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

MgNb2-xTaxO6 (0 less than or equal to x less than or equal to 2) phases can be obtained as the major phase (75 to 90%) by solid state reactions starti ng from oxides. These oxides crystallize in the orthorhombic columbite stru cture till x = 1.75 and the tetragonal triutile structure for MgTa2O6 (x = 2.0). For all the compositions there exist secondary phases like Nb2O5 or T a2O5 in addition to the major AB(2)O(6) phase. Sintered disks (1200 degrees C) show dielectric constants varying between 14.8 and 16.0 for the entire r ange of composition at a frequency of 500 kHz. The dielectric loss is nearl y constant around 0.025 to 0.03 between 0 less than or equal to x less than or equal to 1 but increases to 0.17 for the MgTa2O6 phase (x = 2.0). Scann ing electron micrographs reveal a gradual decrease in grain size with incre ase in Ta concentration with a size of 3 micron for the x = 0 composition ( sintered at 1200 degreesC) while the x = 2 phase shows a grain size of appr oximately 0.5 microns. The microwave dielectric constant at similar to 14 G Hz is found to be 20.9 for the x = 0 composition and 17.7 for the x = 2 com position.