Correlation between structure and microwave dielectric properties of ordered olivine CaLnGaO4 (Ln = Pr, Yb) ceramics

The microwave dielectric properties of olivine-structured CaLnGaO4 (Ln = Pr, Yb) ceramics with a 1:1 order at the octahedra site were investigated using bond valance, P–V-L chemical bond theory, and Raman spectra. The theoretical permittivity εr(C-M) values are far below the porosity-corrected εr(Corr) values, indicating that the dielectric polarizabilities of CaLnGaO4 (Ln = Pr, Yb) were underestimated, and this phenomenon was mainly influenced by rattling cations. The difference in εr is mainly determined by the ionic polarizability per unit volume (αm/Vm). The τf values of CaLnGaO4 (Ln = Pr, Yb) did not decrease with the decrease of the εr, which was due to the larger positive temperature coefficient of dielectric constant (τε) and the higher coefficient of thermal expansion (αL) of CaPrGaO4 ceramic compared to CaYbGaO4, respectively. The difference in Q × f values between CaPrGaO4 and CaYbGaO4 is mainly due to the strain of chemical bonds and the Raman spectrum.