Study On Thermodynamic Modeling And Optical Properties Of The La₂O₃-Nd₂O₃-Sm₂O₃-ZrO₂ System

The optical ceramics of the La₂O₃-RE₂O₃-Zr O₂（RE=Sm or Nd）system are structural-functional combining ceramics with excellent optical and mechanical properties.The phase composition and solid solubility have an extremely important influence on properties of materials.The CALPHAD method allows the calculation of phase relationships for multi-component rare-earth doped zirconia systems,which can contribute significantly to progress in material design.And it also helps to understand how optical properties and densification behaviors are affected by phase equilibria.The main work and research results of this subject are as follows:（1）In this work,phase equilibria of the two pseudo-ternary systems,La₂O₃-Nd₂O₃-Zr O₂ and La₂O₃-Sm₂O₃-Zr O₂,were studied at 1873 K and 1673 K through a series of equilibrium samples.The isothermal sections of these two systems were constructed at the selected temperatures.The homogeneity range of the pyrochlore phase was carefully determined and the phase boundary of the fluorite phase which extends into the ternary system was also constructed via electron probe microanalysis and X-ray diffraction.No ternary compounds have been observed,while the binary La₂Zr₂O₇ and Nd₂Zr₂O₇（Sm₂Zr₂O₇）pyrochlore phases form a continuous solid solution La_2-xNd_xZr₂O₇(La_2-xSm_xZr₂O₇)in the ternary systems.（2）On the basis of present experimental results,the as-obtained data were adopted to determine the mixing parameters for the pyrochlore and fluorite phases in the present thermodynamic modeling.A self-consistent database of the La₂O₃-Nd₂O₃-Zr O₂ and La₂O₃-Sm₂O₃-Zr O₂ systems was accordingly established for the first time and the calculations agreed with the experimental data in the current work.The major feature of the experimental phase diagram was reproduced by the present calculation.（3）Samples with eight different components in La₂O₃-RE₂O₃-Zr O₂（RE=Sm or Nd）ternary systems were prepared by solid state reaction method to investigate how infrared transmittance and densification behaviors are affected by phase equilibria.It was found that samples made up of pyrochlore phase and fluorite phase can achieve similar infrared transmittance as single pyrochlore phase,and the porosity of the samples consisting of two phases is lower than that of the single-phase sample on the La_2-xSm_xZr₂O₇ composition line.Samples with excessive addition of rare earth oxides to the pyrochlore phase achieves maximum infrared transmittance and minimum porosity in the La₂O₃-RE₂O₃-Zr O₂（RE=Sm or Nd）ternary systems.