New high-permittivity AgNb1-xTaxO3 microwave ceramics: Part I, Crystal structures and phase-decomposition relations

The crystal structure of monophasic AgNb1/2Ta1/2O3 was investigated via Rie tveld refinement using powder X-ray diffractometry (XRD) data. The study re vealed a monoclinic unit cell of the P2/m space group with the following un it-cell parameters: a = 3.9286(3) Angstrom, b = 3.9259(2) Angstrom, c = 3.9 302(3) Angstrom, and beta = 90.49(1)degrees. High-temperature XRD studies o f the decomposition of AgNb1/2Ta1/2O3 showed that the kinetics of the decom position are influenced by the volatilization of silver, Suppression of sil ver volatilization by enclosing the sample in a corundum tube and applying an oxygen atmosphere yielded sintered, almost-monophasic AgNb1/2Ta1/2O3 cer amics 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(Nb1-xT ax)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 wi th the follovcing unit-cell parameters: a = 37.116(5) Angstrom, b = 12.432( 3) Angstrom, and c = 7.826(2) Angstrom. Indexed powder diffraction data for Ag-8(Nb,Ta)(26)O-69 have been reported.