Browsing by Author "Gao, Chunxiao"

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Anomalous Structural Transition and Electrical Transport Behaviors in Compressed Zn2SnO4: Effect of Interface
(2015) Zhang, Haiwa; Ke, Feng; Li, Yan; Liu, Cailong; Zeng, Yi; Yao, Mingguang; Han, Yonghao; Ma, Yanzhang (TTU); Gao, Chunxiao
The interface effect is one of the most important factors that strongly affect the structural transformations and the properties of nano-/submicro-crystals under pressure. However, characterization of the granular boundary changes in materials is always challenging. Here, using tetrakaidecahedral Zn2SnO4 microcrystals as an example, we employed alternating current impedance, X-ray diffraction methods and transmission electron microscopy to elucidate the effect of the interface on the structure and electrical transport behavior of the Zn2SnO4 material under pressure. We clearly show that grain refinement of the initial microcrystals into nanocrystals (approximately 5 nm) occurs at above 12.5 GPa and is characterized by an anomalous resistance variation without a structural phase transition. A new phase transition pathway from the cubic to hexagonal structure occurs at approximately 29.8 GPa in Zn2SnO4. The unexpected grain refinement may explain the new structural transition in Zn2SnO4, which is different from the previous theoretical prediction. Our results provide new insights into the link between the structural transition, interface changes and electrical transport properties of Zn2SnO4.
Effects of high pressure on the electrical resistivity and dielectric properties of nanocrystalline SnO 2
(2018) Shen, Wenshu; Ou, Tianji; Wang, Jia; Qin, Tianru; Zhang, Guozhao; Zhang, Xin; Han, Yonghao; Ma, Yanzhang (TTU); Gao, Chunxiao
The electrical transport and structural properties of tin oxide nanoparticles under compression have been studied by in situ impedance measurements and synchrotron X-ray diffraction (XRD) up to 27.9 GPa. It was found that the conduction of SnO2 can be improved significantly with compression. Abnormal variations in resistivity, relaxation frequency, and relative permittivity were observed at approximately 12.3 and 25.0 GPa, which can be attributed to pressure-induced tetragonal- orthorhombic-cubic structural transitions. The dielectric properties of the SnO2 nanoparticles were found to be a function of pressure, and the dielectric response was dependent on frequency and pressure. The dielectric constant and loss tangent decreased with increasing frequency. Relaxation-type dielectric behaviour dominated at low frequencies. Whereas, modulus spectra indicated that charge carrier short-range motion dominated at high frequencies.
Metallization and Electrical Transport Behaviors of GaSb under High-Pressure
(2017) Zhang, Guozhao; Wu, Baojia; Wang, Jia; Zhang, Haiwa; Liu, Hao; Zhang, Junkai; Liu, Cailong; Gu, Guangrui; Tian, Lianhua; Ma, Yanzhang (TTU); Gao, Chunxiao
The high-pressure metallization and electrical transport behaviors of GaSb were systematically investigated using in situ temperature-dependent electrical resistivity measurements, Hall effect measurements, transmission electron microscopy analysis, and first-principles calculations. The temperature-dependent resistivity measurements revealed pressure-induced metallization of GaSb at approximately 7.0 GPa, which corresponds to a structural phase transition from F-43m to Imma. In addition, the activation energies for the conductivity and Hall effect measurements indicated that GaSb undergoes a carrier-type inversion (p-type to n-type) at approximately 4.5 GPa before metallization. The first-principles calculations also revealed that GaSb undergoes a phase transition from F-43m to Imma at 7.0 GPa and explained the carrier-type inversion at approximately 4.5 GPa. Finally, transmission electron microscopy analysis revealed the effect of the interface on the electrical transport behavior of a small-resistance GaSb sample and explained the discontinuous change of resistivity after metallization. Under high pressure, GaSb undergoes grain refinement, the number of interfaces increases, and carrier transport becomes more difficult, increasing the electrical resistivity.
Reversible metallization and carrier transport behavior of In2S3 under high pressure
(2018) Li, Yuqiang; Gao, Yang (TTU); Xiao, Ningru; Ning, Pingfan; Yu, Liyuan; Zhang, Jianxin; Niu, Pingjuan; Ma, Yanzhang (TTU); Gao, Chunxiao
The electrical transport properties of indium trisulfide (In2S3) under high pressure were investigated using the in situ Hall-effect and temperature dependent resistivity measurements. Resistivity, Hall coefficient, carrier concentration, and mobility were obtained at pressures up to 41.6 GPa. Pressure induced metallization of In2S3 occurred at approximately 6.8 GPa. This was determined by measuring temperature dependent resistivity. The metallization transition was also determined from compression electrical parameters, and the decompression electrical parameters indicated that the metallization was a reversible transition. The main cause of the sharp decline in resistivity was the increase in carrier concentration at 6.8 GPa. Superconductivity was not observed at the pressures (up to 32.5 GPa) and temperatures (100-300 K) used in the experiment.