed to be included as independent members of the space lattices. Henceforth, the two new lattices will be called as Wahab lattices (or W lattices) and the sixteen lattices together as Bravais-Wahab lattices (or BW lattices) or simply space lattices as before. The sixteen lattices have been divided into eight crystal systems in the order of their increasing symmetry. The results obtained from the present study help explain the existence of 73 symmorphic space groups in 3-dimensional crystal system. These findings will have immediate as well as far reaching implications.
Single crystals of LTA were grown by slow evaporation solution technique (SEST). Powder X-ray dif... more Single crystals of LTA were grown by slow evaporation solution technique (SEST). Powder X-ray diffractometry (PXRD) confirmed the monoclinic crystal structure, whereas the high resolution X-ray diffractometry (HRXRD) ascertained the good crystalline perfection (FWHM=25 arcsec) of the as-grown single crystal. Optical study demonstrated the high optical transparency (85%). Photoluminescence (PL) spectroscopy illustrated the PL-emission at λ=388 nm and optical band gap ~3.2 eV. The SHG efficiency of LTA single crystal (6.61) is comparatively greater than the referenced (KDP) single crystal (6.08). Thermal analysis revealed that the crystal is thermally stable up to ~170 °C. The calculated value of the activation energy (ΔE) and corrected hardness (H0) for the crystal were found to be equal to 1.16 eV and 46.66 kg/mm2, respectively. The as-grown LTA single crystals can be used as a potential candidate for NLO material as well as in electronic and optoelectronic devices.
Hindawi Publishing Corporation Journal of Polymers, Volume 2014, May, 2014
Acrylic resin (AR) based electromagnetic interference (EMI) shielding composites have been prepar... more Acrylic resin (AR) based electromagnetic interference (EMI) shielding composites have been prepared by incorporation of up to 30 wt% activated charcoal (AC) in AR matrix. These composites have been characterized by XRD, Raman spectroscopy, scanning electron microscopy, dielectric, and EMI shielding measurement techniques. XRD patterns and Raman studies confirm the incorporation of AC particles inside AR matrix and suggest possible interactions between phases. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites especially the formation of porous structure. The dielectric measurements show that 30 wt% AC loading composite display higher relative permittivity value (~79) compared to pristine AR (~5). Further, the porous structure, electrical conductivity, and permittivity value contribute towards EMI shielding effectiveness value of −36 dB (attenuation of >99.9% of incident radiation) for these composites, thereby demonstrating their suitability for making efficient EMI shielding coatings.
Indian Journal of Pure and Applied Physics, Volume 52(3):192-197, March, 2014
Polyvinylpyrrolidone (PVP) doped with different silver concentration (Ag: PVP) composites were pr... more Polyvinylpyrrolidone (PVP) doped with different silver concentration (Ag: PVP) composites were prepared by simple solution casting technique using PVP and silver nitrate. The structural, morphological and optical properties of these as grown composites were characterized by powdered X-ray diffraction, SEM, FTIR and UV-VIS techniques. XRD patterns confirm the incorporation of Ag particles in PVP matrix and indicate the improvement in polycrystalline behaviour by the appearance of more diffraction peaks with increased intensity on increasing AgNO3 concentration in the composites. SEM images reveal the uniform dispersion and increased densification of Ag particles in PVP matrix. Infrared transmission spectra recorded in 4000-400 cm-1 region show the characteristic peaks of PVP bonding groups with the minor shift in their position due to Ag doping. UV-VIS spectroscopy results reflected that absorption increases in asymmetric manner and the absorption peak showed red shift with increasing dopant concentration. These results showed that the simple synthesis process can be used for the preparation of such composites suitable for various practical applications.
Indian Journal of Pure & Applied Physics, Vol. 52, pp. 251-254, April, 2014
Activated Charcoal (AC) filled acrylic resin (AR) based composites have been prepared by solution... more Activated Charcoal (AC) filled acrylic resin (AR) based composites have been prepared by solution processing technique. Different compositions were formulated by variation of AC content between 1 to 30 wt % and the formed composites have been characterized by various techniques to establish a correlation between the filler concentration and the structural, thermal, electrical and morphological attributes. The FTIR spectra show the presence of AC in AR matrix whereas XRD patterns confirm the incorporation of AC particles between lamellar structures of AR. The TGA investigation
revealed that composites are thermally stable up to 200°C after which they display multistep weight loss due to removal of functional groups and decomposition/carbonization of AC as well as polymeric backbone of AR. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites. The electrical measurements show that 30 wt % AC loading composite displays much lower resistivity (104 /Sq) as compared to pure AR (1011 /Sq) and suggest its suitability as static dissipative material. Further, the porous structure and electrically conducting nature of the composites suggest their suitability for making electromagnetic interference shielding coatings.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 123, Pages 376-384, April, 2014
Single crystals of pure and l-Proline (LP) C5H9NO2 doped ammonium dihydrogen phosphate (ADP) (NH4... more Single crystals of pure and l-Proline (LP) C5H9NO2 doped ammonium dihydrogen phosphate (ADP) (NH4) H2PO4 were grown by slow evaporation solution technique (SEST) at ambient conditions. Powder X-ray diffraction (PXRD) analysis was carried out to confirm the crystal structure and no additional phase was observed due to doping except a systematic variation in peak intensities. FT-Raman analysis also confirms that there is no additional phase formation due to doping. Fourier transform infrared spectral analysis was done to examine the presence of various functional groups in the grown crystals. UV–VIS–NIR spectroscopic analysis was carried out to see the change in optical transparency of pure ADP and crystals due to LP with different doping concentrations. The high-resolution X-ray diffraction (HRXRD) analysis was carried out to examine the crystalline perfection and observed reasonable changes with LP doping. Second harmonic generation (SHG) efficiency measurement was done to examine the enhancement in the nonlinear optical characteristics of the grown crystals. The dielectric behavior of the samples shows that the dielectric constant decreased with increase the value of frequency. The effect of LP dopant on crystal morphology, mechanical properties of ADP has also been presented in this paper. The above studies reveal the effect of incorporation of LP into the lattice of ADP crystals.
Journal of Advanced Physics, Volume 3, Number 1, pp. 64-66(3), March, 2014
Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has ... more Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has been performed to verify the phase transformations in polymorphic and polytypic MX type compounds. We measured radial distribution function, total energy and specific heat variation with temperature in CuBr and AgI and confirmed the phenomena of polymorphism and polytypism respectively in these two compounds.
Journal of Advanced Physics, Volume 2, Number 3, pp. 196-199(4), September, 2013
Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has ... more Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has been performed to verify the phase transformations in polymorphic and polytypic elements. We measured radial distribution function, total energy and specific heat variation with temperature in Nickel and Cobalt and confirmed the phenomena of polymorphism and polytypism respectively in these two compounds.
Materials Focus, Volume 2, Number 4, pp. 293-297(5), August, 2013
The LJ parameters have been optimized for AgI, which reproduced successfully the zinc blend struc... more The LJ parameters have been optimized for AgI, which reproduced successfully the zinc blend structure of AgI. The RDF peaks are seen to be broadening and decrease in height with increasing temperature, reflecting enhanced atomic motions. The first peak value has been found to decrease from 2.325 to 2.275 Å, which indicates that Ag I pair comes closer to each other and consequently the bond becomes stronger and molecular in nature. Energy temperature graph does not show any break while a break in the specific heat curve and type transformation are observed. These indicate the second order transformation in AgI and hence polytypic in nature. The maximum disorderness has been observed at 410 K, which is the transformation temperature. The straight-line curve between lnD and 1/T each for Ag and I atoms confirm a well-known Arrhenius plot which also validates our present MSD data.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 103, Pages 199-204, February, 2013
Good quality single crystals of potassium dihydrogen orthophosphate (KDP) were grown with differe... more Good quality single crystals of potassium dihydrogen orthophosphate (KDP) were grown with different doping concentration of Glycine by conventional solution technique in aqueous solution. X-ray diffraction study has been carried out in order to see the effect of dopant on the structural parameters of KDP. There is no additional phase was observed which was further confirmed by Raman spectroscopic analysis. The second harmonic generation efficiency was measured by using Kurtz powder technique. The relative second harmonic generation (SHG) efficiency of the grown crystals was found to be increased with doping concentration up to 2.5 mol%. Optical transmission study also revealed the same behaviour with enhancement up to 2.5 mol% concentration and later decreased but still higher than pure KDP. The mechanical strength was found to increase with increasing the doping concentration.
Journal of Advanced Physics, Volume 2, Number 3, pp. 235-240(6), September, 2013
The crystallographic data of elements existing at room temperature or above have been reviewed on... more The crystallographic data of elements existing at room temperature or above have been reviewed on different basis i.e., the crystal system (crystal symmetry), axial ratio and packing efficiency to know the general nature of distribution of elements based on symmetry. In order to know which of the polymorphic elements will likely to behave as polytypic, the cohesive energies of all the polymorphs have been calculated using 6–12 potential energy equation. The energy difference between the polymorphic forms has been measured in each case to explore the possible reason/condition for a polymorphic element to exhibit polytypism. On that basis it is proposed that cobalt and thorium should also exhibit polytypism.
In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPC... more In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPCCM) by slow evaporation solution technique (SEST) at room temperature and recorded their live growth kinetics with the help of inverted microscope. Crystal size at various stages of growth and its corresponding morphology was also recorded. Powder X-ray diffraction (PXRD) analysis of LPCCM single crystals confirmed the orthorhombic structure. Respective values of crystallite size, strain and dislocation density have been calculated using PXRD data. Metal complex coordination of the single crystal is studied by FTIR spectroscopic. The optical properties of the grown crystals were investigated through UV–VIS spectroscopic studies and shows that the crystals have very low absorption in entire characterized wavelength range 200–800 nm. The optical band gap was calculated and found to be ∼5.6 eV. Optical constants of the material is determined by theoretical calculations. The chemical etching study was also carried out to study the density of defects in the grown crystals. The photoluminous excitation and emission spectra and thermal property by TGA/DTA curve were recorded. Further, the mechanical properties have been studied using Vicker's microhardness tester as well as many parameters such as fracture toughness (Kc), Brittleness index (Bi) and yield strength (σν) are presented. Dielectric studies have been carried out with varying frequency and temperatures.
Radiation Effects and Defects in Solids, Volume 168, 2013 - Issue 9, 2013
The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been gr... more The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been grown by the slow evaporation solution growth technique using N, N-dimethylformamide as the solvent. Single crystals of pure HA were irradiated at room temperature with 100 keV Nitrogen (N+) ions at fluence 1×1016 and 5×1016 ions/cm2. The pure and irradiated HA single crystals were characterized by different characterization technique. The photoluminescence and UV–visible absorption were performed at room temperature. The crystalline perfection of the pure and irradiated single crystals has been examined by high-resolution X-ray diffraction. Vickers microhardness technique was used to study the effect on the mechanical strength of the crystal at different ion fluences. The structural changes were analyzed by powder X-ray diffraction analysis. The functional groups of the synthesized compound have been identified by Fourier transform infrared spectroscopy. The dielectric constant and dielectric loss as a function of frequency were analyzed at room temperature.
In this work, the single crystals of thiourea cadmium iodide were grown by slow evaporation solut... more In this work, the single crystals of thiourea cadmium iodide were grown by slow evaporation solution technique in two different ratios 2:1 and 1:1. During the formation of their single crystals the morphological features and its live growth process were recorded with the help of inverted microscope. Structural studies of the grown crystals have been carried out by powder X-ray diffraction to confirm the crystal system and vibrational modes by Raman spectroscopy. The optical energy band gaps were investigated through UV–vis spectroscopy study. The surface morphology of the grown single crystals was analyzed by using Scanning Electron Microscope and thermal analysis was carried out by using thermogravimetric analysis. The electrical properties were also studied as a function of frequency and the obtained results are discussed.
Zr–Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. Th... more Zr–Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. The crystal structure and lattice parameter of the grown crystals were assessed by powder X-ray diffraction and the strain developed as a result of doping has been calculated (−1.19 × 10−3) by using the Williamson–Hall relation. The incorporated dopant concentration along with the dopant distribution in the specimen crystal was estimated by X-ray florescence spectrometry. A multi-crystal X-ray diffraction analysis was carried out to identify the crystalline perfection of the sample and revealed that the investigated crystal does not contain any structural grain boundaries but does contain point defects and micrometre size mosaic blocks. Birefringence measurements were carried out using a prism coupler spectrometer and found that the optical birefringence is 0.0822 for 532 nm and 0.705 for 1064 nm. A thermal conductivity (κ) study reveals that the doped sample has a lower κ value than the undoped equivalent.
Advanced Science, Engineering and Medicine, Volume 12, Number 3, pp. 289-313(25), March, 2020
Mirror symmetry is found to be the only fundamental symmetry in crystalline solids because all ot... more Mirror symmetry is found to be the only fundamental symmetry in crystalline solids because all other symmetries, such as rotation, inversion, rotoreflection, rotoinversion and translational periodicity can be easily derived from suitable combinations of mirrors. Similarly, the point group symmetries can also be derived from the same. The mirror combination scheme is found to work in accordance with the principle of Wigner-Seitz cells and Brillouin Zones (and not with the conventional unit cells as proposed by Bravais), where the zone boundaries of a Brillouin zone represent different sets of Bragg planes obtained from diffraction pattern of the given crystal, while the diffraction of given crystal takes place in terms of decreasing interplanar spacing in reciprocal space. Because the Wigner Seitz cells, the Brillouin zones and the diffraction patterns possess defined origin and exhibit spherical symmetry, they cannot have translational symmetry of any kind (microscopic or macroscopic). Results obtained on the basis of this concept help us to remove the existing ambiguities in crystallography and make the crystal structure determination simple. Further, prima facie the diffraction patterns are found to take care of the proposed 'systematic absences' arising due to the so called lattice centering, glide planes and screw axes without actually taking them into consideration. This newly and first discovered concept is expected to explain all other complicated or less understood issues related to crystallography.
Advanced Science, Engineering and Medicine, Volume 11, Number 12, pp. 1179-1186(8), December, 2019
An ab-initio calculation of angles has been made between various directions on close packed basal... more An ab-initio calculation of angles has been made between various directions on close packed basal plane with the tilted axis obtained by placing identical atoms on voids. Results obtained from simple calculations provide a lot of important information related to Rhombohedral Close Packed and Hexagonal Close Packed structures, effectively leading to their discovery as independent and genuine space lattices from close packed category of materials. En-route, we also propose a separate equation to calculate the angles between two given directions in the above mentioned close packed crystal systems. Modes of polytype formation in close packing of identical atoms is also briefly discussed.
Materials Focus, Volume 7, Number 3, pp. 321-332(12), June, 2018
For the first time, a large number of geometrically possible rhombohedral modifications (polytype... more For the first time, a large number of geometrically possible rhombohedral modifications (polytypes) have been found to exist in close packing of identical atoms (spheres). The stacking sequence ABC : A... is found to be common to all rhombohedral unit cells. The unit cell volumes of increasing cell height corresponding to this sequence exhibit an interesting geometric series. Polytypic transformations in both hexagonal close packed (HCP) and rhombohedral close packed (RCP) structures have been studied using the ab-initio process. The results obtained from the same are interesting and will be extremely useful in explaining the transformations occurring in the real structures of close packed elements and MX compounds.
Materials Focus, Volume 7, Number 2, pp. 223-231(9), April, 2018
In this paper, genesis and formation of hexagonal close packed (HCP) polytypes from the packing o... more In this paper, genesis and formation of hexagonal close packed (HCP) polytypes from the packing of identical spheres (atoms) have been investigated using a step by step process. The detailed theoretical analysis of the results suggest that both HCP and RCP (rhombohedral close packed) are inherently related to each other and suitable orientations of these units take part in the formation of higher order HCP polytypes. The results shown by the arrangements of three layer sequences (viz. ABA and ABC) have lead to modify the very old Jagodjinski's criteria.
Based on identical sphere (atom) models, a comprehensive study of SH and HCP has been carried out... more Based on identical sphere (atom) models, a comprehensive study of SH and HCP has been carried out for the first time by constructing the unit cells (e.g. the conventional, primitive, Wigner–Seitz, reciprocal and Brillouin zone) of HCP and comparing them with their SH counterparts to resolve the existing ambiguities between them. This has been further supported by a comprehensive crystallographic calculation. Similarly, a thorough study of symmetry of the two unit cells has been carried out to decide their positions in the final crystal system table. The geometrical study suggests the existence of rhombohedral close packing (RCP) and its inherent structural connection with HCP throughout (i.e. as its primitive cell, etc.). Similarly, the study of symmetry suggests the existence of a Trigonal unit cell and its inherent association with SH throughout as a symmetry derivative. The present study resolves clearly that SH, Trigon, HCP and RCP are exclusive and independent lattices where HCP and RCP are exclusively associated with the close packing of identical atoms and hence proposed to be included as independent members of the space lattices. Henceforth, the two new lattices will be called as Wahab lattices (or W lattices) and the sixteen lattices together as Bravais-Wahab lattices (or BW lattices) or simply space lattices as before. The sixteen lattices have been divided into eight crystal systems in the order of their increasing symmetry. The results obtained from the present study help explain the existence of 73 symmorphic space groups in 3-dimensional crystal system. These findings will have immediate as well as far reaching implications.
Single crystals of LTA were grown by slow evaporation solution technique (SEST). Powder X-ray dif... more Single crystals of LTA were grown by slow evaporation solution technique (SEST). Powder X-ray diffractometry (PXRD) confirmed the monoclinic crystal structure, whereas the high resolution X-ray diffractometry (HRXRD) ascertained the good crystalline perfection (FWHM=25 arcsec) of the as-grown single crystal. Optical study demonstrated the high optical transparency (85%). Photoluminescence (PL) spectroscopy illustrated the PL-emission at λ=388 nm and optical band gap ~3.2 eV. The SHG efficiency of LTA single crystal (6.61) is comparatively greater than the referenced (KDP) single crystal (6.08). Thermal analysis revealed that the crystal is thermally stable up to ~170 °C. The calculated value of the activation energy (ΔE) and corrected hardness (H0) for the crystal were found to be equal to 1.16 eV and 46.66 kg/mm2, respectively. The as-grown LTA single crystals can be used as a potential candidate for NLO material as well as in electronic and optoelectronic devices.
Hindawi Publishing Corporation Journal of Polymers, Volume 2014, May, 2014
Acrylic resin (AR) based electromagnetic interference (EMI) shielding composites have been prepar... more Acrylic resin (AR) based electromagnetic interference (EMI) shielding composites have been prepared by incorporation of up to 30 wt% activated charcoal (AC) in AR matrix. These composites have been characterized by XRD, Raman spectroscopy, scanning electron microscopy, dielectric, and EMI shielding measurement techniques. XRD patterns and Raman studies confirm the incorporation of AC particles inside AR matrix and suggest possible interactions between phases. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites especially the formation of porous structure. The dielectric measurements show that 30 wt% AC loading composite display higher relative permittivity value (~79) compared to pristine AR (~5). Further, the porous structure, electrical conductivity, and permittivity value contribute towards EMI shielding effectiveness value of −36 dB (attenuation of >99.9% of incident radiation) for these composites, thereby demonstrating their suitability for making efficient EMI shielding coatings.
Indian Journal of Pure and Applied Physics, Volume 52(3):192-197, March, 2014
Polyvinylpyrrolidone (PVP) doped with different silver concentration (Ag: PVP) composites were pr... more Polyvinylpyrrolidone (PVP) doped with different silver concentration (Ag: PVP) composites were prepared by simple solution casting technique using PVP and silver nitrate. The structural, morphological and optical properties of these as grown composites were characterized by powdered X-ray diffraction, SEM, FTIR and UV-VIS techniques. XRD patterns confirm the incorporation of Ag particles in PVP matrix and indicate the improvement in polycrystalline behaviour by the appearance of more diffraction peaks with increased intensity on increasing AgNO3 concentration in the composites. SEM images reveal the uniform dispersion and increased densification of Ag particles in PVP matrix. Infrared transmission spectra recorded in 4000-400 cm-1 region show the characteristic peaks of PVP bonding groups with the minor shift in their position due to Ag doping. UV-VIS spectroscopy results reflected that absorption increases in asymmetric manner and the absorption peak showed red shift with increasing dopant concentration. These results showed that the simple synthesis process can be used for the preparation of such composites suitable for various practical applications.
Indian Journal of Pure & Applied Physics, Vol. 52, pp. 251-254, April, 2014
Activated Charcoal (AC) filled acrylic resin (AR) based composites have been prepared by solution... more Activated Charcoal (AC) filled acrylic resin (AR) based composites have been prepared by solution processing technique. Different compositions were formulated by variation of AC content between 1 to 30 wt % and the formed composites have been characterized by various techniques to establish a correlation between the filler concentration and the structural, thermal, electrical and morphological attributes. The FTIR spectra show the presence of AC in AR matrix whereas XRD patterns confirm the incorporation of AC particles between lamellar structures of AR. The TGA investigation
revealed that composites are thermally stable up to 200°C after which they display multistep weight loss due to removal of functional groups and decomposition/carbonization of AC as well as polymeric backbone of AR. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites. The electrical measurements show that 30 wt % AC loading composite displays much lower resistivity (104 /Sq) as compared to pure AR (1011 /Sq) and suggest its suitability as static dissipative material. Further, the porous structure and electrically conducting nature of the composites suggest their suitability for making electromagnetic interference shielding coatings.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 123, Pages 376-384, April, 2014
Single crystals of pure and l-Proline (LP) C5H9NO2 doped ammonium dihydrogen phosphate (ADP) (NH4... more Single crystals of pure and l-Proline (LP) C5H9NO2 doped ammonium dihydrogen phosphate (ADP) (NH4) H2PO4 were grown by slow evaporation solution technique (SEST) at ambient conditions. Powder X-ray diffraction (PXRD) analysis was carried out to confirm the crystal structure and no additional phase was observed due to doping except a systematic variation in peak intensities. FT-Raman analysis also confirms that there is no additional phase formation due to doping. Fourier transform infrared spectral analysis was done to examine the presence of various functional groups in the grown crystals. UV–VIS–NIR spectroscopic analysis was carried out to see the change in optical transparency of pure ADP and crystals due to LP with different doping concentrations. The high-resolution X-ray diffraction (HRXRD) analysis was carried out to examine the crystalline perfection and observed reasonable changes with LP doping. Second harmonic generation (SHG) efficiency measurement was done to examine the enhancement in the nonlinear optical characteristics of the grown crystals. The dielectric behavior of the samples shows that the dielectric constant decreased with increase the value of frequency. The effect of LP dopant on crystal morphology, mechanical properties of ADP has also been presented in this paper. The above studies reveal the effect of incorporation of LP into the lattice of ADP crystals.
Journal of Advanced Physics, Volume 3, Number 1, pp. 64-66(3), March, 2014
Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has ... more Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has been performed to verify the phase transformations in polymorphic and polytypic MX type compounds. We measured radial distribution function, total energy and specific heat variation with temperature in CuBr and AgI and confirmed the phenomena of polymorphism and polytypism respectively in these two compounds.
Journal of Advanced Physics, Volume 2, Number 3, pp. 196-199(4), September, 2013
Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has ... more Constant temperature molecular dynamics simulation at different temperatures in NVT ensemble has been performed to verify the phase transformations in polymorphic and polytypic elements. We measured radial distribution function, total energy and specific heat variation with temperature in Nickel and Cobalt and confirmed the phenomena of polymorphism and polytypism respectively in these two compounds.
Materials Focus, Volume 2, Number 4, pp. 293-297(5), August, 2013
The LJ parameters have been optimized for AgI, which reproduced successfully the zinc blend struc... more The LJ parameters have been optimized for AgI, which reproduced successfully the zinc blend structure of AgI. The RDF peaks are seen to be broadening and decrease in height with increasing temperature, reflecting enhanced atomic motions. The first peak value has been found to decrease from 2.325 to 2.275 Å, which indicates that Ag I pair comes closer to each other and consequently the bond becomes stronger and molecular in nature. Energy temperature graph does not show any break while a break in the specific heat curve and type transformation are observed. These indicate the second order transformation in AgI and hence polytypic in nature. The maximum disorderness has been observed at 410 K, which is the transformation temperature. The straight-line curve between lnD and 1/T each for Ag and I atoms confirm a well-known Arrhenius plot which also validates our present MSD data.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 103, Pages 199-204, February, 2013
Good quality single crystals of potassium dihydrogen orthophosphate (KDP) were grown with differe... more Good quality single crystals of potassium dihydrogen orthophosphate (KDP) were grown with different doping concentration of Glycine by conventional solution technique in aqueous solution. X-ray diffraction study has been carried out in order to see the effect of dopant on the structural parameters of KDP. There is no additional phase was observed which was further confirmed by Raman spectroscopic analysis. The second harmonic generation efficiency was measured by using Kurtz powder technique. The relative second harmonic generation (SHG) efficiency of the grown crystals was found to be increased with doping concentration up to 2.5 mol%. Optical transmission study also revealed the same behaviour with enhancement up to 2.5 mol% concentration and later decreased but still higher than pure KDP. The mechanical strength was found to increase with increasing the doping concentration.
Journal of Advanced Physics, Volume 2, Number 3, pp. 235-240(6), September, 2013
The crystallographic data of elements existing at room temperature or above have been reviewed on... more The crystallographic data of elements existing at room temperature or above have been reviewed on different basis i.e., the crystal system (crystal symmetry), axial ratio and packing efficiency to know the general nature of distribution of elements based on symmetry. In order to know which of the polymorphic elements will likely to behave as polytypic, the cohesive energies of all the polymorphs have been calculated using 6–12 potential energy equation. The energy difference between the polymorphic forms has been measured in each case to explore the possible reason/condition for a polymorphic element to exhibit polytypism. On that basis it is proposed that cobalt and thorium should also exhibit polytypism.
In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPC... more In the present work, we have grown single crystals of l-proline cadmium chloride monohydrate (LPCCM) by slow evaporation solution technique (SEST) at room temperature and recorded their live growth kinetics with the help of inverted microscope. Crystal size at various stages of growth and its corresponding morphology was also recorded. Powder X-ray diffraction (PXRD) analysis of LPCCM single crystals confirmed the orthorhombic structure. Respective values of crystallite size, strain and dislocation density have been calculated using PXRD data. Metal complex coordination of the single crystal is studied by FTIR spectroscopic. The optical properties of the grown crystals were investigated through UV–VIS spectroscopic studies and shows that the crystals have very low absorption in entire characterized wavelength range 200–800 nm. The optical band gap was calculated and found to be ∼5.6 eV. Optical constants of the material is determined by theoretical calculations. The chemical etching study was also carried out to study the density of defects in the grown crystals. The photoluminous excitation and emission spectra and thermal property by TGA/DTA curve were recorded. Further, the mechanical properties have been studied using Vicker's microhardness tester as well as many parameters such as fracture toughness (Kc), Brittleness index (Bi) and yield strength (σν) are presented. Dielectric studies have been carried out with varying frequency and temperatures.
Radiation Effects and Defects in Solids, Volume 168, 2013 - Issue 9, 2013
The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been gr... more The potential organic nonlinear optical material of hippuric acid (HA) single crystal has been grown by the slow evaporation solution growth technique using N, N-dimethylformamide as the solvent. Single crystals of pure HA were irradiated at room temperature with 100 keV Nitrogen (N+) ions at fluence 1×1016 and 5×1016 ions/cm2. The pure and irradiated HA single crystals were characterized by different characterization technique. The photoluminescence and UV–visible absorption were performed at room temperature. The crystalline perfection of the pure and irradiated single crystals has been examined by high-resolution X-ray diffraction. Vickers microhardness technique was used to study the effect on the mechanical strength of the crystal at different ion fluences. The structural changes were analyzed by powder X-ray diffraction analysis. The functional groups of the synthesized compound have been identified by Fourier transform infrared spectroscopy. The dielectric constant and dielectric loss as a function of frequency were analyzed at room temperature.
In this work, the single crystals of thiourea cadmium iodide were grown by slow evaporation solut... more In this work, the single crystals of thiourea cadmium iodide were grown by slow evaporation solution technique in two different ratios 2:1 and 1:1. During the formation of their single crystals the morphological features and its live growth process were recorded with the help of inverted microscope. Structural studies of the grown crystals have been carried out by powder X-ray diffraction to confirm the crystal system and vibrational modes by Raman spectroscopy. The optical energy band gaps were investigated through UV–vis spectroscopy study. The surface morphology of the grown single crystals was analyzed by using Scanning Electron Microscope and thermal analysis was carried out by using thermogravimetric analysis. The electrical properties were also studied as a function of frequency and the obtained results are discussed.
Zr–Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. Th... more Zr–Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. The crystal structure and lattice parameter of the grown crystals were assessed by powder X-ray diffraction and the strain developed as a result of doping has been calculated (−1.19 × 10−3) by using the Williamson–Hall relation. The incorporated dopant concentration along with the dopant distribution in the specimen crystal was estimated by X-ray florescence spectrometry. A multi-crystal X-ray diffraction analysis was carried out to identify the crystalline perfection of the sample and revealed that the investigated crystal does not contain any structural grain boundaries but does contain point defects and micrometre size mosaic blocks. Birefringence measurements were carried out using a prism coupler spectrometer and found that the optical birefringence is 0.0822 for 532 nm and 0.705 for 1064 nm. A thermal conductivity (κ) study reveals that the doped sample has a lower κ value than the undoped equivalent.
This book presents a comprehensive theoretical basis of symmetry representations of molecular vib... more This book presents a comprehensive theoretical basis of symmetry representations of molecular vibrations, matrix representation of symmetries, and the elements of group theory that are relevant to other symmetry elements/operations, crystallographic and molecular point groups. The book helps understand the reducible and irreducible representations of symmetry matrices and then derive the normal modes of vibration of different molecules by using suitable techniques independently. Targeted to graduate students and researchers, this book aims not only to derive the normal modes of vibration of any given molecule themselves but also compares and verifies them with the experimentally found modes by using IR and Raman-related techniques. For the first time in the crystallographic history, this book presents the group multiplication tables of all 32 point groups in both international and Schoenflies notations.
This book aims at enhancing the understanding of topics in crystallography through
solving numer... more This book aims at enhancing the understanding of topics in crystallography through
solving numerical problems. Designed into nine chapters on major topics in
crystallography, the book deals with more than 600 carefully selected solved examples,
problems, and multiple-choice questions. Unit cell composition, construction and
calculations, Miller indices, structure factor calculations, and X-ray diffraction methods
are some of the many useful topics discussed in this book. Each chapter begins with a
brief theoretical explanation of the topic followed by solved numerical examples for
further clarity on the subject. The topic “crystallography” is interdisciplinary in nature.
Its rudimentary knowledge, therefore, is essential to the beginners in physics,
chemistry, mathematics, molecular biology, geology, metallurgy, and particularly
materials science and mineralogy. This book also is of immense value to senior
undergraduate and graduate students of physics, chemistry, and other basic sciences.
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Papers by Mohammad Abdul Wahab
The geometrical study suggests the existence of rhombohedral close packing (RCP) and its inherent structural connection with HCP throughout (i.e. as its primitive cell, etc.). Similarly, the study of symmetry suggests the existence of a Trigonal unit cell and its inherent association with SH throughout as a symmetry derivative. The present study resolves clearly that SH, Trigon, HCP and RCP are exclusive and independent lattices where HCP and RCP are exclusively associated with the close packing of identical atoms and hence proposed to be included as independent members of the space lattices. Henceforth, the two new lattices will be called as Wahab lattices (or W lattices) and the sixteen lattices together as Bravais-Wahab lattices (or BW lattices) or simply space lattices as before. The sixteen lattices have been divided into eight crystal systems in the order of their increasing symmetry. The results obtained from the present study help explain the existence of 73 symmorphic space groups in 3-dimensional crystal system. These findings will have immediate as well as far reaching implications.
revealed that composites are thermally stable up to 200°C after which they display multistep weight loss due to removal of functional groups and decomposition/carbonization of AC as well as polymeric backbone of AR. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites. The electrical measurements show that 30 wt % AC loading composite displays much lower resistivity (104 /Sq) as compared to pure AR (1011 /Sq) and suggest its suitability as static dissipative material. Further, the porous structure and electrically conducting nature of the composites suggest their suitability for making electromagnetic interference shielding coatings.
The geometrical study suggests the existence of rhombohedral close packing (RCP) and its inherent structural connection with HCP throughout (i.e. as its primitive cell, etc.). Similarly, the study of symmetry suggests the existence of a Trigonal unit cell and its inherent association with SH throughout as a symmetry derivative. The present study resolves clearly that SH, Trigon, HCP and RCP are exclusive and independent lattices where HCP and RCP are exclusively associated with the close packing of identical atoms and hence proposed to be included as independent members of the space lattices. Henceforth, the two new lattices will be called as Wahab lattices (or W lattices) and the sixteen lattices together as Bravais-Wahab lattices (or BW lattices) or simply space lattices as before. The sixteen lattices have been divided into eight crystal systems in the order of their increasing symmetry. The results obtained from the present study help explain the existence of 73 symmorphic space groups in 3-dimensional crystal system. These findings will have immediate as well as far reaching implications.
revealed that composites are thermally stable up to 200°C after which they display multistep weight loss due to removal of functional groups and decomposition/carbonization of AC as well as polymeric backbone of AR. The SEM images show that incorporation of AC particles leads to systematic change in the morphology of composites. The electrical measurements show that 30 wt % AC loading composite displays much lower resistivity (104 /Sq) as compared to pure AR (1011 /Sq) and suggest its suitability as static dissipative material. Further, the porous structure and electrically conducting nature of the composites suggest their suitability for making electromagnetic interference shielding coatings.
representations of symmetry matrices and then derive the normal modes of vibration of different molecules by using suitable techniques independently. Targeted to graduate students and researchers, this book aims not only to derive the normal modes of vibration of any given molecule themselves but also compares and verifies them with the experimentally found modes by using IR and Raman-related techniques.
For the first time in the crystallographic history, this book presents the group multiplication tables of all 32 point groups in both international and Schoenflies notations.
solving numerical problems. Designed into nine chapters on major topics in
crystallography, the book deals with more than 600 carefully selected solved examples,
problems, and multiple-choice questions. Unit cell composition, construction and
calculations, Miller indices, structure factor calculations, and X-ray diffraction methods
are some of the many useful topics discussed in this book. Each chapter begins with a
brief theoretical explanation of the topic followed by solved numerical examples for
further clarity on the subject. The topic “crystallography” is interdisciplinary in nature.
Its rudimentary knowledge, therefore, is essential to the beginners in physics,
chemistry, mathematics, molecular biology, geology, metallurgy, and particularly
materials science and mineralogy. This book also is of immense value to senior
undergraduate and graduate students of physics, chemistry, and other basic sciences.