Eutectoid decomposition processes of solid solutions in the HfO 2  PrO 1.5 and HfO 2  MgO systems and their influence on the physico-chemical properties of refractory materials

Abstract

Microscopy and electron microprobe analysis were used to study the process of eutectoid decomposition of cubic solid solutions in the HfO 2  PrO 1.5 and HfO 2  MgO systems. In the first system this occurs by forming of a Pr-rich pyrochlore-type phase and monoclinic HfO 2 solid solution. In the HfO 2  MgO system, magnesium concentrates mainly at crystal boundaries yielding a MgO solid solution; the second, MgO-poor phase is a HfO 2-based monoclinic solid solution. As a result of decomposition the electrical conductivity of the cubic solid solutions is reduced by two orders of magnitude in the HfO 2  PrO 1.5 system and more than orders of magnitude in the HfO 2  MgO system.