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.     

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.     

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.     

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.     

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.     

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.     

Irreversible increase in the temperature range of existence of the orthorhombic antiferroelectric phase in PbZr1 ? xTixO3 ceramics (0.02 ≤ x ≤ 0.05)

The influence of thermostating at 450°C on the dielectric and pyroelectric properties of PbZr_{1 − x} Ti _x O₃ polarized ferroelectric specimens the range 0.02 ≤ x ≤ 0.05 has been investigated. An irreversible increase in the temperature of the ferroelectric-antiferroelectric phase transition was observed in all specimens upon their cooling after exposure to an elevated temperature for more than 1 h. The original position of the phase-transition point on the temperature scale was not recovered as a result of afterpoling upon cooling through the Curie temperature. Heating of the same specimens in the bridged mode up to 650°C with subsequent abrupt immersion in silicone oil at room temperature (hardening) is accompanied by an additional increase in the range of existence of the antiferroelectric phase from 3 to 15°C with an increase in the x concentration.     

Effect of polarization on the intensity of anomalous electron emission in the (1 ? x)PbMg1/3Nb2/3O3 + xPbTiO3 system

Spectra of anomalous electron emission from the surface of solid solutions in the (1 − x)PbMg_1/3Nb_2/3O₃ + xPbTiO₃ system with x = 0.06, 0.10, 0.13, 0.20, and 0.25 have been studied. While the energy characteristics of the anomalous electron emission spectra vary monotonically with x, the behavior of integrated intensity was found to be nonmonotonic with a maximum occurring at x = 0.1. According to the proposed interpretation, the results obtained are explained by the effect of the potential barrier on the electron emission; the potential barrier depends, in turn, on the permittivity ε of the samples. Original Russian Text ? A.T. Kozakov, A.V. Nikol’skiĭ, V.P. Sakhnenko, A.N. Pavlov, V.G. Smotrakov, V.V. Eremkin, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 7, pp. 1310–1314.     

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.     

Magnetic, electrical, and optical properties of Ca1 ? x Ce x MnO3 ( x ≤ 0.12) single crystals

The magnetic, electrical, and optical properties of Ca_{1 − x} Ce _x MnO₃ (x≤0.12) manganite single crystals are investigated with the aim of revealing the specific features of the multiphase electronic and magnetic state as a function of the cerium concentration and the atmosphere used for growing single crystals. It is found that the concentration dependence of the low-temperature magnetization M(x) of the single crystals is shifted toward the high-concentration range as compared to the corresponding dependence of the polycrystals, which is explained by the predominant cation deficiency. The electrical resistivity and the reflection spectra of the single crystals in the infrared spectral range indicate that charge carriers exhibit a band nature at temperatures close to room temperature. The temperature dependence of the electrical resistivity of the single crystal with x = 0.08, which has the maximum magnetization in the studied series of Ca_{1 − x} Ce _x MnO₃ compounds, unlike polycrystals, exhibits a metallic behavior over the entire temperature range. The G-type antiferromagnetic phase with the Néel and Curie temperatures T _N(G) = T _C = 100 K is characterized by maxima of the electrical resistivity ρ and the magnetoresistance Δρ/ρ = |(ρ₀ − ρ _H )/ρ₀| = 38% in the magnetic field H = 90 kOe. The magnetoresistance Δρ/ρ of the single crystals at cerium concentrations x = 0.10 and 0.12 with variations in temperature exhibit three specific features: near the temperature of charge ordering T _co, near the temperature of the magnetic phase transition to the C-type antiferromagnetic phase T _N(C), and near the temperature of the phase transition to the magnetic charge-ordered phase T _N(MCO). An anomalous temperature dependence of the magnetization is revealed for a single crystal with x = 0.10 grown in oxygen at a pressure of 5 atm, which is explained by the presence of regions with hole conductivity due to cation deficiency. The inhomogeneous electronic and magnetic state is associated with the interrelation of the charge, orbital, and spin orderings. Original Russian Text ? N.N. Loshkareva, A.V. Korolev, N.I. Solin, E.V. Mostovshchikova, S.V. Naumov, N.V. Kostromitina, A.M. Balbashov, 2009, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 135, No. 1, pp. 98–107.     

Magnetic phases in Pr0.5Sr0.5Mn1 ? xCoxO3 (x ≤ 0.5) solid solutions

The magnetic and magnetotransport properties of Pr_0.5Sr_0.5Mn_{1 − x} Co _x O₃ (x ≤ 0.5) solid solutions have been investigated using neutron diffraction methods. The magnetization and electrical conductivity have been measured in magnetic fields up to 140 kOe. It has been established that, during cooling in the temperature range from 160 to 110 K, the compounds of compositions with a cobalt content x ≤ 0.07 undergo a structural phase transition from the high-temperature ferromagnetic phase to the antiferromagnetic phase. A further substitution of cobalt for manganese leads to a stabilization of the inhomogeneous dielectric ferromagnetic state, whereas a state of the cluster spin-glass type has been revealed in compositions with x = 0.15 and 0.20. At x ≥ 0.25, a new magnetic phase with a Curie temperature up to 210 K is formed as a result of the magnetic interaction between manganese and cobalt ions. A magnetic phase diagram of the system under investigation has been constructed.     

Thermal expansion of (Ba1 ? xLax)Ti1 ? x/4O3 solid solutions

Deformation and the thermal expansion coefficient of ceramic samples of (Ba_{1 − x} La _x )Ti_{1 − x/4}O₃ solid solutions (x = 0, 0.026, 0.036, 0.054) were studied in the temperature range 120–700 K. Based on an analysis of the data obtained, the temperature-composition phase diagram is refined, and the temperature dependence of the polarization is calculated. The results are discussed in combination with the dielectric measurement data. Original Russian Text ? M.V. Gorev, I.N. Flerov, Ph. Sciau, S. Guillemet-Fritsch, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 4, pp. 746–752.     

Optical properties of the HfO2 ? x N x and TiO2 ? x N x films prepared by ion beam sputtering

Optical characteristics of the HfO_{2 − x} N _x and TiO_{2 − x} N _x films obtained by reactive ion beam sputtering have been investigated by spectral ellipsometry. The chemical composition of the films was determined using X-ray photoelectron spectroscopy. The nitrogen content in the oxynitride films (determined by the N₂/O₂ ratio in the gas mixture during synthesis) reached ≈9 at % for TiO_{2 − x} N _x and ≈ 6 at % for HfO_{2 − x} N _x . It is found that the dispersion relations n(λ) and k(λ) for the TiO_{2 − x} N _x films change from those characteristic of titanium dioxide to those typical of titanium nitride with an increase in the nitrogen content from 0 to ≈9 at %. The optical parameters of the HfO_{2 − x} N _x films depend weakly on the nitrogen content in the range 0–6 at %. Original Russian Text ? V.V. Atuchin, V.N. Kruchinin, A.V. Kalinkin, V.Sh. Aliev, S.V. Rykhlitskiĭ, V.A. Shvets, E.V. Spesivtsev, 2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 1, pp. 77–82.     

Growth of the magnetic semiconductor Fe2? x Ti x O3± δ thin films by pulsed laser deposition

The understanding and control of the ilmenite–hematite solid solutions (Fe_2−x Ti _x O_3±δ or IH) thin film structure and properties are crucial for spintronics applications. Good quality films of Fe_2−x Ti _x O_3±δ on Al₂O₃(0001) substrates were obtained by pulsed laser deposition. For the studied compositions (x=1, 0.7, 0.5) in a wide oxygen pressure range all the films were epitaxial, with flat interfaces, and without secondary phases. Unconventional lattice strain relaxation with the increase of in-plane lattice parameter above its relaxed bulk value was observed for different film compositions, oxygen pressures, substrate temperatures, and film growth rates. This phenomenon is most likely explained by the buckling of a few first film monolayers because of a significant compressive stress induced on the film by the sapphire substrate. The IH thin films with x=0.7 and 0.5 exhibited the properties of a room temperature magnetic semiconductor. The resistivity changed over three orders of magnitude in the studied pressure range, thus clearly demonstrating the important role of oxygen stoichiometry in the creation of carriers.     

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.     

Low-field magnetization of ludwigites Co3O2BO3 and Co3 ? xFexO2BO3 (x ≈ 0.14)

Ludwigite single crystals of compositions Co₃O₂BO₃ and Co_{3 − x} Fe _x O₂BO₃ (x ≈ 0.14) have been synthesized. The crystal structure is investigated at room temperature, and the magnetization is studied in the temperature range T = 4.2–100 K in magnetic fields of up to 600 Oe. The orthorhombic symmetry is revealed, and the unit cell parameters are determined. A number of features are established for the temperature dependence of the magnetization. In unsubstituted Co₃O₂BO₃, two magnetic transitions are found at T _C1 = 43 K and T _C2 = 15 K. At temperatures below 40 K, spin-glass state is revealed. Substitution of iron ions for cobalt ions leads to a noticeable shift in the magnetic transitions toward the high-temperature range: T _C1 = 83 K and T _C2 = 74 K. A ferromagnetic ordering of the P type is found in the Co_{3 − x} Fe _x O₂BO₃ (x ≈ 0.14) compound. Original Russian Text ? N.V. Kazak, N.B. Ivanova, V.V. Rudenko, A.D. Vasil’ev, D.A. Velikanov, S.G. Ovchinnikov, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 5, pp. 916–919.     

Mechanism of NdSr2 ? xCaxMn2O7 (0 ≤ x ≤ 2.0) solid solution formation

The mechanisms of formation of NdSr_{2− x} Ca _x Mn₂O₇ (0 ≤ x ≤ 2.0) solid solution have been studied. The dependence of its volume magnetic susceptibility on the calcium concentration is obtained. The stability of this solid solution is compared with that of similar solid solutions in lanthanum-containing systems.     

Optically active Er3+ centers in Si/Si1 ? x Ge x structures under optical pumping

The Si/Si_{1 − x} Ge _x :Er/Si heterostructures, which are of interest for laser applications, have been investigated. The types of optically active Er³⁺ centers making a dominant contribution to the photoluminescence response of the structures studied are analyzed and their relationship with the parameters of the Si_{1 − x} Ge _x :Er heterolayer and the post-growth annealing conditions is shown. On the basis of the PL kinetic analysis of the structures with an isolated type of optically active Er³⁺ centers, it is concluded that population inversion of Er³⁺ ion states can be obtained under optical pumping and the effect of nonradiative recombination channels in Si_{1 − x} Ge _x :Er heterolayers on the excitation efficiency of Er centers and the conditions for population inversion is shown. Original Russian Text ? L.V. Krasilnikova, N.A. Baidakova, M.V. Stepikhova, Z.F. Krasilnik, V.Yu. Chalkov, V.G. Shengurov, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 1, pp. 103–108.