The crystal and magnetic structures of Sr2YRuO6

Time-of-flight powder neutron diffraction data have been used to refine the crystal structure of the ordered, distorted perovskite Sr₂YRuO₆. Yttrium and ruthenium are octahedrally coordinated in this material with average MO bond lengths of 2.202 and 1.955 Å, respectively. Constant wavelength neutron diffraction data show that Sr₂YRuO₆ is a Type I antiferromagnet at 4.2 K with an ordered magnetic moment of 1.85 μ_B per Ru⁵⁺ ion. The Néel temperature of Sr₂YRuO₆ was determined to be 26 K. The data suggest that the 4d³ electrons in this material are localized rather than itinerant.     

The crystal structure of vanadium ditelluride,V1+xTe2

Vanadium ditelluride, V_1.04Te₂, has a Cd(OH)₂-type structure with unit cell dimensions a_h = 3.638 Å and c_h = 6.582 Å above the transition temperature T_t of 482 K. Below T_t the structure is monoclinic, space group $\text{C2}\text{m}$, with cell dimensions a_m = 18.984 Å(≈3a_h√3), b_m = 3.5947 Å (≈a_h), c_m = 9.069 Å (≈√(3a²_h + c²_h)), β = 134.62°. This low-temperature form is isostructural with NbTe₂ and TaTe₂ (which do not show a phase transition); the vanadium atoms form double zigzag chains with VV distances of 3.316 Å, which distort the Te lattice. Complex diffraction patterns were observed due to the simultaneous occurrence of the distortion of the Cd(OH)₂-type structure of vanadium ditelluride in three equivalent directions. Similar patterns were found for the Nb and Ta ditellurides.     

A deuterium NMR study of D(UO2XO4), 4D2O; X = P,As

Deuterium NMR spectra have been obtained by the solid echo technique for polycrystalline samples of DUO₂XO₄, 4D₂O, with X = P (DUP) and As (DUAs). Transitions (II → I) were found, by DSC measurements, to occur at 260 and 290 K for DUP and DUAs, respectively. In the high temperature tetragonal phase I, the NMR lineshapes are consistent with motionally averaged axially symmetric electric field gradient tensors, with values for $\text{〈}\text{e}{}^2\text{qQ}\text{h}\text{〉}{}_{\mathrm{<mtext>av</mtext>}}$ of 39.2 ± 0.2 and 38.2 ± 0.2 kHz for DUP and DUAs, respectively. This requires fast chemical exchange of the deuterium atoms between all of the hydrogen-bond sites in a water layer, and participation of all of the deuterium atoms in the diffusion process. There are no discernible discontinuities in the spectra at the transition temperature suggesting that there is little change in the local structure of the water layers at the transition. The spectra disappeared at about 10 K below T_c and for DUP a distorted broader spectrum became discernible below about 200 K.     

The SO+2 radical-ion

From the complex overall EPR spectrum of ⁶⁰Co gamma-irradiated pure solid sulfur dioxide the spectrum of the SO⁺₂ radical-ion was selected and the following principal values for the g-tensor obtained: g₁ = 1.9620;g₂ = 2.0026;g₃ = 2.0118 (Δg = ± 0.0005).     

Cristallochimie de TlIII6TeVIO12 et TlI6TeVIO6E6: un exemple original de l'activite´ste´re´ochimique de la pairee´lectronique 6s2(E) du thallium(I)

Both crystal structures of Tl₆TeO₁₂ and Tl₆TeO₆E₆ compounds have been determined, the former by X-ray single crystal techniques, the latter by powder neutron diffraction techniques. They crystallize in the trigonal system, space groupR3¯ the corresponding hexagonal cell parameters area = 9.645(2) Å,c = 9.421(2) Å, anda = 9.5722(3) Å,c = 9.3494(4) Å, respectively, withZ = 3. In both compounds tellurium(VI) is octahedrally coordinated to oxygen atoms with TeO distances of 1.936Åfor the Tl(III)-containing compound, i.e., Tl₆TeO₁₂, and 1.946Åfor Tl₆TeO₆ (Tl(I)). Tl(III) is surrounded by seven oxygen atoms sitting at the summits of a distorted monocapped trigonal prism. Tl(I) is linked to three oxygen atoms, forming a distorted TlO₃ pyramid. The lone pairs brought by Tl(I) are in the positions precedingly occupied by oxygen atoms in the crystal structure of Tl₆TeO₁₂. This is an outstanding example of the crystallochemical role of the lone pairsE which act like oxygen atoms, making Tl^I₆Te^VIO₆E₆ isostructural with Tl^IIITe^VIO₁₂. Structural relationships with fluorite type network are discussed.     

The dehydration of CuSr2(HCOO)6 · 8H2O: A crystallographic study

The isothermal dehydration of CuSr₂(HCOO)₆ · 8H₂O single crystals as well as powdered material has been followed by several techniques, mainly X-ray diffraction and optical microscopy. Evidence was found of a two-stage process, with an early appearance of an amorphous state (attributed to internal dissolution) and further recrystallization of the stable phases. One of these (CuSr(HCOO)₄, monoclinic, P_c, Z = 2, a = 7.345(10) Å, b = 8.692(15) Å, c = 6.702(10)Å, β = 97.25(5)°) has not been reported so far in the literature. When dehydration takes place near room temperature, the remaining product (Sr(HCOO)₂) bears a topotactic relationship to the parent matrix ((hk0)//(hk0)′; 〈0k0〉//〈0k0〉′). A striking metric match between both (hk0) sections, as well as the absence of any common structural motive, suggest an inner epitactic growth as the most probable mechanism for the transformation.     

Über Ordnungs-Unordnungsphänomene bei Sauerstoff perowskiten vom Typ A2+3B2+M5+2O9

Perovskites of the type A²⁺₃B²⁺M⁵⁺₂O₉, where A²⁺ = Ba, Sr; B²⁺ = Mn, Co, Ni, Zn; M⁵⁺ = Nb, Ta, show order-disorder phenomena. At lower temperatures a thermodynamically unstable disordered cubic perovskite is formed ($\text{1}\text{3}$ formula unit—$\text{AB}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{M}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{O}{}_3$—in the cell), which transforms irreversibly into a 1: 2 ordered high-temperature form with 3L structure (sequence (c)₃). For A²⁺ = Ba this lattice is hexagonal (space group $\text{P}\text{3}\text{m1}$; one formula unit in the cell); with A²⁺ = Sr a triclinic distortion is observed. For Ba₃CoNb₂O₉ a second transformation into a cubic disordered perovskite takes place at 1500°C. This transition is reversible and of the order-disorder type. The vibrational and diffuse reflectance spectra are discussed.     

Ln(Fe3+M2+)O4 compounds with layer structure [Ln : Y,Er, Tm,Yb, and Lu, M : Mg,Mn, Co,Cu, and Zn]

A series of new compounds Ln(Fe³⁺M²⁺)O₄ [Ln : Y, Er, Tm, Yb, and Lu, M : Mg, Mn, Co, Cu, and Zn] were successfully synthesized and their lattice constants were determined. These compounds have the same crystal structure as YbFe₂O₄ and Fe³⁺ and M²⁺ are both surrounded by five oxygen ions forming a trigonal bipyramid. The synthetic conditions are presented. They are strongly dependent upon the constituent cations of the compound.     

The crystal structures and magnetic properties of Ba2LaRuO6 and Ca2LaRuO6

Profile analysis of high-resolution, powder neutron-diffraction data was used to refine the previously reported structures of the ordered, distorted perovskites Ba₂LaRuO₆ and Ca₂LaRuO₆. Low-temperature neutron diffraction experiments showed that, at 2K, the former is a Type IIIa antiferromagnet while the latter is Type I. Both compounds have an ordered magnetic moment of $\text{μ}{}_{\mathrm{<mtext>Ru</mtext>}}\text{? 1.95μ}{}_{\mathrm{<mtext>B</mtext>}}$ per Ru⁵⁺ ion. The Néel temperature of Ba₂LaRuO₆ was determined to be 29.5K, and the covalent mixing between the ruthenium and nearest-neighbor anions is described by A²_π = 8.2 ± 1% for Ba₂LaRuO₆ and 8.6 ± 1% for Ca₂LaRuO₆. The ionic radius of a Ru⁵⁺ ion is 0.56 Å. These data are consistently interpreted within the framework of a strongly correlated, half-filled π1 band. Extension of this interpretation to the magnetic data for the perovskites CaRuO₃ and SrRuO₃ leads to a fundamental theoretical prediction.     

Crystallography and phase relations of MeOM2O3TiO2 systems (Me = Fe,Mg, Ni; M = Al,Cr, Fe)

Subsolidus phase relations of ternary oxide systems containing divalent Fe, Mg, or Ni, trivalent Al, Cr, or Fe, and tetravalent Ti are characterized by solid solutions at metal/oxygen ratios $\text{3}\text{4}$, $\text{2}\text{3}$, and $\text{3}\text{5}$. At low temperatures only compounds with cubic or hexagonal close-packed oxygen and uniform oxygen coordination remain stable in the crystal structures NaCl, spinel, ilmenite-α-Al₂O₃, TiO₂. The pseudobrookite phases FeTi₂O₅, MgTi₂O₅, Al₂TiO₅, Fe₂TiO₅, the V₃O₅ structure phase Cr₂TiO₅, and the Andersson phases Cr₂Ti_n?2O_2n?1 (n = 4,6,7,8,9) decompose. Additional phases with close-packed oxygen as predicted by a simple structure model for metal/oxygen ratios $\text{7}\text{12}$, $\text{5}\text{6}$, and $\text{11}\text{12}$ do not form but presumably are important for nonstoichiometric solid solutions. Most differences between systems containing transition metals and the MgOAl₂O₃TiO₂ system can be attributed to crystal field effects.     

Solid state reactions to CdTeMoO6 and its structural characterization

CdTeMoO₆ has been obtained by solid state reactions of CdMoO₄ with orth. TeO₂ at 425°C, with tetr. TeO₂ at 470°C, and with H₆TeO₆ at 490°C. Its crystal structure belongs to the tetragonal system (space group $\text{P4}\text{n}$ or $\text{P4}\text{nmm}$ with unit cell dimensions a = 5.279(2) Å, c = 9.056(2) Å. The specificity of this compound in the allylic oxidation reactions should be strictly related to its structural features, among which the presence of cis MoO₂ groups could be very important.     

Dimorphism in triple orthovanadates MIILaTh (VO4)3 (MII = Sr or Pb)

Triple orthovanadates, SrLaTh(VO₄)₃ and PbLaTh(VO₄)₃ are found to be dimorphic, the crystalline form depending upon the firing temperature. The low-temperature form has zircon structure and the corresponding high-temperature form exhibits its well-known monoclinic modification. The X-ray powder diffractograms and infrared spectra are recorded and discussed in comparison with those of structurally related compounds.     

Magnetic order in AVX3 (A = Rb,Cs, (CD3)4 N; X = Cl,Br, I): A neutron diffraction study

AVX₃ (A = Rb, Cs, (CD₃)₄ N; X = Cl, Br, I) crystallize in the hexagonal system, space group $\text{P6}{}_3\text{mmc}$, with chains of face-sharing VX₆ octahedra along the c-axis. This leads to a pronounced one-dimensional character of their magnetic properties with a strong antiferromagnetic exchange interaction J between nearest neighbor V²⁺ ions along these chains. All compounds except [(CD₃)₄N]VCl₃ order three-dimensionally with ordering temperatures T_c between 13 and 32 K. In the ordered phase the magnetic moments, μ, lie in the basal plane in a triangular arrangement typical for antiferromagnetic interchain interaction J′.     

Phases and phase transitions of compounds (CnH2n+1NH3)2MnCl4 with n = 1, 2, 3

Phases and structural phase transitions of the compounds (CH₃NH₃)₂MnCl₄, (C₂H₅NH₃)₂MnCl₄ and (C₃H₇NH₃)₂MnCl₄ have been studied by means of thermoanalytical methods (DSC) and X-ray single crystal and powder diffraction data in the temperature range of 85–480°K at normal pressure. All phases show perovskite-like layer structures. The high temperature phases (α phase) correspond to the K₂NiF₄ type and may be regarded as the aristotype of each polymorphic compound. All transitions are reversible. Transition patterns are:

Based on the DSC peak-shape analysis and diffraction data a model of a tilting system of the MnCl₆-octahedra layer is introduced in order to understand essential features of structures of different phases and their transition behavior. Single crystal film data of (C₃H₇NH₃)₂MnCl₄ phases reveal some disorder phenomena. The ε phase exhibits a superstructure along [010] with a triplication of the shortest axis corresponding to the δ phase. The γ phase of this compound shows strong satellite reflections, due to a transverse distortion wave along the [100] lattice direction.     

Influence of M2+ ions substitution on the structure of lanthanum hexaaluminates with magnetoplumbite structure

A series of compounds with the initial composition LaM_xAl₁₁O_18+x has been studied with x ranging from 0 to 1, and M = Mn, Co, Cu. They exhibit a more or less distorted and defective magnetoplumbite arrangement. Their effective compositions have been determined by X-ray structure refinement. The smaller the content of M²⁺, the higher the disorder in the crystal lattice, the worse the crystal growth, and more intense the diffuse scattering in (001) planes. The role of M²⁺ is compared to that of M²⁺ stabilizing γ-Al₂O₃ to give MAl₂O₄ spinels.     

Phase analysis in the Fe2O3NiO mixed oxides prepared by co-precipitation

Iron-nickel mixed oxides containing up to 10 mole% of NiO have been prepared by hydroxide coprecipitation technique. The oxide samples have been heated to different temperatures ranging from 300 to 1300°C and studied by infrared spectroscopy, magnetic susceptibility, and X-ray diffraction measurements. The maximum solubility of NiO in Fe₂O₃ under the present experimental conditions is found to be 2 mole% when the samples are heated to 550°C. The solubility decreases with increase of sintering temperature and also as the total NiO content of the sample increases. Formation of nickel ferrite phase at concentrations higher than 2 mole% of NiO is clearly indicated.     

Neutron diffraction study on the spinel Cu0.72Co2.28O4

A neutron powder diffraction refinement of the positional and thermal structure parameters of Cu_0.72Co_2.28O₄ spinel has been carried out. It has been found that the spinel is inverse, with inversion parameter approximately equal to one half of the copper content value.     

Über Sauerstoffperowskite mit fünf- und vierwertigem Iridium Verbindungen vom Typ Ba2B3+Ir5+O6 und Ba3B3+Ir4,5+2O9

Perovskites with pentavalent iridium of type Ba₂B³⁺Ir⁵⁺O₆ are for B³⁺ = La, Nd, Sm, Gd, Dy, Y cubic and with B³⁺ = In hexagonal (6 L structure of BaTiO₃ type; sequence (hcc)₂). According to the intensity calculations of powder patterns for Ba₃SmIr₂O₉ and Ba₃YIr₂O₉ the new series Ba₃B³⁺Ir₂O₉ (B³⁺ = Sm, Eu, Gd, Dy, Ho, Yb, Sc, Y, In; mean oxidation state of iridium + 4.5) crystallize in a hexagonal 6 L structure of BaTiO₃ type (space group $\text{P6}{}_3\text{mmc}$; sequence (hcc)₂). The intensity-related R′ value is 8.6% for B³⁺ = Sm and 10.0% for Y. In the octahedral net the double groups of face-connected octahedra are occupied by the iridium atoms, which are dislocated from their ideal positions such that the IrIr distance has increased (2.72₀ Å (Sm) or 2.63₂ Å (Y)). The ir spectra are reported and discussed in connection with the corresponding factor group analysis.     

Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

Ca7Au3 and Ca5Au4, two structures closely related to the Th7Fe3 and Pu5Rh4 types

Two new intermetallic compounds have been synthetized and structurally studied by single crystal diffractometric data: Ca₇Au₃ (oP80, space groupPbca,a = 20.742(8), b = 18.036(8), c = 6.665(2) A?,Z = 8, R = 0.051) and Ca₅Au₄ (mP18, space groupP2₁/c, a = 8.028(3), b = 8.019(6), c = 7.727(3) A?, β = 109.16(6)°,Z = 2, R = 0.104). Both atomic arrangements, which represent new structural types, are based on Au-centered Ca trigonal prisms and are geometrically related to the Th₇Fe₃ and Pu₅Rh₄ structures.