Rattling and compressed cations resulting in distinct microwave dielectric characteristics of SrPrBO4 (B = Ga, Al) with K2NiF4 structure

Abstract

In this work, tetragonal K2NiF4 structured SrPrBO4 (B = Ga, Al) ceramics with I4/mmm space group were synthesized via the conventional solid-phase method. High relative density (>95 %) and excellent microwave dielectric properties of εr = 18.15, Q×f = 36,643 GHz, τf = −20.20 ppm/°C for SrPrAlO4, and εr = 22.02, Q×f = 27,475 GHz, τf = +19.11 ppm/°C for SrPrGaO4 were obtained when sintered at 1500 °C and 1375 °C, respectively. Analyses of the bond valences show that the εr and τf values are closely related to the rattling and compressing effects of the A-site cation. The strong compressed effect of Sr2+ in SrPrAlO4 leads to its εr value less than the εr(C-M); while, the strong rattling effect of Pr3+ in SrPrGaO4 leads to its εr value higher than the εr(C-M), and thus to a positive τf. The Al/Ga–O bonds play a crucial role in the influence of the dielectric loss according to the P–V–L chemical bonding theory analysis. The Edc of SrPrAlO4 (0.99 eV) and SrPrGaO4 (0.52 eV) indicates that the formation mechanisms of oxygen vacancies in both ceramics are different.