Study On The Electrical Transport Properties And Structural Behavior Of In₂O₃ Under High Pressure

In2O3 is a typical IIIA group and n-type semiconductor material. At ambient pressure, it is a direct-gap semiconductor with bixbyite structure. It has high optical transmittance, high conductivity, and high catalytic activity, and therefore can be widely applied in the fields of photoelectric devices, gas sensors and catalytic agents. The application value of In2O3 comes from the tunable nature of energy band structure. Pressure is an important method to change the structure of matter and then change its energy band structure. In this thesis, the phase transition and electrical transport properties of In2O3 have been studied with the methods of high pressure synchrotron radiation X-ray diffraction technique, in-situ high pressure resistivity and Hall effect measurements on diamond anvil cell(DAC), and theoretical calculations. The results are listed as follow:1. With the synchrotron radiation X-ray diffraction, GSAS refinement and Material Studio, the structures of In2O3 have been studied under high pressure. It is found that In2O3 transforms from the bixbyite(Ia-3) structure to rhombohedral corundum(Rc-3) structure at 16.8 GPa. The highest pressure in the experiment is 32.3 GPa. After the decompression, part of rhombohedral corundum phase can remain at ambient pressure, indicating that the phase transition is irreversible.2. With the in-situ high pressure resistivity measurement, it is found that the resistivity of In2O3 increases with the increasing pressure. At 15.1 GPa, the discipline of resistivity increase with the pressure suddenly changes due to the pressure induced structural phase transition. During the decompression, the resistivity cannot recover to the original state, proving that the pressure-induced structual phase transition is irreversible.3. With the fist principle calculation, it is found that both the cubic and rhombohedral In2O3 are direct-gap semiconductors with the band width of 0.780 e V and 1.375 e V respectively. After the decompression to ambient pressure, part of rhombohedral phase remains in the In2O3 sample. The band width of rhombohedral is larger than that of cubic In2O3, and therefore the resistivity after the decompression is larger than the original value.4. With Hall effect measurements, it is found that the pressure-induced structural phase transition leads to the abnormal changes of Hall coefficient, carrier density and carrier mobility at the phase transition pressure. Within the range of experimental pressure, both the cubic and rhombohedral In2O3 are n type semiconductors. The data from the in-situ high pressure Hall effect measurements also indicate that the structural phase transition is irreversible.5. With the in-situ high pressure resistivity measurements under variable temperature, it is found that the resistivity decreases with the temperature increase at the experimental pressure, and therefore the cubic and rhombohedral In2O3 are semiconductors, which consistent with the first principle calculation results. In addition, the resistivity decrease slowly at low temperatures, but fast at high temperatures, because at low temperatures the impurity ionization is dominant in the electrical transport process and the intrinsic excitation is not obvious. As the temperature increasing, the effect of intrinsic excitation begins to emerge, and therefore the resistivity decrease fast with the temperature increasing at high temperatures.6. The pressure dependence of electrical transport activation energy has been obtained according to the temperature dependent resistivity. Under the pressure of 8.8 to 13.4 GPa, the activation energy decrease with the rate of 36.9mev/GPa. After 13.4 GPa, it decrease slowly with the rate of 6.1mev/GPa. The discontinuity at 13.4 GPa results from the change energy band width at phase transition. Part of impurity levels at the top of valence band and in the energy gap deflect from their original position due to the overlap of orbital and entered into the conduction band to take part in the electrical transport, and the impurity levels also generate additional carriers under high pressure, and therefore the electrical transport activation energy decrease.