Emergence of the sub-THz central peak at phase transitions in artificial BaTiO sub(3)/(Ba,Sr)TiO sub(3) superlattices

A prominent central peak in the sub-THz frequency range was observed in the Raman spectra of BaTiO sub(3)/(Ba,Sr)TiO sub(3) (BT/BST) superlattice grown on (001)MgO substrate. Both soft and central mode show an anomaly around 200 K and 280 K, which can be correlated with orthorhombic to monoclinic phase transition of BST and BT, respectively. The observed temperature dependence of the central mode enabled us to explain rather broad temperature dependence of the dielectric permittivity previously observed in BT/BST superlattices. ( copyright 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) The coexistence of the central mode in the sub-THz frequency range corresponding to large-amplitude hopping of Ti ions and the soft mode related to normal small-amplitude vibrations was revealed in Raman spectra of BaTiO sub(3)/(Ba,Sr)TiO sub(3) superlattice. The observed anomalous temperature dependencies provide a comprehensive picture of the lattice dynamics and explain the rather broad temperature dependence of the dielectric permittivity at successive phase transitions in this superlattice.