Microwave dielectric properties of Li 2 SrTa 2(1−x) Nb 2x O 7 ceramics investigated by Raman spectroscopy

Abstract We investigated the crystal structure and microwave dielectric properties of the Li 2 SrTa 2(1− x ) Nb 2 x O 7 ( x =0−1.0) compounds using Raman spectroscopy. The Raman spectra clearly exhibit the orthorhombic structure (Cmcm space group) of these compounds. The Raman mode at 800 cm −1 corresponds to the B–O3 (B=Nb and Ta) bond and shifted towards the higher frequency with increase of Nb content. The increase in separation between the two modes at 589 and 596 cm −1 gives an indication of change in the difference between B–O1 and B–O2 bond lengths. The microwave dielectric properties of these compounds were found to be strongly dependent on the BO 6 octahedra. The peak width of A g (800 cm −1 ) mode and quality factor ( Q×f ) is inversely proportional to each other and the shift of this mode is correlated to dielectric constant ( e r ). Further analysis of the Raman modes at 800, 596 and 589 cm −1 (due to the BO 6 octahedra) indicates the enhancement of octahedral distortion with increase in Nb content, which led to increase of temperature coefficient of resonant frequency ( τ ƒ ).