Ferroelectric phase transitions of uniaxial Sr1-x Ba x Nb2O6 and their composition variation

Elastic properties of uniaxial ferroelectric strontium barium niobate, SrxBa1-xNb2O6 (SBN100x), crystals were studied by Brillouin scattering. With the increase of x, the random fields (RFs) strength becomes strong and the relaxor ferroelectric nature is enhanced. SBN26 (x = 0.26) with very weak RFs undergoes a normal ferroelectric phase transition at the Curie temperature, T-C = 464 K. On cooling from a high temperature, the sound velocity of the longitudinal acoustic mode along the ferroelectric c-axis shows a remarkable softening towards T-C. The sound attenuation of this mode increases markedly towards T-C. These temperature dependences are well fitted by power laws above T-C. The relaxation time of a central peak (CP) shows the critical slowing down towards T-C. In contrast, SBN80 (x = 0.80) with strong RFs shows only a diffusive elastic anomaly in the vicinity of T-C = 289 K and the temperature dependence of a CP is very small. These differences between the observed results of SBN26 and SBN80 can be attributed to the difference of RFs strength. (C) 2019 The Japan Society of Applied Physics