Refinement of the crystal structure of CeOs2Si2 (ThCr2Si2-type)

The crystal structure of CeOs₂Si₂ has been determined from single crystal X-ray counter data. CeOs₂Si₂ is tetragonal, I4/mmm, Z = 2; the cell parameters are a = 0.41617(5) and c = 0.98481(28) nm. The final reliability factor $\text{R}\text{=}\text{|Δ}\text{F}\text{|}\text{|}\text{F}{}_{\mathrm{o}}\text{|}$ is 0.027 for 129 observed reflections (|F_o|>26). CeOs₂Si₂ is isotypic with the ordered structure type of ThCr₂Si₂ (BaAl₄-derivative type).     

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.     

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.     

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.     

Synthesis and crystal structure of the inter-alkali-metal chloride RbLiCl2

The crystal structure of RbLiCl₂ [a= 1441.3(3), b= 412.57(8), c= 720.9(1) pm, Guinier-Simon data, orthorhombic, Ccmm, No. 63, Z= 4] was determined and refined from single crystal data, R= 0.074, R_W= 0.062. The coordination polyhedron of Rb⁺ is a bicapped trigonal prism, Li⁺ is tetrahedrally coordinated. [LiCl₄] tetrahedra are connected via common corners to undulated layers $\text{∞}\text{2}\text{[}\text{LiCl}{}^{\mathrm{c}}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}\text{]}{}^{\mathrm{?}}$ parallel to (100). The structure is closely related to that of SrZnO₂.     

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.     

Concentration quenching of Tb3+ luminescence in LaOBr and Gd2O2S phosphors

The concentration quenching of trivalent terbium ${}^5\text{D}{}_{\mathrm{3,4}}\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions from UV-excited (La, Tb) OBr and (Gd, Tb)₂O₂S phosphors was studied. The activation concentration x was varied from 5·10^?5 to 0.2 for (La_1?xTb_x) OBr and from 10^?3 to 0.1 for (Gd_1?xTb_x)₂O₂S. ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ emissions (blue) were observed to quench first and the Tb³⁺ concentration giving rise to maximum intensity was 0.003 in (La, Tb) OBr and between 0.005 and 0.01 in (Gd, Tb)₂O₂S. The optimum concentration for ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ (green) emissions was 0.05 in (La, Tb) OBr and 0.03 in (Gd, Tb)₂O₂S. Dipole-dipole and dipole-quadrupole interactions are possible mechanisms for the quenching of emissions from the ⁵D₃ and ⁵D₄ levels.A method for determining the Tb³⁺ concentration in these phosphors, based on the intensity ratios of the ${}^5\text{D}{}_3\text{→}{}^7\text{F}{}_{\mathrm{J}}$ and ${}^5\text{D}{}_4\text{→}{}^7\text{F}{}_{\mathrm{J}}$ transitions, is also presented.     

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).     

Growth of YFe2O4 single crystals by floating zone method

The first successful growth of YFe₂O₄ single crystals was carried out by the floating zone method. The atmosphere to give suitable oxygen partial pressures for the crystal growth of YFe₂O₄ was determined. The mixtures of CO₂ and H₂ with the mixing ratio ranging over $\text{CO}{}_2\text{H}{}_2\text{= 0.65 – 0.95}$, or the equivalent CO₂CO mixtures, and the growth speed of 2 mm/hour or slower were found to be the essential conditions. The as-grown boules were aggregates of large single crystal grains with the c-axes perpendicular to the growth direction. A typical separated single crystal was a rectangular chip of 3mm × 1.5mm × 0.5mm. A slower growth speed is suggested for obtaining a bigger single crystal.     

Un oxyde de rhenium en relation de structure avec V2O5

The authors describe a rhenium oxide, Re₂O₅. It was revealed and investigated by means of transmission electron microscopy and single diffraction. The orthorhombic unic cell is related to the ReO₃ cubic cell in terms of: b=c=a_c= 3,747 A and a= 2 $\text{a}{}_{\mathrm{c}}\text{√2= 10,598}\text{A}\text{?}$. The crystal structure is explained from patterns, according to the structural scheme of Me₂O₅ and particularly to vanadium pentoxide structure. It is obvious that there exists a close relationship between them.     

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.     

Interactions of Cr2+ with the F− ligands in CdF2:Cr2+

Superhyperfine structure s.h.f.s. resulting from the Cr²⁺ - F^? interaction was studied in Cr²⁺ doped CdF₂ crystals. The s.h.f.s. observed can be described with by the following spin-Hamiltonian

$\text{H}\text{=}\text{g}{}_{\mathrm{eff}}\text{β}\text{HS}{}_{\mathrm{z}}\text{+ST}{}_{\mathrm{i}}\text{I+ST}{}_{\mathrm{j}}\text{I}$

The constants calculated are $\text{T}{}_{\mathrm{i\perp }}\text{≈}\text{T}{}_{\mathrm{i}}\text{= 50}\text{MHz}$$\text{T}{}_{\mathrm{j\perp }}\text{≈}\text{T}{}_{\mathrm{j}}\text{= 5}\text{MHz}$. The measurements were made with an ESR spectrometer at X band at 4.2 OK.     

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.     

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; $\text{1}\text{6}\text{(Δ}{}^{\mathrm{o}}{}_{\mathrm{(2)}}\text{? Δ}{}^{\mathrm{o}}{}_{\mathrm{(1)}}\text{)=?11.01±0.02}\text{GHz}$.     

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 $\text{I}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{TaSe}{}_4$.     

Macle et structure cristalline de Mn0,75Ga2,17S4

Twins of $\text{Mn}{}_{\mathrm{<mtext>1?</mtext><mtext>x</mtext>}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2</mtext><mtext>3</mtext><mtext>x</mtext>}}\text{S}{}_4$ were used for crystal structure determination. Twinning is explained by a reticular pseudomerihedry. Axis, plane and obliquity of the twin have been determined. Cell dimensions are: $\text{a = b}\text{= 5.456(2)}\text{A}\text{?}$; $\text{c}\text{= 10.220(4)}\text{A}\text{?}$; α = β = γ = 90°; space group 14; Z = 2. The final R value is 0.059. The material is isostructural with CdGa₂S₄.     

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.     

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.     

Contribution a l'etude de composes de structure derivant de la fluorine dans les systemes ZrO2MgO,HfO2MgO et HfO2Sc2O3

In the systems HfO₂MgO and ZrO₂MgO, crystals of β_Mg compounds have been investigated through X-ray diffraction; this bears out the existence of an analogy between these compounds and M₇O₁₂-related phases. The structure of the latter results from the ordering of anionic vacancies within a fluorite structure; this process brings out blocks I which themselves are respectively composed of 7 cations and two vacancies. In the system HfO₂Sc₂O₃, the β_Sc compound structure can be regarded as resulting from a monoperiodic bidimensional modulation (period $\text{1}\text{14}\text{|〈541〉1}{}_{\mathrm{<mtext>F</mtext>}}\text{|}$) in a fluorite structure. The β_Sc structure can thus be defined as a bidimensional stacking of blocks I and fluorite blocks in directions perpendicular to 〈III〉_F.     

Zur kristallstruktur von (NH4)3Ti(O2)F5

The disordered ligand positions in (NH₄)₃Ti(O₂)F₅ (cubic, space group Fm3m - O⁵_h'$\text{a}\text{= 9.23}{}_2\text{A}\text{?}$) has been studied by X-ray single crystal investigation. A 3-dimensional fourier synthesis indicates a distribution of the disordered O-Atoms on the 96j positions (Oyz) similar to (NH₄)₃ZrF₇ where a pentagonal bipyramide has been proposed for geometrie of the ZrF₇-group. Due to the short O-O distance the structure of (NH₄)₃Ti(O₂)F₅ is better described as elpasolite where one of the six octahedral ligand positions are statistically replaced by an ‘edge on’ O^2?₂-group oriented there in two possible directions.