Transparent polycrystalline Gd2Hf2O7 ceramics

• Published in: Journal of the American Ceramic Society Vol. 101; no. 9; pp. 3797 - 3807
• Main Authors: Chen, Ching‐Fong, Brennecka, Geoff L., Synowicki, R. A., Tegtmeier, Eric L., Brand, Michael J., Montalvo, J. D., Ivy, Jacob, Cherepy, Nerine J., Seeley, Zach, Payne, Steven A.
• Format: Journal Article
• Language: English
• Published: Columbus Wiley Subscription Services, Inc 01-09-2018
• Subjects: Ceramics; Ceramics industry; Crystallization; Dielectric properties; Differential thermal analysis; Grain size; Grain size distribution; Gravimetric analysis; Heat treating; Hot isostatic pressing; Particle size distribution; Permittivity; Polycrystals; Porosity; Roasting; Sol-gel processes; Structural analysis; Synthesis; Tangents; Theoretical density; Thermal conductivity; X-ray diffraction
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.15550

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 120 nm. 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 1500°C to achieve >95% theoretical density with closed pore structure followed by a hot isostatic pressing at 1500°C at 207 MPa to achieve a fully dense structure. Microstructural characterization shows a uniform grain size distribution with an average grain size of about 11 μm. 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°C. Thermal conductivity was measured to be ~1.8 W/m°K at room temperature, decreasing to ~1.5 W/m°K by 500°C.