Effect of crystal structure on microwave dielectric properties of Li₂SrTa_2(1−x)Nb_2xO₇ compounds

Highlights: • Synthesis of orthorhombic Li₂SrTa_2(1−x)Nb_2xO₇ compounds • The mechanism for enhancement of quality factor by bond strength. • Deviation of τ_ƒ with octahedral distortion of the compound. - Abstract: The Li₂SrTa_2(1−x)Nb_2xO₇ (x = 0–1.0) with layered-perovskite type structure were synthesized by conventional solid state reaction method. The X-ray diffraction reveals that all these compounds possess orthorhombic crystal structure with Cmcm space group. B-site bond strength and B-site octahedral distortion of these compounds were calculated using bond lengths obtained from Rietveld refinement. The dielectric constant (ϵ_r) decreased from 24.2 to 15.2 with increase in the Nb concentration, which was due to decrease in dielectric polarizability of compound. The non-monotonic variation in quality factor (Q × ƒ) was observed with Nb concentration. This variation of quality factor was correlated with the B-site bond strength. The B-site octahedral distortion was found to increase with Nb content, which was the major factor for increase in temperature coefficient of resonant frequency (τ_f) of these compounds