Effect of Mn2+ ions on spectroscopic and electrical properties of lithium strontium borate glasses

Abstract

Manganese doped lithium strontium borate glasses with chemical composition 25Li2O-15SrO-(60-x)B2O3-xMnO are prepared through the classical melt-quenching method and characterized by various techniques like XRD, DSC, optical absorption, EPR, Impedance spectra and AC conductivity. The XRD and DSC studies revealed the amorphous glassy nature of the prepared samples. The optical absorption spectra of the prepared inorganic glassy samples depict a single extensive absorption band at 470 nm attributed to the 6A1g(S)→4T1g(G) transition of Mn2+ ions belonging to d5 configuration in the octahedral symmetry sites. These spectra also substantiated that the octahedral Mn2+ ions were prevailing up to 0.8 mol% of MnO. The optical band gap energy and Urbach energies were evaluated from these spectra. The EPR spectra show three resonance signals positioned at g ≈ 2.0, 3.1 and 4.3 due to the Mn2+ paramagnetic ions. The resonance peak perceived at g ≈ 2.0 gives a predominant six-line hyperfine structure (hfs), a principal signature of Mn2+ ions. The hyperfine constant (Aavg), spin concentration (N), paramagnetic susceptibility (χ) and zero-field splitting (D) parameters of the prepared glass samples were evaluated and analyzed. The Nyquist (Cole-Cole) plots exhibit only one well-shaped semicircle (single-phase) throughout all the temperatures, which confirms the good homogeneity of the current glass system. The AC conductivity values of the prepared glassy samples are amplified with temperature and frequency. The AC conductivity values changed from 10−8 to 10−3 Ω−1cm−1. The LSBM8 glass sample has the highest AC conductivity; hence these glassy inorganic materials are suitable for solid-state battery applications and other opto-electronic device applications.