Study On The Electrical Transport Properties Of BiAlO₃ Under High Pressure

Bismuth aluminate（BiAlO₃）is a lead-free ferroelectric material,and its advantages of low environmental harm have gradually replaced the status of lead zirconate titanate.Pressure can change the atomic spacing of substances,and then trigger structural phase transitions and electron phase transitions,providing a source for the study of new substances,new properties and new effects.In this paper,BiAlO₃was studied by using high pressure in-situ AC impedance spectroscopy and first-principles calculation,and explained the mechanism.The specific results of the study are as follows:1.Using first-principles calculations,the band structure of R3m phase BiAlO₃under different pressures was obtained.Under normal pressure,the bandgap of BiAlO₃is wider,and the k values corresponding to the lowest space-orbital state and the highest occupied state are different,indicating that it is an indirect bandgap semiconductor and electrons are difficult to transition.Moreover,according to the band distribution characteristics near the bottom of the conduction band（wide window distribution）,it can be seen that its effective electron mass is large,which will lead to low mobility.Under high pressure,the difference between the bottom of the conduction band and the Fermi energy level gradually decreases with the increase of pressure and pressure,which makes it easy for electrons to transition from the valence band to the conduction band,thereby increasing the conductivity of BiAlO₃.Through the state density calculation,we find that the total state density peak of the valence band is similar to the 2p state density peak of O atom,and the total state density peak of the conduction band is similar to the 6p state density peak of Bi atom,indicating that the valence band and conduction band are mainly composed of the 2p state of O atom and the 6p state of Bi atom,respectively.In addition,the state overlap between O atoms and Bi atoms is higher,the hybridization between orbitals is stronger,and their bond energy is larger and the binding is more stable than that between other atoms.2.The high pressure in-situ AC impedance spectroscopy measurement method was used to study the electrical transmission operation behavior of BiAlO₃under high voltage.By fitting the AC impedance spectrum by equivalent circuit method,the relationship between resistance,relaxation frequency and dielectric constant of BiAlO₃with pressure was obtained.The results show that at 4.41GPa and 7.18GPa,the resistance of BiAlO₃changes abnormally with the change law of pressure,which is related to the phase transition of the compressive structure of the material.The change law of dielectric constant with pressure is similar to the change law of resistance,showing a trend of increasing first and then decreasing,reflecting the modulation process of its polarization characteristics under pressure.At the same time,in the study of dielectric loss with frequency,we find that after a pressure cycle of pressurization and unloading,the dielectric loss in the low frequency region will be significantly improved.