NONLINEAR INTERFERENCE IN BARIUM-TITANATE AND POTASSIUM TANTALATE NIOBATE

Raman spectra of the unreduced and reduced barium titanate(BT) and pot assium tantalate niobate(KTN) are examined. The Fano asymmetric cut-of f is on the low-energy sides at Raman features at 196 and 474 cm(-1) i n BT and at 210 cm(-1) in KTN, which indicates nonlinear interference with a positive coupling coefficient. The origin of their lineshape di stortion and sign of the coupling coefficients are discussed owing to nonlinear interaction between one-and two-phonon states. The results a re well compared with those in distorted perovskite oxide Y- and Bi-sy stem superconductors.