High Pressure Studies On ABO₃ -type Tellurium-based Oxides

High pressure physics is a rich and large branch discipline in the field of physics research. It studies the changes of various physical properties of all sorts of materials under high pressure, for example, basically. the variations in the atomic distances and unit cell parameters; microscopically, melting point, ferroelectric and dielectric properties and magnetic resistance, etc. In recent years, perovskite metal oxides have attracted a lot of interests due to their unique properties and potential application. Among this kind of materials, two ABO₃-type compounds BaTeO₃ and SrTeO₃ have shown their applications in the field of LTCC for BaTeO₃ and ferroelectric properties at high temperatures and nonlinear optical and dielectric properties for SrTeO₃.This thesis mainly studies on the structural and spectroscopic properties of BaTeO₃ and SrTeO₃ as measured by the combination of diamond anvil cell (DAC) and Raman spectrometer at room temperature. The high-pressure Raman spectroscopy measurement and the measured synchrotron radiation X-ray diffraction data under high pressure in BaTeO₃ have been presented.The first-principle calculations on Raman vibration modes in BaTeO₃ have been given, and compared to the as-measured Raman modes at ambient pressure. It exhibits a first structural phase transition occurred around 15.3 GPa, and with increasing pressures, a possible second phase transition may appear. The phase transition process is irreversible.As for SrTeO₃, we have illustrated its complex structure by giving its atomic positions and framework layout of 31 atoms. From the Raman spectra under high pressure, we can determine the structural phase transition occurred around 1.55 GPa, and the two phases coexists in the pressure range of 1.55 GPa - 11.29 GPa. After 11.29 GPa, a new phase appears, and this phase transition process is reversible.