Shrinkage features, microstructure evolution and properties of Gd₂O₃-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd2O3 and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd2O3 is proved to have a lower lattice parameter (10.7516 angstrom) using XRD refinement. Pressureless sintering behavior of Gd2O3-MgO with/without 2 at% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400 degrees C while that of the undoped one shrinks sharply at 1250 degrees C due to Gd2O3 phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd2O3 creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3 %-85.6 % at 3-5 mu m, which show good consistency with the calculated values. The refractive index of Zr- Gd2O3 varies from 1.87 at 3 mu m to 1.80 at 5 mu m, which is smaller than those of monoclinic Gd2O3.