Triple‐point phase diagrams for BTO‐based ceramics

The temperature–composition structural phase diagram of the BTO‐based ferroelectric system Ba 0.94 Ca 0.06 Ti 1− x Hf x O 3 (0.05 ≤ x ≤ 0.15) is investigated using high‐angular resolution synchrotron X‐ray powder diffraction and dielectric permittivity measurements. In contrast to the well‐known structural phase transition sequence of the parent compound BaTiO 3 (rhombohedral → orthorhombic → tetragonal → cubic, upon heating), Hf 4+ doping into Ba 0.94 Ca 0.06 Ti 1− x Hf x O 3 results in the gradual disappearance of the intermediate orthorhombic and tetragonal phases at two different, but close, critical concentrations, 0.10 < x c1 < 0.12 and 0.12 < x c2 < 0.135, respectively, revealing the presence of two triple points in the phase diagram.