The optical and 57Fe Mössbauer spectra of lithium diborate (Li2B4O7) in borophosphate glass-ceramics

Abstract

In this paper lithium borophosphate glasses and glass-ceramics in the system 66.6|xB2O3·(100−x)P2O5|. 33.3Li2O:yFe2O3 with 0⩽x⩽100mol% and y=4mol%, were studied by X-ray powder diffraction, 57Fe Mössbauer and infrared spectroscopy. All the samples in the system present a glass or glass-ceramics behavior which is confirmed by X-ray diffraction. The substitution of P5+ by B3+ associated with the increase of the ratio B2O3/P2O5 leads to oxidation of the iron in the samples which was detected by Mössbauer spectroscopy. From our Mössbauer analysis, high-spin Fe2+ and Fe3+ in a distorted octahedral coordination are present in all samples. For heat-treated samples we have the precipitation of crystalline phase of Li2B4O7 and for others lithium borate phases which was confirmed by X-ray powder diffraction. The Mössbauer spectra for some heat-treated samples show, besides the paramagnetic doublets, a magnetic sextet component with hyperfine magnetic field (Bhf=50T). These magnetic phases were not identified up to this point in our study but we believe that these parameters are quite close to Hematite (α-Fe2O3). The boric acid phase H3BO3 were also identified by the X-ray diffraction, and infrared spectroscopy for x=26.6, 40 and 53.3mol%. Such glasses and glass-ceramics containing nonlinear optical materials formed in a controlled crystallization process would be interesting candidates for application in new electro-optic devices.