Measurement and calculation of the ZrO₂-CeO₂-LaO_1.5phase diagram

A thermodynamic assessment of the CeO₂-LaO_1.5 system has been conducted and combined with recently evaluated thermodynamic parameters for the ZrO₂-CeO₂ and ZrO₂-LaO_1.5 systems to predict the ZrO₂-CeO₂-LaO_1.5 ternary phase diagram. Based on the predicted 1400°C isothermal section, twenty-five decisive samples, which were prepared by co-precipitation method and arc melting of melts, were annealed at this temperature for 848 h. The annealed samples were analyzed by using X-ray diffraction method and precise lattice parameter measurement. It was found that the phase assemblages resulting from eighteen of the twenty-five samples can be described by the predicted isothermal section. The agreement between the measured and calculated 1400°C isothermal sections is improved by introducing ternary interaction parameters to the Gibbs energies of Css (cubic solid solution) and Tss (terminal solid solution based on tetragonal ZrO₂). The same samples as above were annealed at 1550°C for 100 h, and the resultant phase assemblages were compared with the 1550°C isothermal section calculated by using the above assessed ternary parameters. The comparison shows that twenty-three o f the twenty-five samples can be reproduced by the calculation. A few isothermal and vertical sections as well as the reaction scheme are calculated for practical use. The combined use of the CALPHAD technique and experimental methods to establish multicomponent ZrO₂ phase diagrams is stressed.