Effect of crystal structure on microwave dielectric properties of Li<inf>2</inf>SrTa<inf>2(1-x)</inf>Nb<inf>2x</inf>O<inf>7</inf> compounds

The Li2SrTa2(1-x)Nb2xO7 (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 (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 ×) 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 (τf) of these compounds.