Na-doped diopside microwave ceramics with dielectric properties influenced by the sintering, lattice vibration and chemical bond characteristics

The Na-doped diopside (CaMg1-xNa2xSi2O6, x = 0–0.18) microwave dielectric ceramics were fabricated via solid-state reaction method. Three phases were identified through the XRD data that was refined with the Rietveld method to obtain structural information. The role of Na+ substitution to promote the densification process could be corroborated by the SEM images and relative density. The P-V-L bond theory was used to explore the chemical bond characteristics and structure-performance relationships. Through discussion, the dielectric constant was determined by relative density rather than the bond ionicity. The Q × f value was dominated by the lattice energy, lattice vibration and was also related to the relative density and grain size. And the linear thermal expansion coefficient was closely correlated with the τf value. Excellent microwave dielectric properties, (εr = 7.573, Q × f = 35049 GHz, tan δ = 4.015 × 10−4, τf = −68.71 ppm/°C) and (εr = 7.646, Q × f = 37844 GHz, tan δ = 3.706 ×10−4, τf = −54.2 ppm/°C) were achieved for the CaMg0.97Na0.06Si2O6 ceramics sintered at 1150 °C/3 h and 1200 °C/3 h, respectively.