Anomalous microwave dielectric behaviour induced by the orthorhombic-tetragonal phase transition in CaLaGaO4 ceramics

In this work, orthorhombic (o-) and tetragonal (t-) phase CaLaGaO4 ceramics were synthesized using a conventional solid-state method. Phase evolution and crystal structure were investigated via XRD and TEM, and oCaLaGaO4 phase with Pna21 space group can be obtained at a low temperature (<1260 C). With the increase in sintering temperature, o-CaLaGaO4 and t-CaLaGaO4 phases (I4/mmm) coexisted when sintered in the range of 1280 degrees C - 1300 degrees C. The microwave dielectric properties of the o-CaLaGaO4 ceramic sintered at 1240 degrees C were er = 11.2, Q x f = 63,900 GHz, and af = -56.6 ppm/celcius. By contrast, the phase transformation in the CaLaGaO4 ceramic led to a significantly increased er (19.5) in t-CaLaGaO4 and a near-zero af (+2.3 ppm/celcius). The theoretical permittivity (eth) was calculated on the basis of the Clausius-Mossotti equation and P-V-L theory. Results indicate that in the low-symmetry-structure o-CaLaGaO4 ceramics, eth can be estimated accurately by the latter.

Automated summary

Orthorhombic and tetragonal phase CaLaGaO4 ceramics were synthesized using a conventional solid-state method in this study. The crystal structure and phase evolution were investigated, and it was found that different phases coexisted at certain sintering temperature ranges, leading to variations in microwave dielectric properties. Theoretical permittivity calculations based on specific equations provided insights into accurate estimation of properties in low-symmetry-structure ceramics.