Study on the interrelationship among structural characteristics, chemical bonds and microwave dielectric properties in novel low-temperature fired KBaRe(MoO4)3 (Re = Ho, Tm) ceramics

Two novel low-firing KBaHo(MoO 4 ) 3 (KBHM) and KBaTm(MoO 4 ) 3 (KBTM) ceramics were synthesized using a conventional solid-state method. Rietveld refinement results of the X-ray diffraction (XRD) have verified that the KBHM and KBTM ceramics are classified within a monoclinic crystal system with C2/c space group. The correlations among structural characteristics, bond features and microwave dielectric properties were comprehensively studied utilizing bond valence, packing fraction, Raman spectroscopy, global instability index, and Phillips−Van Vechten−Levine (P−V−L) theory. The compressive effects exerted by the K + and Ba 2+ mainly contributed to the higher ε theo compared to the ε corr . According to the analysis grounded in P−V−L, the lattice energy and bond energy associated with the Mo−O bond played a substantial role in influencing the Q × f and τ f . Furthermore, the Q × f values had relation to the material's density and its packing fraction. The excellent microwave dielectric properties ( ε r = 8.74, τ f = −30.4 ppm/°C and Q × f = 42, 071 GHz) were obtained in the KBHM ceramic sintered at 800 °C. By comparison, KBTM ceramic sintered at 810 °C exhibited superior properties ( ε r = 8.81, Q × f = 52, 946 GHz and τ f = −31.6 ppm/°C). Moreover, KBTM ceramic can be co-fired with Ag without chemical reactivity, which makes it a promising candidate for low temperature co-fired ceramic (LTCC) technology.