Experimental evidence of the spin-glass transition in the diluted magnetic semiconductor Zn(1-x)Mn(x)In(2)Se(4)

This work reports on magnetic measurements of the quasi-two-dimensional (quasi-2D) system Zn(1-x)Mn(x)In(2)Se(4), with 0.01 <= x <= 1.00. For x > 0.67, the quasi-2D system seems to develop a spin-glass behaviour. Evidence of a true phase transition phenomenon is provided by the steep increase of the nonlinear susceptibility chi(nl) when approaching T(C) from above. The static scaling of chi(nl) data yields critical exponents delta = 4.0 +/- 0.2, phi = 4.37 +/- 0.17 and TC = 3.4 +/- 0.1 K for the sample with x = 1.00 and similar values for the sample with x = 0.87. These critical exponents are in good agreement with values reported for other spin-glass systems with short-range interactions.

UV optical absorption spectra analysis of beryl crystals from Brazil

The spectral decomposition analysis was applied to the optical absorption spectra of green and colorless beryl crystals from the Brazilian Eastern Pegmatitic province in the natural state, Submitted to heat treatment and irradiated with UV light The attributions of the lines were made taking into account highly accurate quantum mechanical calculations The deconvolution of the green beryl spectra revealed four lines, two of them around 12,000 cm(-1) (1 5eV) and two of them around 34,000 cm(-1) (4.2 eV) attributed to Fe(2+) and Fe(3+), respectively The deconvolution of the colorless beryl spectra without any treatment, after heating and for the same heat treatment followed by UV light irradiation revealed five lines The analysis of ratio relations showed that the lines at 36,400 cm(-1) (4.5 eV) and 41,400 cm(-1) (5 1 eV) belongs to a single defect attributed to a silicon dangling bond defect (=Si). Discussions and comparison with reported defects in quartz have supported the allocation of the lines at 61,000 cm(-1) (7.6 eV) and 43,800 cm(-1) (5 4 eV) to diamagnetic oxygen vacancy defect ( Si-Si ) and unrelaxed ( Si Si ) defect, respectively Finally, the line at 39.100 cm(-1) (4.8 eV), quite polarized along the c-axis, was attributed to a (Fe(2+) OH(-)) defect in the structural channels (C) 2009 Elsevier B V All rights reserved

Thermoluminescence dating of Brazilian indigenous ceramics

Two indigenous ceramics fragments, one from Lagoa Queimada (LQ) and another from Barra dos Negros (BN), both sites located on Bahia state (Brazil), were dated by termoluminescence (TL) method. Each fragment was physically prepared and divided into two fractions, one was used for TL measurement and the other for annual dose determination. The TL fraction was chemically treated, divided in sub samples and irradiated with several doses. The plot extrapolation from TL intensities as function of radiation dose enabled the determination of the accumulated dose (D(ac)), 3.99 Gy and 1.88 Gy for LQ and BN, respectively. The annual dose was obtained through the uranium, thorium and potassium determination by ICP-MS. The annual doses (D(an)) obtained were 2.86 and 2.26 mGy/year. The estimated ages were similar to 1375 and 709 y for BN and LQ ceramics, respectively. The ages agreed with the archaeologists` estimation for the Aratu and Tupi tradition periods, respectively.

Dating archeological ceramics from the Valley of Vitor, Arequipa by the TL method

The age of some ancient pottery from the Valley of Vitor in the region of Arequipa, Peru, is determined by the thermoluminescence (TL) method. For dating, a 325 degrees C TL peak was used and irradiation with -dose from 5 to 50Gy was carried out for the additive method, and from 0.4 to 5Gy for the regeneration method. For these dose values, the TL intensity is observed to grow linearly, obtaining an accumulated dose of 1.62 +/- 0.09Gy and 1.36 +/- 0.03Gy for the additive and regeneration methods, respectively. The age (A) of the sample was calculated by the two methods, being A=867 +/- 195 years after Christ (AC) for the additive method and A=1050 +/- 157 years AC for the regeneration method. Both results are within 800-1200 years AC, which is the period of the Wari culture.

Analysis and risk estimates to workers of Brazilian granitic industries and sandblasters exposed to respirable crystalline silica and natural radionuclides

Occupational exposure to respirable crystalline silica and to radiation emitted by natural radionuclides present both in rocks and sands was studied in the Brazilian extractive process and granite product manufacture. Respirable airborne dust samples were collected in working environments, where workers perform different tasks with distinct commercial granites types, and also in places where sandblasters work with sands from different origins. The free crystalline silica contents were determined using X-ray diffraction of the respirable particulate fraction of each sample. Dust samples from granite cutting and sandblasting ambient had the natural radionuclides concentrations measured by gamma spectrometry. Dust concentrations in the workplaces were quite variable, reaching values up to 10 times higher than the respirable particle mass threshold limit value (TLV) set by the American Conference for Governmental Industrial Hygienists of 3 mg m(-3). Also the free crystalline silica concentrations were high. reaching values up to 48 times the TLV of 0.025 mg m(-3). Additionally, our results suggest that the risk of radiation-induced cancer in the granite or marble industries is negligible. However, the combined exposure to dust, gamma radiation, and radon daughter products could result in the enhancement of lung cancer risks associated to sandblasting activities. (C) 2010 Elsevier Ltd. All rights reserved.

Magnetic and optical characterization of Mn-doped PbS nanocrystals supported in oxide glass matrix

The evidence of successful growth of Mn-doped PbS (Pb(1-x)Mn(x)S) nanocrystals (NCs) in SiO(2)-Na(2)CO(3)-Al(2)O(3)-PbO(2)-B(2)O(3) template, using the fusion method, is reported on in this study. The as-grown Pb(1-x)Mn(x)S NC is characterized using optical absorption, electron paramagnetic resonance, and atomic force microscopy. The data are discussed in terms of two distinct scenarios, namely a core-doped and a shell-doped nanostructure. (C) 2008 Elsevier B.V. All rights reserved.

Oxide surface modification: Synthesis and characterization of zirconia-coated alumina

Four aluminas were used as Supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between Support and modifier. The Supports were impregnated with different concentrations Of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount Of Surface modifier Oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide Should be identified above this limit when a complete coating is reached. The results obtained From XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide oil the Surface of alumina Support reached the coating in the limit of 15 Zr nm(-2), without the formation of the ZrO(2) phase. (c) 2009 Elsevier Inc. All rights reserved.

In situ X-ray diffraction studies of phase transition in Pb1-x La x Zr0.40Ti0.60O3 ferroelectric ceramics

The temperature dependence of the crystalline structure and the lattice parameters of Pb1-xLaxZr0.40Ti0.60O3 ferroelectric ceramic system with 0.00 x 0.21 was determined. The samples with x 0.11 show a cubic-to-tetragonal phase transition at the maximum dielectric permittivity, Tmax. Above this amount and especially for the x = 0.12 sample, a spontaneous phase transition from a relaxor ferroelectric state (cubic phase) to a ferroelectric state (tetragonal phase) is observed upon cooling below the Tmax. Unlike what has been reported in other studies, the x = 0.13, 0.14, and 0.15 samples, which present a more pronounced relaxor behavior, also presents a spontaneous normal-to-relaxor transition, indicated by a cubic to tetragonal symmetry below the Tmax. The origin of this anomaly has been associated with an increase in the degree of tetragonality, confirmed by the measurements of the X-ray diffraction patterns. The differential thermal analysis (DSC) measurements also confirm the existence of these phase transitions.

Elaboration and optimization of (Y,Er)Al(3)(BO(3))(4) glassy planar waveguides through the sol-gel process

In this work, a sol-gel route was used to prepare Y(0.9)Er(0.1)Al(3)(BO(3))(4) glassy thin films by spin-coating technique looking for the preparation and optimization of planar waveguides for integrated optics. The films were deposited on silica and silicon substrates using stable sols synthesized by the sol-gel process. Deposits with thicknesses ranging between 520 and 720 nm were prepared by a multi-layer process involving heat treatments at different temperatures from glass transition to the film crystallization and using heating rates of 2 degrees C/min. The structural characterization of the layers was performed by using grazing incidence X-ray diffraction and Raman spectroscopy as a function of the heat treatment. Microstructural evolution in terms of annealing temperatures was followed by high resolution scanning electron microscopy and atomic force microscopy. Optical transmission spectra were used to determine the refractive index and the film thicknesses through the envelope method. The optical and guiding properties of the films were studied by m-line spectroscopy. The best films were monomode with 620 nm thickness and a refractive index around 1.664 at 980 nm wavelength. They showed good waveguiding properties with high light-coupling efficiency and low propagation loss at 632.8 and 1550 nm of about 0.88 dB/cm. (C) 2009 Elsevier B.V. All rights reserved.

Nanograined Ferroelectric Ceramics Prepared by High-Pressure Densification Technique

For the first time, nanograined Pb(1-1.5x)La(x)TiO(3) ferroelectric ceramics, with x=0.2, were produced by a process based on a high-pressure densification technique (HPD) that eliminates the need of high-temperature sintering. Our results showed the production of workable dense ceramics with average grain size around 100 nm and free from secondary phase. Regarding the dielectric measurements, the samples showed satisfactory dielectric losses as well as remarkable diffusivity in the dielectric curves. Moreover, ferroelectric hysteresis measurements showed that samples produced by the HPD technique can stand high electric fields necessary to switch the polarization and thus to induce piezoelectric activity. Our results demonstrated clearly the viability of the proposed method to produce nanograined ferroelectric bulk ceramics, then opening the possibility of developing new technologies.

Microstructural, structural and dielectric properties of Er(3+)-modified BaTi(0.85)Zr(0.15)O(3) ceramics

The (micro)structural and electrical properties of undoped and Er(3+)-doped BaTi(0.85)Zr(0.15)O(3) ceramics were studied in this work for both nominal Ba(2+) and Ti(4+) substitution formulations. The ceramics were produced from solid-state reaction and sintered at 1400 degrees C for 3 h. For those materials prepared following the donor-type nominal Ba(1-x)Er(x)(Ti(0.85)Zr(0.15))O(3) composition, especially, Er(3+) however showed a preferential substitution for the (Ti,Zr)(4+) lattice sites. This allowed synthesis of a finally acceptor-like, highly resistive Ba(Ti,Zr,Er)O(3-delta)-like system, with a solubility limit below but close to 3 cat.% Er(3+). The overall phase development is discussed in terms of the amphoteric nature of Er(3+), and appears to mainly or, at least, partially also involve a minimization of stress effects from the ion size mismatch between the dopant and host cations. Further results presented here include a comparative analysis of the behavior of the materials` grain size, electrical properties and nature of the ferroelectric-to-paraelectric phase transition upon variation of the formulation and Er(3+) content. (C) 2008 Elsevier Ltd. All rights reserved.

Microstructural, structural and electrical properties of La(3+)-modified Bi(4)Ti(3)O(12) ferroelectric ceramics

Bi(4-x)La(x)Ti(3)O(12) (BLT) ceramics were prepared and studied in this work in terms of La(3+)-modified microstructure and phase development as well as electrical response. According to the results processed from X-ray diffraction and electrical measurements, the solubility limit (XL) of La(3+) into the Bi(4)Ti(3)O(12) (BIT) matrix was here found to locate slightly above x = 1.5. Further, La(3+) had the effect of reducing the material grain size, while changing its morphology from the plate-like form, typical of BIT ceramics, to a spherical-like one. The electrical results presented and discussed here also include the behavior of the temperature of the ferroelectric-paraelectric phase transition as well as the normal or diffuse and/or relaxor nature of this transition depending on the La(3+) content. (c) 2008 Elsevier Ltd. All fights reserved.

Er : YAB nanoparticles and vitreous thin films by the polymeric precursor method

The synthesis of Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystalline powders and vitreous thin films were studied. Precursor solutions were obtained using a modified polymeric precursor method using D-sorbitol as complexant agent. The chemical reactions were described. Y(0.)9Er(0.1)Al(3)(BO(3))(4) composition presents good thermal stability with regard to crystallization. The Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystallized phase can be obtained at 1,150 degrees C, in agreement with other authors. Crack- and porosity-free films were obtained with very small grain size and low RMS roughness. The films thickness revealed to be linearly dependent on precursor solution viscosity, being the value of 25 mPa s useful to prepare high-quality amorphous multi-layers (up to similar to 800 nm) at 740 degrees C during 2 h onto silica substrates by spin coating with a gyrset technology.

Thermoluminescence, structural and magnetic properties of a Li(2)O-B(2)O(3)-Al(2)O(3) glass system doped with LiF and TiO(2)

A Li(2)O-B(2)O(3)-Al(2)O(3) glass system, un-doped and doped with LiF, and/or TiO(2) was synthesized by the fusion method and its physical properties were investigated by thermoluminescence (TL), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), atomic force microscopy (AFM) and differential thermal analysis (DTA). The samples were subjected to gamma-rays from a colbalt-60 ((60)Co) source. These techniques provided evidence of LiF and LiF doped with Ti crystal formation in the glass system. A TL glow peak at about 433 K was sensitive to (60)Co gamma-rays and showed good linearity with doses and consequently could be used to quantify radiation doses. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Dosimetric properties of UV irradiated calcium co-doped borate glass-ceramic

The thermoluminescence (TL) response of Dy and Li doped 20CaB(4)O(7)-80CaB(2)O(4) (Wt%) glass-ceramic irradiated with ultraviolet (UV) radiation was studied. In order to act as TL activator ions, the Dy and Li ions were included in the matrix during the melting process to increase its TL efficiency. A single crystalline CaB2O4 phase was present in the glass-ceramic as determined by X-ray diffraction (XRD). The glass-ceramic 20CaB(4)O(7)-80CaB(2)O(4):Dy,Li wt% (named 20CBO7:Dy,Li) is a newly prepared TL material. Its thermoluminescent dosimetric characteristics have shown a linear response under UV radiation exposure and a good TL signal reproducibility, thus proving to be a promising material for using as an ultraviolet radiation dosimeter. (C) 2007 Elsevier B.V. All rights reserved.