Displacive Phase Transformation in Vanadium - Substituted Lanthanum Niobate

The displacive transformations in complex oxides of the type LaNb1-xVxO4 has been studied by x-ray diffraction and Raman scattering for 0 < x < 0.3. X-ray diffraction results indicate that the transformation from the tetragonal high temperature structure (C4h6) to the monoclinic low-temperature structure (C2h6) is higher than first order and that the transformation temperature Tc is depressed significantly by V substitution. Raman scattering results show that the force constant between the nearest (Nb, V)O4 tetrahedral units behave uniquely compared to others. It softens at Tc as a function of composition and it also softens as a function of temperature as Tc is approached from above.