Synthesis and dielectric properties of magnesium niobate-magnesium tantalate solid solutions

Monophasic Oxides of the type MgNb2−xTaxO6 (0 ≤ x ≤ 2) have been synthesized by solid-state reactions using Mg(NO3)2·6H2O as the source of Mg. The oxides crystallize in the orthorhombic columbite structure till x = 1.75 and the tetragonal trirutile structure for pure MgTa2O6 (x = 2.0). Sintered pellets at 1200°C show dielectric constant varying between 16 to 28 for the entire range of composition at a frequency of 500 kHz. The dielectric loss is nearly constant with frequency, and varies between 0.004 and 0.01 for different compositions. The temperature coefficient of dielectric constant (τE) is 3 to −3 ppm/C (30 to 300°C). Scanning electron micrographs reveal a gradual decrease in grain size with increase in Ta concentration with size of 7 to 10 microns for the pure Nb phase sintered at 1200°C while the pure Ta phase shows a grain size of approximately 0.5 to 1 microns.