Un compose a structure feuilietee (LaO)4Ag1,5Ga1,5S5

The compound (LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅ belongs to the quasi-binary La₂O₂SAgGaS₂ system. It undergoes a peritectic decomposition at 1040°C and a order-disorder transition at 750°C. The high temperature variety is tetragonal, with $\text{a}{}_0\text{= 4.18}\text{A}\text{?}$; $\text{c}{}_0\text{= 18.74}\text{A}\text{?}$; Z = 1; space group 1422; it has the same structural type as (CeO)₄Ga₂S₅. The low temperature variety is an orthorhombic superstructure of the preceding one. with a = 17.58 (3 a₀√2); b = 5.90 (a₀√2) and $\text{c}\text{= 18.66}\text{A}\text{?}$ (c₀). The electrical conductivity is mainly of ionic nature. The e.m.f. measurements of a cell Ag/(LaO)₄Ag_{1 · 5}Ga_{1 · 5}S₅/S.C./Pt support this conclusion.     

Refinement of the structure of K2Cr2O7

The parameters for the structure of K₂Cr₂O₇ have been refined from 7511 observed reflections; $\text{a}{}_{\mathrm{o}}\text{= 7.4200(6)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 13.399(3)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 7.3845(9)}\text{A}\text{?}$, cosα = ?0.1396(2) (α = 98°2'), cosβ = ?0.0154(2) (β = 90°53'), cosγ = ?0.1078(2) (γ = 96°11'). The discrepancy factor R(F_o²) = 0.0702 with a type 2 extinction correction. The average CrO distances are 1.609Å (unshared) and 1.783Å (shared).     

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.     

Crystal data and thermal expansion of tricalciumborate

Single crystals of tricalciumborate were grown by the flux method. Ca₃B₂O₆ crystallizes in the rhombohedral system with the unit cell parameters $\text{a}{}_{\mathrm{R}}\text{= 6.3577(7)}\text{A}\text{?}$, α_R = 85.68(8)°, Z = 2. The equivalent hexagonal lattice parameters are a_H = 8.640(1), $\text{C}{}_{\mathrm{H}}\text{= 11.854(1)}\text{A}\text{?}$. The anisotropic thermal expansion parameters α_a = (1.00 ± 0.14) × 10^?5, α_c = (3.60 ± 0.47) × 10^?5 were determined by X-ray methods in the temperature interval 25 – 1000°C.     

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.     

Preparation and structure of sodium rare-earth sulfides,NaLnS2 (Ln; rare earth elements)

Ternary sodium rare-earth sulfides, NaLnS₂ (Ln; rare earth elements), have been prepared and characterized. With an x-ray diffraction analysis of their crystal structure, it has been found that the materials containing La, Ce, and Pr crystallize in a cubic structure, including a Th₃P₄-type compound as a second phase, while the other NaLnS₂ sulfides - except for NaNdS₂ and NaSmS₂ - crystallize in a rhombohedral NaHF₂-type structure, which can be described with a hexagonal unit cell. In NaNdS₂ and NaSmS₂ these two phases, the cubic and the rhombohedral, coexist. The following relationships can be obtained from a comparision of the lattice constants of the cubic and hexagonal cells in NaNdS₂; $\text{a}{}_{\mathrm{<mtext>h</mtext>}}\text{=}\text{a}{}_{\mathrm{<mtext>c</mtext>}}\text{√2}\text{2}$, c^h=a_c2 √3. Based on these relationships, the structural type of the cubic phase can be regarded as analogous to that of NaCl.     

New phase with K2NiF4 structure in the LaLiFeO system

The existence has been proved, for the first time, in the LaLiFeO system of the phase (La_1.75Li_.25) (Fe_.5Li_.5)O_4?x with tetragonal symmetry ($\text{a}{}_{\mathrm{o}}\text{=3.765±0.001}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{=12.918±0.01}\text{A}\text{?}$; $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}\text{=3.43}$) and K₂NiF₄-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A₂BO₄-type mixed oxides. The high $\text{c}{}_{\mathrm{o}}\text{a}{}_{\mathrm{o}}$ ratio suggests a strong elongation of FeO₆ octahedra induced by a high spin Fe(IV) d⁴ configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.     

Synthesis,structural and physical properties of the binary molybdenum chalcogenide phase Mo15Se19 and of the related compounds M2Mo15Se19 and M3Mo15Se19 (M=group 1A metal; Sn,Pb;Cd)

We present the synthesis, structure and physical properties of the binary phase Mo₁₅Se₁₉. This material was synthesized at low temperatures by oxidation of In₂Mo₁₅Se₁₉ or In₃Mo₁₅Se₁₉ by HCl gas. X-ray studies show that Mo₁₅Se₁₉ can exist in two crystallographic forms depending upon the indium phase used as starting material. Both phases contain large open channels and crystallize in a hexagonal unit cell with lattice parameters $\text{a}{}_{\mathrm{h}}\text{= 9.46}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 19.61}\text{A}\text{?}$ when prepared from In₃Mo₁₅Se₁₉ (space group P6₃/m) and $\text{a}{}_{\mathrm{h}}\text{= 9.48}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{h}}\text{= 58.76}\text{A}\text{?}$ when prepared from In₂Mo₁₅Se₁₉ (space group R3?c). The two structural forms of Mo₁₅Se₁₉ were found to be superconducting at 4.3K. The ease with which indium can be removed from the ternary compounds without disturbing the binary Mo-chalcogenide networks suggested that other metallic elements could be substituted for indium. In fact, several new M₂Mo₁₅Se₁₉ and M₃Mo₁₅Se₁₉ phases were synthesized, where M = group 1A element; Sn, Pb, and Cd. Several of their physical properties are also reported.     

Ordering of interstitial nitrogen and oxygen in vanadium near to V8N and V8O

The ordered structure of the V₈N subnitride was studied by X-rays, electron diffraction and electron microscopy. V₈N exists in two different modifications (α′ and α″). The vanadium sublattice of both phases is pseudo-tetragonal, in reality triclinic, with lattice parameters: $\text{α}{}_{\mathrm{<mtext>o</mtext>}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.114}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.5^o ± 0.1^o, γ_o = 90^o. The proposed unit cell of α′-V₈N has dimensions: a = 2√2 a_o, c = 2c_o and corresponds to V₃₂N₄. Doublets of nitrogen atoms occupy two sets of octahedral cavities whose shortest axes are aligned along the x and y directions of the sublattice in an ordered fashion. The α″-V₈N phase is a periodically twinned modification of the α′-V₈N, the twin plane being of the (001) type. The V₈O suboxide has the same structure as the α″-V₈N, the sublattice parameters being: $\text{a}{}_{\mathrm{o}}\text{=}\text{b}{}_{\mathrm{o}}\text{= 3.11}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 2.994}\text{A}\text{?}$, α_o = β_o = 90.3^o ± 0.1^o, γ_o = 90^o.     

A new method of sulfur vapor pressure control and its application to the V-S system

A new apparatus for obtaining partial pressure of sulfur was devised by using liquid sulfur and carrier gas of nitrogen. This successfully works in the range of ～10^?4 to ～1 atm of Ps₂ at any temperature higher than about 400°C up to about 1000°C. As an application of it, the equilibrium study of V-S system was done at 800°C. Two phases V₃S₄ and V₅S₈, each having homogeneity range, were found while no existence of the V₂S₃ phase could be detected thermodynamically and X-ray crystallogrpahically at this temperature. The standard free energy of following reaction, $\text{VS}{}_{\mathrm{<mtext>4</mtext><mtext>3</mtext>}}\text{+}\text{2}\text{15}$$\text{S}{}_2\text{=}\text{VS}\text{8}\text{5}$, was calculated by considering the transition-Ps₂ and the activities and · ΔG° (1073K) = ?1150 cal·mole^?1was obtained with an estimated uncertainty of ± 100 cal to the above reaction.     

Crystal structures and crystal chemistry in the system Na1+xZr2SixP3−xO12

As part of a search for skeleton structures for fast alkali-ion transport, the system Na_1+xZr₂Si_xP_3?xO₁₂ has been prepared, analyzed structurally and ion exchanged reversibly with Li⁺, Ag⁺, and K⁺ ions. Single-crystal x-ray analysis was used to identify the composition NaZr₂P₃O₁₂ and to refine its structure, which has rhombohedral space group R3?c with cell parameters $\text{a}{}_{\mathrm{<mtext>r</mtext>}}\text{= 8.815(1)}\text{A}\text{?}$ and $\text{c}{}_{\mathrm{<mtext>r</mtext>}}\text{= 22.746(7)}\text{A}\text{?}$. A small distortion to monoclinic symmetry occurs in the interval 1.8 ≤x≤ 2.2. The structure for Na₃Zr₂Si₂PO₁₂, proposed from powder data, has space group $\text{C}\text{2}\text{c}$ with $\text{a}{}_{\mathrm{<mtext>m</mtext>}}\text{= 15.586(9)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.029(4)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{<mtext>m</mtext>}}\text{= 9.205(5)}\text{A}\text{?}$, and β = 123.70(5)° Both structures contain a rigid, three-dimensional network of PO₄ or (SiO₄) tetrahedra sharing corners with ZrO₆ octahedra and a three-dimensionally linked interstitial space. Of the two distinguishable alkali-ion sites in the rhombohedral structure, one is completely occupied in both end members, the occupancy of the other varies across the system from 0 to 100 percent. Several properties are compared with the fast Na⁺-ion conductor β-alumina.     

ESR evidence for the existence of rutile-type,nonstoichiometric vanadium antimonate

A nonstoichiometric vanadium antimonate has been synthesized from a high temperature solid state reaction of V₂O₅ and Sb₂O₃. Powder-X-ray diffraction data of this phase could be indexed on a tetragonal basis with $\text{a}\text{= 4.60}\text{A}\text{?}$, $\text{c}\text{= 3.02}\text{A}\text{?}$. The phase exhibits a well resolved hyperfine ESR spectrum at 298 K due to V(4+)(3d′) ions interacting with ${}^{51}\text{V}\text{(}\text{I}\text{=}\text{7}\text{2}\text{)}$, thus establishing its identity as a rutile type phase postulated earlier. The ESR parameters are $\text{g}{}_{\mathrm{}}\text{= 1.933±0.002}$, g_⊥ = 1.984±0.002, $\text{A}{}_{\mathrm{}}\text{= 193±3}\text{G}$, A_⊥ = 75±3G. Present results are discussed in relation to ESR of V(4+) in other rutile-type hosts.     

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′.     

The conversion from CrO2 into orthorhombic CrOOH

The reaction, $\text{2}\text{CrO}{}_2\text{+}\text{H}{}_2\text{O}\text{→ 2}\text{CrOOH}\text{+}\text{1}\text{2}\text{O}{}_2$, was confirmed to be a topotactic reaction by X-ray diffraction technique using a single crystal of CrO₂ as starting material. The crystallographic axial relation between CrO₂ and CrOOH was as follows: ^c(CrO₂^//c(CrOOH), ^a(CrO₂)^∧a(CrOOH)^{= a}(CrO₂)^∧b(CrOOH)^{= 1.7°}.     

Growth and some properties of barium-cadmium formate single crystals: (II) X-ray and infrared studies

An analysis of the powder pattern of BaCd(HCO₂)₄ ·2H₂O shows that the structure belongs to space group p $\text{2}{}_1\text{c}$$\text{a}\text{= 11.907 (4)}\text{A}\text{?}$, $\text{b}\text{= 13.204(4)}\text{A}\text{?}$, $\text{c}\text{= 13.823(3)}\text{A}\text{?}$, β = 31.188(9)° with four molecules per unit cell. The infrared spectra of polycrystalline barium-cadmium formate has been measured in the region 650–4600 cm^?1. The influence of metal ion on carboxylate stretching frequencies of formate ion is investigated and the possible correlations between spectra and structure considered.     

A magnesium oxide defect structure of hexagonal symmetry

When brucite, Mg(OH)₂, is carefully heated in vacuum beyond the dehydration temperature (250–270°C) the (001) x-ray intensity decreases rapidly but does not vanish. The (100) reflection persists up to 480°C. The lattice contracts by 0.2% in $\text{c}$-direction. The thermal expansion in $\text{a}$-direction slows down. This indicates the formation of a nearly anhydrous high defect MgO which retains the brucite structure: $\text{Mg(OH}\text{)}{}_{\mathrm{2?x}}\text{O}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}\text{□}{}_{\mathrm{<mtext>x</mtext><mtext>2</mtext>}}$ with x→2 (□ unoccupied anion site). This relict structure collapses progressively to the cubic MgO.     

K2GeTe4, ein pertelluridogermanat mit kettenstruktur

The new compound K₂GeTe₄ crystallizes in the monoclinic system, space group $\text{P}\text{2}{}_1\text{c}$ (No 14) with lattice constants a = 1270.3 ± 0.6 pm, b = 868.0 ± 0.4 pm, c = 982.9 ± 0.4 pm, ß = 104.8 ± 0.1°. In the structure there are GeTe₄-tetrahedra, connected by Te₂-bridges to infinite chains.     

A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.     

Effet du champ électromagnétique fluctuant sur l'évolution des structures d'une couche métallique trés mince déposée sur substrat amorphe ou cristallin

It is believed that the grains of a thin metallic film are polarized by the electric field of “zero point” electromagnetic oscillations. This polarization causes a bipolar interaction force F which is calculated by using a bipolar approximation which is valid for short intergrain distances l.If the grains are not spherical, the curves F(l) generally exhibit a repulsive maximum between two ranges of the attractive forces. The curves F(a_) indicate the existence of a critical diameter (a_)_c. The grains are fixed by the repulsive forces for $\text{a}{}_{\mathrm{}}\text{? (a}{}_{\mathrm{}}\text{)}{}_{\mathrm{<mtext>c</mtext>}}$. Furthermore, a grain can only grow by the capture of impinging atoms or by the surface diffusion of adatoms.     

The crystal structure and twinning behavior of ferric molybdate,Fe2(MoO4)3

Fe₂(MoO₄)₃ is monoclinic, space group $\text{P}\text{2}{}_1\text{a}$ with a = 15.707, b = 9.231, $\text{c}\text{= 18.204}\text{A}\text{?}$ and β = 125.25°. The structure was solved by the direct method and Fourier technique, and refined by least squares to an R = 0.028. The structure contains isolated MoO₄ tetrahedra and FeO₆ octahedra, which share corners. The rather open structure shows apparent flexibility and an ease to twinning. The twinning behavior is related to the pseudosymmetry and the ferroelastic transition.