Processing and characteristics of transparent Gd 3 TaO 7 polycrystalline ceramics

• Published in: Journal of the American Ceramic Society Vol. 101; no. 5; pp. 1847 - 1856
• Main Authors: Chen, Ching‐Fong, Synowicki, Ron A., Brand, Michael J., Tegtmeier, Eric L., Montalvo, J. D., Ivy, Jacob, Brennecka, Geoff L., Seeley, Zach, Cherepy, Nerine J., Payne, Steven A.
• Format: Journal Article
• Language: English
• Published: 01.05.2018
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.15359

Abstract Transparent polycrystalline Gd 3 TaO 7 ceramics were successfully developed. A sol‐gel process was used to synthesize Gd 3 TaO 7 powder with a uniform composition and an estimated average particle size of 100 nm. 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°C. The calcined powders were hot‐pressed at 1400°C to achieve >96% theoretical density with closed pore structure followed by a hot isostatic pressing at 1400°C at 207  MP a to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 7 μm. In‐line transmission measurements revealed high transparency in the red and infrared. Thermal conductivity was measured to be >1.6 W/ mK at room temperature, decreasing to ~1.3 W/ mK by 500°C. Dielectric properties remain stable with relative permittivity values just above 200 and loss tangents <0.005 up to 350°C.