Novel scheelite-type [Ca_0.55(Nd_1-xBi_x)_0.3]MoO₄ (0.2 ≤ x ≤ 0.95) microwave dielectric ceramics with low sintering temperature

Novel scheelite-type [Ca_0.55(Nd_1-xBi_x)_0.3]MoO₄ (0.2 ≤ x ≤ 0.95) ceramics were prepared using the solid-state reaction method. According to the X-ray diffraction data, a solid solution was formed in 0.2 ≤ x ≤ 0.95 and all the samples belong to pure scheelite phase with the tetragonal structure. As revealed by Raman spectroscopy, the number of vibrational modes decreased with the increase in x value, which further indicated that Bi³⁺ ions occupied A-site of scheelite structure. As the x value increased, the sintering temperature decreased from 740°C to 660°C; the permittivity increased from 12.6 to 20.3; the Qf value first decreased slightly and gradually remained stable. Based on the infrared reflectivity spectrum analysis, the calculated permittivity derived from the fitted data shared the same trend with the measured value. The [Ca_0.55(Nd_0.05Bi_0.95)_0.3]MoO₄ ceramic sintered at 660 °C attained a near-zero value temperature coefficient ~τ_f (−7.1 ppm/°C) and showed excellent microwave dielectric properties with a ɛ_r ~ 20.3 and a Qf ~ 33 860 GHz, making this system a promising candidate in the ultralow temperature cofired ceramic (ULTCC) technology.