Structural chemistry, magnetism and thermodynamic properties of R2Pd2In

We report on magnetisation, resistivity and specific heat measurements of R₂Pd₂In compounds synthesised with the nominal composition R₄₀Pd₄₁In₁₉ (R=La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y). Magnetic and thermodynamic measurements reveal antiferromagnetic order below 32 K for this series except for Y, La, Yb and Lu. An appreciably wide homogeneity range is found for Ce₂Pd_2+xIn_1−x where ferro- or antiferromagnetic order or both occur with typical features of a Kondo lattice. Yb₂Pd₂In exhibits intermediate valent behaviour and no magnetic order could be detected down to 0.3 K.     

Crystal structure of R3Ge4 compounds (R Er, Ho, Tm, Lu)

The crystal structure of binary germanides R₃Ge₄ (R Er, Ho, Tm, Lu) has been determined by means of powder X-ray diffraction. For Er₃Ge₄ a full-structure determination has been performed using the Rietveld method (306 reflections, space group Cmcm,

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). The location of the atoms in Er₃Ge₄ is similar to that in the W₃CoB₃ structure, with the Ge atoms substituting for Co and B. For the other R₃Ge₄ compounds (RHo, Tm and Lu) the lattice parameters are given.     

Determination of the structure of a new tetragonal U2FeAl20 phase

The atomic structure of a new ternary U₂FeAl₂₀ phase appearing in the Al-rich corner of a U–Fe–Al system was solved using electron crystallography and X-ray powder diffraction techniques (XRD). The positions of U atoms were determined from crystallographically processed high-resolution electron microscopy (HRTEM) images. These positions were used as a starting set for determining the coordinates of Fe and Al atoms by difference-Fourier synthesis technique. The U₂FeAl₂₀ phase is tetragonal and belongs to the space group. Its unit cell contains 80 Al, 4 Fe, and 8 U atoms. The lattice parameters obtained after Rietveld refinement are: a = 12.4138 Å, c = 10.3014 Å. The reliability factors characterizing the Rietveld refinement procedure are: R_p = 8.65%, R_wp = 11.2% and R_b = 5.93%.     

Canted antiferromagnetic structure of HoPtGe2

Neutron powder diffraction has been performed on orthorhombic HoPtGe₂ crystallizing in space group Immm. Lattice constants are a=4.321(3) Å, b=16.344(3) Å, and c=8.731(5) Å. Refined atomic positional parameters are given. A magnetic phase transition from paramagnetism into a canted antiferromagnetic structure occurs at the Néel temperature T_N=8.5 K. The ordered moments at Ho sites 4i and 4h are 8.1 μ_B and 4.0 μ_B at 4.2 K, respectively; the moments are aligned within the ab and bc plane, respectively.     

Structural investigation of the phase transitions of Tribromo ammonium mercurate (II) monohydrate, NH4HgBr3·H2O

Single crystal diffraction, Infrared spectroscopy and differential scanning calorimetry DSC techniques have been used to investigate the different phases of NH₄HgBr₃·H₂O, Tribromo ammonium mercurate (II) monohydrate, from room temperature to 120 K. Two anomalies in thermal behaviour were detected for this compound at 198 and 340 K, by DSC experiment. X-ray diffraction measurements confirm the presence of the first anomaly. At room temperature NH₄HgBr₃·H₂O, crystallizes in the orthorhombic space group Cmc2₁, with the lattice constants a = 4.475(1) Å, b = 17.226(2) Å, c = 10.240(2) Å and Z = 4. Below 200 K the structure is monoclinic P2₁ with: a = 4.379(4) Å, b = 17.220(10) Å, c = 10.103(2) Å, β = 90.023(9)° and Z = 2 (T = 120 K). The mercury atom is surrounded by four bromine atoms in an irregular tetrahedron. The tetrahedra are linked at two corners, resulting in infinite chains along the “a” axis. The ammonium groups are located between the chains ensuring the stability of the structure by hydrogen bonding contacts: NHBr, OHBr, NHO. The structural phase transformation was attributed to an orientational disorder of ammonium groups.     

DSC, structural single crystal and X-ray powder diffraction study of the ammonium sulfate selenate tellurate mixed solid solution

Crystal structure of (NH₄)₂(SO₄)_0.73(SeO₄)_0.27Te(OH)₆ (NSSeTe) crystallizes in the monoclinic P2₁/c space group. It was analyzed at room temperature using X-ray diffractometer data. The unit cell parameters are a = 13.7340(2) Å, b = 6.6583(1) Å, c = 11.4582(2) Å, β = 106.8270(6)°, Z = 2, V = 1002.93(3) Å³, R = 0.014, R_w = 0.017 and D_x = 2.426 g cm⁻³. The main feature of this atomic arrangements is the coexistence of three and different anions (SO₄²⁻, TeO₆⁶⁻ and SeO₄²⁻ groups) in the unit cell, connected by hydrogen bonds which make the building of the crystal. The distribution of atoms can be described as isolated TeO₆ octahedra and SO₄ and/or SeO₄ tetrahedra occupying the same positions. The NH₄⁺ cations, are located between these polyhedra. The molecular species present in the lattice are S/SeO₄²⁻ tetrahedra and TeO₆⁶⁻ octahedra disposed in a number of sheets. The thermal analysis of the title compound show three distinct endothermal peaks at 398, 430 and 450 K. X-ray powder diffraction data at different temperatures confirm that the first anomaly at 398 K can be attributed to a structural phase transition.     

Crystal structure and physical properties of the new intermetallics REPt4In4 (RE = Gd – Lu,Y)

A new compound ErPt₄In₄ was synthesized by arc melting and its crystal structure was determined from the single crystal X-ray diffraction data: space group P6₃/mmc, a = 4.5321(9) Å, c = 19.807(13) Å, Pearson symbol hP18. The new structure type is composed of condensed via side edges Er-centered polyhedra [Pt₈In₆] and the corrugated slabs of In atoms alternating in the c-direction. A few isostructural compounds were found to form with Gd–Lu, and Y. The low-temperature physical properties of TbPt₄In₄, DyPt₄In₄ and YbPt₄In₄ were characterized by means of magnetic susceptibility and electrical resistivity measurements. All three compounds exhibit Curie–Weiss paramagnetism, due to the presence of well localized magnetic moments carried on trivalent rare-earth atoms, and metallic character of their electrical conductivity. The compounds TbPt₄In₄ and DyPt₄In₄ order magnetically below 8 and 5 K, respectively, whereas YbPt₄In₄ remains paramagnetic down to 1.7 K.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

Synthesis and structure determination of In3TeO3F7: An indium oxyfluorotellurate IV derived from W bronze structure with Te in hexagonal tunnels

After InTeO₃F and InTe₂O₅F recently described, a new compound In₃TeO₃F₇ is characterized in the In-Te^IV-O-F system. The crystal structure was determined by single X-ray diffraction and refined to R₁ = 0.028. In₃TeO₃F₇ crystallizes in orthorhombic space group Cmmm, a = 7.850(2) Å, b = 27.637(6) Å, c = 4.098(1) Å, V = 889.1(4) Å³ and Z = 4. Its structure consists of the stacking, via vertices, of identical layers composed of InF₆ and InO₂F₄ octahedra sharing corners and of InO₄F₃ pentagonal bipyramids sharing edges and vertices. The Te cations statistically occupy one or the other of two close sites located inside tunnels delimited by the In polyhedra and are bonded to F anions located in the same tunnels.The structure can be considered as an intergrowth of parallel strips of MIn₃F₁₀ and hexagonal tungsten bronze (c)-types. It is compared to other structures such as the bronze Sb_0.157WO₃, TeMo₅O₁₆ and Sb₂Mo₁₀O₃₁, phases also comprising Te⁴⁺ or Sb³⁺ inside hexagonal tunnels. The electronic lone pair of Te⁴⁺ is stereochemically active and a perfect O/F ordering occurs on the anionic sites.     

Synthesis and characterization of new pyrochlore solid solution Bi1.5Sb1.5Cu1−xMnxO7

A new pyrochlore solid solution with formula Bi_1.5Sb_1.5Cu_1−xMn_xO₇ has been synthesized using ceramic method at 1000 °C. The cell parameter decreases linearly with increasing manganese concentration. Rietveld refinements for (B_1.5Mn_0.5)(Sb_1.5Mn_0.5)O₇ compound using X-ray powder diffraction data confirmed an overall A₂B₂O₇ cubic pyrochlore structure with a = 10.42749 (4) Å and Fd-3m symmetry. The reliability factors are R_wp = 3.48%; R_p = 2.37%; R_exp = 1.65% and R_Bragg = 1.58%. The magnetic susceptibility measurements achieved between 4 and 300 K indicate a paramagnetic behaviour with an oxidation state “2+” of the manganese ion. The electric resistance measured using complex impedance spectroscopy method put in evidence a decrease of the electric resistance with the temperature, which reached 5 × 10² Ω at 675 K. Dielectric properties depend on the variation of frequency and temperature, results indicate a conductive compound.     

Crystal structure of Nax(MoO)5(P2O7)4 studied by synchrotron X-ray diffraction

The crystal structure of sodium pentamolybdyl tetradiphosphate Na_x(MoO)₅(P₂O₇)₄ has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo_1.3OP₂O₇ [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo₂ and Mo₃ clusters were erroneously identified in Mo_1.3OP₂O₇. A revised structure of Mo_1.3OP₂O₇ contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)₅(P₂O₇)₄. In both structures, the (MoO)₅(P₂O₇)₄ framework strongly resembles the one in the earlier reported Ag(MoO)₅(P₂O₇)₄, while the location of Na and Ag atoms differ.     

LiSrGe2 and LiBaGe2: One-dimensional chains of in an unusual conformation

Two new isostructural intermetallic germanides, LiSrGe₂ and LiBaGe₂, were synthesized as single crystals from constituent elements in molten Na. They both crystallize in the space group Pnma (no. 62) with a = 7.142(1), b = 4.459(1), c = 11.550(2) Å, Z = 4, and a = 7.381(1), b = 4.617(1), c = 11.837(1) Å, Z = 4, for LiSrGe₂ and LiBaGe₂, respectively. They contain one-dimensional anionic germanide chains, , running along the a-axis. The chains are in an unusual zigzag-like conformation, with weakly alternating Ge–Ge bond lengths of 2.475(1) and 2.498(1) Å, and 2.473(1) and 2.525(1) Å, for LiSrGe₂ and LiBaGe₂, respectively. Extended Hückel calculations suggest that LiSrGe₂ is metallic: the Fermi level lies within bands having anti-bonding character.     

Study on the boundary structures in a series of lanthanide hexacyanoferrate(III) n-hydrates

The properties of a series of lanthanide hexacyanoferrate(III) n-hydrates were studied by means of thermal analysis, IR spectroscopy, Raman spectroscopy and X-ray crystallography. Thermal analyses showed that there were two kinds of complexes in this series, Ln[Fe(CN)₆]·5H₂O (Ln=La–Nd) and Ln′[Fe(CN)₆]·4H₂O (Ln′=Sm–Lu). The boundary complex between them was Nd[Fe(CN)₆]·5H₂O. The IR spectra of the two kinds of complexes were obviously different. For the pentahydrates, there were two sharp CN stretching bands at 2050 and 2140 cm⁻¹, and one band at 1600 cm⁻¹ assigned to the HOH bending. On the other hand, for the tetrahydrates besides the two CN stretching bands at 2050 and 2140 cm⁻¹, a new band was observed at 1940 cm⁻¹, and the HOH bending band split into three bands around 1600 cm⁻¹. From the X-ray crystal analysis, the structure of the boundary complex Nd[Fe(CN)₆]·5H₂O was determined. It belonged to hexagonal, P6₃/m, with a=7.467(2) Å, c=13.793(3) Å and Z=2 (R=0.082, R_w=0.126). Neodymium was nine-coordinated in the form of the NdN₆(H₂O)₃ group. The three coordinated water molecules of the 5H₂O complex with Nd have a large value for the equivalent isotropic thermal parameter. One of the three water molecules was dissociated easily and the 5H₂O complex changed into the stable 4H₂O complex with Nd. The crystal of the 4H₂O complex is orthorhombic, and belongs to the space group Cmcm as well as the other Ln[Fe(CN)₆]·4H₂O (Ln=Sm–Lu). Therefore, the structure of Nd[Fe(CN)₆]·5H₂O is regarded as the boundary structure.     

A new ternary arsenide Eu20Ni42As31: Preparation, crystal structure and physical properties

We have investigated the crystal structure, magnetic and electrical transport properties of the new ternary compound Eu₂₀Ni₄₂As₃₁, crystallizing in the hexagonal Sm₂₀Ni₄₂P₃₁ structure type, space group P6₃/m, a = 21.1496(7), c = 4.0734(2) Å, according to X-ray powder diffraction. From magnetic investigations it is evidenced that in this compound the europium is divalent, Eu²⁺. The compound orders antiferromagnetically at a Neèl temperature T_N = 5 K. However, in moderate magnetic fields an overall ferromagnetic-like magnetization is observed. The measurements of the electrical resistivity prove this magnetic behaviour as well as the metallic character of the compound Eu₂₀Ni₄₂As₃₁.     

Subsolidus phase relationships in the system ZnO–Li2O–WO3

The subsolidus phase relationships of the system ZnO–Li₂O–WO₃ have been investigated by X-ray diffraction (XRD) analyses. There are one ternary compound, five binary compounds and eight 3-phase regions in this system. The new ternary compound Li₂Zn₂W₂O₉ was found by the powder diffraction pattern. The corresponding crystal structure of this compound was refined by Rietveld profile fitting method. It belongs to a trigonal system with space group and lattice constants are a = 5.1438(2) Å, c = 14.1052(3) Å, and its thermal property was studied.     

On the RMgSn rare earth compounds

A new family of ternary rare earth compounds, RMgSn, has been synthesized and their crystal structures, formation thermodynamics and melting behavior have been studied. All of the rare earth elements (including Y) form the 1:1:1 equiatomic phase with Mg and Sn. These compounds crystallize with two different structure types: the RMgSn phases with the light R (R = La, Ce and Pr) adopt the orthorhombic TiNiSi structure type (an ordered derivative of the Co₂Si-type structure, oP12, space group Pnma), while the ones formed by the heavier R (R = Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu, plus Y) have the tetragonal CeScSi-type structure (an ordered derivative of the La₂Sb-type structure, tI12, space group I4/mmm). The observed unit cell volume V_obs and the mean atomic volume V_obs/n (where n is the number of atoms in a unit cell) both decrease as expected due to the lanthanide contraction, but following different trends. The volume of formation (ΔV%) becomes more negative on going from La to Lu along the series.All phases have been found to form congruently (including YMgSn and probably LuMgSn). Their melting temperatures decrease from La to Lu, but with different slopes for the two different structure types.Relationships, between the volume of formation and also the melting points with the lanthanide contraction have been examined. The relationship between the former is anomalous compared to that observed for other R_xM_y series of compounds, while the latter relationship is consistent with previously published results.     

Magnetic and structural properties of the chromium-based Mn1−xCdxCr2S4 thiospinel

The (Mn_1−xCd_x)Cr₂S₄ phases (0 ≤ x ≤ 0.6) have been synthesized from the corresponding elements at 1123 K. These samples were characterized by powder X-ray diffraction (XRD) and magnetic susceptibility. The (Mn_1−xCd_x)Cr₂S₄ compounds crystallize in the space group Fd-3m with cell parameters a = 10.101(6) Å, 10.139(3) Å, 10.165(2) Å, and 10.192(1) Å for x = 0, 0.2, 0.4 and 0.6, respectively. An overall ferrimagnetic behavior is observed for all samples. The ferromagnetic component increases rapidly when manganese is substituted by non-magnetic cadmium, as shown by ZFC/FC measurements. At the same time, the value of the magnetization M₅₀ at 50 kOe, deduced from M(H) loops, also increases with increasing cadmium content because the antiferromagnetic alignment between chromium and manganese spins is progressively lost, leading toward well aligned moments pointing into the same direction. These results are explained by a rearrangement of the chromium spins when Mn located at the tetrahedral sites, is substituted by Cd.     

Crystal structure and microwave dielectric properties of a new A4B3O12-type cation-deficient perovskite Ba3LaTa3O12

A new microwave dielectric ceramic Ba₃LaTa₃O₁₂ has been prepared by conventional solid-state ceramic route. Through Rietveld refinement of X-ray powder diffraction data, the compound is identified as an A₄B₃O₁₂-type B-site cation-deficient perovskite with space group and lattice constants a = 5.7573(2) Å, c = 28.2386(2) Å, V = 810.62(4) Å³ and Z = 3. The microwave dielectric properties of Ba₃LaTa₃O₁₂ were investigated. The compound exhibits a relative dielectric constant (_r) of 36.8, a quality factor Q_u × f of 21,965 at 6.4040 GHz and a small negative temperature coefficient of resonant frequency (τ_f) of −49.6 ppm/°C.     

Structural and magnetic properties of a novel compound with Y3(Fe, V)29 stoichiometry and disordered CaCu5-type structure

A novel phase with nominal composition Y₃Fe_27.5V_1.5 has been synthesized by arc melting elemental constituents, followed by annealing at 1123 K. The samples were analyzed by electron microprobe analysis and the stoichiometric composition was Y_3.04Fe_27.56V_1.44. X-ray diffraction from powder samples shows that the structure is of a disordered CaCu₅-type (Space Group: P6/mmm) with lattice parameters a=4.8769(1) Å, c=4.1729(3) Å. This disordered structure, revealed using standard difference Fourier methods, can be considered as a TbCu₇-type, containing iron dumbbell sites. The disorder is not restricted to the rare earth sites and the dumbbell atoms, but is observed at other sites as well. The stoichiometric formula derived by Rietveld analysis is Y_3.00(3)Fe_28.5(3). Magnetic measurements give a Curie temperature of 439(5) K, and a saturation magnetization of 156.4 and 125.5 A m² kg⁻¹ at 5 and 300 K, respectively. The anisotropy field is 4.76 T at 5 K and 2.43 T at 300 K. X-ray powder diffraction patterns of magnetically aligned powder samples indicate that the magnetocrystalline anisotropy is of easy plane type. This result is supported from the analysis of the magnetization measurements on aligned powders which give K₁<0, K₂>0 and K₁+2K₂<0, a result that confirms the easy plane anisotropy. Mössbauer spectra were also obtained and fitted with a model consistent with the disorder. The average hyperfine fields are 28.4 and 21.5 T at 4.2 and 300 K, respectively.     

Isothermal section at 1673 K of the Mo–Ru–Si diagram and crystallographic structures of ternary phases

Efforts to improve the high temperature behavior of MoSi₂ in oxidizing environments led to the investigation of the Mo–Ru–Si phase diagram. The isothermal section at 1673 K was determined by X-ray diffraction, optical and scanning electron microscopies and EPMA. Five new silicides were identified and their crystallographic structure was characterized using conventional and synchrotron X-ray as well as neutron powder diffraction. Mo₁₅Ru₃₅Si₅₀, denoted α-phase, is of FeSi-type structure, space group P2₁3, a=4.7535 (5) Å, D_x=7.90 g. cm⁻³, Bragg R=7.13. Mo₆₀Ru₃₀Si₁₀ is the ordered extension of the Mo₇₀Ru₃₀ σ-phase with space group P4₂/mnm, a=9.45940(8) Å, c=4.94273(5) Å, D_x=6.14 g. cm⁻³, Bragg R=5.75.