The optical and 57Fe Mössbauer spectra of lithium diborate (Li 2B 4O 7) in borophosphate glass-ceramics

Abstract

In this paper lithium borophosphate glasses and glass-ceramics in the system 66.6| xB 2O 3·(100− x)P 2O 5|. 33.3Li 2O: yFe 2O 3 with 0⩽ x⩽100 mol% and y=4 mol%, 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 P 5+ by B 3+ associated with the increase of the ratio B 2O 3/P 2O 5 leads to oxidation of the iron in the samples which was detected by Mössbauer spectroscopy. From our Mössbauer analysis, high-spin Fe 2+ and Fe 3+ in a distorted octahedral coordination are present in all samples. For heat-treated samples we have the precipitation of crystalline phase of Li 2B 4O 7 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 ( B hf=50 T). 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-Fe 2O 3). The boric acid phase H 3BO 3 were also identified by the X-ray diffraction, and infrared spectroscopy for x=26.6, 40 and 53.3 mol%. 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.