Investigation of the effect of annealing on the magnetic properties of Sn1−xEuxTe single crystals

A study of the effect of annealing on the magnetic properties of single crystals Sn_1−xEu_xTe is reported. The width of the electron paramagnetic resonance line of the crystal is found to decrease upon annealing but its g-value of 1.991 is nearly unaffected. Magnetization results indicate that the pair exchange interaction is weakly antiferromagnetic with a value of −0.67 K for the non-annealed sample and −0.29 K after annealed sample. Susceptibility measurements performed as a function of temperature also indicate the presence of EuTe clusters in the as-grown Sn_1−xEu_xTe crystals. Therefore it was deduced that the Eu²⁺ ions tend to form clusters, particularly pairs, in the as-grown crystal and these clusters disappear after annealing, as the Eu²⁺ ions occupy isolated sites in the SnTe host lattice.     

Fourier Transform Emission Spectroscopy of a New Φ-1Δ System of VO

High-resolution emission spectra of VO have been recorded in the region 3400-19 400 cm⁻¹ using a Fourier transform spectrometer. The molecules were observed from the reaction of VOCl₃ with active nitrogen. Two new bands, with origins near 5539.46 and 5551.69 cm⁻¹, are assigned as the 0-0 bands of the ²Φ_5/2-²Δ_3/2 and ²Φ_7/2-²Δ_5/2 spin-orbit components (respectively) of a ²Φ-1²Δ electronic transition of VO. A rotational analysis of both subbands has been carried out and spectroscopic constants have been extracted. The 1²Δ state is known from the previous analysis of the near infrared doublet transitions of VO and the new ²Φ excited state has rotational constants very similar to those of another ²Φ state observed previously [Merer et al., J. Mol. Spectrosc.125, 465 (1987)].     

Normal state transport properties in single crystals of Ba1−xKxFe2As2 andNdFeAsO1−xFx

Hall effect and magnetoresistance Δρ/ρ(0) (MR) in the normal state have been measured on single crystals of Ba_1?xK_xFe₂As₂ and NdFeAsO_1?xF_x. Detailed analysis reveal the following conclusions: (1) For the parent phases of Ba_1?xK_x Fe₂As₂ and NdFeAsO_1?xF_x, large Hall effect and MR with strong temperature dependence were observed below a characteristic temperature corresponding to the antiferromagnetic/ structural transition. The field dependence of the Hall resistivity ρ_xy exhibits a non-linear behavior, which is accompanied by the violation of the B-square feature of the longitudinal magnetoresistivity Δρ_xx(B)/ρ_xx(0). A closer inspection further indicates that they are well related to each other and could be attributed to the multi-band effect or spin-related scattering. (2) The superconducting samples show much smaller Hall coefficient and MR in the normal state. The Hall coefficient shows a weaker temperature dependence compared to the parent phase, while the mean scattering rate 1/τ_H has a power-law like temperature dependence as 1/τ_H ∝ Tⁿ (n = 2–3). (3) For a Ba_1?xK_xFe₂ As₂ sample with T_c = 36 K, the field dependence of MR is complicated and the feature varies in different temperature regions. A drastic change of Δρ/ρ(0) was found between 80 K and 100 K, which corresponds very well to the maximum of the temperature derivative of the resistivity. This may be attributed to the spin-related scattering of electrons. (4) A comparison between the parent phase and the superconducting sample with T_c = 50 K in NdFeAsO_1?xF_x suggests that the electronic transport properties in the normal state cannot be easily understood with the simple multi-band model, while a picture concerning a suppression to the quasiparticle density of states at the Fermi energy is more reasonable.     

Heat capacity of La1−x SrxMnO3 single crystals in different magnetic states

The heat capacity of three single-crystal samples of La_1?x Sr_xMnO₃ (x=0, 0.2, and 0.3) is measured in the temperature range 4–400 K. It is found that the heat capacity undergoes abrupt changes due to the transitions from the antiferromagnetic phase to the paramagnetic phase (x=0) and from the ferromagnetic phase to the paramagnetic phase (x=0.2 and 0.3). The phonon contribution to the heat capacity and the Debye characteristic temperatures for the La_0.7Sr_0.3MnO₃ sample are determined over a wide range of temperatures. The electronic density of states at the Fermi level is evaluated. It is demonstrated that an increase in the strontium concentration x brings about an increase in the electronic density of states at the Fermi level. The contributions of spin waves to the heat capacity and the entropy are estimated under the assumption that the phonon spectrum remains unchanged upon doping with Sr.     

Determination of the Heat of Adsorption and Desorption of a Volatile Organic Compound Under Dynamic Conditions Using Fourier‐Transform Infrared Spectroscopy

Quantitative Fourier‐transform infrared spectroscopic analysis was used for the determination of adsorption capacity of a model volatile organic compound (VOC) under dynamic conditions. The analytical method used also offers the possibility of distinguishing between reversible and irreversible adsorption as well as further detection of adsorbed VOC transformation. The obtained adsorbed amounts have been used for the determination of the heat of adsorption and the activation energy of desorption using, respectively, isosteric and temperature programmed desorption methods. The approach has been applied to explore the potential use of local clay as an adsorbent material for VOC pollutants.     

Fourier‐Transform Near‐Infrared Spectroscopy as a Tool for Olive Fruit Classification and Quantitative Analysis

Abstract

The potential of diffuse reflectance near‐infrared spectroscopy combined with pattern recognition to discriminate between olives (Olea europaea L.) of different qualities has been tested. The sample set was formed of sound olive fruits and those showing the most common alterations of olives, which lead to decreased oil quality, namely freeze damages, harvest after falling on the ground, fermentation due to prolonged storage time, and olive tree diseases. Near‐infrared (NIR) spectra were recorded between 9900 and 4100 cm^?1. Preliminary studies of the data set structure were performed using hierarchical cluster analysis and principal component analysis. Discriminant analysis provided prediction abilities of 100% for sound, 79% for frostbite, 96% for ground, and 92% for fermented olives using a leave‐a‐fourth‐out cross‐validation procedure. Quantification of oil and water content in the olives was also approached by using partial least squares (PLS) regression. Results, in terms of predictive ability using a leave‐one‐out cross‐validation, were compared for calibration using the whole sample set and calibrations for the sound and damaged samples separately. Relative errors of prediction using all samples were 7.2% and 3.4% for oil content and humidity, respectively. Using only sound samples, relative errors of prediction of 3.8% and 2.8% for oil and water content, respectively, were obtained. Thus, better accuracy could be achieved when classification of the olive samples prior to quantitative analysis was performed. These results demonstrate the utility of NIR spectroscopy to differentiate olives of different qualities. Using NIR, a fast selection of sound olives in a quality‐orientated production facility becomes feasible.     

Inner vibrational modes and anhar-monicity of Mg-OH− complexes in naf single crystals

Abstract

Different inner vibrational modes (stretching, bending and their combination) of the OH^? ion perturbed by lattice defects induced by Mg²⁺ in NaF have been put in evidence and studied by means of optical absorption spectroscopy in the 600–7200 cm^?1 wavenumber range, in the 9–300K temperature range, and for Mg²⁺ molar concentration ranging between 10^?4 and 10^?3. Electrical and mechanical anharmonicity effects have been detected for the stretching modes and analyzed in the framework of the anharmonic oscillator model for a diatomic molecule.     

Specific heat of Na1−x V2O5 single crystals

Temperature dependences of the specific heat C and the magnetic susceptibility χ of Na_1?x V₂O₅ single crystals (x=0, 0.01, 0.02, 0.03, and 0.04) are studied. In NaV₂O₅, the transition to the spin-gap state (T _c =34 K) is accompanied by a sharp decrease in χ, while C exhibits a λ-shaped anomaly. At low temperatures, the specific heat of NaV₂O₅ is approximated by the sum of phonon ～T ³ and magnon ～exp(?Δ/T) contributions, which makes it possible to estimate the Debye temperature Θ_D=336 K and the gap in the magnetic excitation spectrum Δ=112 K. With the departure from stoichiometry, the anomalies observed in the behavior of χ and C are spread and shifted to lower temperatures. The low-temperature specific heat of nonstoichiometric samples is determined by the sum of phonon and magnon components and the contribution due to the presence of defects. The values of magnetic entropy characterizing the phase transitions in Na_1?x V₂O₅ are calculated.     

Birefringence of CuGa(S1−x Sex)2 single crystals

The magnitude and dispersion of birefringence of single crystals of CuGa(S_1?x Se_x)₂ solid solutions is studied in the spectral region of 0.5–2.5 μ at T=300 K. The effect of the substitution of selenium for sulfur on special features of birefringence dispersion is analyzed within the framework of the single-oscillator model.     

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS _x Se_1?x (where x?=?0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8?GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.     

Intrinsic carrier concentration in Hg1−xCdxTe

The effective mass of heavy holes has been determined on the basis of simultaneous analysis of the Hall coefficient and conductivity data obtained in the temperature region 100–300 K on well characterized p-type Hg_1–x Cd_xTe (x0·2) samples. Its value is 0·7m₀. The calculation of intrinsic carrier concentration for 0·19 x0·3 and 50 Kg T 300 K has been carried out using the above value of the effective mass of holes, Hansen's expression for the band gap and momentum matrix element from magneto-optical measurements.     

Mössbauer studies of Fe x Mn1 − x S single crystals

Single crystals of iron manganese sulfides Fe _x Mn_{1 ? x} S (0.25 ≤ x ≤ 0.29) are experimentally investigated using Mössbauer spectroscopy and x-ray diffraction. The Mössbauer spectra measured at 300 K exhibit a single broadened line characteristic of paramagnets. The isomer shift of this line is equal to 0.92–0.94 mm/s, which is typical of Fe²⁺ ions in the octahedral position. The quadrupole splitting (0.18–0.21 mm/s) suggests a distortion of the coordination polyhedron of iron ions in the Fe _x Mn_{1 ? x} S compounds.     

Investigation of phase segregation in Zn1−xMgxO systems

The present work reports on the synthesis of the Zn_1?xMg_xO (x = 0, 0.02, 0.05, 0.10, 0.15 and 0.20) samples by sol–gel method and the investigations on their structural, morphological and optical properties. X-ray diffraction (XRD) data analysis confirms the formation of pure ZnO phase below 10% Mg doping and MgO related phases appears in 10% doped sample indicating that phase segregation of MgO starts at x ≥ 0.10 samples. The phase segregation observed through XRD analysis is also supported by results from Scanning Electron Microscopy (SEM), Raman spectroscopy and photoluminescence studies. Furthermore, the enhancement in optical band gap, with Mg doping, from 3.1 ± 0.1 eV to 3.5 ± 0.1 eV has been observed through UV–Vis spectroscopic analysis. Above results have been discussed on the basis of defects level observed through Raman and photoluminscence studies.     

Electrical properties and electronic structure of Cu1−xZnxInSe2 and Cu1−xZnxInS2 single crystals

Temperature dependence of the electrical conductivity of CuInS₂–ZnIn₂S₄ and CuInSe₂–ZnIn₂Se₄ solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to ~100 to 27 K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150–300 K), in the CuInSe₂–ZnIn₂Se₄ single crystals containing 15 and 20 mol% ZnIn₂Se₄ the thermally activated conductivity with activation energy of 0.018 and 0.04 eV, respectively, is detected. Among the CuInSe₂–ZnIn₂Se₄ single crystals, samples with 5 and 10 mol% ZnIn₂Se₄ were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS₂–ZnIn₂S₄ single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS₂–ZnIn₂S₄ solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar⁺ ion-bombarded surfaces. Our results indicate that the Cu_1−xZn_xInS₂ single-crystal surfaces are sensitive to Ar⁺ ion-bombardment. Additionally, for the Cu_1−xZn_xInS₂ crystal with the highest ZnIn₂S₄ content, namely 12 mol% ZnIn₂S₄, the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum.     

Topographic methods of studying defects in Hg1−xCdxTe crystals

In this paper, three topographic methods of studying defects in Hg_1−xCd_xTe crystals are described: the back-reflection method with a “whiter” beam, the scanning-reflection method with monochromatic radiation, and the glancing-incidence method with a “white” beam. Unique results obtained by these methods are shown: topographs as a referable criterion of various defects are laid down and explanation of the topographs is carried out theoretically. A set of topographs with reversed contrasts is made and the microorientation differences among the mosaic blocks are determined. Topographs of the intensive strain field in the core region of ingots prepared by the quench-recrystallization method are made and the mechanism of crystal growth is interpreted according to these topographs. In addition, typical topographs made by the three methods respectively, are shown.     

Effect of bond polarity in Sb2Te3−x Se x single crystals

Sb₂Te_3?x Se _x (x=0·00?1·25) single crystals were prepared from 5N purity elements using a modified Bridgman method. Measurements of the reflectivity spectra in the plasma resonance frequency range, Hall constantR _H(B∥c) and electrical conductivityσ _⊥C were carried out on these samples at room temperature. With increasing selenium content a shift of the reflectivity minimum towards longer wavelengths was observed as well as an increase of the Hall constant and a decrease of the electrical conductivity — the incorporation of Se atoms into the Sb₂Te₃ crystal lattice results obviously in a decrease in the concentration of free carriers. This effect is accounted for by a change in the polarity of bonds in the Sb₂Te₃ crystal lattice, due to the formation of Se _Te ^x substitutional defects.     

Diamagnetism and muon Knight shift in semiconducting Bi1−x Sb x single crystals

The Knight shift of positive muons (⁺) implanted in semiconducting single crystals of Bi_1–x Sb _x (x=0.085, 0.14, 0.19) has been measured as a function of temperature and sample orientation. The Knight shift (KS) is generally negative and is found to scale with the negative total macroscopic susceptibility; the scaling is independent ofx but dependent on the orientation. One concludes that only the valence and conduction bands near theL-symmetry point in the Brillouin zone contribute to the ⁺ Knight shift, most likely by the contact hyperfine interaction. Furthermore the valence bands and the conduction bands seem to be associated with the same hyperfine coupling constants. These conclusions are quite unexpected and call for a new theoretical approach.     

Depolarization ofμ + muons in GaAs single crystals

ASR study has been carried out on high resistivity single crystal gallium arsenide (GaAs). Three characteristic states involving the ⁺ muon (Mu^*, Mu, ⁺ were shown to exist in a binary semiconductor, similar to the case of elemental semiconductors.