A new stabilization process for CrO2 powders

A new stabilization process, based on a thermal treatment at 623±20 K in inert atmosphere, is proposed for CrO₂ powders used in the manufacture of magnetic recording devices.Magnetic and electroacoustic characteristics of the products indicate this process is a valid alternative for the traditional reduction.     

Electron transport properties of transition metal oxide systems with the K2NiF4 structure

La₂NiO₄ and Nd₂NiO₄ show metallic behaviour above 500 K. La₂CuO₄ is metallic while Sm₂CuO₄ and Nd₂CuO₄ are semiconductors in the range 120–1000 K. These transport properties are explained in terms of the structure and the nature of the delectrons.     

Sodium deintercalation from α-NaFeO2

Chemical deintercalation was investigated on α-NaFeO₂ using bromine as oxidizing agent. The product had a composition about Na_0.9FeO₂ keeping the host layer structure as it was. The crystal lattice was hexagonal and the lattice parameters were $\text{a}\text{=2.997}\text{A}\text{?}$, $\text{c}\text{=16.32}\text{A}\text{?}$. Mössbauer spectrum showed the presence of Fe⁴⁺ in the product. Electrical resistivity was higher than 10⁸Ωcm at room temperature. Na_0.9FeO₂ decomposed to a mixture of α-NaFeO₂ and Fe₃O₄-like ferromagnetic materials above 130°C.     

High pressure synthesis of Cu2GeO4 with hausmannite structure

Copper(II)metagermanate, CuGeO₃, decomposes at high pressure to rutile-type GeO₂ and Cu₂GeO₄. Very small single crystals of Cu₂GeO₄ can be obtained by direct high pressure synthesis from CuOGeO₂ mixtures. The compound has a distorted spinel structure (Hausmannite structure, space group $\text{I}\text{4}{}_1\text{amd}$) with $\text{a}\text{= 5.593}\text{A}\text{?}$, $\text{c}\text{= 9.396}\text{A}\text{?}$, Z = 4.     

Preparation of TiS2 under high pressure

Preparation of stoichiometric TiS₂ was attempted at 1000°C under high pressures. TiS₂ was firstly formed accompanying nonstoichiometric TiS₂ from the starting stoichiometric mixture of Ti and S. The further reaction to stoichiometric TiS₂ takes much longer time than the reaction of equimolar mixtures of Ti and TiS₃. The reaction of Ti and TiS₃ gave an almost stoichiometric TiS₂ at 1000°C after the duration of 2hrs.     

Electrical properties of sintered EuZrO3  EuNbO3 and EuNbO3

Electrical resistivity of two-phase products [yEuZrO₃ + (1 ? y) EuNbO₃] increased continuously with y, and a transition from a metallic to semiconducting characteristic occured at y = 0.14. The resistivity varied almost linearly with temperaure in the range y = 0 to y = 0.24, and thermal coefficients of resistivity at 300 K for the products decreased from +5.9 × 10^?4 K^?1 to ?7.4 × 10^?4 K^?1 according to the value of y. At y = 0.14, the thermal coefficient was almost zero. Thermal coefficients of electrical resistivity for the niobates with various oxygen contents were all positive in the range $\text{2.55 <}\text{O}\text{Nb}\text{< 3.24}$ and exhibited a sharp minimum at $\text{O}\text{Nb}\text{= 2.92}$. In all these niobates, Eu_xNbO₃ was a major phase and Eu₃NbO₆ or EuNbO₂ was detected as a second phase in the range $\text{O}\text{Nb}\text{> 3}$ or $\text{O}\text{Nb}\text{< 3}$ respectively. Peaks in the resistivity curves were correlated with a magnetic ordering temperature for samples with an overall ratio $\text{O}\text{Nb}\text{> 3}$.     

Isotherms and crystallography of the hydrides of the system CaxEu1−xNi5

The hydriding of the system Ca_xEu_1?xNi₅ has been examined for various values of x using in-situ X-ray diffraction and pressure-composition measurement at 298 K. The single phase solutions which exist in this ternary intermetallic system for x = 0 to 0.25 and 0.8 to 1.0 exhibit hydriding behaviour closely related to that of the corresponding end member binary. Significant changes in the stability, ease of activation and the composition range of the hydrides of the ternaries compared to that of the “related” binaries are observed.     

Electrical conduction in γ- irradiated and unirradiated Fe203

The temperature dependence of the electrical conductivity (O^?) of pure and doped Fe₂O₃ using different elements ( Ti, Nb, Sn, Be, Cu, Ni, Mn, Mg and Zn ) in a concentration range of 0.01–2.0 atom % and over a temperature range of 25–500°C was investigated. The addition of Ti, Nb or Sn to pure Fe₂O₃ was observed to lead to an increase in the conductivity (O^?) and to a decrease in the activation energy ( E_a ), whereas the addition of Be, Cu, Ni or Mn showed the reverse action. On using Mg or Zn as a doping element at a concentration of 0.01 atom %, the value of the conductivity ( O^?) decreases and that of the activation energy ( E_a ) increases with respect to those of the pure Fe₂O₃. On the other hand, on using a higher concentration (>0.01 atom % ) the reverse behaviour was observed. Furthermore, the effect of γ -irradiation ( in different doses ) on both the conductivity and the activation energy of pure Fe₂O₃ was studied, and the damage produced was isothermally annealed and studied.The Seebeck voltages of the irradiated and unirradiated Fe₂O₃ samples have been measured. The formation of the Fe(II) ions as a major impurity in the Fe₂O₃ -lattice after the irradiation process was also proved.     

Photoelectrochemical behaviour of undoped ferric oxide (α -Fe2O3) electrodes prepared by spray pyrolysis

The photoelectrochemical behaviour of undoped α-Fe₂O₃ electrodes prepared by spray pyrolysis on SnO₂ coated glass substrates has been examined in basic medium. The I–V characteristics and action spectra have been obtained. Flat band potential has been estimated from photoelectrochemical transients under anodic bias. The α -Fe₂O₃ coated on ordinary Corning glass does not show any photoresponse.     

Trivalent chromium in the solid solution system CrxMo1-xO2 (x ≤ 0.5)

the solid solution system Cr_xMo_1-xO₂ for x ≤ 0.5 was investigated. The following three phases were identified from x-ray powder diffraction analyses: monoclinic distorted rutile (CrMoO₄) for 0.36 ≤ x ≤ 0.5, tetragonal rutile for 0.12 ≤ x < 0.36 and monoclinic (MoO₂) for 0 ≤ x < 0.12. From magnetic data it was shown that throughout the whole range the magnetic ion was trivalent chromium (d³) and the pentavalent molybdenum (d¹) due to its metallic Mo-Mo interactions does not contribute to the magnetic moment.     

Lithium insertion into Li2Ti3O7

Li₂Ti₃O₇ with the ramsdellite-type structure undergoes lithium insertion reactions with n-BuLi. Li_2+xTi₃O₇ phases form with x = 0.5 and 1.0 at room temperature and at 50°C, respectively. The ESR spectrum of Li₃Ti₃O₇ confirms the partial reduction of Ti⁴⁺ ions to Ti³⁺. The electrical conductivity of the fully lithiated phase is several orders of magnitude higher than that of the host compound, suggesting charge hopping in the mixed valent lithiated compound.     

The discharge of a I12TaSe4 cathode for lithium battery

The discharge process was investigated on a lithium battery using $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$ as cathode. The battery works as primary battery. The potential gradually decreased from 2.1V to 1.8V upto a discharging of $\text{Li}\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4\text{≈0.5}$. Then it was almost constant at 1.8V until the discharging of about 2.0. Iodine is partially removed out of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$, keeping the host TaSe₄ chain structure as it was in the first step of discharge. The new product has tetragonal crystal lattice having lattice parameters of $\text{a}\text{=9.532}\text{A}\text{?}$ and $\text{c}\text{=25.31}\text{A}\text{?}$, which is twice of c-parameter of $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$.     

Electronic and spin configurations of Co3+ and Ni3+ ions in oxides of K2NiF4 structure: A magnetic susceptibility study

In La₄LiCoO₈, Li⁺ and Co³⁺ ions are ordered in two dimensions and Co³⁺ ions undergo transitions from the low-spin to the intermediate as well as the high-spin states. Both Sr₄TaCoO₈ and Sr₄NbCoO₈ exhibit low to intermediate-spin state transitions of Co³⁺ ions. In the system LaSr_1?xBa_xNiO₄, the e_g electrons are essentially in extended states forming a band. With increase in x, the band width decreases accompanying an increase in unit cell volume; high-spin Ni³⁺ ions are formed to a small extent with increasing x, but there is no spin-state transition. In LaSrAl_1?xNi_xO₄, at small x, there is a small proportion of high-spin Ni³⁺; when x ≈ 0.6, there is an abrupt decrease in the $\text{c}$/$\text{a}$ ratio, signalling the formation of the band. In LnSrNiO₄, the $\text{c}$/$\text{a}$ ratio decreases sharply between Ln = La and Nd; this is likely to be accompanied by a broadening of the band.     

Electrochemical properties of a new electrode material,Ti4O7

Cyclic voltamograms of Ti₄O₇ (Ebonex) together with its overpotentials for the production of H₂ and O₂ in acidic and basic aqueous solutions are reported. Ti₄O₇ electrode properties are compared to other electrodes: TiO₂, Pt, carbon, and vitreous carbon. Strong adsorption of ruthenium and platinum to the surface of Ti₄O₇ reduces the overpotentials for H₂ and O₂ production and modifies its electrode behavior. ESR results indicate small amounts of higher oxide phases (Magneli phases) may be present in the Ebonex material.     

Electrical properties of La2S3-doped calcium sulfide solid electrolyte

In order to consider the application of La₂S₃-doped calcium sulfide to a solid electrolyte for metal sulfide systems, its electrical properties have been investigated, based on a galvanic cell technique and conductivity measurements at various temperatures and sulfur pressures. The following cell was employed; Cu,Cu₂S |CaS (La₂S₃)| FeS, Fe. The values of the electromotive force obtained in this cell were roughly consistent with the theoretical ones. Based on conductivity measurements under various sulfur pressures at 700–900°C, the electrical conduction of La₂S₃-doped calcium sulfide was found to be ionic at sulfur pressures higher than 10^?6 atm and n-type semiconducting at lower sulfur pressures. The apparent activation energy obtained for the ionic conduction was 19.02 kcal/mol, which was reasonable for the ionic conduction through migration of a Ca²⁺ ion.     

Ionic conductivity of substituted Li2SO4 phases

Lithium ion conductivity of Li₂SO₄-Y₂(SO₄)₃, Li₂SO₄-La₂(SO₄)₃ and Li₂SO₄-Li₃PO₄ systems has been measured as a function of composition and temperature using AC complex impedance methods. Substitution of the trivalent cations results in a small enhancement of the ionic conductivity within the limit of solid solution formation. Considerable increase of the conductivity results by substitution of PO₄^3? for SO₄^2?. The maximum conductivity observed is $\text{1.1×10}{}^{\mathrm{?3}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 300°C for the composition Li_2.2S_0.8P_0.2O₄ with E_a = 0.8 eV. These results are discussed in terms of the structural properties.     

Structure cristalline d'une phase cubique desordonnee de type ReO3 excedentaire en anions : ZrF2,67O0,67

The crystal structure of cubic disordered anion-excess ReO₃-related ZrF_2.67O_0.67 (space group Pm3m, $\text{a}\text{= 3.997(2)}\text{A}\text{?}$) has been determined by single crystal X-ray diffraction techniques and refined to a R = 0.038-value. Two different kinds of anions are found, one X(1) slightly displaced (by 0.27 Å) from the ideal ReO₃-anionic site, the other X(2) more considerably (by 1.16 Å). As previously proposed (8,14) the anion-excess over the parent ReO₃-type structure, is accomodated by the formation of interstitial X(2)-X(2) pairs across a vacant X(1) site.The most likely anionic arrangements around zirconium atoms are assessed and on those basis, the structure is described as a disordered three-dimensional framework of edge sharing ZrX(1)₅X(2)₂ pentagonal bipyramids and corner sharing ZrX(1)₅X(2) distorted octahedra.     

Etude de la solution solide Pb2O(S1−xWxO4) et structure cristalline de la variete alpha du monooxodiplomb (II) tetraoxotungstate (VI) Pb2O(WO4) par diffraction X sur poudres

The Pb₂O(S_1?xW_xO₄) solid solution has been investigated by X-ray diffraction in the 0<x<1 range. Direct synthesis of monooxodilead(II)tetraoxotungstate(VI) by heating 2PbO+WO₃ mixtures at different temperatures, reveals the existence of two polymorphs: alpha-Pb₂ O(WO₄) is obtained for 823<T<833K and beta-Pb₂ O(WO₄) for T>1073K. For 833<T<1073K, mixtures of both polymorphs are obtained. In the present work the alpha-Pb₂O(WO₄) species is characterized for the first time, and crystal structure investigations by X-ray diffraction on polycristalline samples show that this phase is isostructural with its Pb₂O(AO₄) homologues for A = S, Cr and Mo (1).     

Studies on BiCoO3 and BiCo1−xFexO3

BiCoO₃ and BiCo_1?xFe_xO₃ (x ≤ 0.7) prepared at atmospheric pressure are found to possess a cubic structure probably involving the Bi₁₂O₃₆ network. BiCoO₃ is paramagnetic above 100 K, with a negative paramagnetic Curie temperature. BiCo_1?xFe_xO₃ (x = 0.5 or 0.7) is ferromagnetic with T_c ≈ 600K.