STUDY OF THE STABILISATION OF THE ZrO2 CUBIC PHASE AS A FUNCTION OF THE YTTRIUM AND RARE EARTH OXIDE CONTENT

Fully stabilised cubic zirconia is a good solid electrolyte and is used for oxygen sensors. An attempt was made to determine the amount of yttrium and rare earth oxide mixture (YRE) necessary to stabilise the zirconia cubic phase. Both the raw materials are of Brazilian origin. The powder mixtures were obtained via coprecipitation of yttrium and rare earth hydroxides and hydrous zirconia. These mixtures were calcined at 1400 C in air. The values of the interplanar distances (d) of the 5 families of crystalline planes with the larger XRD intensities were correlated with the respective Miller indexes (h k l). Lattice parameter refinements for the tetragonal and cubic phases were made using a computer program, TRIESTE. The parameter relationship c/a for the tetragonal unitary cell was determined and the results showed the tendency for cubic phase stabilisation when these relationships approached the value of 1. The values of the experimental lattice parameters for the cubic phase were compared with the calculated theoretical values using the mathematical model of vacancies. The two techniques used to determine the lattice parameters gave excellent reliable results. 8 refs.