Distinct temperature behavior of the local structure of (1-x)PbTiO3-xBiNi0.5Ti0.5O3 at the morphotropic phase boundary

Abstract

Temperature-dependent Raman spectroscopy was used to study the composition- and temperature-driven structural transformations in the (1-x)PbTiO3-xBiNi0.5Ti0.5O3 solid solution, exhibiting a morphotropic phase boundary (MPB) at xMPB∼0.55 and a relatively high Curie temperature (TC∼680 K at xMPB). The analyses were carried out on ceramic samples, covering a wide temperature range across TC (100–1100 K) and several compositions across xMPB (0–0.70). The results reveal the presence of local ferroic distortions in the paraelectric phase of all compounds and strong composition-induced enhancement of the order-disorder phenomena across the para-to-ferroelelctric phase transition. The MPB compound is distinct by the absence of any temperature dependence of the wavenumber of the lowest-energy A-cation vibrational mode as well as by an equal dynamical weight of BO6 octahedral distortions and tilts below TC. The former indicates that at the MPB, the local-scale structural polarity associated with the A site is purely composition-driven, while the latter reveals competing local-scale polar and antiferodistortive orders related to the B-site sublattice in the ferroelectric state, which do not vanish but become energetically indistinguishable in the paraelectric state.