Thermal, structural, and optical properties of oxychloro manganese phosphate glasses

This paper examines the effect of replacing MnO2 by MnCl2 on the physiochemical properties in 90NaPO3-(10-x)MnO2-xMnCl2, with 0 <= x <= 10 mol% glass system. These materials were synthesized by the conventional melt quenching technique. The resulting glasses exhibited various colors indicating that manganese's oxidizing state was composition-dependent. X-ray diffraction (XRD) verified the non-crystalline nature of the investigated glasses. Replacing the lighter molecule MnO2 (86.93 g mol-1) with heavier MnCl2 (125.84 g mol-1) in the vitreous matrix increased both the density and the molar volume. Differential scanning calorimetry (DSC) showed decreased glass transition temperature by adding MnCl2 content, and the Vickers micro-hardness tests showed a decrease trend; these results are expected since Mn-O is more covalent than Mn-Cl ones The structural approach is performed by IR spectroscopy. This technique highlights the presence of many structural phosphate units, mainly pyrophosphates, and metaphosphates structural groups. The UV-visible spectra of the examined glasses reveal visible absorption bands in the 400-600 nm range corresponding to manganese's existence in trivalent and divalent states. The optical parameters, such as the optical band gap (Eg) and the Urbach energy (Delta E) are determined from the optical spectra and their evolution with the composition is discussed. The crystallization of glasses is induced through heat treatments, followed by the identification of crystalline phases using XRD analysis. The kinetics of crystallization were examined under non-isothermal conditions, leading to the determination of the activation energy (Ec) and the mechanism of the crystallization.