Structure and physical properties of stabilized HfO2- R2O3 ( R = Sc, Yb, Y, Tb, Gd, Er)

Abstract

The structure, Raman and IR reflectance spectra and electrical conductivity of 85 mol% HfO 2 + 15 mol% R 2O 3 ( R = Sc, Yb, Y, Tb, Gd, Er) single crystals have been investigated. It was found that: 1. (1) HfO 2- R 2 O 3 ( R = Sc, Yb, Y, Tb, Gd, Er) are substitutional cubic solid solutions; HfO 2-Sc 2O 3 is either a metastable cubic or stable rhombohedral substitutional arrangement; 2. (2) the observed IR-active phonons and defect-induced Raman spectra are related to the structural differences between HfO 2-R 2O 3 solid solutions, i.e., for R = Yb, Y, Tb, Gd, Er the symmetry is O h 5 and for HfO 2-Sc 2O 3 the symmetry is D 3 7; Kramers-Krönig analysis gave the resonant frequencies ω TO and ω LO ; 3. (3) for all dopants investigated the electrical conductivity decreased as the dopant radius increased. The activation energy for conduction was found to increase with increasing dopant ionic radius. The fact that the highest electrical conductivity among 15 mol% R 2O 3 doped systems was obtained with HfO 2 + Sc 2O 3 suggests that deformation of the coordination polyhedron around cations and the radius ratio r d r h play important roles in determining the electrical conductivity behaviour.