Optical and AC conductivity studies on Li2-xRbxMoO4 (x=0, 0.5, 1) compounds

In this work, we are interested in the new compounds Li1.5Rb0.5MoO4 preparation by the solid state method. Also, we present a comparative study with LiRbMoO4 and Li2MoO4. The X-ray powder diffraction indicates that these compounds crystallize at room temperature in the monoclinic, orthorhombic and trigonal systems with the P2(1), Pcab and R-3 space groups, respectively. The shapes of the grains for these ceramics were observed by means of scanning electron microscopy (SEM) images. The Tauc model was used to determine the optical gap energy (4, 4.3 and 3.9 ev) and the urbach energies (1.51, 0.35 and 1.14 ev) of our compounds. The electric and dielectric proprieties of Li1.5Rb0.5MoO4 have been studied. We carried out complex impedance spectroscopy in the frequency range 200 Hz-5 MHz at different temperatures (575-723 K). The complex impedance diagram showed a single semicircle, implying that the response originates corresponding to the grains. As a result, an electrical equivalent circuit has been proposed. The spectra follow the Arrhenius law with two energies of activation 1.58 eV for impedance measurements and 1.25 eV for that of modulus. The alternative current (AC) electrical conduction of the three compounds is governed by the overlapping large polaron tunneling (OLPT). (C) 2019 Elsevier B.V. All rights reserved.