Sintering behavior, phase structure and microwave dielectric properties of novel glass-free low-temperature cofiring NaCaLn(MoO4)3(Ln = Nd, Sm) ceramics

Abstract

Novel glass-free low-temperature cofiring NaCaLn(MoO4)3 (Ln = Nd, Sm) ceramics were prepared by a conventional solid-state reaction method, and their sintering characteristics, phase composition, micro-morphology and microwave dielectric properties were comprehensively investigated. The pure tetragonal scheelite structure of NaCaLn(MoO4)3 (Ln = Nd, Sm) ceramics were disclosed by the XRD patterns. The extremely dense micro-morphology was revealed in the SEM images, which corresponds to the density measurements results. Those results showed that the change of εr values is closely related to relative density and molecular polarizability. The change in Q × ƒ value are considered influenced by both grain size and packing fraction. In addition, the largest contribution of Mo–O bonds to the Q × ƒ of NaCaLn(MoO4)3 (Ln = Nd, Sm) ceramics was revealed by P–V–L theory. The best dielectric properties were obtained at 850 °C and 875 °C for NaCaNd(MoO4)3 and NaCaSm(MoO4)3, respectively: εr = 11.06, Q × ƒ = 58,442 GHz, τƒ = −37.7 ppm/°C and εr = 11.02, Q × ƒ = 47,190 GHz, τƒ = −43.8 ppm/°C. Furthermore, the good compatibility of these two ceramics with silver powder indicated that they have potential for LTCC applications.