Li-doped zinc oxide (L0.03Z0.97O) thin films are deposited onto Pt/Ti/SiO2/Si substrates via the ... more Li-doped zinc oxide (L0.03Z0.97O) thin films are deposited onto Pt/Ti/SiO2/Si substrates via the radio frequency magnetron sputtering method. The structure evolution with annealing temperature of the predominantly (002)-oriented Li-doped ZnO (LZO) films after in-situ post-annealing process is determined. The largest values of the piezoelectric coefficient (d33) and the remnant polarization (Pr) (22.85 pm/V and 0.655 μC/cm2, respectively) are obtained for LZO films post-annealed at 600 °C, which can be attributed to the predominant (002)-oriented crystalline structure, the release of intrinsic residual compressive stress, and less non-lattice oxygen.
Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray phot... more Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co...
Abstract BiCuSeO epitaxial films were grown on (001)/(110) SrTtO3 (STO) substrates by RF magnetro... more Abstract BiCuSeO epitaxial films were grown on (001)/(110) SrTtO3 (STO) substrates by RF magnetron sputter deposition. A sputter power over 40 W was needed to transfer target composition to substrate, leading to a fast deposition rate over 17.5 nm/min. The films grown on (001) STO at 100−150 °C showed a dominant [110] orientation instead of [001], which was what expected in view of the smallest lattice misfit and perfect match in symmetry between (001) BiCuSeO and (001) STO. This was caused by slow film growth along c-axis that could not follow the fast deposition rate, whereas a fair lattice misfit, combined with strong bonding along directions vertical to c-axis, entails the growth along [110] at low temperature. Preferred [001] orientation only occurred at high temperature (>350 °C) when the kinetic process was accelerated. However, high temperature and the fast deposition rate imposed by the required sputter power led to the growth of multiple orientations. Epitaxial growth of (001) BiCuSeO film on (001) STO was achieved after the deposition rate was reduced to 0.67 nm/min by a periodically opening and closing shutter installed in front of sputter target. Interestingly, (001) BiCuSeO epitaxial film could be grown on (110) STO at a fast deposition rate of 15 nm/min. Such films on (110) STO had to be grown at higher temperature (∼500 °C). In contrast to (001) STO, (110) STO did not had good lattice match with any BiCuSeO orientation other than [001], so fast kinetic process only promoted the growth of single [001] orientation.
Abstract La and Y doped SrTiO3 (STO) thin films were grown on (100) oriented pure STO single crys... more Abstract La and Y doped SrTiO3 (STO) thin films were grown on (100) oriented pure STO single crystal substrates by the RF magnetron sputter technique. The La/Y doped layer is intended for use as bottom electrode for epitaxial growth of various functional oxide films. The results showed that one of the crucial deposition parameters to achieve the epitaxial growth of La/Y doped STO films with a pure phase and good electrical conductivity was sputter power, which must exceed 120 W. The conductivity of the grown films increased with the increase in sputter power and the La0.1Sr0.9TiO3 (LSTO) films deposited at 200 W had the highest conductivity of 292 S/cm. This was ascribed to the increased percentage of Ti3+ ions in the sputtered films, which was confirmed by the X-ray photoelectron spectroscopy. LSTO films deposited at 130 W were (100) oriented but the increased sputter power promoted the growth of a second texture, i.e. (110). On the other hand, Y0.08Sr0.92TiO3 (YSTO) films were able to keep the unique (100) texture in the films deposited over a range of sputter powers up to 200 W, although the conductivity of YSTO was lower, which was 98.0 S/cm for the films sputtered at 200 W.
Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on Si and La... more Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on Si and LaNiO3 (LNO) buffered Si substrates at 700 °C, by co-sputtering from two individual targets of the components.
Abstract Crednerite CuMnO 2 ceramic has been investigated for the first time in this study as a p... more Abstract Crednerite CuMnO 2 ceramic has been investigated for the first time in this study as a potential thermoelectric material based on its low band gap and layer structure. Undoped CuMn 1+ x O 2 (0≤ x ≤0.2) samples with a delafossite structure were prepared via solid-state reactions and sintered at 1353 K for 2.5 h in argon. The phase, microstructure, and thermoelectric properties of the CuMn 1+ x O 2 (0≤ x ≤0.2) samples were discussed by adjusting the sample composition. The crystallinity and microstructure of sintered bulks were analyzed using X-ray diffraction and scanning electron microscopy, respectively. The thermoelectric properties of the samples were studied from room temperature to 573 K. CuMn 1+ x O 2 sintered bulks showed a relative density of 91% and a layered structure. The composition affected the phases and thermoelectric properties of sintered bulks. Bulks with the crednerite CuMnO 2 phase were only obtained at x =0.1 or 0.143. The crednerite CuMn 1+ x O 2 (0≤ x ≤0.2) samples were p-type semiconductors. The Seebeck coefficient ( S ) increased and the electrical conductivity ( σ ) decreased with Mn content up to x =0.1. Excess Mn content ( x >0.143) decreased the Seebeck coefficient and increased electrical conductivity. The power factor (PF) of the CuMn 1+ x O 2 (0≤ x ≤0.2) samples improved due to the significant increase in the Seebeck coefficient. The thermal conductivity ( κ ) decreased with increasing temperature. The lowest κ value (6.79 W m −1 K −1 ) was found for the CuMn 1.1 O 2 sample at 573 K. The dimensionless figure of merit ZT values of the undoped CuMn 1+ x O 2 bulks are too small for these bulks to be candidates for thermoelectric materials due to weak electrical conductivity.
Li-doped zinc oxide (L0.03Z0.97O) thin films are deposited onto Pt/Ti/SiO2/Si substrates via the ... more Li-doped zinc oxide (L0.03Z0.97O) thin films are deposited onto Pt/Ti/SiO2/Si substrates via the radio frequency magnetron sputtering method. The structure evolution with annealing temperature of the predominantly (002)-oriented Li-doped ZnO (LZO) films after in-situ post-annealing process is determined. The largest values of the piezoelectric coefficient (d33) and the remnant polarization (Pr) (22.85 pm/V and 0.655 μC/cm2, respectively) are obtained for LZO films post-annealed at 600 °C, which can be attributed to the predominant (002)-oriented crystalline structure, the release of intrinsic residual compressive stress, and less non-lattice oxygen.
Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray phot... more Eu1−xBaxTi1−yMyO3 (M = Co or Ni) was sintered at 1400 °C under a reduction atmosphere. X-ray photoelectron spectroscopy revealed the mixed valences of Eu2+/Eu3+ and Ti4+/Ti3+ in EuTiO3 and Eu0.7Ba0.3TiO3, as well as some oxygen vacancies required to keep the charge neutrality. The co-doping of Co2+/Ni2+ in Eu0.7Ba0.3TiO3 resulted in the disappearance of oxygen vacancies, as a result of a reduction in Ti3+ numbers and an increase in Eu3+ numbers. On the other hand, Ba2+ doping led to an increased lattice parameter due to its larger ionic size than Eu2+, whereas the Co2+/Ni2+ co-doping resulted in smaller lattice parameters because of the combined effects of ionic size and variation in the oxygen-vacancy numbers. Eu0.7Ba0.3TiO3 exhibited a clear ferroelectricity, which persisted in the Co2+/Ni2+ co-doped samples until the doping levels of y = 0.05 and 0.10, respectively. Eu0.7Ba0.3TiO3 remained to be antiferromagnetic with a reduced transition temperature of 3.1 K, but co-doping of Co...
Abstract BiCuSeO epitaxial films were grown on (001)/(110) SrTtO3 (STO) substrates by RF magnetro... more Abstract BiCuSeO epitaxial films were grown on (001)/(110) SrTtO3 (STO) substrates by RF magnetron sputter deposition. A sputter power over 40 W was needed to transfer target composition to substrate, leading to a fast deposition rate over 17.5 nm/min. The films grown on (001) STO at 100−150 °C showed a dominant [110] orientation instead of [001], which was what expected in view of the smallest lattice misfit and perfect match in symmetry between (001) BiCuSeO and (001) STO. This was caused by slow film growth along c-axis that could not follow the fast deposition rate, whereas a fair lattice misfit, combined with strong bonding along directions vertical to c-axis, entails the growth along [110] at low temperature. Preferred [001] orientation only occurred at high temperature (>350 °C) when the kinetic process was accelerated. However, high temperature and the fast deposition rate imposed by the required sputter power led to the growth of multiple orientations. Epitaxial growth of (001) BiCuSeO film on (001) STO was achieved after the deposition rate was reduced to 0.67 nm/min by a periodically opening and closing shutter installed in front of sputter target. Interestingly, (001) BiCuSeO epitaxial film could be grown on (110) STO at a fast deposition rate of 15 nm/min. Such films on (110) STO had to be grown at higher temperature (∼500 °C). In contrast to (001) STO, (110) STO did not had good lattice match with any BiCuSeO orientation other than [001], so fast kinetic process only promoted the growth of single [001] orientation.
Abstract La and Y doped SrTiO3 (STO) thin films were grown on (100) oriented pure STO single crys... more Abstract La and Y doped SrTiO3 (STO) thin films were grown on (100) oriented pure STO single crystal substrates by the RF magnetron sputter technique. The La/Y doped layer is intended for use as bottom electrode for epitaxial growth of various functional oxide films. The results showed that one of the crucial deposition parameters to achieve the epitaxial growth of La/Y doped STO films with a pure phase and good electrical conductivity was sputter power, which must exceed 120 W. The conductivity of the grown films increased with the increase in sputter power and the La0.1Sr0.9TiO3 (LSTO) films deposited at 200 W had the highest conductivity of 292 S/cm. This was ascribed to the increased percentage of Ti3+ ions in the sputtered films, which was confirmed by the X-ray photoelectron spectroscopy. LSTO films deposited at 130 W were (100) oriented but the increased sputter power promoted the growth of a second texture, i.e. (110). On the other hand, Y0.08Sr0.92TiO3 (YSTO) films were able to keep the unique (100) texture in the films deposited over a range of sputter powers up to 200 W, although the conductivity of YSTO was lower, which was 98.0 S/cm for the films sputtered at 200 W.
Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on Si and La... more Multiferroic composite films of Ni0.5Zn0.5Fe2O4 (NZFO) + BiFeO3 (BFO) were deposited on Si and LaNiO3 (LNO) buffered Si substrates at 700 °C, by co-sputtering from two individual targets of the components.
Abstract Crednerite CuMnO 2 ceramic has been investigated for the first time in this study as a p... more Abstract Crednerite CuMnO 2 ceramic has been investigated for the first time in this study as a potential thermoelectric material based on its low band gap and layer structure. Undoped CuMn 1+ x O 2 (0≤ x ≤0.2) samples with a delafossite structure were prepared via solid-state reactions and sintered at 1353 K for 2.5 h in argon. The phase, microstructure, and thermoelectric properties of the CuMn 1+ x O 2 (0≤ x ≤0.2) samples were discussed by adjusting the sample composition. The crystallinity and microstructure of sintered bulks were analyzed using X-ray diffraction and scanning electron microscopy, respectively. The thermoelectric properties of the samples were studied from room temperature to 573 K. CuMn 1+ x O 2 sintered bulks showed a relative density of 91% and a layered structure. The composition affected the phases and thermoelectric properties of sintered bulks. Bulks with the crednerite CuMnO 2 phase were only obtained at x =0.1 or 0.143. The crednerite CuMn 1+ x O 2 (0≤ x ≤0.2) samples were p-type semiconductors. The Seebeck coefficient ( S ) increased and the electrical conductivity ( σ ) decreased with Mn content up to x =0.1. Excess Mn content ( x >0.143) decreased the Seebeck coefficient and increased electrical conductivity. The power factor (PF) of the CuMn 1+ x O 2 (0≤ x ≤0.2) samples improved due to the significant increase in the Seebeck coefficient. The thermal conductivity ( κ ) decreased with increasing temperature. The lowest κ value (6.79 W m −1 K −1 ) was found for the CuMn 1.1 O 2 sample at 573 K. The dimensionless figure of merit ZT values of the undoped CuMn 1+ x O 2 bulks are too small for these bulks to be candidates for thermoelectric materials due to weak electrical conductivity.
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