Diffuse Phase Transitions and Ferroelectric-Paraelectric Diagram for the BaTiO3-SrTiO3 System

Abstract

The diffuse phase transitions (DPT) in the ST‐BT system are theoretically and experimentally justified by the coexistence of two phases (one tetragonal, the other cubic) in the temperature range of the transition. This fact is emphasized by X‐ray identification of both phases at room temperature in (Ba0.76Sr0.24)TiO3 and (Ba0.715Sr0.285)TiO3 solid solutions. The ferroelectric‐para‐electric (F‐P) and the lower ferroelectric transitions are discussed in terms of thermal phase equilibria in the F‐P diagram proposed.

Composition-related structural, thermal and mechanical properties of Ba1−xSrxTiO3ceramics (0 ≤x≤ 0.4)

“…[2] From practical point of view, barium strontium titanate ferroelectric solid solution is one of the attractive candidate materials for electronic applications such as capacitors with high dielectric constant, dynamic random access memories or tunable frequency devices. The dielectric properties of the BST compositions in the form of both ceramics [3][4][5][6][7][8] and single crystals [9] have been investigated since mid-1940s. However, much attention has been paid to the compositional effects on the Curie temperature and dielectric properties of BST ceramics.…”

Diffuse phase transformations in neodymium-doped BaTiO3 ceramics

“…6 also differs in several aspects from those of the isovalent-ion substituted solid solutions. For (Bal_ySr~)TiO3, the coexistence region is between the ferroelectric and para-electric limit curves, bordering the single-phase regions in the phase diagrams [11]. In Fig.…”

“…The contribution from chemical inhomogeneity (resulting from the Ti/Zr ratio) to the distribution of T c is said to be small. For (Ba~_ySry)TiO3, the DPT behaviour has been explained in terms of the coexistence of two phases in thermal equilibrium [11].…”

“…Point defects arising from inherent non-stoichiometry can also induce DPT behaviour [18]. A diffuse type of transition is noticed in a number of perovskite-type solid solutions such as Ba(Til_~Zry) O 3 [19], (Bai_firy)TiO 3 [11], Ba(Til_ySny)O3 [20] and Ba(Nbl.sZr025)Osa5 [21]. A lowering of T c due to n-type impurities has been reported for BaTiO3 by a number of previous workers.…”

“…Electron paramagnetic resonance (EPR) showed that some fraction of the n-doped BaTiO3 is cubic even at room temperature, and that the cubic fraction increases with donor content [9,10]. The coexistence of more than one phase over a range of temperature is characteristic of a diffuse phase transformation (DPT) [11,12]. The presence of a cubic phase has considerable importance with respect to the electrical properties of BaTiO3 ceramics because the energy levels of the acceptor states are differently located in the cubic as compared to the tetragonal phase [9, 13].…”