Phase transitions and ferroelectric attributes in A5M3F19 compounds with A=Sr, Ba and M=Ti, V, Cr, Fe, Ga

Abstract
Phase transitions have been found in ten new materials, Sr5Ti3F19 at 755 K, Sr5V3F19 at 735 K, Sr5Cr3F19 at 953 K, Sr5Fe3F19 at 720 K, Sr5Ga3F19 at 893 K, Ba5Ti3F19 at 1005 K, Ba5V3F19 at 1020 K, Ba5Cr3F19 at 1090 K, Ba5Fe3F19 at 960 K, and Ba5Ga3F19 at 1070 K, by calorimetric and dielectric permittivity measurement on polycrystalline samples. All ten are isomorphous with archetypal Pb5W3O9F10, which satisfies the structural criteria for crystals exhibiting ferroelectricity. The optical birefringence of single‐crystal Sr5Fe3F19 decreases anomalously at the phase transition.