Ce(Au,Sb)2 with UHg2 structure type, a new member of the AlB2 family

A new ternary compound Ce(Au,Sb)₂, with a homogeneity range has been observed from X-ray powder diffraction of as cast alloys, a = 4.743–4.712 Å, c = 3.567–3.768 Å. Its crystal structure was investigated by X-ray diffraction from Ce(Au_1−xSb_x)₂ (x = 0.266) single crystal: CAD-4 automatic diffractometer, Mo K radiation, a = 4.7256(6) Å, c = 3.6711(6) Å, P6/mmm space group, V = 70.997(17) Å³, Z = 1, ρ = 10.732 Mg/m³, μ = 76.369 mm⁻¹, R₁ = 0.0415, wR₂ = 0.0793 for 99 reflections with I > 2σ(I₀). The coordination polyhedron of X (X = 0.734Au + 0.266Sb) atom is a full-capped trigonal prism [XCe₆X₃X₂]. Ce atom is coordinated by 14 atoms: [CeX₁₂Ce₂]. The compound is isotypic with UHg₂ structure, a deformation derivative of AlB₂ structure type. It forms isostructural compounds with La and Pr.     

On the crystal structure of new series of compounds, RPt2+xSb2−y (x = 0.125, y = 0.25; R = La, Ce, Pr)

A new compound CePt_2+xSb_2−y (x = 0.125, y = 0.25) was synthesized by arc-melting of the elements. The chemical and structural characterizations were carried out at room temperature on as-cast samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. According to the results of X-ray single crystal diffraction this antimonide crystallizes in I4cm space group (no. 108), Z = 32, ρ = 12.19 Mg/m³, μ = 89.05 mm⁻¹ (a = 12.5386(3) Å, c = 21.4692(6) Å (crystal I) and a = 12.5455(2) Å, c = 21.4791(5) Å (crystal II)). The structure and composition were confirmed by powder X-ray diffraction (a = 12.4901(2) Å, c = 21.3620(4) Å) and EDS-microanalysis respectively. Isotypic compounds were observed with La and Pr from X-ray powder diffraction of as-cast alloys at room temperature (a = 12.6266(4) Å, c = 21.4589(6) Å for LaPt_2+xSb_2−y and a = 12.5184(5) Å, c = 21.4178(7) Å for PrPt_2+xSb_2−y). The CePt_2+xSb_2−y structure is derived from CaBe₂Ge₂ (a = 2a₀ − 2b₀, b = 2a₀ + 2b₀, c = 2c₀) and comprises a new atomic arrangement with both vacancy on 4(b) pyramidal site and substitution of antimony atoms (X) by platinum (B) in the B–XX–B layers (referring to the subcell structure) forming two B––1/2B1/2XX–3/4B and two X–BB–X layers per cell. The structure of CePt_2+xSb_2−y is compared with those reported before for URh_1.6As_1.9 and CeNi_1.91As_1.94.     

Structural investigation of ternary RIr3B2 compounds (R=Ce and Pr)

Structural studies were performed for the ternary RIr₃B₂ compounds (R=Ce and Pr) from as cast samples. The crystal structure of the ternary boride CeIr₃B₂ (CeCo₃B₂ structure type, space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 ų, ρ_x=15.154 g cm⁻³) was refined to R₁=0.0470, wR₂=0.1240 from single-crystal X-ray diffraction data. The new ternary boride PrIr₃B₂ was found to be isostructural with the CeIr₃B₂ compound. Its lattice parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray powder diffraction data.     

Nd11Pd4In9 compound – A new member of the homological series based on AlB2 and CsCl types

The Nd₁₁Pd₄In₉ compound was prepared by arc melting of pure metals under an argon atmosphere. Crystal structure was refined from X-ray single crystal diffractometer data (space group Cmmm, a = 14.843(3), b = 22.284(3), c = 3.7857(6) Å, Z = 2, R_I = 0.0584, 653 F₂ values). It has own structure type and together with Mn₂AlB₂, Cr₃AlB₄, Mo₂FeB₂ and Lu₅Ni₂In₄ structure types belongs to homological series based on AlB₂ and CsCl structure types with common formula R_m+nM_2nX_m.     

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.     

Ba3YB3O9: phase transition and crystal structure

A new modification of the compound Ba₃YB₃O₉, β phase, has been attained through solid phase transition from phase at 1125–1134 °C. β-Ba₃YB₃O₉ crystallizes in the hexagonal space group with cell parameters a=13.0529(8) Å, c=9.5359(9) Å. The crystal structure of -Ba₃YB₃O₉ has been determined from powder X-ray diffraction (XRD) data. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=8.8%, and R_wp=11.8% with R_exp=5.65%. In its structure, the isolated [BO₃]³⁻ anionic groups are parallel to each other and distributed layer upon layer along the c-axis. The Y atoms are six-coordinated by the O atoms to form octahedra. The result of IR spectrum confirmed the existence of [BO₃]³⁻ triangular groups.     

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

The effects of milling and doping NaAlH₄ with TiCl₃, TiF₃ and Ti(OBuⁿ)₄, and of cycling doped NaAlH₄ have been investigated by infrared (IR) and Raman spectroscopy and X-ray powder diffraction. Milling and doping produce similar effects. Both decrease the crystal domain size (900 Å for milled and 700 Å for doped, as compared to 1600 Å for unmilled and undoped NaAlH₄) and increase anisotropic strain (by a factor >2.5, mainly along c). They also influence structure parameters such as the axial ratio c/a, cell volume and atomic displacement amplitudes. They show IR line shifts by 15 cm⁻¹ to higher frequencies for the Al–H asymmetric stretching mode ν₃, and by 20 cm⁻¹ to lower frequencies for one part of the H–Al–H asymmetric bending mode ν₄, thus suggesting structural changes in the local environment of the [AlH₄]⁻ units. The broad ν₃ bands become sharpened which suggests a more homogeneous local environment of the [AlH₄]⁻ units, and there appears a new vibration at 710 cm⁻¹. The Raman data show no such effects. Cycling leads to an increase in domain size (1200–1600 Å), IR line shifts similar to doped samples (except for TiF₃: downward shift by 10 cm⁻¹) and a general broadening of the ν₃ mode that depend on the nature of the dopants. These observations support the idea that some Ti diffusion and substitution into the alanate lattice does occur, in particular during cycling, and that this provides the mechanism through which Ti-doping enhances kinetics during re-crystallisation.     

Investigation of cation-deficient quaternary thiospinels: single crystal study of Ag1.4Cr1.47Sn2.53S8

Single crystals of the quaternary thiospinel Ag_1.41(1)Cr_1.47(5)Sn_2.52(5)S₈ have been obtained by heating stoichiometric mixtures of elemental metals and sulfur at 750 °C. Structural analysis by single crystal X-ray diffraction shows that the above phase crystallizes in the space group with a = 10.4142(3) Å (R₁ = 0.0156 and wR₂ = 0.0416). The Ag-deficiency has been confirmed by solving the structures of crystals prepared in different batches and was observed to vary slightly between crystals. Magnetic studies on a monophasic powder sample with a nominal composition of Ag_1.63CrSn₃S₈ indicates anti-ferromagnetic ordering at low temperature. The high temperature susceptibility leads to a magnetic moment of 3.45 B.M. suggesting that chromium exists predominantly in a trivalent state.     

Synthesis and crystal structure of CaAgBi and BaAg1.837Bi2

Two ternary alkali earth silver bismuthides, CaAgBi and BaAg_1.837Bi₂, have been synthesized by solid-state reactions of the corresponding metals in welded Nb tubes at high temperature. Their structures have been established by single-crystal X-ray diffraction studies. CaAgBi crystallizes in the hexagonal space group P6₃mc (No.186) with cell parameters of a = b = 4.8113(4) Å, c = 7.8273(9) Å, V = 156.92(3) Å³, and Z = 2. BaAg_1.837Bi₂ belongs to tetragonal space group P4/nmm (No.129) with cell parameters of a = b = 4.9202(2) Å, c = 11.628(1) Å, V = 281.50(3) Å³, and Z = 2. The structure of CaAgBi is of the LiGaGe type, and features a three-dimensional four-connected (3D4C) anionic network with Ca²⁺ encapsulated in the channels formed by [Ag₃Bi₃] six-membered rings. BaAg_1.837Bi₂ is isostructural with CaBe₂Ge₂, a variant of the tetragonal ThCr₂Si₂-type structure. Its structure exhibits a three-dimensional anionic network built of (0 0 1) and (0 0 2) puckered [Ag₂Bi₂] layers interconnected via additional Ag–Bi bonds along the c-axis. BaAg_1.837Bi₂ is metallic based on band structure calculations.     

Hydrothermal synthesis and characterization of a new layered compound Li2VGeO5

The new compound Li₂VGeO₅ with a layered structure has been synthesized at 580 °C via the hydrothermal method. The compound crystallizes in the space group P4/n of the tetragonal system with two formula units in a cell of dimensions a=6.5187(9) Å, c=4.5092(9) Å (T=298 K), V=191.61(5) Å³. The structure is composed of layers made of repeating [(VO₅)(GeO₄)]¹⁻ units. Li⁺ ions reside between the layers. The magnetic susceptibility data show an antiferromagnetic coupling below 5 K with C=0.47 emu K mol⁻¹, and θ=−13 K with μ_eff=1.89μ_B for each Li₂VGeO₅ unit.     

The crystal structure and magnetic properties of the Gd6Cr4Al43 compound

The crystal structure of intermetallic compound Gd₆Cr₄Al₄₃ has been investigated by means of X-ray diffraction data (Ho₆Mo₄Al₄₃ structure type, space group P6₃/mcm, Pearson symbol hP106, a = 10.9144(7) Å, c = 17.7361(13) Å).

SQUID magnetic measurements carried out for the title compound point to the existence of two antiferromagnetic phase transitions observed at T_N1 = 19.0(1) K and T_N2 = 6.8(1) K, respectively.     

Hydrogenation of oxygen-stabilized Zr3NiOx compounds

It is shown that oxygen-stabilized compounds Zr₃NiO_x (x=0.4, 0.6, 0.8, 1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with a filled Re₃B-type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.65 H/f.u. for Zr₃NiO_0.4 down to 5.58 H/f.u. for Zr₃NiO_1.0. A slight decrease of the crystal lattice parameters of the parent compounds and a substantial increase of these parameters for the saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, ΔV/at. H, increases from 2.333 ų for Zr₃NiO_0.4H_6.65 to 3.047 ų for Zr₃NiO_1.0H_5.58. Joint Rietveld refinement using X-ray and neutron powder diffraction data showed a distribution of deuterium atoms on similar positions as in oxygen-free Zr₃FeD_x and Zr₃CoD_x. The oxygen atoms move during deuteration from the octahedral site to one trigonal bi-pyramidal and two tetragonal interstices that are fully occupied in the saturated deuterides jointly by deuterium and oxygen. After deuterium desorption the oxygen atoms fully return to the initial octahedral site.     

High-pressure synthesis and crystal structures of two new polyphosphides, NaP5 and CeP5

Two novel polyphosphides, NaP₅ and CeP₅, were prepared in a BN crucible by the reaction of elemental components under a high pressure of 3 GPa at 800–950 °C. The X-ray structural analysis showed that NaP₅ crystallizes in an orthorhombic space group Pnma with a=10.993(2) Å, b=6.524(1) Å, c=6.903(1) Å, Z=4 and CeP₅ in the monoclinic group P2₁/m with a=4.9143(5) Å, b=9.6226(8) Å, c=5.5152(4) Å, β=104.303(6)°, Z=2. The crystal structure of NaP₅ consists of a three-dimensional framework _∞³[P₅]¹⁻ constructed by P---P bonds among four crystallographically inequivalent phosphorus sites, with large channels hosting the sodium cations, while CeP₅ is a layered compound containing _∞²[P₅]³⁻ polyanionic layers that are separated by Ce³⁺ ions. NaP₅ exhibits the diamagnetic behavior, while the temperature-dependent magnetic susceptibility of CeP₅ essentially follows the Curie–Weiss law.     

X-ray investigations of ternary R3Pd4Ge4 samples

Ternary R₃Pd₄Ge₄ samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er₃Pd_3.68(1)Ge₄ compound belongs to the Gd₃Cu₄Ge₄ structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R₁=0.0484 for 598 reflections with F_o>4σ(F_o) from X-ray single crystal diffraction data. No ternary R₃Pd₄Ge₄ compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd₃Pd₄Ge₄ and Eu₃Pd₄Ge₄ alloys and their crystallographic characteristics are the following: NdPd₂Ge₂, CeGa₂Al₂ structure type, space group I4/mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd_0.6Ge_1.4, AlB₂ structure type, space group P6/mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd_0.464(1)Ge_0.536(1))₂, KHg₂ structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R₁=0.0402 for 189 reflections with F_o>4σ(F_o) (X-ray single crystal diffraction data); Eu(Pd,Ge)₂, AlB₂ structure type, space group P6/mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2₁/c, and ternary compound with unknown structure (X-ray powder diffraction data).     

Synthese und kristallstruktur von KCr0,8Al0,2Mo2O8

Single crystals of KCr_0.8Al_0.2Mo₂O₈ were prepared and investigated by the X-ray diffractometer technique. It shows a structure type related to trigonal KAIMo₂O₈, monoclinic NaCrMo₂O₈ or orthorhombic KInMo₂O₈, space group C_2h⁶—C2/c; a=17.445 Å, b=5.649 Å, c=8.997 Å, β=119.37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ is characterized by isolated MoO₄ tetrahedra, isolated (Cr/Al)O₆ octahedra and a distorted square antiprism around K⁺. The crystal structure is discussed with respect to those of related compounds.

Zusammenfassung

Einkristalle von KCr_0.8Al_0.2Mo₂O₈ wurden synthetisiert und mit Vierkreisdiffraktometertechnik röntgenographisch untersucht. Sie zeigen einen mit trigonal-KA1Mo₂O₈, monoklin-NaCrMo₂O₈ oder orthorhombisch-KlnMo₂O₈ verwandten Strukturtyp, Raumgruppe C_2h⁶—C2/c; a=17,445 Å, b=5,649 Å, c=8,997 Å, β=119,37°; Z=4. KCr_0.8Al_0.2Mo₂O₈ zeichnet sich durch isolierte MoO₄-Tetraeder, isolierte (Cr/Al)O₆-Oktaeder und ein verzerrtes quadratisches Antiprisma um K⁺ aus. Die Kristallstruktur wird mit solchen verwandter Verbindungen diskutiert.     

An investigation of the structures of the compounds in the tin-rich part of the Dy–Sn system: Crystal structure of Dy5Sn11 and Dy5Sn13

The structural properties of the compounds in the tin-rich part of the dysprosium–tin system have been studied by X-ray powder diffraction. The crystal structures of six compounds DySn_2+x (0 < x < 1) have been characterized. There are four compounds with known structural types: DySn₂ with the ZrSi₂ structure, Dy₃Sn₇ with the Gd₃Sn₇ structure, Dy₂Sn₅ with the Er₂Ge₅ structure, DySn₃ with the DyGe₃ structure and two compounds characterized by new body-centred orthorhombic types (Immm): Dy₅Sn₁₁ (a = 4.411 Å, b = 42.50 Å and c = 4.328 Å) and Dy₅Sn₁₃ (a = 4.341 Å, b = 48.05 Å and c = 4.405 Å) which result from various insertions of AuCu₃ and Po slabs into the ZrSi₂ structure. The relationships and structural evolution are discussed.     

Influence of A-site cation size-disorder on structural, magnetic and magnetocaloric properties of La0.7Ca0.3−xKxMnO3 compounds

The structural and magnetic properties of perovskite oxides La_0.7Ca_0.3−xK_xMnO₃ (0 ≤ x ≤ 0.15) have been investigated to explore the influence of the A-site cation size-disorder (σ²). The materials were prepared by the solid-state method and then characterized by X-ray diffraction (XRD). The XRD data have been analyzed by Rietveld refinement technique. For K doping concentration x ≤ 0.075, the samples crystallize in the orthorhombic structure, while for x ≥ 0.1, the structure becomes rhombohedral. The variation of the magnetization M as a function of the applied magnetic field μ₀H reveals the presence of a structural distortion leading to a reduction of the magnetization at low μ₀H values. When increasing μ₀H, the structural distortion decreases and for a high applied magnetic field, the M (μ₀H) curves saturate indicating the disappearance of the structural distortion. The influence of K doping concentration and the applied magnetic field on the magnetocaloric properties has been considered. A large magnetic-entropy change (|ΔS_M|  5 J/kg K) is obtained in all samples at Curie temperatures between 270 and 280 K for an applied magnetic field of 3 T. These results show that these materials can be used as candidates for magnetic refrigerants near room temperature.     

UCo2Sn, UCo4Sn and UCo5Sn: a crystallographic and magnetic investigation

In our investigation of Co-rich alloys in the ternary U–Co–Sn system, we have identified three intermetallic compounds with composition UCo₂Sn, UCo₄Sn and UCo₅Sn, respectively. The existence and the crystal structure of the first compound, already known in the literature, have been confirmed, while the latter two compounds have been identified for the first time. The crystal structure of these compounds was determined by X-ray diffraction methods, performed both on powders (all samples) and single crystals (UCo₄Sn and UCo₅Sn). The crystal data are as follows (lattice constants from Guinier powder patterns): UCo₂Sn [UPd₂Sn-type, orthorhombic, oP16-Pnma, a = 9.402(3), b = 4.321(1), c = 6.615(2) Å], UCo₄Sn [MgCu₄Sn-type, cubic, , a = 6.992(2) Å] and UCo₅Sn [CeCu_4.38In_1.62-type, orthorhombic, oP56-Pnnm, a = 10.250(1), b = 16.012(2), c = 4.837(1) Å]. The physical properties of the compounds have been studied by electric transport (1.5–300 K), heat capacity (1.8–40 K) and magnetic measurements (1.8–300 K). The magnetisation data reveal weakly paramagnetic behaviour (with weak low temperature upturn due to parasitic impurity phases) in all the three alloys and absence of long-range magnetic ordering, despite the presence of uranium and a substantially high concentration of cobalt. The results for UCo₂Sn are in agreement with earlier reports in the literature. The magnitudes of the coefficients of the linear term in the heat capacity and the T² term in the low temperature resistivity track the room temperature magnetisation.     

Electronic structure and thermoelectric power of CeNi4Si

The studies of the thermoelectric power and band structure calculations for CeNi₄Si are reported. These studied are supported by magnetic susceptibility, electrical resistivity, specific heat and X-ray photoemission spectroscopy measurements. CeNi₄Si is paramagnetic down to 2 K and follows the Curie–Weiss law with μ_eff = 0.52μ_B/f.u. and the paramagnetic Curie temperature θ_P = −2 K. This effective paramagnetic moment is lower than the free Ce³⁺ value. The obtained values for the f occupancy n_f and for the coupling Δ of the f level with the conduction states are in good agreement with the values found for mixed valence compounds. Below the Fermi energy the total density of states contains mainly the d states of Ni atoms. The narrow peaks of the f states of Ce atoms were found above the Fermi level. CeNi₄Si is characterized by γ = 16 mJ mol⁻¹ K⁻² and θ_D = 335 K.     

Structure and anelasticity of Fe3Ge alloy

The structure and anelastic properties of Fe-27 at.%Ge alloy are studied. Long-term annealing of the as-cast alloy at 1273 K leads to homogenising and several transformations take place below 873 K. These low temperature transitions are studied by several methods: X-ray diffraction, calorimetry, vibrating-sample magnetometry and internal friction, and are related to magnetic transitions in the different phases. A high stability of the hexagonal (D0₁₉) phase at room temperature is recorded. The hexagonal β (B8₁) phase is also detected in the alloy at room temperature, while the presence of the ′ and phases is doubtful. A broad internal friction relaxation peak with the relaxation strength of Δ = 0.0036, the activation energy of about 1.78 eV and the preexponential relaxation time of τ₀ = 2 × 10⁻¹⁷ s was discovered and classified as the Zener peak in both the and β phases.