摘要
Raman spectra of a complex perovskite system(Pb_(1-x)Ba_(x))(Yb_(0.5)Ta_(0.5))O_(3),x=0.0;0.1 and 0.2 have been studied at low temperature in the range of 10–250 K.The fascination of the system is that it undergoes a crossover from a highly ordered antiferroelectric(x=0.0)to ferroelectric(x=0.1)to disordered relaxor ferroelectric(x=0.2).The nature of splitting that prevails in F_(2g)(≈60 cm^(-1)),F_(1g)(≈538 cm^(-1))modes and their gradual merging and disappearance with x indicates an orthorhombic symmetry for x=0.0 and a pseudo-cubic structure for x=0.2.The mode at 420 cm^(-1) suggests the existence of rhombohedral distortion in all the compositions.The soft mode behavior of the F2g modes has been analyzed by fitting the data with the power law ω_(s)=A(T_(C)-T)^(β).
