Determination of the structure of UFe2Al10 compound

The atomic structure of a new ternary phase UFe₂Al₁₀ appearing in the U–Fe–Al system was determined using direct methods applied to X-ray powder diffraction data. High resolution electron microscopy combined with the methods of crystallographic image processing was used for the verification of the structural model. The UFe₂Al₁₀ phase is orthorhombic and belongs to Cmcm space group, its unit cell contains 40 Al, eight Fe, and four U atoms. The lattice parameters obtained after Rietveld refinement are: a=8.919 Å, b=10.208 Å, and c=9.018 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p=5.9%, R_wp=8.1%, and R_b=2.9%.     

Structural and magnetic properties of Sm2Fe17−xCrxC2 nanocrystalline carbides with 0≤x≤2

The crystallographic and the Curie temperature of the Sm₂Fe_17−xCr_xC₂ (x=0.5, 1, 1.5 and 2) carbides have been extensively studied. X-ray diffraction studies have shown that all these alloys are approximately single phases corresponding to the Th₂Zn₁₇ type rhombohedral structure with a small amount of -Fe. The amount of this residual -Fe phase decreases with increasing the Cr atomic content. It decreases from 1 wt% for x=0.5 to 0.4 wt.% for x=2. The lattice parameter c increases as a function of the Cr atomic content x from x=0 to x=1.5 and then decreases. This is due to the Cr atoms which prefer to substitute the Fe atoms in the 6c sites located along the c-axis. The lattice parameter a and the unit-cell volume decrease in all substitution ranges. The insertion of the C atoms leads essentially to an increase of the distances between the 9d and 18h sites and the 9d–18f sites. The Curie temperature reaches a maximum value of 583 K for x=1.5 and then decreases to 551 K for x=2. The enhancement of the T_c for lower Cr contents is due to a lowering of the hybridization of the iron atoms with their neighbors, the magnetovolume effect and the reduction of antiferromagnetic interactions. However, the decrease in T_c for higher Cr content is due to the reduction in the number of Fe–Fe pairs due to the magnetic dilution effect. For given interatomic distances, the exchange coupling of the Cr–Cr atoms is not of antiferromagnetic type and the exchange integral of the Cr–Cr pair is higher than that of the Fe–Fe pair.     

Crystal field splitting and anomalous thermal expansion in YbVO4

We have investigated the Yb³⁺ crystal-field-level structure in YbVO₄ using inelastic magnetic neutron-scattering measurements and crystal-field model calculations. We determined the temperature dependence of the a and c lattice parameters of the tetragonal unit cell by neutron diffraction and observed a minimum at ca. 120 K in the c lattice parameter. This anomaly in the thermal expansion is interpreted as arising from a coupling of the anisotropic low-lying crystal-field states of the Yb³⁺ ions and the crystal lattice at low temperatures.     

Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds

The crystal structure of new ternary R₃Si_1.25Se₇ (R = Pr, Nd and Sm) compounds (Dy₃Ge_1.25S₇ structure type, Pearson symbol hP22.5, space group P6₃, a = 1.05268 (3) nm, c = 0.60396 (3) nm, R_I = 0.0897 for Pr₃Si_1.25Se₇; a = 1.04760 (3) nm, c = 0.60268 (3) nm, R_I = 0.0891 for Nd₃Si_1.25Se₇; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm₃Si_1.25Se₇) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom.     

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.     

Crystal structure, phase stability and elastic properties of the Laves phase ZrTiCu2

The crystal structure of the ternary Laves phase ZrTiCu₂ with unusual stoichiometry has been determined from combined refinement of X-ray powder, X-ray single crystal and neutron powder intensity data. The derived structure is of type MgZn₂ (space group P6₃/mmc) with lattice parameters a = 0.51491(3) nm, c = 0.82421(8) nm. Crystal symmetry and composition reveal a high degree of atomic disorder, because Ti and Zr atoms share the 4f sites, whereas Ti and Cu atoms are found at the 6h sites. The 2a sites, however, are exclusively occupied by Cu. Lattice parameters for alloys Zr_1−xTi_1−xCu_2+2x (annealed at 800 °C) as a function of the concentration of Cu for a constant ratio of Zr/Ti = 1 vary in a nonlinear way, which is consistent with the described complex atomic substitution mechanism. At a load of 2 N the micro-hardness was measured to be 7.5 ± 0.3 GPa, which is significantly larger than for most of the binary Ti–Cu or Zr–Cu phases. By a density functional theory ab initio approach the site preferences of Zr, Ti and Cu were calculated indicating that a random mixture of Ti and Cu atoms at the 6h lattice sites is a key factor to stabilize the proposed structure, which is unique for a Laves phase. Lattice parameters, elastic constants and shear moduli for polycrystalline ZrTiCu₂ were also derived. The Vickers hardness of 6.2 GPa was estimated by applying a correlation between shear modulus and hardness. Data as calculated by the ab initio approach are in good agreement with the experimental findings.     

Single crystal preparation and crystal structure of the Cu2Zn/Cd,Hg/SnSe4 compounds

Single crystals of Cu₂Zn/Cd/SnSe₄ were grown using a solution-fusion method. The crystal structure of the Cu₂Zn/Cd,Hg/SnSe₄ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the stannite structure (space group I 2m) with the lattice parameters: a=0.56882(9), c=1.13378(9) nm, c/a=1.993 (Cu₂ZnSnSe₄), a=0.58337(2), c=1.14039(4) nm, c/a=1.955 (Cu₂CdSnSe₄) and a=0.58288(1), c=1.14179(2) nm, c/a=1.959 (Cu₂HgSnSe₄). Atomic parameters were refined in the isotropic approximation (R_I=0.0517, R_I=0.0511 and R_I=0.0695 for Cu₂ZnSnSe₄, Cu₂CdSnSe₄ and Cu₂HgSnSe₄, respectively).     

Growth and dielectric properties of Ca3NbGa3Si2O14 crystals

A new langasite type single crystal Ca₃NbGa₃Si₂O₁₄ (CNGS) was grown by Czochralski (CZ) method. The structure of CNGS crystal was determined by X-ray powder diffraction, the lattice parameters were a=0.8087 ± 0.0001 nm, c=0.4974 ± 0.0002 nm, V=0.2817 ± 0.0002 nm³; The congruency of CNGS was examined by measuring the chemical composition of the grown crystal by quantitative X-ray fluorescent (XRF) analysis. The melting point of CNGS crystal was measured by using the differential scanning calorimetry (DSC). Dielectric properties of (1 1 0) wafer plate were studied in the temperature range from 298.15 to 873.15 K; the frequency dependence of dielectric loss in the frequency range 10 Hz–13 MHz was measured.     

Kristallstrukturen und Eigenschaften neuer ternärer iridiumphosphide

Four new ternary iridium phosphides were prepared by reaction of the elements at 900–1100 °C. Their structures were determined by means of single-crystal X-ray methods. EuIrP (a = 6.272(1) Å) and BaIrP (a = 6.531(1) Å) crystallize in a SrSi₂-type derivative structure (LaIrSi-type structure; P2₁3; Z = 4). EuIr₂P₂ (a = 6.671(1), c = 7.055(1) Å) and SrIr₂P₂ (a = 6.693(1), c = 7.061(1) Å) form a new structure (P3₂21; Z = 3). All the P atoms and half of the Ir atoms build up a three-dimensional framework with the Eu(Sr) atoms and the remaining Ir atoms in the cavities. The latter atoms form threefold screws along [001] with short Ir---Ir distances. Magnetic measurements of EuIrP and EuIr₂P₂ show that europium is divalent in both compounds.

Zusammenfassung

Vier neue ternäre Iridiumphosphide wurden durch Umsetzung der Elemente bei 900–1100 °C dargestellt. Die Bestimmung der Strukturen erfolgte mit Röntgen-Einkristallmethoden. EuIrP (a = 6,272(1) Å) und BaIrP (a = 6,531(1) Å) kristallisieren in einer Besetzungsvariante der SrSi₂-Struktur (LaIrSi-Typ; P2₁3; Z = 4). EuIr₂P₂ (a = 6,671(1), c = 7,055(1) Å) und SrIr₂P₂ (a = 6,693(1), c = 7,061(1) Å) bilden eine neue Struktur (P3₂21; Z = 3). Die P- sowie die Hälfte der Ir-Atome sind miteinander zu einem dreidimensionalen Gerüst verknüpft, in dem sich schraubenförmige Kanäle entlang [001] erstrecken. Diese werden von den Eu(Sr)- sowie den restlichen Ir-Atomen besetzt, wobei letztere in Form regulärer 3-zähliger Schrauben mit kurzen Ir---Ir-Abständen angeordnet sind. Magnetische Messungen an EuIrP und EuIr₂P₂ zeigen, daβ Europium in beiden Verbindungen zweiwertig vorliegt.     

Ce–Ti–Ge system at 1170 K

Phase equilibria in the Ce–Ti–Ge system were investigated by X-ray powder diffraction, electron probe X-ray analysis and the isothermal section at 1170 K was obtained. We confirmed the CeFeSi-type CeTiGe compound (a=0.4135 (1) nm, c=0.7921 (1) nm, space group P4/nmm, No. 129). A new compound, Ce₂₀Ti₂₀Ge₆₀, was found (a=0.3967(6) nm, c=6.054 (2) nm, space group P4). It is obvious that the ThSi₂-type Ce₃₃Ti₇Ge₅₄ compound (a=0.4217 (1) nm, c=1.4184 (3) nm, space group I4₁/amd, No. 141) belongs to the extended solid solution region of the ThSi₂-type CeGe₂ compound.     

Subsolidus phase relation in the system ZnO–Li2O–MoO3

The subsolidus phase relation of the system ZnO–Li₂O–MoO₃ has been investigated by X-ray diffraction (XRD) analyses. The phase diagram has been constructed. There are six binary compounds and one ternary compound in this system. The phase diagram comprises nine three-phase regions. The ternary compound Li₂Zn₂(MoO₄)₃ is refined by the Rietveld method. It belongs to an orthorhombic system with space group Pnma and lattice constants a = 5.1114 Å, b = 10.4906 Å, c = 17.6172 Å.     

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.     

Phase transformations after long-time annealing in metastable Fe–Cr alloy films prepared by pulsed laser deposition

Metastable Fe–Cr alloy films of various composition prepared by cross-beam pulsed laser deposition using two different procedures are investigated by wide-angle X-ray scattering. Depending on the Fe–Cr composition of the samples in an extended range, a body-centered cubic (bcc) phase or metastable phases with body-centered tetragonal (bct), face-centered orthorhombic (fco) or primitive orthorhombic (po) and primitive cubic (pc) lattices are formed in the films prepared by simultaneous co-deposition of Fe and Cr. In the films produced by layer-by-layer deposition of thin separate Fe and Cr layers (thickness of about 1 nm), only bcc and bct Fe–Cr phases were observed. A long-time annealing (50 h) at a temperature of 425 °C near the low-temperature existence limit of the σ-phase under equilibrium conditions followed by slow cooling (rate 0.5 °C/min) has been performed and various phase transformations were observed. In addition to known equilibrium and metastable Fe–Cr crystalline phases (mainly bcc and bct phases in the films prepared by layer-by-layer technique and bcc, bct and σ-FeCr phases in co-deposited films), a new metastable Fe–Cr superstructure characterised by a primitive tetragonal lattice with parameters a and c of about 0.57 and 0.63 nm, respectively, has been identified. It is shown that the formation of ″-crystallites with preferred orientation in the metastable Fe–Cr alloy films during dedicated long-time annealing gives rise to a spatially periodic modulation of chemical composition resulting in the formation of multilayers with periods of one or a few atomic monolayers of individual Fe and Cr components.     

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.     

Crystal structures of the Ag4HgGe2S7 and Ag4CdGe2S7 compounds

The crystal structures of the Ag₄HgGe₂S₇ and Ag₄CdGe₂S₇ compounds were investigated using X-ray powder diffraction. These compounds crystallize in the monoclinic Cc space group with the lattice parameters a=1.74546(8), b=0.68093(2), c=1.05342(3) nm, β=93.398(3)° for Ag₄HgGe₂S₇ and a=1.74364(8), b=0.68334(3), c=1.05350(4) nm, β=93.589(3)° for Ag₄CdGe₂S₇. Atomic parameters were refined in the isotropic approximation (R_I=0.0761 and R_I=0.0727, respectively).     

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.     

Formation of a tetragonal phase hydride in Ti–Mo–H system

The structural relationship between the hydride phases in Ti–Mo–H solid solution system (Mo content up to 15 at% in the alloy) during dehydrogenation process under annealing has been studied by conventional and in situ X-ray powder diffraction and transmission electron microscopy (TEM) analysis. During dehydrogenation, the saturated hydrides of the Ti–Mo alloys with fcc δ-phase structure transfer into bcc β-phase at higher temperatures. An associated hydrogen concentration reduction for the δ-phase hydride is observed in the process. However, as the hydrogen concentrations decrease to certain values (H/M  1.1–1.7), the unsaturated δ-phase formed at high temperature would become unstable at lower temperature, and transfer into a tetragonal phase (denoted the -phase here). Unlike that of the -phase in Ti–H system, the phase transition does not occur for the saturated δ-phase with hydrogen concentration close to the stoichiometric limit. The hydrogen concentration of this -phase hydride is in between that of the tetragonal γ and -phase in Ti–H system, but more close to the γ-phase. The occurrence region of this -phase expands along with the increase of the Mo content in the alloys. The phase has a lattice similar to that of the -phase in Ti–H system with corresponding fct unit-cell c/a < 1.     

The molybdenum diphosphate Mo1.3O(P2O7), containing Mo2 and Mo3 clusters

A novel molybdenum diphosphate, Mo_1.3O(P₂O₇), was obtained by electrochemical lithium deintercalation. The diphosphate crystallises in space group I2/a with the lattice parameters a=22.88(1), b=22.94(2), c=4.832(1) Å, γ=90.36°, Z=8. Its original framework is built up from MoO₆ octahedra, P₂O₇ groups and also from MoO₄, Mo₂O₄ and Mo₃O₈ units containing Mo₂ and Mo₃ clusters. These polyhedra delimit large octagonal and z-shaped tunnels running along c, in which the inserted cations may be located.     

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.     

Red photoluminescence properties and crystal structure of sodium rare earth oxyborate

The subsolidus phase relations of the system Y₂O₃–Na₂O–B₂O₃ are reported. There are seven binary compounds and two ternary compounds in this system. A new ternary compound Na₂Y₂B₂O₇ is identified. The structure has been determined for the compound Na₂Y₂B₂O₇ from powder X-ray diffraction. The lattice constants of P2₁/c for the compound Na₂Y₂B₂O₇ are a=10.5993(1) Å, b=6.2311(1) Å, c=10.2247(1) Å, β=117.756(1)° and z=4. The structure can be described as being made up of isolated BO₃ triangles and YO₈ polyhedra. The photoluminescence properties of Eu ion-doped Na₂Y₂B₂O₇ and Na₃Y(BO₃)₂ show strong red-emission of the ⁵D₀–⁷F₂ transitions at 611 and 615 nm, respectively. The results of emission spectra are in good agreement with the crystallographic study. The relationship between Eu ion content and emission intensity is analyzed too.