Correlation of crystal structure and microwave dielectric properties of Nd1.02(Nb1−xTax)0.988O4 ceramic
The phase structures of Nd1.02(Nb1−xTax)0.988O4 ceramics were analyzed via multiphase structure refinement. The X-ray diffraction patterns of Nd1.02(Nb1−xTax)0.988O4 showed that the monoclinic fergusonite structure of NdNbO4 and a second phase NdTa7O19 were obtained. The oxygen octahedron distortion was investigated according to the supercell of the NdNbO4 ceramic. The correlations between packing fractions, bond valences and microwave dielectric properties were discussed. For the main phase NdNbO4, as the polarizabilities increased, the ε increased. The Q × f value was mainly attributed to the packing fraction. With the increase of bond valence of the B-site and the oxygen octahedron distortion, the τf value decreased. The substitution of Ta5+ for Nb5+ effectively influenced the microstructure and the microwave dielectric properties of NdNbO4 ceramics. Optimal microwave dielectric properties can be obtained for Nd1.02(Nb0.94Ta0.06)0.988O4 ceramics at x = 0.06.