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

摘要

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 <degrees>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.

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