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

[摘要] 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 (1200°C) 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 1200°C) 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.

[关键词] Ceramics;electronic materials;oxides.