Phase transitions and dielectric properties of perovskite-type oxyfluorides (1-x)KNbO3-xKMgF3

Abstract (1- x )KNbO 3 - x KMgF 3 was synthesized using a sealed silica tube with an oxygen generator (KNMOF-O 2 ) or a high-pressure and high-temperature apparatus (KNMOF-hp). The variations in phase transition temperature and dielectric properties were investigated. The temperatures of a tetragonal-to-cubic phase transition and an orthorhombic-to-tetragonal phase transition decreased with x , whereas the temperature of a rhombohedral-to-orthorhombic phase transition increased with it. The temperature variation, however, became constant for x  ≥ 0.05 and did not merge into one. In the temperature dependence of dielectric permittivity for x  = 0.05 (KNMOF-hp), a broad maximum was observed in the vicinity of 400 K and its value reached approximately 2200 which is higher than that of a KNbO 3 dense ceramic. Considering the variation of phase transition temperatures and dielectric measurements, it is concluded that the relaxor-like behavior was realized for x  = 0.05 (KNMOF-hp).