I.F. Vasconcelos

Raman and infrared spectra of KNbO3 in niobate glass-ceramics

Potassium niobophosphate glasses and glass-ceramics of the family [xNb2O5.(50-x) P2O5.50K2O]:yFe2O3 were studied by x-ray powder diffraction, infrared and Raman scattering spectroscopy. For the potassium-phosphate samples [50P2O5-50K2O] the iron oxide presents a network former behaviour, for 2 mol% of Fe2O3 doping. The precipitation of crystalline K4Nb6O17 and ferroelectric KNbO3 crystals was confirmed by x-ray powder diffraction in the samples with x = 40 and 50 mol% respectively. The infrared and Raman scattering spectroscopy results suggest that the increase of the ratio Nb2O5/P2O5 leads the niobium to sites of octahedral symmetry and consequently to the formation of ferroelectric KNbO3, as seen by x-ray diffraction analysis.

Structural studies of lithium triborate (LBO–LiB3O5) in borophosphate glass-ceramics

Abstract In this paper lithium borophosphate glasses and glass-ceramics in the system 0.75| x B 2 O 3 .(100− x )P 2 O 5 |.25Li 2 O. y Fe 2 O 3 with 0≤ x ≤100 mol.% and y =4 mol.%, were studied by X-ray powder diffraction, Mossbauer and infrared spectroscopy. All the samples in the system present a glass or glass-ceramic behavior which was confirmed by X-ray diffraction. From our Mossbauer analysis, high spin Fe 2+ and Fe 3+ in a distorted octahedral coordination are present in all samples. One can conclude that both iron ions are at sites of distorted octahedral coordination, acting as network modifiers (NWM) in a very broad site distribution, which is characteristic of an amorphous structural neighborhood. Such glasses and glass-ceramics containing nonlinear optical materials formed in a controlled crystallization process would be interesting candidates for applications in new nonlinear optical devices.

Magnetic properties study on Fe-doped calcium phosphate

Calcium phosphates are very important for applications in medicine due to their properties such as biocompatibility and bioactivity. In order to enhance these properties, substitution of calcium with other ions has been proposed. Partial substitution of calcium by different ions has been made in order to improve the properties of the calcium phosphates and also to allow new applications of apatite in medicine. In this work, hydroxyapatite [Ca10(PO4)6(OH)2?HAP] was prepared by high-energy dry milling (20?h) and mixed with iron oxide (5?wt.%). The mixture was calcinated at 900??C for 5?h with a heating rate of 3??C?min?1 in an attempt to introduce iron oxide into the HAP structure. The sintered sample was characterized using x-ray diffraction (XRD) and magnetization. The 57Fe-M?ssbauer spectra of the calcium phosphate oxides were also measured, revealing the presence of iron in three different phases: Ca2Fe2O5, Fe2O3 and hydroxyapatite.