The Structural And Electrical Properties Study Of LiTaO₃ Under High Pressure

Ferroelectric materials,characterized by good properties of photoelectricity,photorefraction,nonlinear optics and electro-mechanical conversion,have been widely used in electro-optic modulators,harmonic producers,speed-sensitive switches,holographic storage devices,heat detectors and filters and extensively studied in many fields such as physics,chemistry and materials.As we all know,under high pressure,the atomic distance is greatly compressed,which changes the structure,finally induce many strange physical and chemical phenomena that do not exist under atmospheric pressure appear.This paper aims to study the structure and electrical transport properties of lithium tantalate?LiTaO₃?,a ferroelectric material,under high pressure,so as to expand people's understanding of ferroelectric materials under extreme conditions.The technology platform of diamond anvil cell is used to study the high-pressure in-situ structure and electrical transport properties of LiTaO₃.The results are as follows:1.The high-pressure synchrotron radiation X-ray diffraction is used to study the change of crystal structure of LiTaO₃ under high pressure.When the pressure increases to 38.1 GPa,the structural phase transition of LiTaO₃ happens,changing from space group R3c to Pnma.The results of High-pressure Raman spectrum show that the Raman peak of LiTaO₃ sample is weakening after 30GPa,but non-crystallization doesn't occur,which is significantly different from the previous conclusion that non-crystallization occurs at 33.2GPa.It may be related to the sample's polycrystalline morphology and good hydrostatic environment.2.From the high-pressure in-situ AC impedance spectrum,it is found that when the pressure is lower than 35.1 GPa,an inductance is always existing in the low-frequency range of Nyquist impedance spectrum.When the pressure increases to 37.2GPa,the inductance arc disappears.The pressure of the disappearance of the inductance arc is close to that of the phase transition,which proves that the disappearance of the inductance arc is related to the phase transition of the structure.By equivalent circuit fitting,it is believed that the existence of inductance arc is closely related to the electro strictive effect in LiTaO₃,and the relationship between inductance and pressure is obtained.In addition,the high pressure in-situ UV-visible absorption spectrum of LiTaO₃ is measured.It is found that the band gap increases with the increasing pressure,which leads to the increase of LiTaO₃ resistance with the increase of pressure.