Tn-situ High Pressure Studies Of The Crystal Structures Of Vanadium-based Perovskite Oxides

In a typical crystal structure of perovskite oxide ABO3, the A and B site can beoccupied by different cations. By varying these cations, different crystal structuresand a rich variety of novel physical properties can be found in these compounds. Thevanadium-based perovskite oxides have attracted a lot of interests owing to theirunique crystal and electronic structures, which make them as the important functionalmaterials. Recently, the high pressure research works on these oxides have attractedmore attentions.In this thesis, the vanadium-based perovskite oxides (SrVO3, SmVO3and NdVO3)have been studied by high pressure synchrotron X-ray powder diffraction in adiamond anvil cell. The detailed structural evolutions with increasing pressures havebeen analyzed by the Rietveld refinement method and the octahedral distortions inthese compounds have been discussed. Our innovative results are as follows:(1) The crystal structure of SrVO3is cubic and its crystal structure is stable up tothe highest pressure (30.3GPa). The VO6octahedra have no change with increasingpressures. The EOS is obtained with the bulk modulus (B0) of267(7) GPa.(2) The phase of SmVO3has orthorhombic symmetry and its crystal structure isstable up to28.2GPa. The bond lengths of V1-O1and V1-O2gradually decrease withincreasing pressure. The bond angles of V1-O1-V1and the V1-O2-V1increase withincreasing pressure and it indicates that the tilting of these inter VO6octahedrareduces with increasing pressures in SmVO3. The EOS is obtained with the bulkmodulus (B0) of247(8) GPa.(3) The crystal structure of NdVO3is orthorhombic and its crystal structure doesnot show any sign of phase transition up to23.2GPa. The bond lengths of V-Ogradually decrease with increasing pressure. The bond angles of two adjacent VO6octahedra increase with increasing pressures and it indicates that the tilting of theseinter VO6octahedra reduces with increasing pressures in NdVO3. The EOS is obtained with the bulk modulus (B0) of209(6) GPa.