Correlations between crystal structure and dielectric properties of high-Q materials in rock-salt structure Li2O-MgO-BO2 ( B = Ti, Sn, Zr) systems at microwave frequency

A series of ultra-low loss microwave dielectric materials Li2O-MgO-BO2 (B = Ti, Sn, Zr) were prepared by the conventional solid-state method. The Li2O-MgO-BO2 (B = Ti, Sn, Zr) ceramics with nearly full density were sintered at a range of 1320 degrees C to 1520 degrees C for 4 h with excellentmicrowave properties of dielectric constants of 14.42 (at 9.14 GHz), 10.04 (at 11.05 GHz), 12.17 (at 10.2 GHz), Qf values of 15.3 x 10(4) GHz, 14.5 x 10(4) GHz, 11.3 x 10(4) GHz and temperature coefficient (tau(f)) values of - 11.07, - 14.15, - 17.13 ppm degrees C (1). During the entire range of sintering temperatures a single phase of rock-salt structure Li2O-MgO-BO2 (B = Ti, Sn, Zr) cerami(c)s could be obtained and then structural parameters such as the packing fraction and B-site octahedral distortions due to B-site cations were investigated to be associated with microwave properties based on Rietveld refinements. Based on the Raman spectrum for B = Ti, Zr, Sn ions the Raman shifts were assigned to be 478.91 cm(-1), 479.17 cm(-1), and 479.3 cm(-1) and the FWHM values were 10.97 cm(-1), 11.82 cm(-1), and 11.28 cm(-1) correspondingly. The dielectric constants showed an inverse correlation with Raman shifts of vibration modes and an inverse correlation also existed between the FWHM and dielectric loss. Moreover, based on the complex bond theory the crystalline structure refinement, chemical bond ionicity, and lattice energy were calculated to evaluate the correlations between the crystalline structure and dielectric properties.