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.     

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.     

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.     

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.     

Refinement of the crystal structure of HoRu2Si2 (ThCr2Si2-type)

The crystal structure of HoRu₂Si₂ has been determined from single crystal X-ray counter data obtained from a single crystal specimen which was prepared from an arc melted sample heat-treated at 500° C for 4 weeks and quenched. HoRu₂Si₂ is tetragonal with space group I4/mmm, and cell parameters a=4.1552(9) and $\text{c}\text{=9.5178(68)}\text{A}\text{?}$; Z = 2. The final reliability factor $\text{R}\text{=}\text{solΣΔ}\text{F}\text{|}\text{Σ|}\text{F}{}_{\mathrm{o}}\text{|}$ is 0.052 for 97 independent reflections; $\text{|}\text{F}{}_{\mathrm{o}}\text{| > 2 б}$. HoRu₂Si₂ is isotypic with the ordered structure type of ThCr₂Si₂ (BaAl₄-derivative type).     

High pressure synthesis of Gd3InO6, Tb3InO6 and Lu3InO6

Three new compounds, X₃InO₆ (X = Gd, Tb, Lu) were prepared at 1–4 GPa, ～1050°C. They are monoclinic, space group $\text{P}\text{2}{}_1\text{n}$ with $\text{a}\text{? 8.9}\text{A}\text{?}$, $\text{b}\text{? 9.8}\text{A}\text{?}$, $\text{c}\text{? 5.9}\text{A}\text{?}$, β ～ 95° and Z = 4.     

Structure determination of (3D) P2NbS8

Tridimensional P₂NbS₈ crystallizes in P4?n2 tetragonal space group, with $\text{a}\text{= 12.0483(4)}\text{A}\text{?}$, $\text{c}\text{= 7.2070(5)}\text{A}\text{?}$, $\text{V}\text{= 1046.2(1)}\text{A}\text{?}{}^3$ and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb₂S₁₂] biprismatic bicapped units (average $\text{d}{}_{\mathrm{Nb?S}}\text{= 2.571}\text{A}\text{?}$) made of S^?II and S^?II₂ anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated Nb^IV ? Nb^IV pairs ($\text{d}{}_{\mathrm{Nb?Nb}}\text{= 2.859(1)}\text{A}\text{?}$) in these niobium group otherwise linked to each other through (PS₄) tetrahedral units (average $\text{d}{}_{\mathrm{P?S}}\text{= 2.051}\text{A}\text{?}$) themselves constituting interbonded [P₄S₁₂] rings. The P₂NbS₈ three-dimensional network thus obtained is compared to the (2D) P₂NbS₈, layered phase already described.     

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).     

Chromium-doped CdF2 crystals by ESR spectroscopy

Single crystals of Cr-doped CdF₂ in which only Cr²⁺ ions were present were obtained by heating CdF₂:CrF₃ samples in Cd vapors. The crystals produced were studied by ESR spectroscopy at X band at 4.2 ^oK. The spectrum obtained is described by the effective spin Hamiltonian:

g⁽²⁾_eff = 4g_zcosΘ, g⁽¹⁾_eff = 2g_zcosΘ, where i = 1 for the doublet of the spin S = 1, and i = 2 for the doublet of the spin S = 2; net effective spin $\text{S}\text{=}\text{1}\text{2}$; g_z=1.85±0.03; |Δ₍₂₎|=3.08±0.07 GHz; |Δ₍₁₎|=5.85±0.07 GHz; $\text{1}\text{6}\text{(Δ}{}^{\mathrm{o}}{}_{\mathrm{(2)}}\text{? Δ}{}^{\mathrm{o}}{}_{\mathrm{(1)}}\text{)=?11.01±0.02}\text{GHz}$.     

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.     

Stable Po2-region of ordered perovskites Ca2FeMoO6 and Sr2FeMoO6 at 1200°C

Stable Po₂-region of the title compounds at 1200°C has been determined via an isothermal gravimetry. Ca₂FeMoO₆ was stable within the region $\text{?8.9 ≧}\text{log Po}{}_2\text{≧ ?12.5}$, decomposed by reduction into a triphasic mixture of CaO + Mo + ε-Fe₃Mo₂, and by oxidation into a biphasic mixture of CaMoO₄ (Scheelite structure) + CaFeO_2.5 (Brownmillerite structure). Sr₂FeMoO₆ was stable within the region $\text{?9.8 ≧}\text{log Po}{}_2\text{≧ ?13.5}$, decomposed by reduction into SrO + Mo + ε-Fe₃Mo₂ and by oxidation into SrMoO₄ (Scheelite structure) + SrMoO_3?x (non-stoichiometric perovskite structure).     

An outline of the crystal-structure of Bi2Mo2O9

An outline of the structure of the catalyser component Bi₂Mo₂O₉ has been determined from X-ray powder diffractometer diagrams. The space group is $\text{P}{}^2\text{l}\text{n}$ ($\text{=}\text{P}{}^2\text{l}\text{c}$) with cell constants: $\text{a}\text{= 11.946 (2)}\text{A}\text{?}$, $\text{b}\text{= 10.795 (2)}\text{A}\text{?}$, $\text{c}\text{= 11.876 (2)}\text{A}\text{?}$ and β = 90.15 (2)°. There are eight formula units per cell. The positions of the metal-ions could directly be derived from the intensities of the strongest reflexions. With difference terms calculated from 19 strong reflexions a Δ F-synthesis was calculated, which revealed the approximate positions of the O^2?-ions. From packing considerations it was apparent that of 9 0^2?-ions one is only coordinated by Bi³⁺ and that Mo⁶⁺ must be tetrahedrally surrounded by 0^2?. These tetrahedra may be strongly distorted. The structure is not related to the scheelite-structure as has been assumed by some authors.     

Structure de PbU2Se5

PbU₂Se₅ crystallizes in a monoclinic unit cell $\text{a}\text{= 8,605}\text{A}\text{?}$; $\text{b}\text{= 7,788}\text{A}\text{?}$; $\text{c}\text{= 12,27}\text{A}\text{?}$; β = 90° of space group $\text{P}\text{2}{}_1\text{c}$, Z = 4. The crystal structure has been determined for 1251 independant reflections and refined to a final R value of 0,068. Two kinds of uranium sites are found; the average U-Se distances are 2,97 Å for eight-coordination and 2,88 Å in seven-coordination. The average Pb-Se distance for eight-coordination is 3,20 Å. This structure explains the solid solution between PbU₂Se₅ and U₃Se₅.     

Structure and staging of intercalated AgxTaS2 and AgxTiS2

The crystal structure of the intercalation compounds Ag_xTaS₂ ($\text{0≤}\text{x}\text{≤}\text{2}\text{3}$) and Ag_xTiS₂ (0≤x≤0.42) are reported. For both intercalated dichalcogenides only stages n=2 and 1 are observed and there is no evidence for higher staging. In stage 1 $\text{Ag}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{TaS}{}_2$, the silver ions reside in tetrahedral sites and the 2H_b?TaS₂ structure changes to that of MoS₂. For stage 2 $\text{Ag}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{TaS}{}_2$, we observe a six layer unit cell with the silver ions again in tetrahedral sites. In stage 1 Ag_0.42TiS₂ and stage 2 Ag_0.2TiS₂, the silver ions are in octahedral sites and there is no change of the host lattice stacking. The samples were prepared both thermally and electrolytically and the same lattice parameters were obtained in both cases.     

Preparation and structure of EuIINb4O11

The occurrence of compound in the system has been studied by means of X-ray powder diffraction. A compound, Eu^IINb₄O₁₁, was found. The X-ray powder diffraction data for Eu^IINb₄O₁₁ could be indexed on a tetragonal cell with $\text{a}\text{=52.52}\text{A}\text{?}$, $\text{C}\text{=7.69}\text{A}\text{?}$. The temperature dependence of the magnetic susceptibility for this compound is expressed by the equation, $\text{X}{}_{\mathrm{M}}\text{=}\text{7.10}\text{(}\text{T}\text{+0.20)}$. This compound is oxidized at about 290°C or above in air.     

La liaison metal — metal dans les clusters M12O36: II — Preparation et etude structurale de la phase La3Ru3O11

La₃Ru₃O₁₁ was prepared either by oxidation of mixtures of $\text{3}\text{2}\text{La}{}_2\text{O}{}_3$: 3 Ru with KClO₃ at 900°C or by the oxidation of LaRuO₃ at 920°C with KClO₃, both in a gold boat introduced in a sealed silica tube. The crystal structure of this compound ($\text{a}\text{= 9.466(2)}\text{A}\text{?}\text{, S.G. Pn}\text{3,}\text{Z}\text{=4}$) has been solved by Fourier and least-squares methods to R = 0.022 (R_W = 0.031). As for the previously described Bi₃Ru₃O₁₁ and La₄Ru₆O₁₉, it contains ruthenium in formal oxidation state of 4.33; however, there is no longer metal - metal interaction, owing to the greater Ru - Ru distance (3.00 Å) and the closer approach of bridging oxygen (2.47 Å) within the dimeric unit Ru₂O₁₀. Therefore, this interaction is not a prerequisite for the formation and stability of the three-dimensional network Ru₁₂O₃₆.     

On the pyrochlore type Ln2V2O7 (Ln: Rare-earth elements)

Pyrochlore type rare-earth vanadites (Ln₂V₂O₇) were prepared and some physical properties were investigated. Ln₂V₂O₇ (Ln:Tm, Yb or Lu) crystallized in the cubic space group $\text{O}{}_{\mathrm{<mtext>h</mtext>}}\text{=}\text{Fd}{}_3\text{m}\text{,}\text{a}{}_0\text{= 9.9575}\text{A}\text{?}\text{, 9.9346}\text{A}\text{?}\text{and}\text{9.9231}\text{A}\text{?}$ for Tm₂V₂O₇, Yb₂V₂O₇ and Lu₂V₂O₇, respectively. These compounds were all n-type semiconductors and paramagnets in the temperature range 90–300K.     

Preferential oxygen sputtering from Nb2O5

The bombardment of Nb₂O₅ with Kr⁺ or O⁺₂ ions leads to the development of a surface layer NbO. The layer begins to form at (2–4) × 10¹⁵ ions cm^-2 as random nuclei which can be resolved by transmission electron microscopy. It is half complete at (4–8) × 10¹⁶ ions cm^?2, a much higher dose than that required for sputter equilibrium to be half complete. The final thickness is roughly 31 nm. These features, together with the further result that the layer forms independently of the bombarding current provided beam heating is avoided, can be understood from a model which combines preferential oxygen sputtering at the surface, diffusion of the relevant point defects, and random nucleation of a phase with lower stoichiometry. The governing equation is an extended form of the diffusion equation

$\text{?C}\text{?t}\text{=}\text{D?}{}^2\text{C}\text{?x}{}^2\text{+}\text{υ?C}\text{?x}\text{?}\text{DC}\text{L}{}^2$

where υ is the velocity of the surface recession due to sputtering and L is the diffusion length for trapping. Appropriate solution of the equation suggests that the altered layer will have a mean thickness similar to L, will be formed with a half-dose given by $\text{0.693LN}\text{S}$ where S is the sputtering coefficient, and will involve a total amount given by $\text{DC}{}_0\text{υ}$ atoms cm^?2, where C₀ is the stoichiometry at the outer surface. Current independence follows if the diffusion is bombardment enhanced, so that D is approximately proportional to υ. The main difficulty with the model is that it is strictly valid only for low concentrations.     

Determination de la structure cristalline de la variete a des hydroxycarbonates de terres rares LnOHCO3 (Ln = Na)

A probable model for the structure of the orthorhombic A - type neodymium hydroxycarbonate is presented. It relies on an optical determination of the site symmetry of OH^?, CO^2?₃, and Nd³⁺ atoms from infrared and visible absorption spectra, together with a computation of 50 X-ray diffraction lines intensities of a high resolution Guinier orthorhombic powder pattern ($\text{a}\text{= 4,953}\text{A}\text{?}$, $\text{b}\text{= 8,477}\text{A}\text{?}$, $\text{c}\text{= 7,210}\text{A}\text{?}$; space group Pmcn (n^o62)). The CO^2?₃ groups lies flat between mettalic planes as in the aragonite type of structure and are linked to OH^? by hydrogen bond ($\text{d(CO}{}^{\mathrm{2?}}{}_3\text{?}\text{OH}{}^{\mathrm{?}}\text{) = 2,52}\text{A}\text{?}$). The rare earth coordination is nine fold: two OH^? groups being closer (2,58 Å) than the seven oxygen from the CO^2?₃ groups (2,58 to 2,70 Å).     

Un nouveau fluorure de platine : PtIIPtIVF6

From a temperature dependent study of the platinum-flourine system, a new fluoride Pt^IIPt^IVF₆ has been isolated, which contains platinum in an oxidation state lower than that found in the already known platinum fluorides PtF₄, PtF₅ and PtF₆. The material has been characterized by various analytical methods. The fluoride Pt^IIPt^IVF₆ crystallizes in the rhombohedral LiSbF₆ - type structure (R3) with the lattice parameters $\text{a}\text{= 5.56}{}_5\text{A}\text{?}$, α = 53.85°. Magnetic studies on polycristalline samples have shown that Pt^IIPt^IVF₆ orders ferromagnetically below 16 K. This is the first example of platinum (+II) in a fluorine environment and with a high spin structure in an octahedral surrounding.