THE STRUCTURE OF THE PHI-1-PHASE CAZR4O9 IN CALCIUM STABILIZED ZIRCONIA

Vacancy and cation ordering in the Φ1-phase CaZr4O9 in ZrO2-CaO system has been investigated. A sample with precipitates of the Φ1-phase has been prepared by annealing a cubic stabilized zirconia single crystal (Zr0.85Ca0.15O1.85) at 1300 K for one month in air. Using the powdered material the structure has been determined by analysing X-ray and neutron diffraction data by the Rietveld method. The Φ1-phase has the monoclinic space group C2 c. The relation of its lattice parameters to the lattice parameter of the cubic phase was confirmed. The ordering of the calcium ions along the fluorite 〈110〉 direction and the ordering of the vacancies separated by 1 2〈111〉 along the fluorite 〈111〉 direction were obtained from the X-ray and neutron data, respectively. All calcium ions are 8-fold coordinated by oxygen ions, while 12 zirconium ions are 6-, 40 zirconium ions 7-, and 12 zirconium ions 8-fold coordinated. The high B-factors (up to 0.18 nm2) and some anomalous small ZrO distances (down to 0.169 nm) indicate incomplete order of the Φ1-phase. © 1990.