Microwave dielectric properties trends in a solid solution (Bi _1-xLn_x)₂Mo₂O₉ (Ln=La, Nd, 0.0≤x≤0.2) system

The influence of La³⁺ and Nd³⁺ substitution for the Bi³⁺ cations in the low-firing Bi₂Mo₂O ₉ system is considered in regard to the sintering behavior, density, phase composition, and microwave dielectric properties. All the compositions can be sintered to high densities in temperature range of 620°-680°C. In (Bi_1-xLn_x)₂Mo₂O₉ (Ln=La, Nd) ceramics, when x≤0.2 the solid solution is within a monoclinic phase (P2₁/n) and the phase had an increase in melting temperature with the doping. In the La substitution case, the (Bi_0.8La_0.2) ₂Mo₂O₉ ceramics had the best microwave dielectric properties with a permittivity of 32.7, a Qf value (f=resonant frequency, Q=1/dielectric loss at f) of 13 490 GHz and a temperature coefficient of -4.6 ppm/°C. With the Nd-substituted samples, the (Bi_0.9 Nd_0.1) ₂Mo₂ O₉ ceramics had the best microwave dielectric properties with a permittivity of 33.9, a Qf value of 15 200 GHz and a temperature coefficient of +8.05 ppm/°C. The substitution of La and Nd can effectively modify the microwave dielectric properties of Bi ₂Mo₂O₉ ceramic and in particular adjust the temperature coefficient to near zero. The (Bi_1-xLn_x) ₂Mo₂O₉ (Ln=La, Nd) ceramics are very interesting new materials for an ultralow-temperature cofired ceramics technology that is compatible with Al metal electrodes.