Structural, spectroscopic and electrical properties of iron doped oxyfluoride bismuth borate glasses

Glasses with compositions xFe2O3.(55-x)B2O3.10Bi2O3.10CaO.25LiF (x = 0, 1, 2, 3, 5 and 7 mol% abbreviated as CaF0, CaF1, CaF2, CaF3, CaF5 and CaF7 respectively) have been synthesized using standard melt quench technique. Structural, spectroscopic, electrical, optical and thermal properties of these glasses are explored using X-ray diffraction (XRD), Fourier transform infrared (FTIR) absorption spectra, electron paramagnetic resonance (EPR) spectra, dielectric measurements, ac conductivity, equivalent circuit analysis, modulus analysis, dc conductivity, UV-Vis-NIR spectra and differential thermal analysis (DTA). Non-crystalline nature is confirmed using XRD and FTIR. UV-Vis and EPR spectra show that Fe3+ exists in distorted octahedral coordination. Dielectric parameters (ε′, ε″ and tanδ) are found to show similar variation and decrease with increasing frequencies. Modulus analysis and impedance spectroscopy revealed non-Debye type relaxation phenomena with a shift in and maxima of Mmax towards higher frequency at higher temperature. Nyquist's plot was fitted to equivalent circuit which consisted of series combination of two constant phase elements and a resistor connected in parallel. Variation in ac conductivity for all samples follows Jonscher's power law. Frequency exponent parameter (s) was calculated to analyse conduction mechanism by different conductivity models. Variation of dc conductivity with temperature confirms semiconducting behavior of prepared glasses and no deviation in linearity of Arrhenius plot depicts contributions due to ionic conduction principally. Optical band gap obtained from DRS is found to be in range 2.45-3.66 eV with a decreasing trend with increased iron content.