Stability and structure of noncentrosymmetric hexagonal LnInO 3 (Ln = Eu, Gd, Tb, Dy, Ho, Y)

Abstract

LnInO 3 (Ln = Eu-Ho, Y) can be prepared at atmospheric pressure. These phases are hexagonal, a ∼ 6.3 A ̊ , c ∼ 12.3 A ̊ , Z = 6 , and possess the noncentrosymmetric space group P6 3 cm and the LuMnO 3 structure. The In 3+ ions are located in fivefold-coordinated trigonal-bipyramidal sites, and the Ln 3+ ions are sevenfold coordinated. HoInO 3 and YInO 3 transform to cubic solid solutions with the C-type rare-earth oxide structure above ∼ 1000°C. TbInO 3, GdInO 3 and EuInO 3 transform to ∼9% denser orthorhombic perovskite at elevated pressure, but DyInO 3, HoInO 3 and YInO 3 first transform to novel ∼6% denser pseudohexagonal orthorhombic phases at ∼20 kbar, 1000°C. No hexagonal form of ErInO 3 could be prepared at 950–1050°C, 0–34 kbar.