Xiaoding Qi - Academia.edu (original) (raw)
Papers by Xiaoding Qi
Journal of materials chemistry. A, 2024
Proceedings of SPIE, Mar 4, 2015
Two kinds of pulsed laser sources, femtosecond laser (fs laser) and nanosecond laser (ns laser), ... more Two kinds of pulsed laser sources, femtosecond laser (fs laser) and nanosecond laser (ns laser), were used in the pulsed laser deposition (PLD) system to synthesize copper indium gallium selenium (CIGS) thin films at the substrate temperature from room temperature (RT) and 500o C. Different surface morphology, crystallinity, and stoichiometric ratio were observed on CIGS thin films deposited by femtosecond pulsed laser deposition (fs-PLD) and nanosecond pulsed laser deposition (ns-PLD) respectively, that resulted in different optical and electrical properties. It is proposed that the laser absorption of CIGS target with different laser wavelength caused the difference in laser penetration depths into the target, so that the stoichiometric ratio of the evaporated materials splashing from the target were different between fs-PLD and ns-PLD processes.
John Wiley & Sons, Inc. eBooks, Apr 30, 2012
Applied Physics A, May 5, 2017
Ceramics International, Nov 1, 2015
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.
Journal of Alloys and Compounds, Jun 1, 2017
Applied Physics Letters, Dec 10, 2001
Applied Physics Letters, 2005
High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to st... more High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to study BiFeO3 thin films grown on the bare and SrRuO3 buffered (001) SrTiO3 substrates. Reciprocal space mapping (RSM) around (002) and (103) reflections revealed that BFO films with a thickness of about 200 nm were almost fully relaxed and had a rhombohedral structure. Cross-sectional, high-resolution TEM showed that the films started to relax at a very early stage of growth, which was consistent with the RSM results. A thin intermediate layer of about 2 nm was observed at the interface, which had a smaller lattice than the overgrown film. Twist distortions about the c axis to release the shear strain introduced by the growth of rhombic (001) BiFeO3 on cubic (001) SrTiO3 were also observed. The results indicate that a strained, coherent BiFeO3 film on (001) SrTiO3 is very difficult to maintain and (111) STO substrates are preferable.
Journal of Crystal Growth, Mar 1, 1996
... ELSEVIER Journal of Crystal Growth 160 (1996) 111 118 I ..... CRYSTAL GROWTH Potential laser ... more ... ELSEVIER Journal of Crystal Growth 160 (1996) 111 118 I ..... CRYSTAL GROWTH Potential laser gain media with the stoichiometric formula RETiNbO6 X. Qi, R. Illingworth, HG Gallagher *, TPJ Han, B ... 3. A CO2 laser beam creates a molten zone on top of the source rod. ...
Thin Solid Films, 2021
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.
Ceramic Transactions Series, 2012
Journal of Superconductivity and Novel Magnetism, 2015
Materials
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...
Journal of Applied Physics, 2012
Journal of Alloys and Compounds
Abstract BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized... more Abstract BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized from chemical solution via hydrothermal route at 200 °C. However, for many applications, ceramic samples of reasonable bulk density (>80%) have to be sintered at temperature over 700 °C, which in this case results in a significant reduction in resistivity due to increased amounts of Fe2+. Interestingly, doping of a few percent Sb minimized such a problem and the sintered Sb:BFO ceramics retained a similarly high resistivity as samples cold-pressed from the chemical-solution synthesized powders. However, for cold-pressed samples, Sb:BFO actually had higher conductivity than undoped BFO. Temperature-dependent conductivity showed that cold-pressed samples of both undoped and Sb doped BFO had the similar activation energy of 1.0 eV, typical for electrons trapped in oxygen vacancies. After sintering, the activation energy of Sb:BFO remained almost unchanged, but the activation energy of undoped BFO changed to 0.4 eV, which is associated to electron hopping between Fe2+/Fe3+. X-ray photoelectron spectroscopy (XPS) showed a significant increase in Fe2+/Fe3+ ratio from 6.6/93.4 to 25.7/74.3 in undoped BFO after sintering, while for 1% Sb doped BFO the increase was much milder from 10.9/89.1 to 14.1/85.9. XPS also showed that Sb had single +3 oxidation state before sintering, but after sintering a fairly large portion of Sb5+ occurred. So, charge compensation for oxygen vacancies in undoped BFO was achieved dominantly by reduction of Fe3+ to Fe2+, while in Sb:BFO it was achieved more by cation vacancies.
Journal of materials chemistry. A, 2024
Proceedings of SPIE, Mar 4, 2015
Two kinds of pulsed laser sources, femtosecond laser (fs laser) and nanosecond laser (ns laser), ... more Two kinds of pulsed laser sources, femtosecond laser (fs laser) and nanosecond laser (ns laser), were used in the pulsed laser deposition (PLD) system to synthesize copper indium gallium selenium (CIGS) thin films at the substrate temperature from room temperature (RT) and 500o C. Different surface morphology, crystallinity, and stoichiometric ratio were observed on CIGS thin films deposited by femtosecond pulsed laser deposition (fs-PLD) and nanosecond pulsed laser deposition (ns-PLD) respectively, that resulted in different optical and electrical properties. It is proposed that the laser absorption of CIGS target with different laser wavelength caused the difference in laser penetration depths into the target, so that the stoichiometric ratio of the evaporated materials splashing from the target were different between fs-PLD and ns-PLD processes.
John Wiley & Sons, Inc. eBooks, Apr 30, 2012
Applied Physics A, May 5, 2017
Ceramics International, Nov 1, 2015
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.
Journal of Alloys and Compounds, Jun 1, 2017
Applied Physics Letters, Dec 10, 2001
Applied Physics Letters, 2005
High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to st... more High-resolution x-ray diffraction and transmission electron microscopy (TEM) have been used to study BiFeO3 thin films grown on the bare and SrRuO3 buffered (001) SrTiO3 substrates. Reciprocal space mapping (RSM) around (002) and (103) reflections revealed that BFO films with a thickness of about 200 nm were almost fully relaxed and had a rhombohedral structure. Cross-sectional, high-resolution TEM showed that the films started to relax at a very early stage of growth, which was consistent with the RSM results. A thin intermediate layer of about 2 nm was observed at the interface, which had a smaller lattice than the overgrown film. Twist distortions about the c axis to release the shear strain introduced by the growth of rhombic (001) BiFeO3 on cubic (001) SrTiO3 were also observed. The results indicate that a strained, coherent BiFeO3 film on (001) SrTiO3 is very difficult to maintain and (111) STO substrates are preferable.
Journal of Crystal Growth, Mar 1, 1996
... ELSEVIER Journal of Crystal Growth 160 (1996) 111 118 I ..... CRYSTAL GROWTH Potential laser ... more ... ELSEVIER Journal of Crystal Growth 160 (1996) 111 118 I ..... CRYSTAL GROWTH Potential laser gain media with the stoichiometric formula RETiNbO6 X. Qi, R. Illingworth, HG Gallagher *, TPJ Han, B ... 3. A CO2 laser beam creates a molten zone on top of the source rod. ...
Thin Solid Films, 2021
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.
Ceramic Transactions Series, 2012
Journal of Superconductivity and Novel Magnetism, 2015
Materials
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...
Journal of Applied Physics, 2012
Journal of Alloys and Compounds
Abstract BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized... more Abstract BiFeO3 (BFO) samples with nearly perfect ferroelectric hysteresis loops were synthesized from chemical solution via hydrothermal route at 200 °C. However, for many applications, ceramic samples of reasonable bulk density (>80%) have to be sintered at temperature over 700 °C, which in this case results in a significant reduction in resistivity due to increased amounts of Fe2+. Interestingly, doping of a few percent Sb minimized such a problem and the sintered Sb:BFO ceramics retained a similarly high resistivity as samples cold-pressed from the chemical-solution synthesized powders. However, for cold-pressed samples, Sb:BFO actually had higher conductivity than undoped BFO. Temperature-dependent conductivity showed that cold-pressed samples of both undoped and Sb doped BFO had the similar activation energy of 1.0 eV, typical for electrons trapped in oxygen vacancies. After sintering, the activation energy of Sb:BFO remained almost unchanged, but the activation energy of undoped BFO changed to 0.4 eV, which is associated to electron hopping between Fe2+/Fe3+. X-ray photoelectron spectroscopy (XPS) showed a significant increase in Fe2+/Fe3+ ratio from 6.6/93.4 to 25.7/74.3 in undoped BFO after sintering, while for 1% Sb doped BFO the increase was much milder from 10.9/89.1 to 14.1/85.9. XPS also showed that Sb had single +3 oxidation state before sintering, but after sintering a fairly large portion of Sb5+ occurred. So, charge compensation for oxygen vacancies in undoped BFO was achieved dominantly by reduction of Fe3+ to Fe2+, while in Sb:BFO it was achieved more by cation vacancies.