Phase analysis and dielectric properties of oxides obtained in the MgO–(1–x)Nb2O5–(x)Ta2O5 system

MgNb2–xTaxO6 (0≤x≤2) phases can be obtained as the major phase (75 to 90%) by solid state reactions starting from oxides. These oxides crystallize in the orthorhombic columbite structure till x = 1,75 and the tetragonal trirutile structure for MgTa2O6 (x = 2,0). For all the compositions there exist secondary phases like Nb2O5 or Ta2O5 in addition to the major AB2O6 phase. Sintered disks (1200C) show dielectric constants varying between 14,8 and 16,0 for the entire range of composition at a frequency of 500 kHz. The dielectric loss is nearly constant around 0,025 to 0,03 between 0≤x≤1 but increases to 0,17 for the MgTa2O6 phase (x = 2,0). Scanning electron micrographs reveal a gradual decrease in grain size with increase in Ta concentration with a size of 3 micron for the x = 0 composition (sintered at 1200C) while the x = 2 phase shows a grain size of approximately 0,5 microns. The microwave dielectric constant at ~14 GHz is found to be 20,9 for the x = 0 composition and 17,7 for the x = 2 composition