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

The crystal structure of monophasic AgNb 1/2 Ta 1/2 O 3 was investigated via Rietveld refinement using powder X‐ray diffractometry (XRD) data. The study revealed a monoclinic unit cell of the P 2/ 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 AgNb 1/2 Ta 1/2 O 3 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 AgNb 1/2 Ta 1/2 O 3 ceramics with >97% of the theoretical density. The Ag 8 (Nb,Ta) 26 O 69 phase, which regularly appeared as a result of partial decomposition of Ag(Nb 1− x Ta x )O 3 , was studied by energy‐dispersive spectroscopy analysis and XRD. The Ag 8 (Nb,Ta) 26 O 69 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 Ag 8 (Nb,Ta) 26 O 69 have been reported.