Phase equilibria in the Sn–As–Ge and Sn–As–P systems

T–x diagrams of polythermal GeAs–SnAs, GeAs–Sn₄As₃ sections of the Sn–As–Ge system and Sn₄P₃–Sn₄As₃ section of the Sn–As–P system were constructed using the results of X-ray powder diffraction and differential thermal analyses. It was found that the section GeAs–Sn₄As₃ is not quasi-binary due to realization of four-phase peritectic transformation L + SnAs ? GeAs + Sn₄As₃ at the temperature of 834 K. The quasi-binary section GeAs–SnAs represents a phase diagram of the eutectic type with the following coordinates of eutectic reaction: temperature of the eutectic point is 840 K, and composition is 20 mol% GeAs. In the Sn–As–P system, the existence of the solid-solution range indicated as (Sn₄As₃) _x (Sn₄P₃)_1?x  was defined. The polythermal section Sn₄P₃–Sn₄As₃ is not quasi-binary due to the fact that in the composition range with a high content of tin arsenide discussed section intersects the peritectic part of the three-phase volume (L + SnAs + α) of the ternary diagram.     

Darstellung,Struktur und Temperaturabhängigkeit der Phasenbreite der Phase Ca2−xAs1−xBr1+x und thermisches Verhalten der Verbindung Ca3AsBr3

Preparation, Crystal Structure, and Temperature Dependence of the Homogeneity Range of the Phase Ca_2-xAs_1-xBr_1+x and Thermal Behaviour of Ca₃AsBr₃ The phase (Ca_2-x□_x)(As_1-xBr_1+x) (yellow, NaCl type lattice, x ? degree of substitution) was prepared from “Ca₃As₂” and CaBr₂ in different molar ratios in steel ampoules under argon at 900 and 950°C resp. The lattice constant as a function of the composition, the homogeneity range, and dependence of the bromine rich phase boundary on the temperature were determined. The structure was deduced from single crystal X-ray investigation and density measurements at different compositions. The thermal behaviour of Ca₃AsBr₃ (colourless, isotypic to Mg₃NF₃, prepared at 850°C) was studied by annealing samples in molybdenum ampoules under argon in the temperature range 900–1250°C and by differential thermal analysis. From the experimental results a section of the phase diagram Ca₃As₂?CaBr₂ was constructed.     

New transparent conductors with the M7O12 ordered oxygen-deficient fluorite structure: from In4Sn3O12 to In5.5Sb1.5O12

A new transparent conductor, containing pentavalent antimony, In_4+xSn_3−2xSb_xO₁₂, has been synthesized for 0?x?1.5. The latter exhibits an ordered oxygen-deficient fluorite structure with an ordered distribution of Sb⁵⁺ and In³⁺/Sn⁴⁺ species in the octahedral and seven-fold coordinated sites, respectively. More importantly, it is shown that the electronic conductivity of this transparent conducting oxide (TCO) at room temperature, is one order of magnitude larger for x=1 (In₅SnSbO₁₂) than for x=0 (In₄Sn₃O₁₂) and it turns to a semi-metallic behavior in contrast to In₄Sn₃O₁₂ which is a semi-conductor. The potential of this new material, as TCO, is also shown by its reflectance spectra, similar to In₄Sn₃O₁₂, involving only a small increase of the optical bandgap, by 0.15 eV.     

Preparation, crystal structure, and photoluminescence of Ca2SnO4:Eu, Y

Eu³⁺-doped Ca₂SnO₄ (solid solutions of Ca_2−xEu_2xSn_1−xO₄, 0?x?0.3) and Eu³⁺ and Y³⁺-codoped Ca₂SnO₄ (Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄) were prepared by solid-state reaction at 1400 °C in air. Rietveld analysis of the X-ray powder diffraction patterns revealed that Eu³⁺ replaced Ca²⁺ and Sn⁴⁺ in Eu³⁺-doped Ca₂SnO₄, and that Eu³⁺ replaced Ca²⁺ and Y³⁺ replaced Sn⁴⁺ in Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄. Red luminescence at 616 nm due to the electric dipole transition ⁵D_o→⁷F₂ was observed in the photoluminescence (PL) spectra of Ca_2−xEu_2xSn_1−xO₄ and Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ at room temperature. The maximum PL intensity in the solid solutions of Ca_2−xEu_2xSn_1−xO₄ was obtained for x=0.1. The PL intensity of Ca_1.8Y_0.2Eu_0.2Sn_0.8O₄ was 1.26 times greater than that of Ca_2−xEu_2xSn_1−xO₄ with x=0.1.     

Sn4As3 revisited: Solvothermal synthesis and crystal and electronic structure

A facile one pot method of synthesis of tin arsenide Sn₄As₃ starting from metallic tin and elemental arsenic under mild solvothermal conditions in ethylenediamine in the presence of ammonium chloride is offered. The dissolving of the tin metal in ethylenediamine and the role of NH₄Cl are discussed. The crystal structure of Sn₄As₃ has been re-determined. It is shown to crystallize in the trigonal non-centrosymmetric space group R3m, (a=4.089(1) Å, c=36.059(6) Å, Z=3), which differs from the previously reported centrosymmetric structure . The crystal structure of Sn₄As₃ consists of alternating layers of arsenic and tin atoms that are combined into seven-layer blocks and build up along the c-axis. The major structural feature is the short tin-tin distances (3.24 Å) between the adjacent blocks. The analysis of the density of states and band structure reveals that Sn₄As₃ should have metallic properties, which is in line with the previously reported experimental observations. Analysis of chemical bonding employing the electron localization function shows that only for the shortest Sn-As contacts the bonding is pairwise, while four-center bonds are formed between arsenic and tin atoms at relatively long distances (>2.85 Å). Moreover, each tin atom holds an electron lone-pair.     

Investigation par analyse thermique differentielle du systeme Gd2(MoO4)3-Bi2(MoO4)3

The phase diagram of the system Gd₂(MoO₄)₃-Bi(MoO₄)₃ has been studied by differential thermal analysis (DTA). Sealed platinum tubes were used as sample holders, in order to prevent the loss of Bi₂O₃ and MoO₃ through volatilization at high temperature. Various solid solutions and new phases are reported: α-Gd_2-x-Bi_x(MoO₄)₃, β -Gd_2-x-Bi_x(MoO₄)₃, α-Bi_2-xGd_x(MoO₄)₃, 3Gd₂(MoO₄)₃·2Bi₂(MoO₄)₃, etc.     

Synthesis and investigation of calcium-containing phosphatosilicates with NaZr2(PO4)3 structure

Calcium-containing phosphatosilicates of the type Ca_0.5(1+x)Zr₂(PO₄)_3?x (SiO₄) _x were obtained by sol-gel method using the salting out process. Phase formation was studied, and optimal temperature and time regimes of synthesis providing the formation of one-phase reaction products were established. It is found that phases of NZP-structure are formed. Boundaries of phase stability of phosphatosilicates at the heterovalent isomorphic substitutions P⁵⁺→Si⁴⁺: 0 ≤ x ≤ 0.5 are established. On the basis of powder X-ray analysis data the crystalline structure of Ca_0.75Zr₂(PO₄)_2.5(SiO₄)_0.5 was refined by the full-profile analysis (Rietveld method). Hydrolytic stability of phosphatosilicates was studied.     

Ionic conductivity and crystal chemistry of ramsdellite type compounds,Li2+x(LixMg1−xSn3)O8, 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8, 0 ≤ x ≤ 1

Solid solution phases Li_2+x(Li_xMg_1−xSn₃)O₈: 0 ≤ x ≤ 0.5 and Li₂Mg_1−xFe_2xSn_3−xO₈: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li_2+x(Li_xMg_1−xSn₃)O₈ solid solutions exhibit conductivities 4 × 10⁻⁶–5 × 10⁻⁴ (Ω cm)⁻¹ at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li_2.3(Li_0.3Mg_0.7Sn₃)O₈, x = 0.3. In the solid solution series Li₂Mg_1−xFe_2xSn_3−xO₈, the highest conductivity was exhibited by Li₂Fe₂Sn₂O₈, 2 × 10⁻⁵ (Ω cm)⁻¹ at 573 K.     

Local structure and hyperfine interactions of Fe and Sn atoms in brownmillerite-like ferrite Sr2Fe1.98Sn0.02O5+x

Mössbauer spectroscopy has been applied for studying local environment of ⁵⁷Fe and ¹¹⁹Sn probe atoms within tin-doped Sr₂Fe_1.98Sn_0.02O_5+x (x?0.02) ferrite with the brownmillerite-type structure. ⁵⁷Fe Mössbauer spectra indicate no appreciable local distortions induced by the tin dopant atoms. The ¹¹⁹Sn spectra recorded below the magnetic ordering temperature (T_N) can be described as a superposition of two Zeeman sextets, which indicate that Sn⁴⁺ dopant ions are located in two non-equivalent crystallographic and magnetic sites. The observed hyperfine parameters were discussed supposing Sn⁴⁺ cations to replace iron cations in the octahedral (Sn_O) and tetrahedral (Sn_T) sublattices. It has been supposed that Sn⁴⁺ cations being stabilized in the tetrahedral sublattice complete their nearest anion surrounding up to the octahedral oxygen coordination “Sn_T⁴⁺”. Annealing of the Sr₂Fe_1.98Sn_0.02O_5+x in helium flux conditions at 950°C leads to formation of divalent Sn²⁺ cations with a simultaneous decrease of the contribution for the Sn_T⁴⁺ sub-spectrum. The parameters of combined electric and magnetic hyperfine interactions of the ¹¹⁹Sn²⁺ sub-spectrum underline that impurity atoms are stabilized in the sp³d-hybrid state in the oxygen distorted tetragonal pyramid. The analysis of the ¹¹⁹Sn spectra indicates a chemical reversibility of the processes Sn_T²⁺?Sn_T⁴⁺ within the tetrahedral sublattice of the brownmillerite-type ferrite.     

ChemInform Abstract: The Crystal Structures of Ni3+xSn4Zn and Ni6+xSn8Zn and Their Structural Relations to Ni3+xSn4, NiSn and Ni5‐δZnSn4.

Two new compounds, Ni_3+xSn₄Zn (x≈1.35, monoclinic, space group I2/m, Z = 2, single crystal XRD) and Ni_6+xSn₈Zn (x≈1.35, monoclinic, space group C2/m, Z = 2) are prepared by solid state reaction of the elements (Al₂O₃ crucible in evacuated quartz tubes, 1453 K).     

Phase formation in the Ag2MoO4-CoMoO4-Al2(MoO4)3 system

The subsolidus region of the Ag₂MoO₄-CoMoO₄-Al₂(MoO₄)₃ ternary salt system was studied by X-ray powder diffraction analysis. New compounds Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.4) and AgCo₃Al(MoO₄)₅ were detected to form. The variable-composition phase Ag_1?x Co_1?x Al_{1 + x} (MoO₄)₃ is of the NASICON structure type (space group \(R\bar 3c\) ). AgCo₃Al(MoO₄)₅ crystallizes in the triclinic symmetry (space group \(P\bar 1\) Z = 2) with the unit cell parameters a = 6.9101(6), b = 17.519(1), c = 6.8241(6) Å, α = 87.356(7)°, β = 101.078(7)°, and γ = 91.985(9)°. The compounds are thermally stable until 770–780 and 760°C, respectively.     

Phase diagram and metal distribution of the (CrxTi1−x)3Se4 system (0 ≤ x ≤ 1) with the Cr3S4-type structure

The phase diagram and metal distribution of the (Cr_xTi_1?x)₃Se₄ system were studied by X-ray, neutron diffraction, and DTA measurements. The metal distribution of M′M₂X₄ with the Cr₃S₄-type structure, which was estimated from the composition dependence of lattice parameters in the solid solution (M′_xM_1?x)₃X₄ system, was in good agreement with results from other measurements such as neutron diffraction and Mössbauer effect.     

Analysis of the electronic structure of Hf(Si0.5As0.5)As by X-ray photoelectron and photoemission spectroscopy

The ternary hafnium silicon arsenide, Hf(Si_xAs_1−x)As, has been synthesized with a phase width of 0.5?x?0.7. Single-crystal X-ray diffraction studies on Hf(Si_0.5As_0.5)As showed that it adopts the ZrSiS-type structure (Pearson symbol tP6, space group P4/nmm, Z=2, a=3.6410(5) Å, c=8.155(1) Å). Physical property measurements indicated that it is metallic and Pauli paramagnetic. The electronic structure of Hf(Si_0.5As_0.5)As was investigated by examining plate-shaped crystals with laboratory-based X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (PES). The Si 2p and As 3d XPS binding energies were consistent with assignments of anionic Si¹⁻ and As^1-. However, the Hf charge could not be determined by analysis of the Hf 4f binding energy because of electron delocalization in the 5d band. To examine these charge assignments further, the valence band spectrum obtained by XPS and PES was interpreted with the aid of TB-LMTO band structure calculations. By collecting the PES spectra at different excitation energies to vary the photoionization cross-sections, the contributions from different elements to the valence band spectrum could be isolated. Fitting the XPS valence band spectrum to these elemental components resulted in charges that confirm that the formulation of the product is Hf²⁺[(Si_0.5As_0.5)As]²⁻.     

Cation ordering in the fluorite-like transparent conductors In4+xSn3−2xSbxO12 and In6TeO12

The cation ordering in the fluorite-like transparent conductors In_4+xSn_3−2xSb_xO₁₂ and In₆TeO₁₂, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb₇O₁₂-type structure with a strong preference of the smaller 4d¹⁰ cations (Sn⁴⁺, Sb⁵⁺, Te⁶⁺) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM₄ tetrahedral network of the antistructure. The relationships between the M₇O₁₂ and the M₂O₃ bixbyite-type structures are explored. Within the whole series of compositions In_4+xM_3−xO₁₂ (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M₇O₁₂ type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb.     

Phase equilibria,thermal analysis,and reactivity of tin tungsten bronzes and related phases

Crystal chemistry and phase relations of the bronze forming region of the SnWO system have been investigated. Above 780°C the tin bronzes Sn_xWO₃ are shown to be thermally unstable and an equilibrium diagram is established at 700°C which shows that the composition limits of the tetragonal phase are 0.21 ? x ? 0.29. Below x = 0.21 a series of single and two phase regions containing orthorhombic bronzes exists for which the composition limits have been established. In the range 0.29 ? x ? 0.76 the system comprises the tetragonal bronze, Sn₂W₃O₈ and SnWO₄, while above 0.76 there is no bronze, only Sn₂W₃O₈, SnWO₄ and free Sn. The phase Sn₂W₃O₈ has been isolated and shown to have a hexagonal unit cell, a = 7.696 Å, c = 18.654 Å. The evidence of differential thermal analysis and X-ray studies suggests that this hexagonal phase arises from the decomposition of the tungsten bronze phase and is itself decomposed to cubic SnWO₄ above 700°C. Small thermal effects observed in the DTA scans of tin-containing tetragonal bronzes are interpreted in terms of an order-disorder phenomenon arising from asymmetric tunnel occupancy by Sn²⁺ ions caused by the presence of the lone pair of electrons. Hydrogen reduction of Sn_xWO₃ has been shown to result in complete removal of oxygen, producing Sn + α-W in the range 600–850°C. Some activation energy data are given for the reduction process.     

Electronic state and local surrounding of <Superscript>119</Superscript>Sn in calcium-substituted holmium orthochromites

The influence of Ca²⁺ doped into the holmium sublattice on the magnetically active surrounding of Sn⁴⁺ ions located in the chromium sublattice of Ho_1–x Ca _x Cr_0.997Sn_0.003O₃ (x = 0, 0.003, and 0.1) compounds was studied by ¹¹⁹Sn Mössbauer spectroscopy. At concentrations [Ca] = [Sn] = 0.3 mol %, an increase was observed in the spectral contribution of Sn⁴⁺ sites, having the full number of nearest-neighbor Cr³⁺cations (n = 6), where they perceived a magnetic field H(Sn)_{4.2 K} = 82 kOe, compared to the contribution of the relevant sites in the undoped chromite (x = 0). This observation was interpreted as resulting from a reduced probability of appearance of Cr³⁺ vacancies in the nearest surrounding of heterovalent Sn⁴⁺ ions. For x = 0.1, on the contrary, the ¹¹⁹Sn spectrum revealed a reduced contribution from the Sn⁴⁺ sites with n = 6. This evolution is shown not to be due neither to the appearance of Cr⁴⁺ nor Cr⁶⁺ ions in the nearest neighborhood of Sn⁴⁺ in the chromium sublattice to balance the charge deficiency of the Ca²⁺ ions doped into the holmium sublattice. This allowed us to suggest that the observed effect was due to the onset of Sn⁴⁺ segregations in the structure of Ho_0.9Ca_0.1Cr_0.997Sn_0.003O₃, which contained a far greater amount of Ca²⁺ ions whose charge deficiency was balanced mostly by Cr⁴⁺ formation. Studies of samples that were prepared under a hydrogen atmosphere revealed the reduction of Sn⁴⁺ to the oxidation state +2, with the concomitant stabilization of the formed Sn²⁺ ions on crystallite surfaces on sites having low coordination numbers.     

Phase equilibria in the Ag4SSe–As2Se3 system

The phase diagram of the system Ag₄SSe–As₂Se₃ is studied by means of X-ray diffraction, differential thermal analyses and measurements of the microhardness and the density of the materials. The unit-cell parameters of the intermediate phases 3Ag₄SSe·As₂Se₃ (phase A) and Ag₄SSe·2As₂Se₃ (phase B) are determined as follows for phase A: a=4.495 Å, b=3.990 Å, c=4.042 Å, α=89.05°, β=108.98°, γ=92.93°; for phase B: a=4.463 Å, b=4.136 Å, c=3.752 Å, α=118.60°, β=104.46°, γ=83.14°. The phase 3Ag₄SSe·As₂Se₃ and Ag₄SSe·2As₂Se₃ have a polymorphic transition α?β consequently at 105 and 120°C. The phase A melts incongruently at 390°C and phase B congruently at the same temperature.     

Vaporization thermodynamics of PdAsx (liquid), Pd0.75(As1 − xBx)0.25 (liquid) and elemental arsenic

Liquid PdAs_x, and Pd_0.75(As_{1 − x}B_x)_0.25 were studied by mass spectrometry combined with Knudsen effusion to determine the variation of arsenic and palladium activity with composition and temperature. Equations are given which describe the thermodynamic properties. At 1200 K, Pd_0.75As_0.25 is the congruently vaporizing composition and the high palladium phase limit is Pd_0.79As_0.21.The thermodynamic properties of the binary liquid are essentially unchanged by carbon or tungsten saturation. However, the activity of palladium in Pd(s) is lowered causing the liquid phase boundary to move to a higher arsenic composition.The Pd_0.75(As_{1 − x}B_x)_0.25 liquid has a positive deviation from ideality which indicates a repulsive energy between arsenic and boron in solution.The arsenic monomer pressure over elemental As(1) can be represented by log₁₀P(atm) = −14846/T + 7.116 between 1400 K and 1700 K.     

K2Mg5−xSn3 and K3Mg18Tt11 (Tt=Sn, pb) with two types of Mg-Sn/Pb frameworks

K₂Mg_5−xSn₃ (x=0.28) and K₃Mg₁₈Tt₁₁ (Tt=Sn, Pb) have been synthesized by reacting the mixture of the corresponding pure elements at high temperature, and structurally characterized by single-crystal X-ray diffraction studies. K₂Mg_5−xSn₃ (x=0.28) is isostructural with Ni_7−xSbQ₂ (Q=Se, Te) series and features 2D corrugated [Mg_5−xSn₃] layers that are separated by K⁺ cations. The structure of K₃Mg₁₈Tt₁₁ (Tt=Sn, Pb) is closely related to the Ho₂Rh₁₂As₇ structural type and features 3D [Mg₁₈Tt₁₁] framework composed of 1D [Mg₁₈Tt₁₁] columns that are interconnected via Mg-Tt bonds, forming 1D hexagonal tunnels occupied by the K+ cations. Electronic structure calculations indicate that Mg atoms can function as either electron donor or as a participator in the network along with Tt atoms. Magnetic property measurements and band structure calculations indicate that these compounds are metallic.