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

Abstract

Monophasic Oxides of the type MgNb_2−xTa_xO₆ (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 (Τ_E) 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.