Crystal structure of the perovskites Ba<Subscript>2</Subscript>A<Superscript>II</Superscript>UO<Subscript>6</Subscript> (A<Superscript>II</Superscript> = Zn,Cd, Pb)

The compounds Ba₂ZnUO₆, Ba₂CdUO₆, and Ba₂PbUO₆ were prepared by high-temperature solidphase reactions. Their structures (space group Fm \(\bar 3\) m) were refined by the Rietveld method. In the morphotropic series Ba₂A^IIUO₆, correlations were found between the A^II-O, U-O, and Ba-O bond lengths and the crystal-chemical radius of A^II.     

Chemical Thermodynamics of the Compounds AIIUO2(SO4)2·nH2O (AII = Mn, Fe, Co, Ni, Cu, Zn)

The standard enthalpies of formation of anhydrous 3d transition metal uranyl sulfates and their pentahydrates at 298.15 K were determined by reaction calorimetry. The heat capacities of the compounds A^IIUO₂(SO⁴)₂·5H₂O (A^II = Mn, Fe, Co, Ni, Cu, Zn) and CuUO₂(SO₄)₂ at 7– 300 K were determined by adiabatic vacuum calorimetry, and the thermodynamic functions of these compounds were calculated. The standard entropies and Gibbs energies of formation of these compounds at 298.15 K were determined. The thermodynamics of dehydration of A^IIUO₂(SO₄)₂·5H₂O and of the precipitate-solution equilibria involving these compounds were studied. __________ Translated from Radiokhimiya, Vol. 47, No. 2, 2005, pp. 110–122. Original Russian Text Copyright ? 2005 by Karyakin, Knyazev, Gavrilova.     

A physicochemical study of the perovskites M<Superscript>II</Superscript>(In<Subscript>2/3</Subscript>U<Subscript>1/3</Subscript>)O<Subscript>3</Subscript> (M<Superscript>II</Superscript> = Sr,Ba) at low temperatures

The heat capacity of crystalline Sr(In_2/3U_1/3)O₃ and Ba(In_2/3U_1/3)O₃ in the range 80–350 K was determined by adiabatic vacuum calorimetry, and the thermodynamic functions of these compounds in the range from T → 0 to 350 K were calculated. The standard entropies of formation of these compounds at 298.15 K were calculated. The absolute entropies and standard entropies of formation of perovskites M^II(A^III _2/3U_1/3)O₃ (M^II = Sr, A^III = Sc, In, Fe; M^II = Ba, A^III = Sc, In, Y, Nd-Lu) were estimated.     

New ferromagnetics based on manganese-alloyed chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

This review describes the principles of semiconductor spintronics, represents the physicochemical properties of materials based on manganese-alloyed A^IIB^IVC₂^V compounds, considers the results from theoretical simulation of magnetic properties of A^IIB^IVC₂^V alloyed with 3d metals, summarizes the basic approaches to explanation of ferromagnetism with Curie points above room temperature arising in A^IIB^IVC₂^V:Mn, and indicates promising ways to synthesize and study magnetic semiconductors based on chalcopyrites A^IIB^IVC₂^V in order to produce a suitable material for spintronic devices.     

Synthesis and characterization of some chalcogenides of AIB2IICIIID4VI composition

A number of quaternary diamond-like semiconducting phases of A^IB₂^IIC^IIID₄^VI composition (A^I = Cu,Ag; B^II = Zn, Cd; C^III = Ga, In; D^VI = Se,Te) were investigated. Microstructure, DTA and roentgenographic examinations, carried out on samples obtained by direct synthesis, show that the characteristics of homogeneity and single-phase seem to be restricted to copper (CuB₂^IIC^IIID₄^VI) and silver (AgCd₂InTe₄) based compositions, characterized by a generally incongruent metling and by cubic or hexagonal cells.     

Physical chemistry of magnesium and calcium uranophosphate and uranoarsenate AII(BVUO6)2·nH2O

Temperature dependences of the isobaric heat capacity of A^II(B^VUO₆)₂·nH₂O (A^II = Mg, Ca; B^V = P, As) was measured. The standard entropies and Gibbs energies of formation of the compounds were calculated. From these values, the solubility of the compounds in water at T = 25°C was evaluated.     

Solubility of Uranovanadates AII(VUO6)2·nH2O (AII = Mg,Ca, Sr,Ba, Co,Ni, Cu,Pb) in Water and Aqueous Solutions

Solubility of uranovanadates A^II(VUO₆)₂·nH₂O (A^II = Mg, Ca, Sr, Ba, Co, Ni, Cu, Pb) in water and acid aqueous solutions under various conditions was studied. Based on these data, the standard Gibbs energies of formation of the uranovanadates were calculated, which would allow analysis of their state under conditions that were not studied experimentally.     

Highly effective phototransducers based on polycrystalline heterostructures of AIIBVI compounds

Thin-film polycrystalline heterostructures based on A^IIB^VI compounds were prepared, and related highly effective surface-barrier phototransducers of the p-Cu_1.8S/n-A^IIB^VI/n-A^IIB^VI type (with a quantum efficiency of ∼0.9) were obtained. The heterostructures are promising materials for the creation of solar cells and UV photodetectors insensitive to the visible light.     

Bibliography on AIIBIVC22 V ternary compounds

In the introduction, some of the applications of the A^IIIB^V compounds are indicated. Their limitations are mentioned and two possibilities are suggested for overcoming these. In view of the A^IIIB^V compounds' outstanding contribution in recent years, the investigation of their isoelectric analogues, the A^IIB^IVC ₂ ^V compounds, is suggested as a logical step. CdSnAs₂ is shown to be the most investigated compound in this group, although several phosphides have potentialities as materials with energy gaps in the visible region of the spectrum. A comprehensive bibliography of the published work on A^IIB^IVC_2/suV compounds is given.     

Phase transitions and thermal expansion of apatite-structured compounds

The phase transitions and thermal expansion of apatite-structured compounds with the general formula M₅^II(A^VO₄)₃L (M^II = Ca, Sr, Cd, Ba, Pb; A^V = P, V; L = F, Cl) have been studied by high-temperature X-ray diffraction and differential thermal analysis. The Pb-containing apatites are shown to undergo phase transitions involving a reduction in unit-cell symmetry from hexagonal to monoclinic. The thermal expansion anisotropy in the hexagonal phases increases in the order Ca < Sr < Ba < Pb < Cd, and the monoclinic phases are less anisotropic but have larger thermal expansion coefficients in comparison with the hexagonal phases.     

Thermochemistry and thermal characteristics of Ba2MIIUO6 (MII = Mg, Ca, Sr, Ba)

A series of uranium compounds with the composition Ba₂M^IIUO₆ (M^II = Mg, Ca, Sr, Ba) were synthesized by a solid-phase procedure. The polymorphism for Ba₂SrUO₆ was studied by high-temperature X-ray diffraction, and the coefficients of thermal expansion were determined. The standard enthalpies of formation of crystalline Ba₂M^IIUO₆ at 298.15 K were determined by the reaction calorimetry.     

Synthesis,structure, and physicochemical properties of bivalent element hexanitratothorates

Compounds of the composition M^IITh(NO₃)₆·8H₂O (M^II = Mg, Mn, Co, Ni, Zn) were prepared by precipitation from solution. The structure and thermal decomposition of these compounds were examined by X-ray diffraction and thermal analysis. The previously unknown standard enthalpies of formation of the compounds at 298.15 K were determined by reaction calorimetry.     

Varied roles of Pb in transition-metal PbMO3 perovskites (M = Ti,V, Cr,Mn, Fe,Ni, Ru)

Different structural chemistries resulting from the Pb²⁺ lone-pair electrons in the PbMO₃ perovskites are reviewed. The Pb²⁺ lone-pair electrons enhance the ferroelectric transition temperature in PbTiO₃, stabilize vanadyl formation in PbVO₃, and induce a disproportionation reaction of Cr^IV in PbCrO₃. A Pb²⁺ + Ni^IV = Pb⁴⁺ + Ni^II reaction in PbNiO₃ stabilizes the LiNbO₃ structure at ambient pressure, but an A-site Pb⁴⁺ in an orthorhombic perovskite PbNiO₃ is stabilized at modest pressures at room temperature. In PbMnO₃, a ferroelectric displacement due to the lone pair electron effect is minimized by the spin–spin exchange interaction and the strong octahedral site preference of the Mn^IV/III cation. PbRuO₃ is converted under pressure from the defective pyrochlore to the orthorhombic (Pbnm) perovskite structure where Pb–Ru interactions via a common O −2p orbital stabilize at low temperature a metallic Imma phase at ambient pressure. Above P_c a covalent Pb–Ru bond is formed by Pb²⁺ + Ru^IV = Pb⁴⁺ + Ru^II electron sharing.     

Preparation,Thermal Diffusivity,and Thermal Conductivity of Phosphate Ceramics with the Tridymite Structure

We have synthesized powders of the CsM^IIPO₄ (M^II = Mg, Mn, Co) phosphates with the β-tridymite structure. Phosphate ceramics were produced by conventional cold pressing with inorganic sintering aids, followed by programmed annealing, and by an innovative method: high-speed spark plasma sintering. The thermal diffusivity and thermal conductivity (0.3–0.4 W/(m K)) of the CsM^IIPO₄ ceramics indicate that they are heat insulators with a high working temperature.     

On the ternary compound MgSiP2 grown from antimony solution

The ternary semiconducting compound MgSiP₂ has been obtained for the first time from solution in antimony. The method of preparation is described and compared with that of crystallization in tin. A general analysis of ternary semiconductors of the A^IIB^IVC^V₂ type is also given.     

Ferromagnetism in (Zn,Cr)Se Layers Grown by Molecular Beam Epitaxy

Magnetization measurements of MBE grown epilayers of (Zn,Cr)Se with relatively large Cr content of 0.014 and 0.021 are presented. We evidence the presence of a strong ferromagnetic coupling between Cr ions, but also suggest a significant clustering due to a pronounced superparamagnetic behavior found in the layers. We estimate the intraparticle Curie temperature to be about 100 K, which combined with other arguments appears to indicate that some magnetic properties of Cr-rich layers might be dominated by the presence of small grains of A^II–Cr₂–B₄ ^VI spinels.     

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.     

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.     

Effects of mixed-mode ratio and step-shaped micro pattern surface on crack-propagation resistance of carbon-fiber-reinforced plastic/adhesive interface

This study investigated the effects of the mixed-mode ratio of applied loads (G_II/G) and aspect ratio A of step-shaped micro patterns on the crack-propagation resistance of a carbon-fiber-reinforced plastic (CFRP)/adhesive interface fabricated by in-mold surface modification. Experiments showed that the fracture behaviors change and that the apparent mixed mode fracture toughness G_C increases with G_II/G and A. We used the Benzeggagh–Kenane (B–K) failure criterion for the mixed-mode fracture toughness considering the transition of the failure mode of the step-shaped micro patterns. The B–K criterion agreed well with the improvement of G_C due to an increase in G_II/G for various fixed values of A. We clarified the relationship between the aspect ratio A and the parameter η, which is required to describe the B–K criterion, and therefore, η can be estimated from A. Consequently, it was verified that G_C of the CFRP/adhesive interface with step-shaped micro patterns can be predicted for arbitrary G_II/G and A values by substituting the η–A relationship in the B–K criterion.     

Crystal growth of AIIBIVC2V chalcopyrites

Crystal growth techniques were investigated for the synthesis of A^IIB^IVC₂^V chalcopyrites. High quality single crystals of ZnGeP₂ were grown by a Bridgman technique; samples showed near-theoretical transmission in the 3 to 8 μm range. The Bridgman technique was also applied to the growth of ZnSiAs₂ and CdGeAs₂. A controlled reaction process was developed for synthesis of compounds containing volatile constituents, and demonstrated for ZnP₂, an intermediate in the preparation of ZnSiP₂ and ZnGeP₂. A single-stage procedure in which the constituent elements are reacted and crystal growth ensues by vapor transport under a controlled overpressure of phosphorus was also pursued for ZnSiP₂.