Physical Propetries And Structure Transformations Of AB₂O₆Compounds Under High Pressure

ANb2O6and ATa2O6(A=Mg, Zn and Mn) are known as excellent microwavedielectric ceramic materials, which are promising candidates in wirelesscommunications technologies. Excellent dielectric properties due to the structure inwhich the oxyen atoms assume the octahedral. This paper investigate lattice vibration,and crystal structure on AB2O6(A=Mg, Zn and Mn; B=Nb, Ta) under high pressureand room temperature by Raman scattering and angle dispersive X-ray diffractiontechnology with diamond anvil cell. Investigation on variation of the crystal structuredue to distortion of the NbO6and TaO6units under high pressure, can help tounderstand the transition mechanism in AB2O6with the octahedral. The knowledge isextremely important to search for the ceramic materials with more excellent dielectricproperties. The original and innovational research results including:High pressure X-ray diffraction and Raman scattering studies have been carriedout on MgNb2O6in a DAC at room temperature. A softening of the internal modeν9(B3g) was observed though pressure-induced phase transition, accompanied by thedistortion of the NbO6octahedra decreasing and dielectric ability was suppressedunder high pressure. The Grüneisen parameters were extracted, which suggested thathigh pressure had various effects on the optical lattice modes. The equation of state(EOS) for MgNb2O6in low pressure phase I obtained by third-order Birch-Murnaghanmethod, yielding a zero-pressure bulk modulus B0and its pressure derivative B0’ of187.12GPa and4, respectively.High pressure X-ray diffraction and Raman scattering studies have been carried out on ZnNb2O6in a DAC at room temperature. The high pressure phase transition at9.7GPa was observed, accompanied with two softening of the internal vibrationν7(B2g) and ν8(B2g). Distortion of the NbO6octahedra decreasing and dielectric abilitywas suppressed under high pressure. The Grüneisen parameters were extracted, whichsuggested that high pressure have various effects on the optical lattice modes. Theequation of state (EOS) for ZnNb2O6in low pressure obtained by third-orderBirch-Murnaghan method, yielding a zero-pressure bulk modulus B0and its pressurederivative B0’ of123.28GPa and4, respectively.High pressure X-ray diffraction and Raman scattering studies on manganeseniobate (MnNb2O6) have been carried out in a diamond anvil cell (DAC) at roomtemperature up to41GPa. A pressure-induced phase transition was observedaccompanied with the softening of two internal vibration ν10(B2g) and ν8(Ag) modes.The volume dependencies of the optical lattice mode frequencies and their respectiveGrüneisen parameters were extracted, which suggested that suggested that highpressure have various effects on the optical lattice modes. The X-ray diffractionresults also reflect a trend of pressure induced amorphization with the pressureincrease. The equation of state (EOS) for MnNb2O6in low pressure phase I obtainedby third-order Birch-Murnaghan method, yielding a zero-pressure bulk modulus B0and its pressure derivative B0’ of154.35GPa and4.1, respectively.We have performed a high-pressure study on the ZnTa2O6at room temperatureby using high pressure X-ray diffraction and Raman scattering studies in a diamondanvil cell. A pressure-induced phase transition was observed at11.8GPa. The Ramanmodes were assigned, and the Grüneisen parameters were extracted by the the volumedependence of the optical lattice vibration frequencies, illustrating that high pressurehave various effects on the optical lattice modes. The EOS for ZnTa2O6in lowpressure phase I was obtained with third-order Birch-Murnaghan method, yielding azero-pressure bulk modulus B0and its pressure derivative B0’ of262.26GPa and4,respectively.High pressure X-ray diffraction and Raman scattering studies on MgTa2O6werestudied in DAC, two structural changes were found at about12.5GPa and20GPa. Variation curve of the Raman shift with pressure analysis confirmed a softening of thelattice modes for the first transformation obtained, and the second transformation isrelated with the strong deformation of the double Ta2O10units.