J. A. C. De Paiva

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.

Raman and infrared spectroscopy studies of LiNbO3 in niobate glass-ceramics

Abstract Optical and structural properties of lithium niobophosphate glasses, with composition [ x Nb 2 O 5 · (50 − x )P 2 O 5 · 50Li 2 O ]: y Fe 2 O 3 , were studied by X-ray powder diffraction, in spectroscopies. Precipitation of ferroelectric LiNbO 3 crystals was confirmed by X-ray powder diffraction in the sample 10Nb 2 O 5 − 40P 2 O 5 − 5OLi 2 O:2Fe 2 O 3 , under heat treatment. The crystallization process groups of different degrees of complexity, such as LiPO 3 , LiP 2 O 7 and Li 3 PO 4 , were observed. The infrared and Raman spectroscopy results suggest that the increase of the ratio Nb 2 O 5 P 2 O 5 leads the niobium to sites of octahedral symmetry and consequently to the formation of ferroelectric LiNbO 3 , as observed by X-ray diffraction analysis.

The properties and crystallization of LiNbO3 in lithium niobophosphate glasses

Lithium niobophosphate glasses [(xNb2O5.(0.5-x)P2O5).0.5Li2O]:yFe2O3 were studied using infrared spectroscopy and X-ray powder diffraction. The use of the two techniques gives new information about the structure of niobium phosphate glasses and glass ceramics. It was observed that under heat treatment phosphorus-oxygen groupings of different degrees of complexity, like LiPO3, Li4P2O7 and Li3PO4, were formed. Ferroelectric LiNbO3 crystals were also detected for x=0.1 niobium content samples.

Effect of the pH on the piezoelectric properties of collagen films

Abstract In this paper, we did a study of the physicochemical, dielectric and piezoelectric properties of collagen films, considering the development of new biomaterials which have potential applications in coating of cardiovascular prostheses, support for cellular growth and in systems for controlled drug delivery. The piezoelectric strain tensor element d 14 , the elastic constant S 55 , and the dielectric permittivity e 11 were measured for collagen films. It was observed that the collagen samples submitted to different pH treatment lead to different electrical behavior. For sample S2 (pH=5.2 ) one has a higher denaturation temperature ( T d =80.55°C), lowest density ( ρ =909.6 kg m −3 ), highest dielectric function, lowest frequency constant product ( f × L =320.33 kHz.m) and higher piezoelectricity ( d 14 =0.122 pC/N) which is our major interest in this study. The loss factor Q −1 measured for all the samples shows that for all the electrodes dimensions sample S2 present the highest loss factor which is between 0.68 and 0.76. We believe that the different pH treatment is critical to the final level of organization of the microscopic structure of the sample, which could result in an increase of the piezoelectricity.

Piezoelectric and Dielectric Properties of Collagen Films

In this paper we studied the piezoelectric and dielectric properties of collagen films, considering the development of new biomaterials which have potential applications in coating of cardiovascular prostheses, support of cellular growth and in systems for controlled drug delivery. The resonance technique was used to measure the piezoelectric strain tensor element d 14 , the elastic constant S 55 , and the dielectric permittivity e 11 , for collagen films. The resonance measurement of the piezoelectric strain constant d 14 of collagen gives 0.096 pC/N, which is in good agreement with values reported in the literature measured using other experimental techniques. We believe that the use of the resonance technique is very efficient in the study of piezoelectricity in films of biological materials.

Crystallization of ferroelectric LiNbO3 in niobophosphate glasses

Niobophosphate glasses [(xNb2O5(0.5 − x)P2O5)0.5Li2O]: yFe2O3 were prepared by the melt-quenching method and analysed by means of infrared spectroscopy and x-ray powder diffraction. LiNbO3 crystals were detected for high niobium contents samples. The use of both techniques gives new information about the structure of niobium-phosphate glasses and glass-ceramics.

Spectroscopic Studies of Iron Niobophosphate Glasses

We investigated iron niobiophosphate glasses [0.1Nb 2 O 5 . 0.4P 2 O 5 . 0.5Li 2 O]yFe 2 O 3 (y = 0, 0.1, 0.2, 0.3, 0.4, 0.5) prepared in ambient atmosphere using the melt quenching technique. The samples were studied using X-ray powder diffraction Fe Mossbauer and infrared spectroscopy, in order to investigate the effect of the increasing concentration of α-Fe 2 O 3 in the glass matrix. According to Mossbauer results high spin Fe 3+ and high spin Fe 2+ at distorted octahedral sites are present in all samples. The distortion of the Fe 3+ and Fe 2+ ions sites increases from low (y = 0.1) to high (y = 0.3) iron content samples. The measurements of the infrared absorption, X-ray powder diffraction and Mossbauer spectroscopy also indicate that LiFePO 4 and α-Fe 2 O 3 crystalline phases are present for high iron content samples (y = (1.4, 0.5). The limit of solubility of α-Fe 2 O 3 in these glasses is around 23 mol%.

Thermally stimulated depolarization current and Mössbauer spectroscopy of iron-doped niobophosphate glasses

Niobophosphate glasses (P2O5-PbO-Nb2O5-K2O-XFe2O3), were studied using thermally stimulated depolarization currents and Mössbauer spectroscopy in samples of different iron concentrations, and were subjected to oxidation and reduction processes. The use of both techniques provided new information about the distribution of iron and niobium between tetrahedral and octahedral sites.

Infrared and complex dielectric function studies of LiNbO3 in niobate glass-ceramics

Niobate glasses and ceramics [(x Nb2O5 (0.5 − x) P2O5) 0.5 Li2O] were prepared by the melt-quenching method and analysed by means of infrared spectroscopy, X-ray powder diffraction and complex impedance methods. LiNbO3 crystals were detected for high niobium content samples. The study of the complex dielectric function of the LiNbO3 ceramics revealed a very broad acoustic resonance mode around 3 MHz. This resonance was associated to the thickness mode of the LiNbO3 plate ceramic resonator. Electrical poling was performed at 300°C for 6 hours under an applied dc potential of 1 kV. Strong changes were observed on the complex dielectric function of the niobate ceramic after the poling. The study of the properties of these ferroelectric ceramics is important in view of possible applications in ultrasonic devices such as delay lines and transducers.

Structure of iron niobophosphate glasses investigated by DTA, infrared and Mössbauer spectroscopy

Activation energies for crystallization of 50 glasses, with x = 0, 5 and 10 mol%, were determined by differential thermal analysis (DTA). The structure was investigated by infrared and M?ssbauer spectroscopy. Samples with x = 5 mol% of show larger activation energy . Absorptions at P-O-P, P=O, and units are presents in these glasses. P=O absorptions disappear at compositions with x = 5 and 10 mol% of , which shows absorption around , attributed to units. According to M?ssbauer results high spin and at distorted octahedral sites are present in samples with x = 5 and 10 mol% of , thus working as a network modifier.