Relationship between bond characteristics and microwave dielectric properties of REVO4 (RE = Yb, Ho) ceramics

摘要

? 2022 Elsevier Ltd and Techna Group S.r.l.Two novel low-εr REVO4 (RE = Yb, Ho) microwave dielectric ceramics with the symmetry of the zircon structure, space group I41/amd, were prepared using the solid-state method. Dense REVO4 (RE = Yb, Ho) ceramics sintered at 1200 °C and 1160 °C performed εr ～ 12.3 ± 0.1 and 13.3 ± 0.1, Q × f ～ 28,200 ± 300 GHz and 24,100 ± 300 GHz, τf ～ ?18.8 ± 0.5 ppm/°C and ?17.4 ± 0.5 ppm/°C, along with thermal expansion coefficient (αL) of 9.0 ppm/°C and 8.1 ppm/°C, respectively. Bond valence results indicated that the slightly rattling RE3+ cations at the A-site and compressed V5+ at the B-site occurred in both ceramics. The positive deviations (Δεr) of porosity corrected εr(Corr) from those calculated by the Clausius-Mosotti equation εr(C-M), 8.1% for YbVO4 and 17.7% for HoVO4, were observed, implying that the rattling effect of RE3+ in dodecahedral A-site were greater than those of compressed V5+ in tetrahedral B-site. Rattling effect also led REVO4 (RE = Yb, Ho) to develop higher εr, and smaller τε and ταm, then closer to zero τf values than other zircon-structured REVO4 (RE = Ce, Nd, Sm, Eu) ceramics with large negative τf. The differences in sintering temperature and microwave dielectric performance of both ceramics were discussed using the packing fraction, full width at half maximum (FWHM) of Raman modes and Phillips-Van Vechten-Levine (P–V-L) theory.