STRUCTURE AND PHYSICAL-PROPERTIES OF STABILIZED HFO2-R2O3 (R=SC, YB, Y, TB, GD, ER)

The structure, Raman and IR reflectance spectra and electrical conductivity of 85 mol% HfO2 + 15 mol% R2O3 (R = Sc, Yb, Y, Tb, Gd, Er) single crystals have been investigated. It was found that: (1) HfO2-R2O3 (R = Sc, Yb, Y, Th, Gd, Er) are substitutional cubic solid solutions; HfO2-Sc2O3 is either a metastable cubic or stable rhombohedral substitutional arrangement; (2) the observed IR-active phonons and defect-induced Raman spectra are related to the structural differences between HfO2-R2O3 solid solutions, i.e., for R = Yb, Y, Tb, Gd, Er the symmetry is O(h)5 and for HfO2-Sc2O3 the symmetry is D3(7); Kramers-Kronig analysis gave the resonant frequencies omega(TO) and omega(LO); (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% R2O3 doped systems was obtained with HfO2 + Sc2O3 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.