Microwave dielectric properties of Li2SrTa2(1−x)Nb2xO7 ceramics investigated by Raman spectroscopy. Issue 6 (1st May 2016) - Singh, Santosh Kumar
Abstract: We investigated the crystal structure and microwave dielectric properties of the Li2 SrTa2(1− x ) Nb2 x O7 ( 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 BO6 octahedra. The peak width of Ag (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 ( ε r ). Further analysis of the Raman modes at 800, 596 and 589 cm −1 (due to the BO6 octahedra) indicates the enhancement of octahedral distortion with increase in Nb content, which led to increase of temperature coefficient of resonant frequency ( τ ƒ ).