Processing and characteristics of transparent Gd3TaO7 polycrystalline ceramics

Transparent polycrystalline Gd3TaO7 ceramics were successfully developed. A sol-gel process was used to synthesize Gd3TaO7 powder with a uniform composition and an estimated average particle size of 100nm. 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. 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 1400 degrees C to achieve >96% theoretical density with closed pore structure followed by a hot isostatic pressing at 1400 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 7 m. In-line transmission measurements revealed high transparency in the red and infrared. Thermal conductivity was measured to be >1.6W/mK at room temperature, decreasing to similar to 1.3W/mK by 500 degrees C. Dielectric properties remain stable with relative permittivity values just above 200 and loss tangents <0.005 up to 350 degrees C.