New High-Permittivity AgNb1-xTaxO3 Microwave Ceramics: Part I, Crystal Structures and Phase-Decomposition Relations

• Published in: Journal of the American Ceramic Society Vol. 82; no. 1; pp. 81 - 87
• Main Authors: Valant, Matjaz, Suvorov, Danilo, Meden, Anton
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01.01.1999; Blackwell; Wiley Subscription Services, Inc
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Condensed matter: structure, mechanical and thermal properties; Electrotechnical and electronic ceramics; Exact sciences and technology; Inorganic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Technical ceramics; Water, oxides, hydroxides, peroxides; Inorganic compounds; Phase studies; Thermal decomposition; Transition element compounds; Tantalum oxides; XRD; Experimental study; Closed systems; Solid solutions; Silver oxides; Chemical preparation; Volatilization; Niobium oxides; Chemical composition; Electroceramics; Crystal structure
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1999.tb01726.x

The crystal structure of monophasic AgNb1/2Ta1/2O3 was investigated via Rietveld refinement using powder X‐ray diffractometry (XRD) data. The study revealed a monoclinic unit cell of the P2/m space group with the following unit‐cell parameters: a= 3.9286(3) Å, b= 3.9259(2) Å, c= 3.9302(3) Å, and β= 90.49(1)°. High‐temperature XRD studies of the decomposition of AgNb1/2Ta1/2O3 showed that the kinetics of the decomposition are influenced by the volatilization of silver. Suppression of silver volatilization by enclosing the sample in a corundum tube and applying an oxygen atmosphere yielded sintered, almost‐monophasic AgNb1/2Ta1/2O3 ceramics with >97% of the theoretical density. The Ag8(Nb,Ta)26O69 phase, which regularly appeared as a result of partial decomposition of Ag(Nb1−xTax)O3, was studied by energy‐dispersive spectroscopy analysis and XRD. The Ag8(Nb,Ta)26O69 phase exhibited a bronzelike orthorhombic structure with the following unit‐cell parameters: a= 37.116(5) Å, b= 12.432(3) Å, and c= 7.826(2) Å. Indexed powder diffraction data for Ag8(Nb,Ta)26O69 have been reported.