Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature unde... more Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature under compression up to pressures of 8 GPa by means of single-crystal X-ray diffraction, Raman spectroscopy, and density-functional theory. According to X-ray diffraction, the orthorhombic phase undergoes an isostructural phase transition at 4.0(5) GPa with the thermodynamic character being first-order. This conclusion is supported by Raman spectroscopy studies which have detected the phase transition at 4.5(2) GPa and by the first-principles computing simulations. The structure solution at different pressures has provided information on the change with pressure of unit-cell parameters as well as on the bond and polyhedral compressibility. A Birch-Murnaghan equation of state has been fitted to the unit-cell volume data. We found that chalcomenite is highly compressible with a bulk modulus of 42 – 49 GPa. The possible mechanism driving changes in the crystal structure is discussed, being the ...
ABSTRACT The present work was an in-depth study related to synthesis of carbon nanospheres (CNSs)... more ABSTRACT The present work was an in-depth study related to synthesis of carbon nanospheres (CNSs) at different scales (lab and pilot) with the end goal to economize the production of these materials on a large scale. Synthesis of large amounts of CNSs relies on the careful control of the operating conditions such as space velocity (helium flow rate), hydrocarbon (benzene) content in feed stream, and synthesis time. The alteration of these variables caused important changes in both the yield and properties of the obtained materials. In general, characterization results of the synthesized CNSs demonstrated that they showed low BET surface area and pore volume values typical of spherical geometrical bodies, good thermal stability, and good crystallinity. Normally, CNSs are presented as conglomerates as consequence of the accretion via the carbon atoms at the edge of the “curling” graphitic flakes. Finally, results demonstrated a successful scale up, obtaining a CNSs yield at pilot scale considerably superior (factor of 3.9) to that obtained at laboratory scale.
The electronic and transport properties of Fe(IO3)3 have been characterized under compression. A ... more The electronic and transport properties of Fe(IO3)3 have been characterized under compression. A nice correlation of bandgaps of iodates to orbital configuration is proposed giving an explanation for the 2.1 eV bandgap of Fe(IO3)3.
Pressure-induced energy blue- and red-shifts of theF→Inear-infrared emission lines of Ndions in Y... more Pressure-induced energy blue- and red-shifts of theF→Inear-infrared emission lines of Ndions in YAlOperovskite nano-particles have been measured from ambient conditions up to 29 GPa. Different positive and negative linear pressure coefficients have been calibrated for the emission lines and related to pressure-induced changes in the interactions between those Ndions and their twelve oxygen ligands at the yttrium site. Potentiality of the simple overlap model, combined with ab initio structural calculations, in the description of the effects of these interactions on the energy levels and luminescence properties of the optically active Ndion is emphasized. Simulations show how the energies of the 4fground configuration and the barycenters of the multiplets increase with pressure, whereas the Coulomb interaction between f-electrons decreases and the crystal-field strength increases. All these effects combined explain the wavelength blue-shifts of some near-infrared emission lines of Nd...
This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O... more This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and compare nicely with theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk In2O3 is discussed.
Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature unde... more Synthetic chalcomenite-type cupric selenite CuSeO3∙2H2O has been studied at room temperature under compression up to pressures of 8 GPa by means of single-crystal X-ray diffraction, Raman spectroscopy, and density-functional theory. According to X-ray diffraction, the orthorhombic phase undergoes an isostructural phase transition at 4.0(5) GPa with the thermodynamic character being first-order. This conclusion is supported by Raman spectroscopy studies which have detected the phase transition at 4.5(2) GPa and by the first-principles computing simulations. The structure solution at different pressures has provided information on the change with pressure of unit-cell parameters as well as on the bond and polyhedral compressibility. A Birch-Murnaghan equation of state has been fitted to the unit-cell volume data. We found that chalcomenite is highly compressible with a bulk modulus of 42 – 49 GPa. The possible mechanism driving changes in the crystal structure is discussed, being the ...
ABSTRACT The present work was an in-depth study related to synthesis of carbon nanospheres (CNSs)... more ABSTRACT The present work was an in-depth study related to synthesis of carbon nanospheres (CNSs) at different scales (lab and pilot) with the end goal to economize the production of these materials on a large scale. Synthesis of large amounts of CNSs relies on the careful control of the operating conditions such as space velocity (helium flow rate), hydrocarbon (benzene) content in feed stream, and synthesis time. The alteration of these variables caused important changes in both the yield and properties of the obtained materials. In general, characterization results of the synthesized CNSs demonstrated that they showed low BET surface area and pore volume values typical of spherical geometrical bodies, good thermal stability, and good crystallinity. Normally, CNSs are presented as conglomerates as consequence of the accretion via the carbon atoms at the edge of the “curling” graphitic flakes. Finally, results demonstrated a successful scale up, obtaining a CNSs yield at pilot scale considerably superior (factor of 3.9) to that obtained at laboratory scale.
The electronic and transport properties of Fe(IO3)3 have been characterized under compression. A ... more The electronic and transport properties of Fe(IO3)3 have been characterized under compression. A nice correlation of bandgaps of iodates to orbital configuration is proposed giving an explanation for the 2.1 eV bandgap of Fe(IO3)3.
Pressure-induced energy blue- and red-shifts of theF→Inear-infrared emission lines of Ndions in Y... more Pressure-induced energy blue- and red-shifts of theF→Inear-infrared emission lines of Ndions in YAlOperovskite nano-particles have been measured from ambient conditions up to 29 GPa. Different positive and negative linear pressure coefficients have been calibrated for the emission lines and related to pressure-induced changes in the interactions between those Ndions and their twelve oxygen ligands at the yttrium site. Potentiality of the simple overlap model, combined with ab initio structural calculations, in the description of the effects of these interactions on the energy levels and luminescence properties of the optically active Ndion is emphasized. Simulations show how the energies of the 4fground configuration and the barycenters of the multiplets increase with pressure, whereas the Coulomb interaction between f-electrons decreases and the crystal-field strength increases. All these effects combined explain the wavelength blue-shifts of some near-infrared emission lines of Nd...
This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O... more This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and compare nicely with theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk In2O3 is discussed.
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Papers by Alfonso Munoz