A substitution of nickel by antimony:: Crystal and electronic structure of the new antimonide Hf6Ni1−xSb2+x

The ternary antimonides Hf₆M_1−xSb_2+x (M=Fe, Co, Ni) were prepared by arc-melting of stoichiometric mixtures of Hf, HfSb₂ and M. According to the single crystal structure analyses, performed on Hf₆NiSb₂ and Hf₆Ni_0.76Sb_2.24, Hf₆M_1−xSb_2+x crystallizes in an ordered variant of the Fe₂P structure type with the M and Sb atoms occupying the two P positions on 1b and 2c of space group P

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2m, respectively (Zr₆CoAl₂ type). The 3d metal atoms M can partially be replaced by antimony, leading to significant, anisotropic changes in the lattice dimensions which are a=765.6(1) pm, c=362.10(7) pm, V=183.81(5)×10⁶pm³ for Hf₆NiSb₂, and a=760.5(1) pm, c=372.40(7) pm, V=186.53(5)×10⁶pm³ for Hf₆Ni_0.76Sb_2.24 as determined by single crystal data. Calculations of the electronic structure of Hf₆NiSb₂ using the Extended Hückel approximation show strong bonding Hf–Hf, Hf–Ni, and Hf–Sb interactions.     

Structure and magnetic properties of Gd3(Fe1−xTix)29 (x=0.011–0.034)

Single-phase compounds Gd₃(Fe_1−xTi_x)₂₉ (x=0.0110.034) have been synthesized. Gd₃(Fe_1−xTi_x)₂₉ crystallises in a monoclinic lattice with space group P2₁/c, and the crystal structure is refined by the Rietveld technique based on X-ray powder diffraction data. Thermomagnetic analysis indicates that the Curie temperature of the compounds ranges from 517 K to 538 K. The saturation magnetizations of the Gd₃(Fe_1−xTi_x)₂₉ (x=0.011, 0.022, 0.034) at 1.5 K are 103.6, 102.0 and 94.3 Am²/kg, and the anisotropy fields at 1.5 K are 6.0, 6.2 and 6.4T, respectively.     

Influence of B site substituent Ti on the structure and thermophysical properties of A2B2O7-type pyrochlore Gd2Zr2O7

Since the structural integrity of A₂B₂O₇-type pyrochlores relies mostly on the interconnecting BO₆ octahedra, Ti⁴⁺ was selected to partially substitute Zr⁴⁺ in Gd₂Zr₂O₇ in order to distort the pyrochlore structure in order to improve the material’s thermophysical properties for potential use as high-temperature thermal insulation. As evidenced by X-ray diffraction and Raman spectroscopy studies, incorporation of Ti⁴⁺ simultaneously leads to long-range ordering of the pyrochlore structure as well as local lattice distortion. These two effects have been shown to be competitive in determining the crystal energy of the Gd₂(Zr_1−xTi_x)₂O₇ series and result in a minimum value of the Young’s modulus at x = 0.3 and a maximum value of the coefficient of thermal expansion at x = 0.2. At lower temperatures, the thermal conductivity of Gd₂Zr₂O₇ was significantly reduced by Ti⁴⁺ doping, and its composition dependence was accurately modeled by taking into account the phonon scattering by mass and strain fluctuations at the B site.     

Multiphase magnetic state of Ca1 ? x La x MnO3 ? δ single crystals ( x = 0.03, 0.05, 0.07) containing oxygen vacancies

Magnetic properties (magnetization, dynamic and static susceptibility) and transport properties (resistance and magnetoresistance) have been studied in a temperature range of 2–600 K in magnetic fields to 90 kOe for single crystals of Ca_{1 − x} La _x MnO_{3 − δ} with a weak electron doping (x ≤ 0.07) grown in argon and oxygen atmospheres. The magnetic state of Ca_{1 − x} La _x MnO_{3 − δ} single crystals is multiphase. Below T = T _N(G) ∼ 110 K, in all the crystals there coexists an AFM G phase with an FM contribution and an AFM C phase. In crystals with x = 0.07, a transition from the paramagnetic phase into the AFM C phase occurs in part of their volume below T ∼ 130–150 K. In crystals with x = 0.05 annealed in oxygen, an anomaly of paramagnetic susceptibility is observed near T ^* ∼ 270 K, which is related to the formation of FM clusters near defects. At x = 0.05 and 0.07, AFM correlations are retained in the paramagnetic state (to 600 K). The differences in the magnetic and transport properties of single crystals grown in argon and oxygen are explained by the various content of oxygen vacancies and by their possible ordering. Original Russian Text ? N.N. Loshkareva, A.V. Korolev, T.I. Arbuzova, N.I. Solin, A.M. Balbashov, N.V. Kostromitina, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 103, No. 3, pp. 261–270.     

Structure and element distribution in the UFe10-xAlxSi2 system

The neutron diffraction studies of powdered alloys withx = 2,2.5, and 3 gave detailed information on crystallographic data of the compounds. The structure refinement at 300 K for allx = 2,2.5, and 3 and at 450 K forx = 2 confirmed the ThMn₁₂ type of structure with uranium located in 2(a) positions, iron in 8(f), 8(i), and 8(j) positions, aluminum atoms in 8(i) and 8(j) positions, and Si atoms in 8(f) and 8(j) positions. Impurity phases, FeAl and UFe₂Si₂ have been detected in all investigated compounds.     

Indirect heteronuclear 17O-207Pb interaction in the superconductive oxides BaPb1 ? xBixO3 (x ≤ 0.21)

In this paper, we present the results of measurements of the spin-echo double-resonance signal of ¹⁷O-²⁰⁷Pb in superconductive oxides BaPb_{1 − x} Bi _x O₃ (x ≤ 0.21). The constants of the spin-spin (¹⁷O-²⁰⁷Pb) interactions of nuclear spins, which are proportional to spin susceptibility, have been determined. The direct estimations of the constants of indirect interaction between the nuclei of nearest neighbors (O-Pb and Pb-Pb atoms) give convincing evidence in favor of the development of a microscopically inhomogeneous state of the electron system in the metallic phase of the oxides, for which, according to X-ray diffraction data, there are no signs of macroscopic phase separation.     

Magnetic study of Ti-substituted NiFe2O4 ferrite

The Ni_1+xTi_xFe_2−2xO₄ (0 ≤ x ≤ 0.1) ferrite systems prepared by a semi-chemical route, have been studied by electron paramagnetic resonance (EPR) at X-band, Mössbauer spectroscopy and magnetization measurements at various temperatures. EPR spectra of these samples comprise generally a broad and asymmetric EPR signal. The variation of g_eff and peak-to-peak line width ΔH_pp, with Ti concentration and temperature are attributed to the variation of dipole–dipole interaction and the superexchange interaction. Mössbauer spectra comprise two sets of sextet attributed to Fe³⁺ at two distinct sites-A and -B. Ti⁴⁺ ions are concluded to occupy the octahedral B-sites. Magnetic moment is found to decrease with the increase of Ti⁴⁺ concentration. The effective magnetic field H_eff at the A-sites also follows a similar trend. The reason is attributed to the canted structure of spins in the Ti-doped samples. An anomalous behavior at x = 0.015 is observed in the properties studied here and some sort of phase change is believed to occur at 473 K in these ferrites.     

Study of the electrical conduction behaviour of the Ba1−xLaxTi1−xNixO3 (x 0.10) system

The electrical conduction behaviour of the Ba_1−xLa_xTi_1−xNi_xO₃ (x 0.10) system has been studied by complex plane impedance analysis and measurements of a.c. conductivity in the temperature range 400–575 K. The values of the bulk resistance for these samples are obtained from a circular arc passing through the origin in their impedance plots. A.c. conductivity obeys the relation σ_a.c.αω⁸ in the temperature range of measurements. These results indicate that conduction occurs in this system because of hopping of charge carriers between localized nickel sites.     

Hydrogen in lanthanum-magnesium-nickel alloys with structures of the L 22, D 2 d , and L 60 types

A statistical theory of the solubility of hydrogen in alloys with structures of the L2₂, D2 _d , and L6₀ types and in phase mixtures of these alloys is developed. The isotherms of absorption and desorption have been studied; their dependence on the activity of hydrogen and concentration of magnesium has been established. It is shown that with an increase in the magnesium concentration and a decrease in the activity of hydrogen, a plateau (a horizontal segment) appears and is lengthened in the isotherms. Hysteresis effects have been investigated with allowance for volume effects; the hysteresis coefficients have been estimated. The decrease in the hysteresis coefficient with increasing magnesium concentration is substantiated. The results of the theoretical calculations are compared with experimental data. Original Russian Text ? S.Yu. Zaginaichenko, Z.A. Matysina, D.V. Shchur, 2007, published in Fizika Metallov i Metallovedenie, 2007, Vol. 104, No. 5, pp. 453–464.     

Thermoelectric properties of Sn1−x−yTiySbxO2 ceramics

Thermoelectric properties of Sn_1−x−yTi_y Sb_xO₂ ceramics were investigated in detail. The addition of Sb into SnO₂ matrix increased the electric conductivity, σ. The increase in the σ value should be caused by the increase in the carrier concentration. The Seebeck coefficients of all the samples were negative, which means that these samples have n-type conduction. The samples of this study have porous structure. The maximum Z value of all the samples measured in this study was 2.4 × 10⁻⁵ K⁻¹.     

Particular properties of Ti2O and TiNx nanoparticles prepared by thermal decomposition

Particular properties of Ti₂O and TiN_x prepared by thermal decomposition were introduced. A precursor prepared by titanium powder reacting with oxalate acid was thermally decomposed in nitrogen atmosphere at 840°C for 15 min, and relatively pure Ti₂O was then obtained. Conductive TiN_x was also prepared after altering reaction conditions. Samples were characterized by resistivity, X-ray powder diffraction, transmission electron microscope, Ultraviolet-Visible diffuse reflection, and electromagnetic shielding efficiency. The results indicate that both Ti₂O and TiN_x have good conductivity. Moreover, Ti₂O shows a better solar photocatalytic activity and TiN_x does well in the electromagnetic shield.     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

Investigation of the dependency of the upper critical magnetic field on the content x in Y1−xYbx/2Gdx/2Ba2Cu3O7−y superconducting structures

The Y_1−xYb_x/2Gd_x/2Ba₂Cu₃O_7−y superconducting samples for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by using the solid-state reaction technique. Resistivity measurements of the samples were performed in QD–PPMS system under different magnetic fields up to 5 T in zero fields cooling regime. Using the resistivity data, the upper critical magnetic field H_c2(0) at T = 0 K for 50% of R_n was calculated by the extrapolation H_c2(T) to the temperature T = 0 K. The coherence length in T = 0 K were calculated from H_c2(0) and the effects of x in the composition on both the coherence length and the upper critical magnetic field were examined. The results showed that H_c2(0) varied from 84.05 to 122.26 T with the content x. The upper critical magnetic field in the temperature T = 0 K slightly decreased with increasing the content x. Using the content x, the upper critical magnetic field can be controlled and this can be used in the superconductivity applications.     

Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Na_x(MoO)₅(P₂O₇)₄ has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo_1.3OP₂O₇ [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo₂ and Mo₃ clusters were erroneously identified in Mo_1.3OP₂O₇. A revised structure of Mo_1.3OP₂O₇ contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)₅(P₂O₇)₄. In both structures, the (MoO)₅(P₂O₇)₄ framework strongly resembles the one in the earlier reported Ag(MoO)₅(P₂O₇)₄, while the location of Na and Ag atoms differ.     

Electronic state and magnetism of the rare-earth carbide GdCx (x 0.33)

The electronic state and the magnetism of GdC_x (x = 0.33) were investigated by the discrete variational (DV)-Xα calculation method together with those of Gd metal. Magnetic moments on the gadolinium atoms located at the center of the Gd₁₇ and Gd₄C₂ clusters extracted from Gd metal and Gd_tC were calculated to be 8.38 and 9.70 μ_B, in qualitative agreement with the experimental values (7.96 and 8.28 μ_B respectively). The exchange splitting of the Gd 4f band in Gd₃C was found to increase from that of Gd metal and accounts for the higher Curie temperature of GdC₁ compounds observed in experiments. The calculated results show that the carbon atoms are charge acceptors in these compounds. The higher Curie temperature values (T_c = 350 K) observed in the GdC_x (x 0.33) compounds compared with Gd metal (T_c = 293 K) are discussed on the basis of the spin-fluctuation theory.     

Phase composition and magnetic properties of nanocrystalline SmFe11 ? xGaxC1.25 (2 ≤ x ≤ 5) alloys

As-cast and rapidly quenched alloys (RQAs) SmFe_{11 − x} Ga _x C_1.25 (2 ≤ x ≤ 5) have been studied. The RQAs were prepared by melt spinning on a steel wheel rotating at a velocity V = 10−40 m/s. Fragments of the RQAs were annealed in a vacuum at T _ann = 500−850°C. The as-cast alloys are multiphase; the maximum volume fraction in them corresponds to the Sm₂(Fe, Ga)₁₇C compound with a rhombohedral structure. The rapid quenching leads to the formation of the Sm(Fe, Ga)₁₁C compound (1: 11) with a tetragonal BaCd₁₁-type structure; the maximum volume fraction of the compound is reached in the alloy with x = 3 quenched to a wheel rotating at V = 30 m/s. The melt spinnins of the alloys with x = 2−4 at V = 40 m/s is accompanied by their substantial amorphization. During annealing, the amorphous phase crystallizes mainly with the formation of the 1: 11 phase. A nonequilibrium phase diagram of the alloys quenched at V = 40 m/s and annealed at T _ann = 500−850°C has been constructed. The 1: 11 compound has a single-phase region near x = 3 at T _ann ≥ 600°C. As the volume fraction of the 1:11 phase increases, the coercive force H _c of nanocrystalline RQAs increases. The maximum coercive force is observed for the SmFe₈Ga₃C_1.25 alloy quenched at V = 40m/s and subsequently annealed at 700°C; it is 0.8 and 12 kOe at 293 and 50 K, respectively. The high coercive force obtained indicates that the Sm(Fe, Ga)₁₁C phase is magnetically uniaxial and has a high magnetic anisotropy energy. The magnetic anisotropy constant K ₁ of the compound at T = 50 K was estimated to be 3.1 × 10⁷ erg/cm³.     

Analyses of HCP/D019 and D019/L10 phase boundaries in Ti-Al-X (X=V, Mn, Nb, Cr, Mo, Ni, and Co) systems by the cluster variation method

The cluster variation method (CVM) based on the octahedron and tetrahedron approximation was applied to the calculation of γ(TiAl, L1₀)/α ₂(Ti₃Al, D0₁₉) phase equilibrium in the Ti-Al-X (X=V, Mn, Nb, Cr, Mo, Ni, and Co) systems. The antiphase boundary (APB) energy, the long-range order (LRO) parameter, and the substitution behavior of the γ(TiAl, L1₀) were calculated. The results of calculations were in good agreement with the data determined experimentally.     

Dielectric properties and crystal structure of La(Mg1/2Ti1/2)O3 ceramics with Mg substituted by Co

Solid solutions of (1 − x)La(Co_1/2Ti_1/2)O₃-xLa(Mg_1/2Ti_1/2)O₃ were used to prepare La(Mg_1−xCo_x)_1/2Ti_1/2O₃ using solid-state synthesis. X-ray diffraction patterns of the sintered samples revealed single phase formation. A maximum density of 6.01 g/cm³ was obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ (x = 1) ceramics sintered at 1375 °C for 4 h. The maximum values of the dielectric constant (?_r = 29.13) and the quality factor (Q × f = 80,000 GHz) were obtained for La(Mg_1−xCo_x)_1/2Ti_1/2O₃ with 1 wt% ZnO additive sintered at 1375 °C for 4 h. The temperature coefficient of resonant frequency τ_f was −59 ppm/°C for x = 0.3.     

Synthesis and photoluminescence properties of color-tunable BaLa2WO7:Eu phosphor

Color-tunable phosphors BaLa_2−xEu_xWO₇ were synthesized via a solid-state reaction. The absorption, excitation, emission and decay curves were obtained to study the luminescence properties. The experimental results indicate that BaLa_2−xEu_xWO₇ phosphors have two regions in the excitation spectra: one is assigned to the charge-transfer state (CTS) band at about 338 nm, and the other is assigned to the intra-4f transitions at 360-600 nm. The emission spectra of BaLa_2−xEu_xWO₇ phosphors excited at 395 nm exhibit a series of sharp peaks, which are attributed to the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. Luminescence from higher excited states, such as ⁵D₁, ⁵D₂, and ⁵D₃, were also observed at low Eu³⁺ concentration. The optimal emission intensity of ⁵D₀ → ⁷F₂ red emission is at x = 0.4 (BaLa_1.6Eu_0.4WO₇). The chromaticity coordinates of BaLa_2−xEu_xWO₇ phosphors vary with Eu³⁺ content from white, orange-red, to red, making it a candidate for a white-light-emitting phosphor in UV-LEDs.     

Effect of the deviation of the chemical composition from the stoichiometric composition on the structural and phase transformations and properties of rapidly quenched Ti50 + xNi25 ? xCu25 alloys

Methods of X-ray diffraction, transmission and scanning electron microscopy, and electron diffraction have been used to study phase composition and structure of an almost stoichiometric alloy Ti₅₀Ni₂₅Cu₂₅. The alloys of the quasi-binary section TiNi-TiCu to be studied, which exhibit in the initial ascast state thermoelastic martensitic transformations B2 ↔ B19 and related shape-memory effects, have been produced by rapid quenching of the melt (melt spinning technique). The chemical composition of the Ti_{50 + x} Ni_{25 − x} Cu₂₅ alloys was varied with respect to titanium and nickel within x ≤ ±1% (from Ti₄₉Ni₂₆Cu₂₅ to Ti₅₁Ni₂₄Cu₂₅). It has been shown that the rapid quenching from the melt at a cooling rate of 106 K/s provides amorphization for all the alloys under consideration. Heating to 723 K or higher temperatures leads to the devitrification of the amorphous alloys with the formation of a polycrystalline structure of the B2 austenite. The mechanical properties of the alloys have been measured in the initial amorphous state and after subsequent heat treatment. It has been established that, depending on the degree of deviation of the alloy from the stoichiometric composition, which leads to solid solution decomposition in the process of nanocrystallization upon heat treatment, there occur regular changes in the mechanical properties and shape-memory effects of the alloys. The characteristic temperatures of the onset and finish of the process of crystallization from the amorphous and amorphous-crystalline states and the critical temperatures of the onset and finish of the forward and reverse thermoelastic martensitic transitions have been determined by measuring temperature dependences of the electrical resistivity of the alloys. The diagram of the dependence of the critical temperatures on the chemical composition of the alloy has been constructed.