Structural refinement, Raman spectroscopy, optical and electrical properties of (Ba1−xSrx)MoO4 ceramics

Abstract

In this paper, structural refinement, Raman spectroscopy, optical and electrical properties of barium strontium molybdate [(Ba1−x Sr x )MoO4] ceramics with different (x) contents (x = 0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; and 1) were synthesized by the solid state reaction method. These ceramics were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, and micro-Raman spectroscopy. The shape of the grains for these ceramics was observed by means of scanning electron microscopy (SEM) images. The optical properties were investigated using ultraviolet–visible (UV–Vis) absorption spectroscopy and photoluminescence (PL) measurements. The dielectric and ferroelectric properties were analyzed by permittivity (er), loss tangent (tan δ) and polarization versus electric field (P–E) hysteresis loop. XRD patterns, Rietveld refinement, and micro-Raman spectra showed that all ceramics are monophasic with a scheelite-type tetragonal structure. A decreased of lattice parameters and unit cell volume was observed with the increase of Sr2+ ions into BaMoO4 lattice. Rietveld data were employed to model the [BaO8], [SrO8] and [MoO4] clusters in the tetragonal lattices. The SEM images indicate that increased x content promotes a decrease in the grain size and modifications in the shape. UV–Vis spectra indicated a decrease in the optical band gap values with an increase in x content in the (Ba1−x Sr x )MoO4 ceramics. PL emissions exhibit a non-linear behavior to increase or decrease with the increase of Sr2+ ions in the tetragonal lattices, when excited by a wavelength of 350 nm. The P–E decreases along with slim hysteresis loop towards higher Sr2+ ions concentration. These effects are correlated with decrease in lattice parameters and c/a ratio in this tetragonal lattice. The microwave dielectric constant and quality factor were measured using the method proposed by Hakki–Coleman. Temperature coefficient and quality factor of these materials were measured by vector network analyzer.