X-ray powder diffraction and Mössbauer studies on the formation of Cd0.5Ni0.5Fe2O4/Zn0.5Ni0.5Fe2O4 spinel solid solutions

Structural investigations by X-ray powder diffraction, magnetic measurements and by Mössbauer spectroscopy, applied to a series of solid solutions formed between two mixed spinels, zinc–nickel ferrite and cadmium–nickel ferrite, indicates the difference in the cation arrangement in the solid solution obtained hydrothermally, compared to that of ferrites sintered at high temperatures. The ferrimagnetic crystalline Cd–Zn–Ni ferrite series, of a composition of Cd_0.5-αZn_αNi_0.5Fe₂O₄, have been prepared by hydrothermal treatment of the coprecipitated amorphous Cd–Zn–Ni–Fe hydroxide mixtures. The hydrothermally obtained samples displaying a defected spinel structure, with clearly noticeable non-stoichiometry, may be considered as precursors for the preparation of stoichiometric products by further thermal treatment. The first approach to the Mössbauer spectra of the system (Cd_0.5-αZn_αFe_0.5)_tetr[Ni_0.5Fe_1.5]_octO₄ analysis has been undertaken.     

X-ray,transport, magnetic and catalytic studies of the system Cd1–x Cu x FeCrO4

The compounds of the system Cd_1–x Cu_xFeCrO₄, where 0.0 x 1.0, synthesized by the co-precipitation technique have been studied with a view to investigating the cation distribution and the transport and magnetic properties, and to correlating the physical properties of oxidic spinels with their catalytic behaviour in the decomposition of benzyl alcohol. All the compounds of the system were crystallized with the cubic-spinel structure. The activatio-energy values of electronic conduction varied between 0.69 and 0.16 eV. Thermoelectric power measurements indicated a p-type semiconducting nature for all the compounds. Magnetic hysteresis studies indicated that the compounds with x 0.4 were ferrimagnetic. The Curie temperatures increased with increases in the Cu²⁺ -ion concentration. A good correlation could be established between the physical properties and the catalytic behaviour of the system.     

X-ray diffraction study of nonstoichiometry in CuInSe2 + §

CuInSe₂ alloys with the stoichiometric Cu : In ratio and varying Se content were studied by x-ray diffraction. The lattice parameters of the alloys, atomic positional parameterx, and the bond lengths lcu-se and l_in-Se were determined. The lattice parameters were found to increase with decreasing Se content on the Se-poor side of CuInSe₂ and to pass through a flat minimum around 50.5 at. % Se. The results are interpreted as indicating that the dominant intrinsic defects in Se-deficient CuInSe₂ are Cu interstitials. In the Se-enriched alloys containing more than ≃50.5 at. % Se, the dominant defects are cation vacancies, Se interstitials, and/or Se_Cu and Se_In antisite defects.     

The substrate problem in X-ray diffraction of boron-rich amorphous FeB alloys

Energy-dispersive X-ray diffraction spectra of boron-rich amorphous FeB alloys are presented. Special attention is paid to the preparation of the samples in a sputtering apparatus specially designed to give very pure materials. A solution is given to the “substrate problem”. The amorphous films are sputtered onto thin polycarbobate foils 2 μm thick fixed to a copper backing by means of SIRA adhesive wax. It is shown that the data evaluation is greatly simplified when the polycarbonate is directed towards the incident X-ray beam during the measurements.     

Mössbauer studies of Li0.5Fe2.5-xGaxO4 system: canted spin alignment and cation distribution

Based on⁵⁷Fe Mössbauer effect studies conducted at 4.2 K with and without an external magnetic field of 40 kG, the exact distribution of Fe³⁺ between the octahedral and tetrahedral sites has been determined for the Li_0.5Fe_2.5-x Ga _x O₄ system for 0.0 x 1.1. Gallium ions show a slight preference for tetrahedral sites. The values of canting angle _yk have been determined for octahedral Fe³⁺ ions using both relative intensity of different peaks and hyperfine field values. The effect of sintering on the values of hyperfine field, cation distribution and canting angle has been studied for Li_0.5Fe_1.4Ga_1.1O₄. The effect of gallium substitution on the values of hyperfine interaction parameters and the occurrence of a magnetically collapsed doublet is also discussed.     

Formation of oxide phases in the system Fe2O3−Gd2O3

The formation of oxide phases in the system (1 -x) Fe₂O₃ +xGd₂O₃ was investigated for 0 x 1. On the basis of XRD measurements the distribution of oxide phases, -Fe₂O₃, Gd₃Fe₅O₁₂, GdFeO₃ and Gd₂O₃ was determined, as a function ofx. No solid solutions were observed with certainty even at the very ends of the concentration range. This was also confirmed by⁵⁷Fe Mössbauer spectroscopy. New accurate crystallographic data for Gd₃Fe₅O₁₂ are given. The formation of oxide phases in the system Fe₂O₃- Gd₂O₃ is compared with the data for analogous system Fe₂O₃-Eu₂O₃.     

Powder X-ray diffraction identification of some new phases in the Na2SAl2S3 system

Four new phases in the Na₂SAl₂S₃ system have been identified by powder X-ray diffraction analysis. All four phases have Na₂S:Al₂S₃ ratios greater than 1:1. Analysis with X-ray diffraction and energy dispersive spectroscopy with a scanning electron microscope indicated provisional stoichiometries of α-Na₃AlS₃, β-Na₃AlS₃, and Na₅AlS₄ for three of the new phases. The fourth phase has yet to be identified.     

Dielectric behaviour and a.c. conductivity in Cu x Fe3−x O4 ferrite

The dielectric properties (dielectric constant and loss) for the system Cu _x Fe_3−x O₄ with x = 1.0, 0.8, 0.6, 0.4 and 0.2, were studied in the temperature range 300 ∼ 800 K and also in the frequency range 1 kHz ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.     

An X-ray diffraction study of Rb[UO2(SeO4)F]·H2O

An X-ray diffraction study of Rb[UO₂(SeO₄)F]·H₂O (I) was performed. The compound crystallizes in the rhombic system with the following unit cell parameters: a = 8.4753(6), b = 13.5234(9), c = 13.5296(9) Å, space group Pnma, Z = 8, V = 1550.7(2) ų; R = 0.0248. The principal structural units of crystals of I are [UO₂(SeO₄)F]^? layers belonging to crystal-chemical group AT³M² (A = UO ₂ ²⁺ , T³ = SeO ₄ ^2? , M² = F^?) of uranyl complexes. The uranium-containing layered units are combined via electrostatic interaction with Rb cations and via a system of hydrogen bonds involving outer-sphere water molecules.     

Mössbauer study of oxo derivatives of iron in the Fe2O3-Na2O2 system

Various compositions of oxo derivatives of iron reacting with sodium peroxide have been studied by Mössbauer spectroscopy. We have examined several mathematical models of the measured spectra. The results obtained are inconsistent with hypotheses made previously that such conditions may lead to the formation of compounds of iron in oxidation states above (6+). We demonstrate that a large excess of an alkali peroxide leads, most likely, to the formation of at least two iron(V) derivatives in tetrahedral coordination. In their Mössbauer spectra, they have isomer shifts of ?0.45 and ?0.51 mm/s and unusually large quadrupole splittings: 1.32 and 1.94 mm/s (at room temperature).     

Superconductivity Enhancement in Fe3O4 Doped YBa2Cu3O7−δ

Flux pinning can lead to the enhancement of J _c in superconductor. In order to study the effect of magnetic particles on superconductivity, the composites of (YBa₂Cu₃O_7?δ )_0.98(Fe₃O₄)_0.02 and (YBa₂Cu₃O_7?δ )_0.98(α-Fe₂O₃)_0.02 are synthesized with former sintered at different temperatures. The field-cooling measurements show that the T _c of the samples has not changed. The superconducting properties are enhanced when the samples are sintered at high temperature (750 ^°C), but suppressed for the samples without sintering or sintered at low temperature (350 ^°C). Scanning electron microscopy images show that the doped Fe₃O₄ are diffused into intergrain sites. With the increase of sintering temperatures, the grain size of the sample grows up and the flux pinning, which leads to the enhancement of J _c is formed by the addition of Fe₃O₄ nanoparticles. The extended X-ray absorption fine structure and X-ray absorption near edge structure experiments prove that after sintered at high temperatures the addition of Fe₃O₄ can induce disorder of local structures of YBa₂Cu₃O_7?δ . Also, the transition from the tetragonal phase to the orthorhombic phase is observed by the X-ray diffraction spectra. By the above analysis of experimental data, the enhancement of diamagnetic signal, which represents the superconducting properties can be attributed to the disorder enhancement of local structures and structural phase transition of the cuprates induced by the addition of Fe₃O₄.     

Analysis of the spatial distribution of Y2BaCuO5 inclusions in large-grain YBa2Cu3O7-δ

High values of critical current density, Jc, in large-grain superconducting melt-processed YBa2Cu3O7- (YBCO, Y-123) have been reported to correlate closely with the distribution of Y2BaCuO5 (Y-211) particles in the Y-123 phase matrix. Extensive image analysis of the homogeneity of the Y-211 particle distribution in a large-grain sample has been performed on high-resolution, secondary scanning electron micrographs of seeded melt-processed YBCO. The variation of key parameters, such as area fraction, number density and size along the a/b axis of the Y-123 grain has been investigated in detail as a function of distance from the centre of the seed. Both area fraction and number density of Y-211 particles are observed to increase continuously with distance, whereas the mean and standard deviation of the size distribution decrease slightly towards the grain boundary. This suggests that the increase in area fraction can be attributed to an increase in number density of the Y-211 particle distribution along the a/b axis of the specimen. The implications for Y-211 particle pushing, ripening and coalescence are discussed in the light of these results. © 1998 Chapman & Hall     

Experimental investigation of phase equilibria in the Cu–Ni–Zr system

Phase equilibria in the Cu–Ni–Zr ternary system have been measured through alloy sampling combined with diffusion couple approach. According to the phase relations identified with electron probe microanalysis and X-ray diffraction techniques, isothermal sections at both 1073 and 1293 K were constructed. It is evident that remarkable ternary solubility occurs in almost all binary intermetallic phases at both temperatures. The formerly reported ternary compounds T1 (Cu_20–40Ni_40–60Zr₂₀) and T2 (Cu_20–25Ni_60–65Zr₁₅) were not verified in this work. No other ternary compound was detected. In addition, continuous dissolution between Cu₁₀Zr₇ and Ni₁₀Zr₇ at 1073 K was observed.