Phase evolution and microwave dielectric properties of (Bi_1−xLn_x)₂MoO₆ (Ln=Nd and La, x≤0.3) ceramics

(Bi_1−xLn_x)₂MoO₆ (Ln=Nd and La) ceramics were prepared by conventional solid state reaction method. Solid solutions crystallizing in a monoclinic structure with a space group P21/c were obtained in the (Bi_1−xLa_x)₂MoO₆ (x≤0.3) ceramics. For the (Bi_1−xNd_x)₂MoO₆ ceramics, tetragonal Nd₂MoO₆ phase with a space group I4₁/acd was detected when x value reached 0.2 besides the Bi₂MoO₆ solid solution. Temperature stability and quality factor Qf value at microwave frequencies were improved by appropriate substitution for Bi³⁺ by Nd³⁺ and/or La³⁺ in Bi₂MoO₆ system. When x=0.2, for both (Bi_1−xNd_x)₂MoO₆ and (Bi_1−xLa_x)₂MoO₆ ceramics, Qf values reached maximum about 30,200 GHz and 32,900 GHz, respectively. TCF value shifted towards zero with substitution of Bi³⁺ by Nd³⁺ and/or La³⁺. When x=0.3, TCF values of (Bi_1−xNd_x)₂MoO₆ and (Bi_1−xLa_x)₂MoO₆ ceramics were −70 and −85 ppm/°C, respectively. Relation between crystal structure, microstructure and microwave dielectric properties were discussed.