Lanthanum–lithium–sodium double chromates as ionic conductors

Lanthanum–lithium–sodium double chromates Li_1−xNa_xLa(CrO₄)₂ were prepared and analysed by means of admittance spectroscopy. Their a.c. conductivity parameters are correlated with structural details of high and low temperature forms of pure lanthanum–lithium double chromates. Lithium compounds show the lowest conductivity values and the highest activation energy for ion motion, while the sample Li_0.5Na_0.5La(CrO₄)₂ exhibits the highest conductivity 10⁻⁵ S cm⁻¹ and the lowest activation energy 0.58 eV.     

超级双相不锈铸钢电化学极化表面腐蚀产物的XPS分析

采用X射线光电子能谱(XPS)技术研究了超级双相不锈铸钢在人工海水中经电化学极化后表面腐蚀产物。结果表明：双相不锈钢在人工海水中极化后的钝化膜表层主要以CrO₃、CrOOH、Cr(OH)₃和Fe(OH)₃等氢氧型化合物为主,内层主要以CrO₃、Cr₂O₃、FeO和Ni₂O₃等氧化物为主,同时膜内层存在Fe、Cr、Ni和Mo单质。MoO₄^2-和NH₄⁺吸附在钝化膜表面,对钝化膜起到保护作用。     

Crystal structures and structural relationships of KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2

The new phases KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe₂(SeO₂OH)(SeO₃)₃: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 ų, Z = 2; SrCo₂(SeO₂OH)₂(SeO₃)₂: space group P2ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 ų , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively.

The atomic arrangement in KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂ is based on isolated MO₆ octahedra (M = Fe³⁺, Co²⁺), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se⁴⁺ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe₂(SeO₃)₄ by distance least squares refinement (program ).     

Phase relationships and crystallography in the pseudobinary system Gd5Si4---Gd5Ge4

A study of phase relationships and crystallography in the pseudobinary system Gd₅(Si_xGe_1−x)₄ revealed: (1) that both terminal binary compounds Gd₅Si₄ and Gd₅Ge₄ crystallize in the Sm₅Ge₄-type orthorhombic structure, and (2) the appearance of an intermediate (ternary) phase with a monoclinic crystal structure which is similar to both Gd₅Si₄ and Gd₅Ge₄. The formation of the monoclinic phase at 0.24≤x≤0.5 [between Gd₅(Si_0.96Ge_3.03)Gd₅(Si₁Ge₃) and Gd₅(Si₂Ge₂)] is probably due to the large difference in bonding characteristics of Si and Ge in the Gd₅Si₄-Gd₅Ge₄ pseudobinary system which limits the ability of the mutual substitution of Si for Ge and vice versa without a change of the crystal structure. For the composition Gd₅(Si₂Ge₂) the lattice parameters of the monoclinic structure (space group P112₁/a) are a=7.580865), b=14.802(1), c=7.7799(5)Å, γ=93.190(4)°. A distinct difference in the magnetic behaviors of the alloys from three different phase regions in this system follows the distinct difference in the crystal structures observed for the alloys from the three phase regions.     

Peculiarities of the R3(Fe,Si)29 phase formation in the Sm---Fe---Si system

The phase content of the Sm(Fe_1−xSi_x)_y alloys (0.05≤x≤0.15; 8.5≤y≤12) has been studied by X-ray diffraction using micromonocrystals. The compounds Sm₂(Fe,Si)₁₇, Sm(Fe,Si)₁₂ and a novel Sm₃(Fe,Si)₂₉ compound with a monoclinic unit cell are found. The lattice parameters of Sm₃(Fe,Si)₂₉ are: a=1.056 nm, b=0.850 nm, c=0.966 nm, β=96.8°. This compound forms as a result of a solid state transformation from the high-temperature Sm₂(Fe,Si)₁₇ phase. Diffuse effects observed in rocking photographs suggest transition structures arising from this transformation. The Curie temperatures of Sm₃(Fe,Si)₂₉ vary in the interval 496–521 K.     

Magnetocrystalline anisotropy and exchange interactions in the novel R3(Fe, V)29 compounds (R = Y, Nd, Sm)

A type of magnetocrystalline anisotropy and exchange interactions of the novel ternary R₃(Fe, V)₂₉ compounds (R = Y, Nd, Sm) have been investigated. The compounds are uniaxial ferromagnets with easy magnetization direction along the [ 0 1] axis of the monoclinic lattice at room temperature. The temperature variations of the magnetic moment and the first anisotropy constant for Y₃(Fe, V)₂₉ are presented. The first order magnetization process along the hard magnetization direction takes place for Sm₃(Fe, V)₂₉ at T < 120 K. A magnetic anomaly is detected in the temperature dependence of the a.c. susceptibility for Nd₃(Fe, V)₂₉ which can be related to a spin reorientation.     

Structural chemistry and phase relations in intermetallic systems Ti–{Pd,Pt}–Al

Phase relations in the ternary systems Ti–{Pd,Pt}–Al have been experimentally established for the partial isothermal sections at 950°C in the Pd/Pt-poor region (<25 at.% Pd/Pt). The investigation is based on X-ray powder diffraction, metallography, SEM and EMPA techniques on about 45 alloys, which were prepared by various methods employing arc melting, levitation melting under argon or by powder reaction sintering in closed crucibles. Three ternary compounds were observed at 950°C in the Ti–Pd–Al system: τ₃-(Ti,Pd)(Ti,Pd,Al)₂ with Laves-MgZn₂-type, τ₂-(Ti,Al)₆(Ti,Pd,Al)₂₃₊₁ with a filled Th₆Mn₂₃₊₁-type and τ₁-(Ti,Pd,Al)(Ti,Pd,Al)₃ with AuCu₃-type. Due to the wide extension of the Laves phase field, there is no compatibility among γTiAl and τ₂-(Ti,Al)₆(Ti,Pd,Al)₂₃₊₁. The Ti–Pt–Al system at 950°C contains three ternary compounds: τ₃-(Ti,Al)(Ti,Pt,Al)₂ with Laves-MgZn₂-type, τ₂-(Ti,Al)₆(Ti,Pt,Al)₂₃₊₁ with the filled Th₆Mn₂₃₊₁-type and τ₁-(Ti,Pt,Al) with Cu-type. Compatibility exists for Al-rich γTiAl and τ₂-(Ti,Al)₆(Ti,Pt,Al)₂₃₊₁. The typical feature for both alloy systems studied is the three-phase equilibrium: ₂Ti₃Al+γTiAl+τ₃-(Ti,Pd/Al)(Ti,Pd/Pt,Al)₂. The solid solubility of palladium and platinum in the binary titanium aluminides, as observed from EMPA and X-ray data, is rather small and at 950°C accounts to about 2.5 at.% Pd and 2.0 at.% Pt. Two new oxide compounds Ti₃PdAl₂O_x and Ti₃PtAl₂O_x with a filled Ti₂Ni-type are observed in both quaternary systems.     

Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

Thermal expansion studies on Th(MoO4)2, Na2Th(MoO4)3 and Na4Th(MoO4)4

Thermal expansion behavior of Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO₄)₂ was synthesized by reacting ThO₂ with 2 mol of MoO₃, at 1073 K in air and Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were prepared by reacting Th(MoO₄)₂ with 1 and 2 mol of Na₂MoO₄, respectively at 873 K in air. The XRD data of Th(MoO₄)₂ was indexed on orthorhombic system where as XRD data of Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO₄)₂, Na₂Th(MoO₄)₃ and Na₄Th(MoO₄)₄ were determined from the high temperature data.     

Structural and thermal studies on Na2U(MoO4)3 and Na4U(MoO4)4

In Na–U(IV)–Mo–O system, two quaternary compounds Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were prepared by solid state reactions of Na₂MoO₄, UMoO₅ and MoO₃ in the required stoichiometric ratio at 500 °C in evacuated sealed quartz ampoules. The crystal structure of both the compounds were derived from X-ray powder diffraction data in the tetragonal system by Rietveld profile method. Na₂U(MoO₄)₃ has scheelite structure, whereas Na₄U(MoO₄)₄ has scheelite superlattice structure.

TG curves of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ did not show any significant weight change up to 750 °C in an inert atmosphere. During the heating cycle in an inert atmosphere, DTA curves of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ showed endothermic peaks due to the melting of the compounds at 740 °C and 730 °C, respectively. Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄, when heated in air atmosphere at 1200 °C, decomposed to form Na₂U₂O₇ which was confirmed by weight loss calculation and XRD.     

Preparation, characterization and crystal structure of 4,4′-bipyridinium nitrate trinitratodioxo-uranium(VI) and 4,4′-dipyridinium diaqua hexanitrato-thorate(IV)

The compounds 4,4′-bipyridinium nitrate trinitratodioxo-uranium(VI) [UO₂(NO₃)₃][4,4′-bipyH]·HNO₃ (1) and 4,4′-dipyridinium diaqua hexanitrato-thorate(IV) [Th(NO₃)₆][4,4′-bipyH₂]·2H₂O (2) were prepared and characterized. Their crystal structures have been determined using X-ray diffraction techniques. Both complexes crystallize in the monoclinic system with space groups P2₁/c for 1 and C2/c for 2. The geometry of the anion in 1 is a distorted hexagonal bipyrimidial coordination, while that in 2 is a distorted icosahedron. The cation in 1 is formed from hydrogen-bonded monoprotonated bipyridyl with a neutral nitrate molecule, whereas the cation in 2 is formed from hydrogen-bonded diprotonated bipyridyl with a water molecule. The cations in both complexes are connected with the anions through hydrogen bonds via the nitrate molecule in 1 and the water molecule in 2.     

Magnetic properties of novel compounds R3(Fe,Cr)29Xy (R=Nd, Sm and X=N, C)

The novel ternary rare-earth iron-rich interstitial compounds R₃(Fe,Cr)₂₉X_y (R=Nd, Sm and X=N, C) with the monoclinic Nd₃(Fe,Ti)₂₉ structure have been successfully synthesized. Introduction of the interstitial nitrogen and carbon atoms led to a relative volume expansion ΔV/V of about 6% and an enhancement of Curie temperatures T_c about 268 K for the nitride and about 139 K for the carbide, respectively. The Nd₃Fe_24.5Cr_4.5X_y compounds have a planar anisotropy at room temperature. A first-order magnetization process (FOMP) with critical field B_cr=4.4 T and 3.1 T at room temperature were observed for the Nd-nitride and carbide compounds, respectively. The Sm₃Fe₂₄Cr₅X_y compounds were found to have a large uniaxial anisotropy of about 18 T at 4.2 K and about 11 T at 293 K. A FOMP with B_cr=2.3 T was also observed in the Sm-nitride compounds at 4.2 K. Magnets with coercivity of μ_OjH_c0.8 T at 293 K has been successfully developed from the Sm₃Fe₂₄Cr₅X_y (X---N and C) phases.     

The ytterbium-copper-aluminium system

The isothermal section of the Yb---Cu---Al phase diagram at 870 K over the whole concentration region has been constructed using X-ray structure and phase analysis. We have confirmed the existence of earlier reported ternary compounds: YbCuAl (ZrNiAl type) and YbCu₄Al₈ (CeMn₄Al₈ type); the previously reported compound YbCu₄Al proved to be a solid solution of aluminium in the binary compound YbCu₅ (CaCu₅). New ternary aluminides such as Yb₄(Cu_0.26Al_0.74)₃₃ (new structure type), Yb₂(Cu_0.57Al_0.43)₁₇ (Th₂Zn₁₇), Yb(Cu_0.85Al_0.15)₆ (YbMo₂Al₄)₇ Yb₆(Cu_0.74Al_0.26)₂₃ (Th₆Mh₂₃) and Yb(Cu_0.30Al_0.70)₃ (PuNi₃) have been prepared for the first time and their crystal structures have been determined. The limits of solid solutions of the binary compound YbCu₅ and the homogeneity ranges of the ternary phases Yb(CuAl)₁₂, Yb(CuAl)₁₇ and Yb(CuAl)₂ have been established.     

Structural investigation of the alluaudite-like mixed-valence iron phosphate: Na1.25Mg1.10Fe1.90(PO4)3

A new mixed-valence iron phosphate Na_1.25Mg_1.10Fe_1.90(PO₄)₃ has been synthesized as single crystals by a flux technique and its structure has been refined from X-ray data to a residual R₁ = 0.032. The compound crystallizes in the monoclinic space group C2/c with the parameters: a = 11.7831(3) Å, b = 12.4740(3) Å, c = 6.3761(2) Å, β = 113.643(2)° and Z = 4. The structure belongs to the alluaudite structural type, and thus it obeys to the X(2)X(1)M(1)M(2)₂(PO₄)₃ general formula. The X(2) and X(1) sites are occupied by sodium while the M(1) and M(2) sites feature a statistical distribution of iron and magnesium.

Additional information about the cation distribution has been extracted from a Mössbauer spectroscopy study which confirmed the mixed valency of the compound. A magnetic susceptibility study has also been undertaken and has shown the compound to be antiferromagnetic with a Neel temperature of about 35 K.     

The ternary system Al–Ni–Ti Part I: Isothermal section at 900°C; Experimental investigation and thermodynamic calculation

Phase relations in the ternary system Al–Ni–Ti have been experimentally established for the isothermal section at 900°C for concentrations 0.1x_Al0.7. The investigation is based on X-ray powder diffraction, metallography, SEM and EMPA-techniques on about 40 ternary alloys, prepared by argon-arc or vacuum-electron beam melting of proper elemental powder blends. The existence of four ternary compounds, τ₁ to τ₄, is confirmed, however, in contrast to earlier investigations at significantly different compositions and with different shape of the homogeneity regions. This is particularly true for the phase regions of τ₃-Al₃NiTi₂ with the MgZn₂-type structure ranging from Al₃₀Ni₂₈Ti₄₂ (composition lowest in Al) to Al₅₀Ni₁₆Ti₃₄ (composition richest in Al) and for τ₂-Al₂NiTi. The complex atom site substitution mechanism in τ₃ changing from Ti/Al exchange at Al-poor compositions towards Ni/Al replacement for the Al-rich part was monitored in detail by quantitative X-ray powder diffraction techniques (Rietveld analyses). In contrast to earlier reports, claiming a two-phase region Ni{Al_xTi_1-x}₂+τ₃, we observed two closely adjoining three-phase equilibria: ₂-AlTi₃+Ni{Al_xTi_1-x}₂+ τ₄-AlNi₂Ti and ₂-AlTi₃+τ₃-Al₂NiTi₂+τ₄-AlNi₂Ti. The earlier reported “homogeneous phase at Al₂₃Ni₂₆Ti₅₁′” was shown by high resolution microprobe and X-ray diffraction measurements to be an extremely fine-grained eutectic. The experimental results are in fine agreement with the thermodynamic calculation.     

Complex susceptibility and penetration depth of BEDT-TTF based layered superconductors

We have obtained the parallel penetration depth of two representative compounds of layered organic superconductors, κ-(BEDT-TTF)₂Cu[N(CN)₂]Br and -(BEDT-TTF)₂NH₄(SCN)₄ by ac susceptibility measurements. The former salt gives the depth of 190 μm, while that for the latter is 1.4 mm. These values demonstrate that the NH₄(SCN)₄ salt is more highly-two-dimensional than the Cu[N(CN)₂]Br salt. The ac susceptibility under dc magnetic field probes peculiarities of tile vortex dynamics.     

Crystal structure of the (ET)8[Hg4Br12· (PhCl)2] organic metal and the (ET)8[Hg4Br12·(MePbCl)2] organic semiconductor: The products of the same synthesis

X-ray study of the cation-radical salts (ET)₈[Hg₄Br₁₂·(PhCl)₂] (metal up to 90 K) and (ET)₈[Hg₄Br₁₂·(MePhCl)₂] (semiconductor) preparated in the same synthesis has shown considerable differences in the structures of their cationic and anionic layers. It is these differences that account for different electrophysical properties of these compounds.     

IR- und ramanspektren der rheniumclusterverbindungen Rb4Re6S13 und Cs4Re6S13,5

IR and Raman spectra of Rb₄Re₆S₁₃Rb₄[Re₆S₈]S_2/2(S₂)_4/2 and Cs₄Re₆S_13,5Cs₄[Re₆S₈]S_2/2(S₂)_3/2(S₃)_1/2 are presented and discussed with respect to the S₂ and S₃ bridging units and the ([Re₆S₈]S₆) clusters. The S---S stretching modes observed (425–480 cm⁻¹), which correlate fairly well with the respective S---S bond lengths, reveal mainly covalent nature of the disulfide groups present. The S₃ group could be identified by the spectra of Cs₄Re₆S_13,5. The bands of the rhenium sulfide units are significantly shifted to higher wavenumbers compared to those of ([Mo₆Cl₈]Cl₆)²⁻ and [Mo₆S₈] units (Chevrel compounds) despite the larger mass of rhenium. This indicates strong Re---Re and Re---S bonding.

Zusammenfassung

Die IR- und Raman-Spektren von Rb₄Re₆S₁₃Rb₄[Re₆S₈]S_2/2(S₂)_4/2 und Cs₄Re₆S_13,5Cs₄[Re₆S₈]S_2/2(S₂)_3/2(S₃)_1/2 werden mitgeteilt und im Hindblick auf die S₂- und S₃-Brücken sowie die ([Re₆S₈]S₆)-Baugruppen diskutiert. Die beobachteten S---S-Streckschwingungen (425–480 cm⁻¹) korrelieren mit den zugehörigen S---S-Bindungsabständen und weisen auf weitgehend kovalente Disulfid-Brücken hin. Die Trisulfid-Brücken konnten in den Spektren des Cs₄Re₆S_3,5 nachgewiesen werden. Die Schwingungsbanden der Rhenium-Schwefel-Baueinheiten sind im Vergleich zu denen der ([Mo₆Cl₈]Cl₆)²⁻- und [Mo₆S₈]-Einheiten (Chevrel-Phasen) trotz der gröβeren Masse des Rheniums deutlich zu gröβeren Wellenzahlen verschoben. Dies läβt auf sehr starke Re---Re- und Re---S-Bindungen schlieβen.     

Physical and chemical properties of MDSe-TTF and EDSe-TTF salts

The Se-containing unsymmetrical donor, MDSe-TTF and EDSe-TTF, were synthesized. θ-(MDSe-TTF)₂Au(CN)₂ and (MDSe-TTF)₂Aul₂ are metallic dawn to 15K and 40K respectively and in the former salt, the metal-insulator transition is suppressed down to 0.4K under 2kbar. The ESR measurements show that the intensity of (EDSe-TTF)₂Aul₂ remains finite at 4K, while (EDT-TTF)₂Aul₂ has a distinct T_MI = 40K. The Se-introduced donor salts show the metallic behaviors down to lower temperatures, compared with S-introduced analogue. Not only Aul₂ and Au(CN)₂ salts but also other salts are presented.     

Kinetic study on Li2.8(V0.9Ge0.1)2(PO4)3 by EIS measurement

Kinetics for lithium ion transfers in the fast ionic conductor Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ prepared by solid-state reaction method has been studied by electrochemical impedance spectroscopy (EIS) at various temperatures and the results were correlated with observed cathodic behavior. The specific conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ (x = 0.9–2.8) versus temperatures were analyzed from blocking-electrodes by Wagner's polarization method and the activation energy was calculated. It was observed that electronic conductivities of Li_x(V_0.9Ge_0.1)₂(PO₄)₃ increased with lithium contents in the materials. The compounds show a reversible capacity of 131 mAh g⁻¹ at low current density (13 mA g⁻¹). Modeling the EIS data with equivalent circuit approach enabled the determination of charge transfer and surface film resistances. The Li ion diffusion coefficient (D_Li⁺) versus voltage plot shows three valleys during the first charge cycle coinciding with the irreversible plateau of the voltage versus lithium content profiles reflecting the irreversible phase change in the compound. The obtained D_Li⁺ from EIS varies within 10⁻⁸ to 10⁻⁷ cm² s⁻¹, so Li_2.8(V_0.9Ge_0.1)₂(PO₄)₃ shows excellent chemical diffusion performance.