Frequency dependence of the quasi-soft Raman-active modes in rotationally distorted R ~(3+)B ~(3+)O _3 perovskites (R ~(3+)rare earth, B ~(3+)=Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga)

摘要

The structural data and Raman spectra of distorted R ~(3+)B ~(3+)O _3 perovskites (R ~(3+)rare earth, B ~(3+)=Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga) with BO _6 octahedral tilts were critically reviewed in order to obtain the frequency (ω) versus BO _6 tilt angle (α) dependence of the quasi-soft vibrational modes. It was found that the relation ω=α is satisfied in a good approximation for each RBO _3family with fixed B atom, despite the different spatial tilt orientations for compounds of the same series with either orthorhombic Pnma or rhombohedral structure. The dependence of the proportionality coefficient on the averaged BO octahedral distance can be described using different functions (power, linear and exponential ones). The established dependences can be used for analysis of Raman data and heuristic prediction of structural second-order transitions.