High temperature quantum paraelectricity in perovskite-type titanates Ln_1/2Na_1/2TiO₃(Ln = La, Pr, Nd, Sm, Eu, Gd and Tb)

Abstract

Abstract The La3+ ion of a quantum paraelectric perovskite La1/2Na1/2TiO3 was substituted with the smaller tripositive lanthanide ions Ln3+. The X-ray structural study and Rietveld refinement of Ln1/2Na1/2TiO3 for Ln=Pr to Tb showed that they are synthesized as orthorhombic perovskite structure with the space group Pnma. Their lattice parameters and dielectric constants decreased from Pr to Tb with an increasing volume of TiO6-octahedron. A high temperature quantum paraelectricity was found for Ln = Pr to Eu. Because of negative extrapolated Curie temperature, the process of explanation used for the typical quantum paraelectric SrTiO3 is not applicable to the quantum paraelectricity in Ln1/2Na1/2TiO3 for Ln = La ∼ Eu.