Sintering characteristics, phase transitions, and microwave dielectric properties of low-firing [(Na 0.5Bi 0.5) x Bi 1− x ](W x V 1− x )O 4 solid solution ceramics

A series of high-k [(Na_0.5Bi_0.5)_xBi_1−x](W_xV_1−x)O₄ solid solution ceramics with a scheelite-like structure are synthesized by a modified solid-state reaction method at a temperature range of 680-760 °C. The monoclinic (0 ≤ x < 0.09) to tetragonal scheelite (0.09 ≤ x ≤ 1.0) structural phase transition is confirmed by XRD, Raman and IR analyses. The effect of structural deformation and order-disorder caused by Na⁺/Bi³⁺/W⁶⁺ complex substitution on microwave dielectric properties is investigated in detail. The compositional series possess a wide range of variable relative permittivities (24.8 ~ 80) and TCF values (-271.9 ~ 188.9 ppm/°C). The maximum permittivity of 80 and a high Q × f value of ~10,000 GHz are obtained near the phase boundary at x = 0.09. Furthermore, a temperature stable dielectric ceramic sintered at 680 °C with excellent microwave dielectric properties of  = 80.7, Q × f = 9,400 GHz (at 4.1 GHz) and TCF value = -3.8 ppm/°C is designed by mixing the x = 0.07 and x = 0.08 components. In summary, the similar sinterability and structural compatibility of scheelite-like solid solution systems make it potential for the LTCC applications.