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.     

Electronic properties of LiMn2?xTixO4

Ti-substituted LiMn₂O₄ (LiMn_2−x Ti _x O₄, x=0, 0.15, 0.30, 0.45, 0.60, and 0.75) has been synthesized using solid-state reactions. Their crystal and electronic structures were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). XRD data suggested that the lattice parameters of LiMn_2−x Ti _x O₄ increase due to the replacement of Mn by Ti ions. XPS results indicated that the substituted Ti ions were in +4 oxidation state; consequently, the normal oxidation state of Mn ions has been detected by measuring the binding energy splitting of Mn 3s states, which decreases with the content of substituted Ti. The valence band spectra suggested that the intensity of e _g level of Mn 3d orbitals increased due to the increase of the Mn³⁺/Mn⁴⁺ ratio.     

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.     

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.     

M?ssbauer study of compounds of Cu3 ? xFexSnS4 and Cu2Fe1 ?xZnxSnS4 systems

A M?ssbauer study of the structural and charge states of ⁵⁷Fe and ¹¹⁹Sn atoms in the compounds of Cu_{3 −x} Fe _x SnS₄ and Cu₂Fe_{1 − x} Zn _x SnS₄ systems was performed. It was shown that the iron atoms in the compounds of both systems were in the divalent and trivalent states occupying the tetrahedral positions of the structure. The character of the changes of the degree of covalency of the Fe²⁺-S, Fe³⁺-S and Sn⁴⁺-S bonds during the isomorphic substitution in the systems was established.     

Emission centers in Ca1–xPrxF2+x (x = 0.35) solid solutions

Luminescence spectra of Ca_0.65Pr_0.35F_2.35 solid solutions are studied. It is found that, depending on the excitation energy, different kinds of emission centers appear in these spectra. An interconfigurational 4f ¹5d¹ →4f² luminescence is typical for single Pr³⁺ ions in tetragonal sites. Data on the structure of the solid solutions show that the emission centers involved in ¹S₀ → 4f² transitions can be attributed to Pr³⁺ ions contained in clusters.     

Micro-Raman response and phonon oscillator parameters in solid solutions Pb1 ? xCaxTiO3 (0.40 < x < 0.62)

The temperature (295 K < T < 650 K) investigations of the polarized Raman spectra measured for a single-crystal sample of the Pb_0.54Ca_0.46TiO₃ solid solution in the frequency range 10 < ν < 1200 cm⁻¹ have established the existence of at least one specific temperature (T _c ≈ 392 K) at which the oscillator parameters of phonon modes exhibit noticeable anomalies. Similar phenomena are observed in solutions with 0.4 < x < 0.5. A sharp increase in the intensity of the spectral lines corresponding to polarization waves at temperatures immediately below T _c suggests a transformation of Pb_{1 −x} Ca _x TiO₃ (0.4 < x < 0.5) into a polar state, which does not exist for x > 0.5. Original Russian Text ? A.N. Chabanyuk, V.I. Torgashev, Yu.I. Yuzyuk, V.V. Lemanov, P. Simon, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 1, pp. 155–163.     

Magnetic phase transitions in Nd1 ? xDyxFe3(BO3)4 ferroborates

The magnetic properties of ferroborate single crystals with substituted compositions Nd_{1 − x} Dy _x Fe₃(BO₃)₄ (x = 0.15, 0.25) with competing exchange Nd-Fe and Dy-Fe interactions are investigated. For each composition, we observed a spontaneous spin-reorientation transition from the easy-axis to the easy-plane state and step anomalies on the magnetization curves for the spin-flop transition induced by a magnetic field B | c. The measured parameters and effects are interpreted using a unified theoretical approach based on the molecular field approximation and on calculations performed in the crystal-field model for the rare-earth ion. The experimental temperature dependences of the initial magnetic susceptibility from T = 2 K to T = 300 K, anomalies on the magnetization curves for B | c in fields up to 1.8 T, and their evolution with temperature, as well as temperature and field dependences of magnetization in fields up to 9 T are described. In the interpretation of experimental data, the crystal-field parameters in trigonal symmetry for the rare-earth subsystem are determined, as well as the parameters of Nd-Fe and Dy-Fe exchange interactions.     

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.     

Novel synthesis of NixZn1?xFe2O4 (0?≤?x?≤?1) nanoparticles and their dielectric properties

Nanocrystalline Ni _x Zn_1−x Fe₂O₄ (0 ≤ x ≤ 1) ferrite powders with average particle size 15–20 nm have been successfully prepared at a very low temperature (180 °C) by a novel auto combustion process using citric acid and ethylenediamine as a coordinating agent and bridging ligand, respectively. Phase purity of the solid solutions has been confirmed by X-ray diffraction. Morphological characterizations of the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. Extensive Fourier transformed infrared spectroscopic characterization has been carried out to identify the plausible mechanism of the synthesis process. Composition-dependent electrical properties (resistivity and dielectric constant) of the synthesized solid solution have been investigated. Interestingly, a non-linear variation of dielectric permittivity with respect to composition has been observed. The room temperature electrical resistivity as well as the dielectric permittivity of Ni_0.5Zn_0.5Fe₂O₄ was found to decrease with the decrease of particle size.     

Phonon spectroscopy of submicron ceramic materials based on Ce1–xGdxO2–y solid solutions

The specific features of the kinetic characteristics of subterahertz phonons in ceramic samples based on Ce_1–x Gd _x O_2–y electrolyte solid solutions have been investigated in the range of liquid-helium temperatures. It has been demonstrated that the observed anomalies of the transport characteristics of thermal phonons in this system are caused by the formation of structural defects associated with the position of vacancies in the anion sublattice with respect to impurity cations. The activation energy of the two-level system Δ = 8.53 K has been determined from an analysis of the experimental results.     

Study of high-temperature oxygen permeability in Sr1 ? xLaxCo0.8 ? yNbyFe0.2O3 ? z perovskites

The oxygen permeability of ceramic SrCo_{0.8 − y} Fe_0.2Nb _y O_{3 − z} (0 ≤ y ≤ 0.2) and La_0.3Sr_0.7Co_0.6Fe_0.2Nb_0.2O_{3 − z} disc membranes as a function of temperature and oxygen partial pressure was studied. Kinetic analysis was performed based on the experimental data on oxygen permeability as a function of oxygen partial pressure.     

Anomalous behavior of the coercive force of dilute nickel ferrites NiGaxAlxFe2 ? 2 xO4 with a frustrated magnetic structure

The behavior of the spontaneous magnetization σ _s (T) and coercive force H _c (T) of dilute nickel ferrites NiGa _x Al _x Fe_{2 − 2x} O₄ (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8) has been studied. Above the transition temperature T _t , the coercive force H _c is found to reveal an anomalous behavior for compositions with x ≥ 0.4, namely, the temperature dependence of the coercive force H _c (T) exhibits a maximum in the range from T _t to T _C. For the reduced temperature θ₂ = 0.8 T _C, at which ferrites with the substitution x ≥ 0.4 reside in the spin glass state, the coercive force H _c is observed to increase sharply with x. The assumption is made that the clusters prevailing in the spin glass state are no larger than 3 nm in size. Original Russian Text ? L.G. Antoshina, A.B. Korshak, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 5, pp. 900–903.     

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.     

Phase formation in near-morphotropic region of the PbZr1 ? xTixO3 system, structural defects, and electromechanical properties of the solid solutions

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 (T = 25°C) is constructed containing in single-phase regions isosymmetric states characterized by different concentration dependences of the structural and electrophysical parameters. There are also regions where these states coexist, with their unit cell volume remaining unchanged. The existence of these states is interpreted in terms of the real (defect) structure of the ceramics. Several reasons are indicated that are responsible for the appearance of the phase states and related to the crystallochemical peculiarities of the solid solutions: the alternate valence of titanium ions; the infinitely adaptive structure of titanium dioxide; and the formation, ordering, and rotation of the planes of crystallographic shear. It is shown that the transition from the rhombohedral to tetragonal phase occurs indirectly, through two intermediate phases with lower symmetry whose appearance is favored by the defects in the solid solutions. 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, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 5, pp. 958–965.     

Yb:Y2－2xLa2xO3激光透明陶瓷的光谱性能

对一种低温易烧结的Yb:Y_2-2xLa_2xO₃激光透明陶瓷的光谱性能进行了初步研究，Yb:Y_2-2xLa_2xO₃激光透明陶瓷具有宽的吸收带和大的吸收截面，在最强的吸收峰977nm处吸收截面达4.0×10^-20cm²；其荧光发射寿命为1.1ms，发射截面在1033nm处为1.0×10^-20cm²，在1077nm处为0.7×10^-20cm².Yb:Y_2-2xLa_2xO₃陶瓷的各项光学性能指标接近或达到单晶的指标. 关键词： 氧化镧钇 激光陶瓷 低温烧结 光谱性能     

Studying the local structural features of Zn2 ? 2xCd2xV2O7 by NMR and IR spectroscopy

The local structure of pyroanion groups in the incommensurate phase X-Zn_{2 − 2x} Cd_2x V₂O₇ (0.11 ≤ x ≤ 0.48) with a zero volumetric expansion coefficient is studied. Comparative analysis of IR and NMR spectra of samples in the X-phase and of ZnCdV₂O₇ revealed that vanadium atoms have a similar structural and an identical charge environment. Additional bands in the IR spectra of the X-phase in the range of end vibrations are due to the influence of the cation sublattice.