A.S. de Menezes

Effect of Ni(II) doping on the structure of L-histidine hydrochloride monohydrate crystals

In this paper, we study the effect of Ni(II) doping on the structure of L-histidine hydrochloride monohydrate crystals using x-ray diffraction and Raman spectroscopy. X-ray powder diffraction shows no significant change in the unit cell parameters of the doped single crystal, whereas x-ray multiple diffraction using synchrotron radiation indicates that the Ni ions are located in interstitial positions in the crystal lattice. The temperature-dependent Raman spectra reveal a structural phase transition in the 10–300 K temperature range. The proposed mechanism of this phase transition supports the suggestion that the Ni ions occupy interstitial positions.

Piezoelectric coefficients of L-histidine hydrochloride monohydrate obtained by synchrotron x-ray Renninger scanning

The method for determining piezoelectric coefficients based on synchrotron radiation x-ray multiple diffraction (Avanci et al 1998 Phys. Rev. Lett. 81 5426) has been used in the case of a single crystal of the amino acid L-histidine·HCl·H2O. The method relates the E-induced strain with the angular shift in the multiple diffraction peak position. Thus, it allowed us to determine all three (d14 = 2.25(9) × 10 −10 CN −1 , d25 = 4.1(5) × 10 −11 CN −1 and d36 = 2.3(2) × 10 −10 CN −1 ) piezoelectric coefficients of L-histidine·HCl·H2O, using the (10 0 0) and (0 0 4) primary reflections.

Dielectric Properties of Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC)–CaCu3Ti4O12 (CCTO) Composite

The main object of this work is to study two materials with giant dielectric constants: CaCu3Ti4O12 (CCTO) and Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC). CBTC1−x–CCTOx composites were also obtained to create a new dielectric material with dielectric properties between these two phases. Structural properties were studied by x-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and dielectric measurements. CCTO showed a cubic phase and CBTC an orthorhombic phase. An interesting result was that the dielectric constant (K) did not follow the rule of the mixture of Lichtnecker, and this happened due to the presence of other phases of its crystalline structure, which decreases the value of K when compared to the predicted values of Lichtnecker. It was also found that the dielectric properties of the composite are very promising for use in microelectronics, according to the miniaturization factor, which is crucial for those applications.

Synchrotron x-ray multiple diffraction in the study of Fe+ ion implantation in Si(0 0 1)

In this work, x-ray multiple diffraction has been used as a three-dimensional high-resolution probe to study the Fe+ ion implantation process in Si(0?0?1). The semiconducting ?-FeSi2 crystallographic phase has been synthesized by Fe ion co-implantation in Si(0?0?1) followed by ion-beam-induced epitaxial crystallization (IBIEC) and thermal treatment. This phase was clearly detected by the conventional techniques, micro-Raman scattering spectroscopy, transmission electron microscopy (TEM) and grazing incidence x-ray diffraction. Synchrotron radiation rocking curves (?-scans) and mapping of the Bragg surface diffraction (BSD) of the Si matrix, as-implanted, after the IBIEC process and thermally treated, have enabled the detection of co-implanted regions formation that present distinct lattices in comparison with the matrix one clearly observed by TEM. Also, the compressive strain of both regions in depth by rocking curve and in-plane has been determined by using BSD, which is one order of magnitude smaller.

Low-temperature phase transformation studies in the stearic acid: C form.

This paper reports the temperature-dependent measurements in the C form of stearic acid. Raman scattering, X-ray diffraction, and differential scanning calorimetry measurements were performed at low temperatures. The polarized Raman spectra were measured for temperatures ranging from 8 to 300 K over the spectral range of 30-3000 cm(-1). The spectral changes observed in both the lattice vibrational modes and the internal vibrational modes regions of the Raman spectrum, allowed to identify a phase transition undergone by the stearic acid crystal occurring between 210 and 170 K and a change in the structure continues to be observed down to 8 K. The anharmonicity of some vibrational modes and the possible space groups presented by the crystal at low temperatures were also discussed. Low-temperature X-ray diffraction measurements were performed from 290 to 80 K and the results showed slight changes in the lattice parameters at ∼200 K. Furthermore, the evidence of the phase transformation was provided by the differential scanning calorimetry measurements, which identified an enthalpic anomaly at about 160 K.

Role of rare-earth ionic radii on the spin–phonon coupling in multiferroic ordered double perovskites

In this paper, we investigated the influence of rare-earth ionic radii on spin–phonon coupling in RE2NiMnO6 double perovskites by Raman spectroscopy. Spin–phonons in dense Nd2NiMnO6 and Gd2NiMnO6 ceramics were investigated by Raman spectroscopy at low temperatures. The magnitude of the observed coupling in comparison with other isostructural compounds shows that coupling is not influenced by the rare-earth ionic radius, as well as the deviation in position of the stretching phonon in the ferromagnetic phase in relation to the anharmonic contributions follows a power law.

Physicochemical analysis of Permian coprolites from Brazil

In this paper we performed the study of two coprolites (fossilized feces) collected from the exposed levels of the Pedra de Fogo Formation, Parnaiba Sedimentary Basin, and Rio do Rasto Formation, Paraná Sedimentary Basin, both of the Palaeozoic era (Permian age). They were characterized using X-ray diffractometry, infrared, Raman and energy dispersive spectroscopy techniques in order to aid our understanding of the processes of fossilization and to discuss issues related to the feeding habits of the animals which generated those coprolites, probably cartilaginous fishes. The results obtained using a multitechnique approach showed that although these coprolites are from different geological formations, 3000km away from each other, they show the same major crystalline phases and elemental composition. The main phases found were hydroxyapatite, silica, calcite and hematite, which lead to infer that those coprolites were formed under similar conditions and produced by a similar group of carnivore or omnivore fishes.

Conformational change in the C form of palmitic acid investigated by Raman spectroscopy and X-ray diffraction

Fatty acids are substances found in most living beings in nature. Here we report the effect of the low temperature in the vibrational and structural properties of the C form of palmitic acid, a fatty acid with 16 carbon atoms. The Raman spectra were obtained in the temperature interval from 300 to 18K in the spectral range between 30 and 3100 cm(-1). The assignment of the duly observed bands was done based on the density functional theory. On cooling, the main changes observed in the lattice mode region of the Raman spectra were interpreted as a conformational modification undergone by the palmitic acid molecules in the unit cell. The X-ray diffraction measurements were obtained from 290 to 80K showing a slight modification in the lattice parameters at about 210K. Differential scanning calorimetry (DSC) measurements were recorded between 150 and 300K and no enthalpic anomaly in the DSC thermogram was observed. These techniques provided strong evidence of the conformational change in the molecules of palmitic acid at low temperatures.

High pressure studies on bis (L-histidinate) nickel (II) monohydrate

Raman spectra of bis(l-histidinate)nickel(II) monohydrate crystal were obtained for pressures up to 9.5GPa. Our results show the disappearance of some of the Raman modes and the appearance of other modes. These modifications evidence that the sample undergoes phase transitions at around 0.8 and 3.2GPa. The role played by the Ni ions and hydrogen bonds in the dynamics of the phase transitions is discussed. Under decompression, down to atmospheric pressure, the original Raman spectra are recovered, showing that both phase transitions are fully reversible.

Structural, vibrational and thermal studies on bis(l-glutaminato)copper(II)

Copper(II) complexes of amino acids have been widely studied as potentials medicines and dietary supplementation, so the knowledge about the metal-ligand sites, thermal stability and behavior of these complexes is an important subject of study. Although the Raman spectroscopy could help to elucidate the nature of the interactions into crystal there are only few information about vibrational study of this compound in the literature and no data depending on the temperature. In addition, there is no temperature-dependent X-ray diffraction study of this material. We report here Raman Spectroscopy and Powder X-ray Diffraction measurements, both as a function of temperature and as a way of studying the thermal stability of the material. After the synthesis of the sample and confirmation of its crystal structure by Powder X-ray Diffraction, Raman measurements were performed in the 70-3600 cm-1 spectral region as a function of temperature from 10 up to 300 K. Some peaks become more evident during the cooling, due to a decrease in width and an increase in intensity. There is a discontinuity in the wavenumbers evolution around 110 K, that should be associated with a conformation of the structure. Optimized geometry and vibrational frequencies were obtained by means of Density Functional Theory and for the first time the analysis of the vibrational modes was done in terms of the Potential Energy Distribution. X-ray diffraction measurements as a function of temperature and Rietveld refinement showed discontinuities in the lattice parameters and degradation around 493 K (at air atmosphere) and 513 K (under vacuum). These results were corroborated by the thermal analysis which indicates that the compound is stable up to 493 K.