J. M. Sasaki

Structural properties of CaCu3Ti4O12 obtained by mechanical alloying

Mechanical alloying has been used successfully to produce nanocrystalline powders of CaCu3Ti4O12 (CCTO), for the first time, using two different experimental procedures. The milled CCTO were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. For two different milling procedures, CCTO was obtained after a couple of hours of milling (in average 30 h of milling, depending on the reaction procedure). The X-ray diffraction (XRD) patterns indicate that the crystallite size is within the range of 20 � /35 nm. After 100 h of milling the formation of CCTO was confirmed by X-ray powder diffraction in both procedures, with good stability. We also prepare the CCTO ceramic using the traditional procedure described in the literature and compared the physical properties of these samples with those ones obtained by milling process and good agreement was observed. The infrared and Raman scattering spectroscopy results suggest that the increase of the milling time leads to the formation of nanocrystalline CCTO, as seen by XRD analysis. These materials are attractive for capacitor applications and certainly for microelectronics, microwav ed evices (cell mobile phones for example), where the decrease of the size of the devices are crucial. This milling process presents the advantage that melting is not necessary and the powder obtained is nanocrystalline with extraordinary mechanical properties. The material can be compacted and transformed in solid ceramic samples or used in others procedures of film preparation. The high efficiency of the process opens a way to produce commercial amount of nanocrystalline powders. Due to the nanocrystalline character of this powder, their mechanical properties have changed and for this reason a pressure of 1 GPa is enough to shape the sample into any geometry. # 2002 Elsevier Science B.V. All rights reserved.

Structural analysis of zeolite NaA synthesized by a cost-effective hydrothermal method using kaolin and its use as water softener

Zeolite 4A (LTA) has been successfully synthesized by a hydrothermal method, where kaolin was used as silica and alumina source. The synthesized zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser granulometry, and FTIR spectroscopy. XRD data from the Rietveld refinement method confirmed only one crystallographic phase. Zeolite A morphology was observed by SEM analysis, and it showed well-defined crystals with slightly different sizes but with the same cubic shape. Particle size distribution of the crystals was confirmed by laser granulometry, whereas FTIR spectroscopy revealed significant structural differences between the starting material and the final zeolite product used as water softener.

Development of a graphical interface for the Rietveld refinement program DBWS

The DBWS program, the latest version of which is 9807a (Young et al., 1999), an upgraded version of DBWS-9411, described by Young et al. (1995), is written in Fortran and can carry out Rietveld re®nements using digitized data (from a neutron or X-ray diffractometer) stored in a text ®le. It also requires an Input Control File (ICF), constructed by the user, which stores information about the material and program execution. The ICF is a text ®le that contains crystallographic information about the material and program settings in lines and columns. Given the size of the input ®le needed by DBWS, compiling it can be confusing, dif®cult and time consuming (an ICF for quartz plus alumina, which has only two phases, uses an ICF with more than 60 lines). Most users edit new ICFs by opening previously used ®les in a non-formatted text editor (such as Microsoft Notepad or DOS Edit) and then substituting the old values for new ones. Editing these ®les manually can be confusing because the user needs to know the placement of each parameter in the ICF; furthermore, small errors in the format of the ICF may cause problems when the program runs. After the program has run, a text ®le containing the re®ned data is returned, along with, optionally, a binary ®le that is used to plot the diffraction pattern using a graphics program such as DMPlot (Marciniak, 1997). To solve the aforementioned problems, a graphical interface for DBWS (which works with versions 9411 and 9807 and runs under Windows 95/98/NT) has been developed. Known as DBWS Tools, the program makes DBWS much easier to use and manages each step of the process, from the creation of the ICF to the plotting of the diffraction pattern using the external program DMPlot. In this way, the user need not consult the program manual every time a new sample is analysed (because the meaning of each data ®eld is shown on screen) and the entire process is much faster and user-friendly.

Coexistence of triclinic and monoclinic phases in WO3 ceramics

The coexistence of phases in WO3 ceramics sintered within the 600–1000 °C temperature range is investigated using Raman microprobe spectroscopy. The analysis of vibrational modes indicates the existence of triclinic (VI) P1 and monoclinic (V) P21/n phases mixing. The concentration ratio between WO3 microcrystals in the former and the latter phases is shown to depend on the ceramics sintering temperature, reaching a maximum value favouring the triclinic (VI) P1 phase at the 800 °C sintering temperature. Copyright

Piezoelectric properties of collagen-nanocrystalline hydroxyapatite composites

In this paper we did a study of the physicochemical, dielectric and piezoelectric properties of anionic collagen and collagen-hydroxyapatite (HA) composites, considering the development of new biomaterials which have potential applications in support for cellular growth and in systems for bone regeneration. The piezoelectric strain tensor element d14, the elastic constant s55, and the dielectric permittivity ɛ11 were measured for the anionic collagen and collagen-HA films. For the collagen-HA composite film (Col-HACOM) the main peaks associated to the crystalline HA is present. For the nanocrystalline composite, nanometric HA powder (103 nm particle size) (HAN), obtained by mechanical milling were used. For the composite film (Col-HAN) the HA and CaH(PO4)2H2O phases were detected. One can see that the HA powder (HAN) present the main peaks associated to crystalline HA. The IR spectroscopy measurements on HA-COM and HAN powders, Col-HACOM and Col-HAN composite films and collagen film (Col) presents the main resonances associated to the modes of (PO4)3−, (CO3)2−. The IR spectra of Collagen Film (Col) shows the bands associated to amide I (C=O), amide II (N–H) and amide III (C–N) vibrational modes. The scanning electron photomicrography of the Col-HACOM and Col-HAN films, respectively, shows deposits of HA on the surface of collagen. It also shows that HACOM crystals has a dense feature, whereas the HAN crystals has soft porous surface. Energy-dispersive spectroscopy (EDS) analysis showed that the main elements of the hybrid sponge were carbon, oxygen, calcium, and phosphorus. The EDS of HACOM crystal, present in the Col-HACOM composite showed a molar ratio Ca/P = 1.71, whereas the Col-HAN composite the molar ratio of calcium and phosphorus (Ca/P = 2.14) and the amount of carbon were greater. The piezoelectric strain tensor element d14 obtained for the anionic collagen was around 0.102 pC/N. The collagen composite with nanocrystalline HA crystals (Col-HAN) present a better result (d14 = 0.040 pC/N) compared to the composite with the commercial ceramic (d14 = 0.012 pC/N). This is an indication that the nanometric particles of HA present little disturbance on the organization of the collagen fibers in the composite. In this situation the nanometric HA are the best candidates in future applications of these composites.

High‐pressure Raman study of taurine crystal

Single-crystal samples of taurine, NH3C2H4SO3, were studied by Raman spectroscopy in a diamond-anvil cell up to pressures of 5.6 GPa. From the analysis of the results we observed that the crystal undergoes a phase transition at about 0.7 GPa. The transition is accompanied by the appearance of a phonon in the external mode region of the spectrum and by changes of both the wavenumber of the CCN bending and of the CSH torsional vibrations. Additionally evidence for a second phase transition occurring at 5.2 GPa was observed. Pressure coefficients for all modes observed in this work are also given. Copyright

Piezoelectric coefficients of l-arginine hydrochloride monohydrate obtained by X-ray multiple diffraction using synchrotron radiation

In this paper, a very useful development to improve the application of a method based on the multiple-diffraction technique to determine the piezoelectric coefficients of crystals is described. The idea is to choose any specific crystallographic direction (plane) through the secondary peaks in the Renninger scan instead of those directions related to the electric field by the piezoelectric tensor. For a set of multiple-diffraction planes, it is possible to obtain an equation system based on the ordinary peak position for each H secondary plane that appears in the Renninger scan. This useful development was successfully applied to the amino acid L-arginine hydrochloride monohydrate in order to provide the d 21 , d 22 , d 23 and d 25 piezoelectric coefficients by applying the electric field along the [010] crystallographic direction.

In situ system for X-ray absorption spectroscopy experiments to investigate nanoparticle crystallization.

A new furnace, based on a halogen lamp, and a sample cell have been designed and constructed for in situ X-ray absorption spectroscopy experiments in conventional and dispersive mode (transmission and fluorescence geometries). The main application of the apparatus is thermal treatment studies under controlled conditions for dynamical processes. The sol-gel (gelatin) method has been utilized to synthesize NiO nanoparticles. During this heating process, in situ Ni K-edge X-ray absorption near-edge structural measurements provided evidence of the evolution of a Ni environment until complete NiO nanoparticle crystallization. This case is reported in order to show the furnace performance in dispersive mode.

Taninos hidrolisáveis em Bixa orellana L.

The aqueous material found in the fruits of Bixa Orellana L. was collected, dried, and characterized using several experimental techniques, namely phytochemical analysis in order to identify the biologically active constituents, Fourier transform infrared (FT-IR) spectroscopy for vibrational analysis, and X-ray powder diffraction in order to identify the presence of crystalline phases in the sample. The results showed that the aqueous material possesses high concentrations of hydrolyzable tannin. This result justifies the anti-inflammatory activity of this substance reported in other studies.

Rochelle salt piezoelectric coefficients obtained by x-ray multiple diffraction

In this paper, the theory of the method which uses the sensitivity and versatility of the multiple diffraction phenomenon to probe small lattice deformation induced by electric field (Avanci et al 1998 Phys. Rev. Lett. 81 5426) was implemented to provide a relationship between the E-induced strain in the Rochelle salt (ferroelectric phase) crystal and the shift in the Renninger scan peak position. From that, all piezoelectric coefficients in a piezoelectric tensor row (d21 = 7.0(6) × 10 −10 CN −1 ,d 22 = 2.2(9) × 10 −9 CN −1 , d23 = 2.1(9) × 10 −9 CN −1 and d25 = 3.7(8) × 10 −11 CN −1 ) were determined by using the primary reflections ( 600 ) and ( 800 ) found as the best choices for the experiments with E parallel to the [0 1 0] direction (the b-axis).