IR reflection and Raman spectra of β-Tl1 ? x Cu x InS2 (0 ≤ x ≤ 0.015) single crystals

The IR reflection and Raman spectra of β-Tl_{1 − x} Cu _x InS₂ (0 ≤ x ≤ 0.015) single crystals have been studied in the temperature range 84–300 K. It is shown that partial replacement of thallium by copper atoms leads to a decrease in the frequencies of the corresponding oscillations in the frequency range 40–500 cm⁻¹ and does not induce (at given concentrations) local oscillations. Analysis of the transformation of the IR reflection spectra at T ₂ ≈ 185 K revealed a ferroelectric phase transition. Original Russian Text ? A.N. Georgobiani, A.Kh. Matiyev, C.V. Bulyarski, T.A. Matiyeva, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 138–140.     

Effect of oxygen deficiency on the magnetic, electrical, magnetoelectric, and magnetoelastic properties of La1 ? x Sr x MnO3 ? δ manganites

This paper reports on a study of the effect of oxygen deficiency on the magnetic and electrical properties of the La_{1 − x} Sr _x MnO_{3 − δ} manganites (x = 0, 0.2, 0.4; δ = 0, 0.13, 0.2). In compositions with x = 0 and δ = 0.13 and 0.2, the temperature dependence of the magnetization M (T) can be approximated by the Langevin function with the moment of superparamagnetic clusters μ = 77μ_B (δ = 0.13) and 86μ_B (δ = 0.2) at temperatures of 25 K ≤ T ≤ 250 K, with the exception of a small temperature range near 132 K in which a maximum characteristic of the LaMnO₃ antiferromagnet is seen. These compositions, as well as Sr-doped compositions with δ ≠ 0, reveal a difference between the magnetizations of the sample cooled in a weak magnetic field and in zero field. At T = 6 K in a magnetic field of 16 kOe, the compositions with x = 0.2 and 0.4, δ = 0.13 possess a magnetic moment per formula unit lower than that with δ = 0, as well as reveal an anomalous relation between the Curie temperature T _C and the Curie paramagnetic point gJ, namely, T _C > gJ. The magnetization of compositions with x = 0.2 and 0.4, δ = 0.2 follows the Langevin function with μ = 40μ_B and 130μ_B, respectively. The electrical resistivity of samples with x = 0.4 and δ = 0.13 and 0.2 is one to two orders of magnitude larger than that of the composition with x = 0.4, δ = 0, which evidences partial or complete compensation of acceptor defects (Sr²⁺ ions) by donor defects (doubly charged O²⁻ vacancies). The above properties of oxygen-deficient compositions suggest that they contain an insulating ferro-antiferromagnetic magnetically double-phase state. The magnetoresistance and volume magnetostriction in samples with x = 0.4 and δ = 0, 0.13, and 0.2 are small; indeed, in a magnetic field of 8 kOe, they do not exceed 1.4% and 6 × 10⁻⁶, respectively. On this basis, it is concluded that the unbalanced doubly charged donors (O vacancies) are in the state with antiparallel spins and, thus, do not initiate the formation of ferron-type ferromagnetic clusters. The significance of both compensated and unbalanced doubly charged donors consists in that they give rise to the formation of fractured Mn-O-Mn bonds, which bring about lowering of the magnetic moment per formula unit in compositions with x = 0.2 and 0.4 and δ = 0.13 and the transition to superparamagnetism in compositions with x = 0.2 and 0.4, δ = 0.2. Original Russian Text ? L.I. Koroleva, D.M. Zashchirinskiĭ, T.M. Khapaeva, L.I. Gurskiĭ, N.A. Kalanda, V.M. Trukhan, R. Szymczak, B. Krzumanska, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 12, pp. 2201–2205.     

Dispersion of the refractive index in β-Tl1 ? x Cu x InS2 crystals (0 ≤ x ≤ 0.015)

The refractive index dispersion in β-Tl_{1 − x} Cu _x InS₂ (0 ≤ x ≤ 0.015) crystals has been studied using intrinsic interference. It is shown that these crystals are characterized by anomalous-dispersion regions at wavelengths slightly exceeding those corresponding to exciton peaks. It is established that, using intrinsic interference, one can detect excitons in these crystals at room temperature. Modulation of interference patterns is revealed, and explanation of this phenomenon is proposed. Original Russian Text ? A.N. Georgobiani, A.Kh. Matiyev, S.V. Bulyarski, T.A. Matiyeva, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 10, pp. 1523–1525.     

Phase x-T diagram of actual solid solutions of the (1 ? x )PbZrO3- x PbTiO3 system (0.37 ≤ x ≤ 0.57)

Ceramics of PbZr_{1 − x} Ti _x O₃ solid solutions were systematically studied in the range 0.37 ≤ x ≤0.57. The x-T phase diagram of the system is constructed in the range 25°C ≤ T ≤ 650°C. The diagram has a region of an indefinite symmetry in the vicinity of the transition to the nonpolar cubic phase. It is established that solid solutions in this region are characterized by weak distortions and temperature-time instability of the crystal structure. Three concentration regions are separated differing in the value of the jump in the unit cell volume ΔV at the line of transitions from the rhombohedral (tetragonal) phase to the region of indefinite symmetry. It is revealed that there are three temperature ranges differing in the behavior of the temperature dependence of the inverse permittivity, which are due to the existence of two critical Curie points at the boundary separating the ferroelectric phases from the cubic phase. Original Russian Text ? L.A. Reznichenko, L.A. Shilkina, O.N. Razumovskaya, E.A. Yaroslavtseva, S.I. Dudkina, O.A. Demchenko, Yu.I. Yurasov, A.A. Esis, I.N. Andryushina, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 8, pp. 1469–1475.     

Charge state of manganese ions and the nonstoichiometry of Ca1 ? xLayMnO3 ? δ single crystals

The charge states and effective spins of manganese ions in nonstoichiometric single crystals of Ca_{1 − x} La _y MnO_{3 − δ} (x = 0, 0.05, 1) manganites have been determined from the exchange splitting of Mn 3s X-ray photoelectron spectra. The chemical composition of the manganite samples under investigation, including the concentration of oxygen, has been determined using the data of the X-ray microanalysis of cations. It has been found that the manganite single crystals under investigation have large defectiveness in both the cation and oxygen sublattices. The efficiency of the complex use of 3s photoelectron spectroscopy and X-ray microanalysis in the determination of the charge state of manganese ions and violations of stoichiometry in doped and defected manganites has been demonstrated.     

Crystal structure and properties of Bi1 ? x Ca x FeO3 and Bi1 ? x Ca x FeO1 ? x Ti x O3 solid solutions

Systems of solid solutions Bi_{1 − x} Ca _x FeO₃ (I) and Bi_{1 − x} CaxFeO_{1 − x} Ti _x O₃ (II) have been obtained and their properties have been studied using neutronography and M?ssbauer spectroscopy; magnetization and permittivity have been measured. It is shown that an increase in the concentration of calcium ions in system I for x > 0.2 changes rhombohedral distortions of a unit cell (space group R3c) to tetragonal distortions (space group I4/mcm), while rhombohedral distortions in system II for x > 0.2 are replaced by orthorhombic distortions (space group Pnma). Analysis of the crystal structure has revealed strong anisotropy in vibrations of Bi and O ions in system I compounds. Systems I and II are characterized by G-type antiferromagnetic ordering of magnetic moments. In system II, spontaneous magnetization associated with the Dzyaloshinskii-Moriya interaction has been detected. According to M?ssbauer spectroscopy data, iron ions in compounds I and II are in the trivalent state and charge compensation occurs due to the formation of oxygen vacancies. The permittivity increases with the calcium concentration. Original Russian Text ? I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinskii, O. Prokhnenko, M. Kopcevicz, R. Szymczak, J. Pietosa, 2008, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 134, No. 1, pp. 105–112.     

Enhanced magnetization of nanoparticles of Mg x Fe(3? x )O4 (0.5≤ x ≤1.5) synthesized by combustion reaction

For the first time nanocrystalline magnetic particles of Mg _x Fe_(3−x)O₄ with x ranging from 0.5 to 1.5 have been synthesized by a combustion reaction method using iron nitrate Fe(NO₃)₃.9H₂O, magnesium nitrate Mg(NO₃)₂.6H₂O, and urea CO(NH₂)₂ as fuel without intermediate decomposition and/or calcining steps. X-ray diffraction patterns of all systems showed broad peaks consistent with cubic inverse spinel structure of MgFe₂O₄. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures the phase purity. The mean crystallite sizes determined from the prominent (311) peak of the diffraction using Scherrer’s equation and transmission electron microscopy micrographs were c.a. 40 nm with spherical morphology. Fourier transform infrared spectra of the as-prepared material showed traces of organic and metallic salt by-products; however, these could be removed by washing with deionized water. Typical hysteresis curves were obtained for all specimens in magnetic field up to 14 T between 4 and 340 K. The saturation magnetization was 48.3 emu/g and 31.3 emu/g, 44.8 emu/g, and 28.4 emu/g for x=1.0 and 0.8 at 4 K and 340 K, respectively. The saturation magnetization, M _s , of nanoparticles of the MgFe₂O₄ specimen is about 50% higher when compared to the bulk. The enhanced magnetization measured in our nanoparticles MgFe₂O₄ specimens may be attributed to the uncompensated magnetic moment of iron ions between the A- and B-sites, i.e., changes in the inversion factor. Our magnetization results of MgFe₂O₄ specimens are comparable to the existing data for the same compound but with different particle size and prepared by different synthesis methods.     

Effect of excess oxygen on the electrical and magnetic properties of La1 ? xAgxMnO3 (x = 0.05, 0.1, 0.2) at 77 K < T < 300 K

A study has been made of the magnetic and electrical properties of oxygen-enriched La_{1 − x} Ag _x MnO_3.1 manganites at 77 K < T < 300 K. The samples have been produced by the sol-gel technique. The study has revealed an increase of the Curie temperature and a shift of the maximum in magnetoresistance toward high temperatures.     

Dependences of the dielectric and pyroelectric properties of (1 ? x)PbFe1/2Nb1/2O3?xPbTiO3 ferroelectric ceramics solid solutions on the PbTiO3 content in a compositional range of 0 ≤ x ≤ 0.08

(1 − x)PbFe_1/2Nb_1/2O_3−x PbTiO₃ (PFN-xPT) ferroelectric ceramics with low dielectric loss and pronounced anomalies of dielectric and pyroelectric properties near the ferroelectric-ferroelectric phase transition was obtained by doping with lithium. The temperature dependence of the position of the morphotropic boundary between the rhombohedral (monoclinic) and tetragonal phases in the x-T phase diagram of the PFN-xPT system was determined for the first time.     

Dielectric properties of perovskite ceramics of (1–x)BiFeO3 ? x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions from impedance spectroscopy data

The dielectric properties of the ceramics of (1 − x)BiFeO₃ − x(KBi)_1/2TiO₃ (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range 25–10⁶ Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition. The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation (δE _M ) and dc charge carriers (ΔE _dc) are determined. It has been established that, in the vicinity of 460 K, ΔE _dc increases jumpwise as the temperature increases.     

Electrical and magnetic properties of manganites La1 ? xAgxMnO3 (x = 0.05, 0.1, and 0.2) at 77 K < T < 300 K

The electrical conductivity, magnetization, and magnetoresistance of manganites La_{1 − x} Ag _x MnO₃ have been investigated in the temperature range 78–300 K. The samples have been synthesized by the sol-gel method. At room temperature, the magnetic field of 0.6 T has no effect on the electrical conductivity. As the temperature decreases, an abrupt jump is observed in the magnetization curve due to the semiconductor-metal phase transition. This transition hardly affects the temperature dependence of the resistance.     

Anomalies of the pyroelectric and dielectric properties of ferroelectric ceramics of the PbZr1- x Ti x O3 system with 0.06 ≤ x ≤ 0.35 at the R3 c ? R 3 m phase transition

The temperature dependences of the pyroelectric and dielectric properties of ferroelectric ceramics of the PbZr_{1 − x} Ti _x O₃ binary system with x = 0.06, 0.07, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35 have been obtained synchronously for each sample in the range of the structural phase transition between the states with the symmetry space groups R3c ↔ R3m. It is established that the temperatures of this phase transition for unpolarized and polarized samples coincide in the range 0.06 ≤ x ≤ 0.15. In this case, the x−T phase diagram, constructed on the basis of the pyroelectric and dielectric data, is in excellent agreement with the X-ray diffraction data on single crystals in this concentration range. The effect of dc electric fields from 5 × 10⁵ V m⁻¹ did not lead to any temperature shifts of the R3c ↔ R3m phase transition for the compositions with 0.06 ≤ x ≤ 0.25. Original Russian Text ? Yu.N. Zakharov, A.G. Lutokhin, N.A. Korchagina, V.G. Kuznetsov, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 4, pp. 589–591.     

Growth, optical parameters, and spectroscopic properties of crystals of disordered scheelite-like molybdates NaLaxGd1 ? x(MoO4)2 (x = 0–1) activated by Tm3+ ions

Polarized optical absorption spectra in the range of 450–2000 nm have been recorded for the Czochralski-grown concentration series of single crystals of mixed scheelite-like molybdates NaLa _x Gd_{1 − x} (MoO₄)₂(x = 0–1) activated by Tm³⁺ ions. The intensity parameters Ω _t (t = 2, 4, 6) of the crystals grown were determined by the Judd-Ofelt method, and the values found were used to estimate the probabilities and emission branching ratios for a number of radiative transitions of Tm³⁺ ions. The main optical constants of an Na_0.909La_0.490Gd_0.498Tm_0.035Mo_2.020O_8.048 crystal were found and the temperature dependences of the refractive index for the ordinary and extraordinary waves were investigated in the temperature range of 293–373 K. The spectral dependences of the emission cross section for the expected ³ F ₄ → ³ H ₆ laser transition of Tm³⁺ ions in an Na_0.908La_0.301Gd_0.676Tm_0.048Mo_2.019O_8.043 crystal were measured in the spectral range of 1500–2000 nm. The gain cross section of the active medium on the ³ F ₄ → ³ H ₆ laser transition of Tm³⁺ ions in this crystal was calculated using the spectral dependences of the absorption and emission cross sections.     

Magnetic and band parameters of (3HgS)1–x(Al2S3)x (x = 0.5) crystals doped with manganese

Investigations of magnetic susceptibility (χ) of (3HgS)_1–x (Al₂S₃) _x (x = 0.5) crystals doped with manganese investigated by the Faraday method in the range of Т = 77–300 K and Н = 0.25–4 kOe demonstrate that peculiar magnetic properties can be due to the presence of clusters of the Mn–S–Mn–S type in these crystals. Based on the investigation of kinetic coefficients of the crystals performed for Т = 77–300 K and Н = 0.5–5 kOe, it is established that the crystals demonstrate conductivity of the n-type, and their electric conduction only very slightly depends on the temperature and shows a maximum, the Hall coefficient is independent of the temperature, while the temperature dependences of mobility exhibit a maximum. Using the concentration dependence of the effective electron mass at the Fermi level, the width of the forbidden band, the matrix element of interatomic interaction, and the effective mass on the conduction-band bottom are obtained. Based on investigations by optical methods, the presence of direct optical interband transitions in the crystals is established and the value of the optical forbidden band (at Т = 300 K) is determined.     

Ferroelectric phase stabilization, phase transformations and?thermal properties in (1? x )PbZrO3– x Pb(Co1/3Nb2/3)O3 solid solution

The solid solution between the antiferroelectric PbZrO₃ (PZ) and relaxor ferroelectric Pb(Co_1/3Nb_2/3)O₃ (PCoN) was synthesized by the columbite method. The phase structure and thermal properties of (1−x)PZ–xPCoN, where x=0.0–0.3, were investigated. With these data, the ferroelectric phase diagram between PZ and PCoN has been established. The crystal structure data obtained from XRD indicates that the solid solution PZ–PCoN, where x=0.0–0.3, successively transforms from orthorhombic to rhombohedral symmetry with an increase in PCoN concentration. The AFE→FE phase transition was found in the compositions of 0.0≤x≤0.10. The AFE→FE phase transition shift to lower temperatures with higher compositions of x. The width of the temperature range of FE phase was increased with increasing amount of PCoN. It is apparent that the replacement of the Zr⁴⁺ ion by (Co_1/3Nb_2/3)⁴⁺ ions would decrease the driving force for antiparallel shift of Pb²⁺ ions, because they interrupt the translational symmetry. This interruption caused the appearance of a rhombohedral ferroelectric phase when the amount of PCoN was more than 10 mol%.     

Synthesis and study of photocatalytic activity of nanoscale quasi-one-dimensional Ti1 ? xVxO2 (0 ≤ x ≤ 0.13) and Zn1 ? xCoxO (0 ≤ x ≤ 0.3) oxides

A original method of synthesis of quasi-one-dimensional Ti_{1 − x} V _x (OCH₂CH₂O)₂ (0 ≤ x ≤ 0.13) and Zn_{1 − x} Co _x (HCOO)(HOCH₂CH₂O) (0 ≤ x ≤ 0.3) has been developed. The synthesis products were used as a basis for nanoscale extended Ti_{1 − x} V _x O₂ and Zn_{1 − x} Co _x O oxides. The compounds obtained and products of their thermolysis were investigated by X-ray diffraction, microscopy, IR spectroscopy, thermogravimetry, and chemical analysis; the shape and size of particles were determined by scanning electron microscopy. The good prospects of Ti_{1 − x} V _x O₂ and Zn_{1 − x} Co _x O solid solutions as photocatalysts for hydroquinone oxidation are shown.     

Thermal conductivity of single crystals of Ca1 ? xErxF2 + x and Ca1 ? xTmxF2 + x solid solutions

The thermal conductivity of single crystals of Ca_{1 − x} Er _x F_{2 + x} (x = 0.01, 0.05, 0.07, and 0.10) and Ca_{1 − x} Tm _x F_{2 + x} (x = 0.02, 0.04, and 0.06) solid solutions is studied in the temperature ranges 50–300 and 298–673 K. With increasing content of rare-earth elements, the behavior of thermal conductivity in these solid solutions changes from the characteristic of defect single crystals to glasslike. The concentration dependences of thermal conductivity for the two systems differ insignificantly.