Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Structure cristalline et proprietes physiques de Cu0.75 VS2

A new compound with composition Cu_0.75 VS₂ has been prepared. Its preparation, X-Ray structure, electrical and magnetic properties are reported. The structure is related to the CdI₂-type, as in the case of the previously described Cu_xTiS₂ (1); in Cu_0.75 VS₂, Cu atoms are ordered in tetrahedral sites between the CdI₂-type subunits, whereas in Cu_xTiS₂ Cu atoms are disordered in two independent sites. The vanadium atoms are shifted with respect to the titanium sites which leads a monoclinic distortion of the hexagonal cell. The relation between the CdI₂ unit cell and the true monoclinic cell of Cu_0.75 VS₂ is:

$\text{a}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}\text{3}\text{;}\text{b}{}_{\mathrm{<mtext>mono</mtext>}}\text{=}\text{4}\text{3}\text{a}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{+}\text{c}{}^2{}_{\mathrm{<mtext>hex</mtext>}}\text{9}\text{;}\text{c}{}_{\mathrm{<mtext>mono</mtext>}}\text{= 2}\text{a}{}_{\mathrm{<mtext>hex</mtext>}}$

In Cu_0.75 VS₂, vanadium atoms occupy two independent sites, three vanadium atoms forming a triangular cluster (V₂—V₃ distances are 2.91 Å and V₃—V₃ are 2.92 Å) while one vanadium atom is isolated ($\text{V}{}_1\text{?}\text{V}{}_2\text{= 3.36}\text{A}\text{?}$ and $\text{V}{}_1\text{?}\text{V}{}_3\text{= 3.37}\text{A}\text{?}$. The physical properties exhibit a transition at 50°K approximately, the magnetic susceptibility being temperature-independent above and temperature dependent below the transition (Curie-Weiss behavior). Resistivity and Hall measurements confirm the metallic nature of the compound and show the existence of the low temperature transition. The observed properties could be interpreted as a result of the low temperature localisation of the 3d electron of V₁.     

Proprietes d'echange ionique du pyrochlore TlNbO3 en presence de nitrates fondus ou solides

We have checked the ion-exchange properties of TlNbO₃ in molten or solid nitrates. For Ag⁺ and Pb⁺⁺, limited solid solutions of pyrochlore type are observed: T1_1?xAg_xNbO₃ (x < 0,75) and $\text{T}\text{1}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Pb}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}\text{NbO}{}_3\text{(}\text{x}\text{≤ 0,75)}$. Localisation of Ag⁺ and Pb⁺⁺ on the 16d positions of the space group Fd3m is confirmed by analysis of X-ray powder diffraction data. The thermal stability of the solid solutions is described and competition between pyrochlore and perovskite type is discussed.     

The role of TiO2 and ZrO2 in Na2OMO2SiO2 glasses

The glass transition temperatures of $\text{(1?x)}\text{Na}{}_2\text{O}\text{·}\text{1}\text{2}\text{x}\text{MO}{}_2\text{·2}\text{SiO}{}_2$ and Na₂O·xMO₂·(2 ?x)SiO₂ glasses, with M = Ti or Zr, have been related to the structural role and coordination of Ti and Zr. The role of network-former, intermediate or modifier of a cation has been fundamentally linked to ionic field strength; T_g values depend on ionic field strength and coordination. Titanium behaves like an intermediate oxide; its coordination ranges between four and six, depending on $\text{Ti}\text{Si}$ ratio. The role of zirconium changes according to the degree of substitution for Na or Si and progressively approaches that of a modifier ion.     

Studies on the formation of a solid solution compound in Li2O impregnated CuAl2O4 catalyst

Li₂O impregnated CuAl₂O₄ samples were calcined at two temperatures (673 K and 1173 K). X-ray analysis showed that the lattice parameter of the spinel phase decreased with increasing calcining temperature. X-ray studies on the solid solution series Cu_1?x$\text{Li}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}$$\text{Al}{}_{\mathrm{<mtext>2+</mtext><mtext>x</mtext><mtext>2</mtext>}}$ O₄ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) showed that the lattice parameter decreased with increasing concentration of lithium and from the comparison of lattice parameters it appears that Cu_0.84 Li_0.08 Al_2.08 O₄ is formed in the impregnated sample calcined at 673 K. Electrical resistivity measurements are consistent with the formation of a solid solution compound.     

LixCoO2 (0<x<-1): A new cathode material for batteries of high energy density

A new system Li_xCoO₂ (0<x〈-1) has been prepared by electrochemical extraction of lithium from the parent LiCoO₂ ordered rock-salt structure. Measured open-circuit voltages with respect to lithium metal are approximately twice those of Li_xTiS₂ (0〈-x〈-1), and a theoretical energy density of 1.11 kWh kg^?1 is calculated for $\text{Li}{}_{\mathrm{x}}\text{CoO}{}_2\text{Li}$. Preliminary voltage-composition curves show low overvoltages and good reversibility for current densities up to 4 mA cm^?2 over a large range of x.     

Preparation chimioue et structure cristalline des tellurites de sodium et d'argent: Na2TeO3, Ag2TeO3

Sodium and silver tellurites are isotypic. The space group is $\text{P}\text{2}{}_1\text{a}$. For Ag₂TeO₃, the parameters of the monoclinic unit cell are: a = 7.000(2), b = 10.509(5), $\text{c}\text{= 4.911(2)}\text{A}\text{?}$, β = 91°51(5). The structures of sodium and silver tellurites has been determined. For Ag₂TeO₃, a R value of 0.047 is reached with 829 reflexions and for Na₂TeO₃ R = 0.024 with 1125 reflexions. The framework is built with MeO₆ edge sharing octahedra, Me = Ag,Te. Ag₂TeO₃ is a distortion of NaCl Structure.     

The SrFeO2.5 | SrFeO3.0 system. Evidence of a new phase Sr4Fe4O11 (SrFeO2.75)

Evidence is presented for a new phase of ideal composition SrFeO_2.75 in the system SrFeO_3?x (0.5 ? x ? 0). Electron diffraction evidence suggests orthorhombic or body-centred tetragonal symmetry with lattice parameters related to the cubic perovskite lattice parameter a_c by $\text{a}\text{? 2√2}\text{a}{}_{\mathrm{c}}$, $\text{b}\text{? 2}\text{a}{}_{\mathrm{c}}$. $\text{c}\text{? 2√2}\text{a}{}_{\mathrm{c}}$. A plausible model for the structure is presented which is related to that of SrFeO_2.5. Powder x-ray diffraction photographs reveal only a simple cubic perovskite cell for SrFeO_2.75, presumably because the ordered domains giving rise to the superstructure observed in electron diffraction are small in extent. At other intermediate compositions slow cooling gives mixtures of the new phase and either SrFeO_2.5 or SrFeO₃. The two-phase regions narrow at high temperatures and thermogravimetric studies at 1 atm pressure of oxygen indicate a single phase between SrFeO_2.5 and SrFeO_2.75 between 500°C and 950°C.     

Stationary photoconductivity of mixed Tl1−xAgxInSe2 crystals

Tl_1?xAg_xInSe₂ (x = 0 to 0.03) single crystals of solid solution were grown by Bridgeman-Stockbarger techniques. Photoelectric measurements were taken at 300 and 77 K. With an increase in the value of x, the equilibrium concentration is increased 10 to 100 times. At 77 K a region of impurity photosensitivity has been detected which is bordered by the fundamental absorbtion edge. The photosensitivity ($\text{R}{}_{\mathrm{d}}\text{R}{}_{\mathrm{p}}$) of the solid solution crystals at 77 K increases from 8.2 (x = 0) to 55.2 (x = 0.03) the conclusion is made that when Tl is replaced by Ag then the sensitization of semiconductor.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

TlxTi6Se8 and TlxNb6Se8, two phases with filled up Nb3Te4 type of structure showing pronounced cation disorder

The new ternary chalcogenides Tl_xTi₆Se₈ (x= 0.76) and Tl_xNb₆Se₈ (x= 0.70) crystallize with a partially filled up Nb₃Te₄-structure: space group $\text{P}\text{6}{}_3\text{m}$, z= 1 with

$\text{a= 9.882(1) c= 3.590(1)}\text{A}\text{?}\text{(Tl}{}_{0.76}\text{Ti}{}_6\text{Se}{}_8\text{)}$

$\text{a= 10.033(2) c= 3.475(1)}\text{A}\text{?}\text{(Tl}{}_{0.70}\text{TNb}{}_6\text{Se}{}_8\text{)}$

The crystal structures were determined from single crystal diffractometer data and refined to a conventional R-value of 0.077 and 0.055 respectively. The T1 atoms in the octahedral channels cannot be localized. In Tl_xTi₆Se₈ diffuse scattering indicates one-dimensional short range order. A model of the cation distribution in Tl_0.76Ti₆Se₈ is discussed.     

Chemical and electrochemical study of the LixFeS2 cathodic system (0 < x ⩽ 2)

The Li_xFeS₂ (0 < x ? 2) cathodic system has been studied through room temperature oxydoreduction by using a non-aqueous electrolyte lithium cell. Three phases have been characterized : Li_xFeS₂ (γ) (1.09 ? x < 1.5), Li_xFeS₂ (ν) (1.5 < x ? 2) and $\text{Li}{}_{\mathrm{<mtext>x</mtext><mtext>?0</mtext>}}\text{FeS}{}_2$ (λ). The (γ) phase is thought to belong to a CdI₂ structural type. The cycling of the $\text{Li}{}_{\mathrm{<mtext>x</mtext>}}\text{FeS}{}_2\text{Dioxolane}$$\text{(2}\text{M LiClO}{}_4\text{)}\text{Li}$ has shown promising behavior with small polarisation.     

Structural changes with composition and temperature in rhombohedral Li1−xHxNbO3

Polycrystalline Li_1?xH_xNbO₃ (0.07≤x≤0.87) has been prepared by exchange of LiNbO₃ in benzoic acid/lithium benzoate and $\text{Mg}\text{(}\text{NO}{}_3\text{)}{}_2\text{·6}\text{H}{}_2\text{O}\text{LiNO}{}_3$ melts. X-ray diffraction measurements for these materials show complex structural behavior, with three distinct rhombohedral (LiNbO₃ structure) phases in the range x≤0.75. Samples with 0.65<x<0.75 were found to undergo a reversible phase transition at ～ 150°C. These results explain why proton-exchanged LiNbO₃ waveguides made in neat benzoic acid are prone to refractive index instabilities, and show how such problems can be avoided by limiting the maximum value of x in the guides.     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

Intercroissances des structures de type perovskite et SrO deficitaires en oxygene : Les oxydes Ln2−xSr1+xCu2O6−x/2 (Ln = Sm,Eu, Gd)

New oxides Ln_2?xSr_1+xO_6?x/2 (Ln = Sm, EU, GD), corresponding to oxygen deficient intergrowths of double perovskite and SrO layers have been isolated for 0.70 ≤ x ≤ 0.90. They are characterized by an orthorhombic cell, $\text{a}\text{?}\text{a}{}_{\mathrm{p}}\text{? 3.9}\text{A}\text{?}$, $\text{b}\text{?}\text{3a}{}_{\mathrm{p}}$, and $\text{c}\text{? 20}\text{A}\text{?}$. A structural model has been obtained, showing that this structure, although closely related to that of La_2?xSr_1+xCu₂O_6?x/2+δ exhibits a different distribution of the oxygen vacancies, involving for copper several coordinations. The semi-conductive properties of these compounds, very different from the semi-metallic behaviour of La_2?xSr_1+xCu₂O_6?x/2+δ is explained by the distribution of the oxygen vacancies in the structure.     

The region of existence of CuInS2

It is shown from quenching experiments followed by X-ray analysis that the region of existence of CuInS₂ is very small and in fact is limited to 0<x<0.05 in $\text{Cu}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{In}{}_{\mathrm{<mtext>1+</mtext><mtext>x</mtext>}}\text{3}{}^{\mathrm{<mtext>S</mtext>}}\text{2}$. Furthermore, an indication of solid state transition in this compound was obtained from DTA experiments.     

Some optical and electrical properties of the As2Se3−xTex system

Some optical and electrical properties of the As₂Se_3?xTe_x system (0 ≤ x ≤ 0.15) have been studied. The value of the optical gap decreases from 1.74 eV to 1.59 eV. The slope of the absorption edge changes, so that value of E_o from the relation α ～ exp ($\text{h}\text{?}\text{ω}\text{E}{}_{\mathrm{o}}$) exhibits a maximum value in neighbourhood of composition As₂Se_2.9Te_0.1. The d.c. and a.c. conductivities have been studied. The value of the activation energy E_el ～ 1.8 eV is almost unchanged up to x = 0.15. The a.c. conductivity fulfils the relation $\text{б(ω) ～ ω}{}^{\mathrm{<mtext>s</mtext>}}$ where s ? 1 and 1.1. at frequencies f < 1 kHz and f > 1 kHz respectively.     

Solid solution phases from thermally crystallized Li2O-MgO-Al2O3-SiO2 glasses

Phase transformations have been studied in glasses related in composition to Li₂O-MgO-SiO₂ (930° C) eutectic glass modified by $\text{Al}{}_2\text{O}{}_3\text{Li}{}_2\text{O}$ replacement on a cation per cation basis. Crystallization processes and changes in the solid solutions of the mineral phases developed during the controlled heating of the glasses have been followed using X-ray and microscopic techniques.Solid solutions of lithia aluminosilicate phases (B-eucryptite and/or B-spodumene s.s.) are the essential minerals that crystallize in glasses through most of the heat treatment applied. Lithium metasilicate, disilicate, clinoenstatite and cordierite are also encountered.B-eucryptite s.s. is formed in early stage of crystallization of the glass which transforms into B-spodumene s.s. at higher temperature (800° C). However, in some cases, it persists at temperatures as high as 1000° C.Metastable B-eucryptite-B-quartz s.s. can accomodate considerable amounts of Mg²⁺ and Al³⁺ ions in its lattice especially at lower temperature. At higher temperature for long duration, a redistribution of the elements takes place, and the cordierite phase then developed.     

Supporting electrolytes containing tetrabutylammonium ions in Li/TiS cells intercalation of tetrabutylammonium ions in TiS

In context with the development of $\text{Li}\text{TiS}{}_2$ cells, the role of tetrabutylammonium bromide (TBAB) was investigated as Supporting Salt in LiSCN-1:3 dioxolane organic electrolytes. TBAB had little effect on the overall conductivity. A deterioration of cell performance was noted upon addition of TBAB to the electrolyte in spite of an improvement in the lithium half-cell. This behavior is attributed to the intercalation of TBA⁺ ions which have been shown in independent experiments to insert into TiS₂ to form the new compound TBA_x⁺ TiS₂.     

Layer-like cation ordering in a perovskite-type compound Ca3(CaTa2)O9 with monoclinic symmetry

A structural scheme to fit in a monoclinic cell of the ordered perovskites Ca₃(XZ₂)O₉ is proposed based on a layer-like ordering of X and Z ions. According to this scheme, the structure of compound Ca₃(CaTa₂)O₉ was analyzed with X-ray powder method. The structure is found to involve an alternate stacking of one Ca-layer and two Ta-layers in the octahedral cation sites, and has a base-centered monoclinic Bravais lattice with the constants a=9.808 A,b=5.533 A,c=7.061 A, and ß=89°1′. The space group is $\text{C}\text{2}\text{m-C}{}_{\mathrm{2h}}{}^3$. The unit cell contains six triclinic perovskite units with the lattice constants a′=b′=4.000 A, c′=3.996 A, α′=ß′=89°32′, and γ′=87°32′.