Transparent polycrystalline Gd2Hf2O7 ceramics

We have successfully developed transparent polycrystalline Gd2Hf2O7 ceramics with high in-line transparency. A sol-gel process was used to synthesize the Gd2Hf2O7 powder. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as-synthesized sol-gel powders. The calcined powder is single phase and was formed with an estimated average particle size of 120nm. Crystallization was confirmed by x-ray diffraction (XRD) and a single phase was achieved by calcining at 1000 degrees C. The calcined powders were hot-pressed at 1500 degrees C to achieve >95% theoretical density with closed pore structure followed by a hot isostatic pressing at 1500 degrees C at 207MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 11m. In-line transmission measurements revealed high transparency in the red and infrared. Dielectric properties remain stable with relative permittivity values around 180 and loss tangents less than 0.005 up to 350 degrees C. Thermal conductivity was measured to be similar to 1.8W/m degrees K at room temperature, decreasing to similar to 1.5W/m degrees K by 500 degrees C.