Dy5Ni0.66Bi2.34 and Lu5Ni0.56Sb2.44 – Substitution derivatives with the orthorhombic Yb5Sb3-type structure. Magnetocaloric effect of Dy5Ni0.66Bi2.34

Dy₅Ni_0.66Bi_2.34 and Lu₅Ni_0.56Sb_2.44 were synthesized by arc-melting and were found to adopt an orthorhombic Yb₅Sb₃-type structure. Cell parameters are a = 12.075(2), b = 9.165(2), c = 8.072(1) Å for Dy₅Ni_0.66Bi_2.34 and a = 11.6187(9), b = 8.933(1) and c = 7.8377(6) Å for Lu₅Ni_0.56Sb_2.44. Dy₅Ni_0.66Bi_2.34 undergoes a step-like ferromagnetic transition around 66 K. Magnetocaloric effect in terms of the magnetic entropy change, ΔS, reaches −3.73 J/kg K at 75 K for Dy₅Ni_0.66Bi_2.34.     

Hydrogen in polar intermetallics: Syntheses and structures of the ternary Ca5Bi3D0.93, Yb5Bi3Hx, and Sm5Bi3H∼1 by powder neutron or single crystal X-ray diffraction

The syntheses of the title compounds are described in detail. Structural characterizations from refinements of single crystal X-ray diffraction data for Yb₅Bi₃H_x and Sm₅Bi₃H_∼1 and of powder neutron diffraction data for Ca₅Bi₃D_0.93(3) are reported. These confirm that all three crystallize with the heavy atom structure type of β-Yb₅Sb₃, and the third gives the first proof that the deuterium lies in the center of nominal calcium tetrahedra, isostructural with the Ca₅Sb₃F-type structure. These Ca and Yb phases are particularly stable with respect to dissociation to Mn₅Si₃-type product plus H₂. Some contradictions in the literature regarding Yb₅Sb₃ and Yb₅Sb₃H_x phases are considered in terms of adventitious hydrogen impurities that are generated during reactions in fused silica containers at elevated temperatures.     

The new ternary silicide Gd5CoSi2: Structural, magnetic and magnetocaloric properties

Gd₅CoSi₂ was prepared by annealing at 1003 K. Its investigation by the X-ray powder diffraction shows that the ternary silicide crystallizes in a tetragonal structure deriving from the Cr₅B₃-type (I4/mcm space group; a=7.5799(4) and c=13.5091(12) Å as unit cell parameters). The Rietveld refinement shows a mixed occupancy on the (8h) site between Si and Co atoms. Magnetization and specific heat measurements performed on Gd₅CoSi₂ reveal a ferromagnetic behaviour below T_C=168 K. This magnetic ordering is associated to an interesting magnetocaloric effect; the adiabatic temperature change ΔT_ad is about 3.1 and 5.9 K, respectively, for a magnetic field change of 2 and 4.6 T.     

Synthesis, crystal structures, magnetic and electric transport properties of Eu11InSb9 and Yb11InSb9

Two new rare-earth metal containing Zintl phases, Eu₁₁InSb₉ and Yb₁₁InSb₉ have been synthesized by reactions of the corresponding elements in molten In metal to serve as a self-flux. Their crystal structures have been determined by single crystal X-ray diffraction—both compounds are isostructural and crystallize in the orthorhombic space group Iba2 (No. 45), Z=4 with unit cell parameters a=12.224(2) Å, b=12.874(2) Å, c=17.315(3) Å for Eu₁₁InSb₉, and a=11.7886(11) Å, b=12.4151(12) Å, c=16.6743(15) Å for Yb₁₁InSb₉, respectively (Ca₁₁InSb₉-type, Pearson's code oI84). Both structures can be rationalized using the classic Zintl rules, and are best described in terms of discrete In-centered tetrahedra of Sb, [InSb₄]⁹⁻, isolated Sb dimers, [Sb₂]⁴⁻, and isolated Sb anions, Sb³⁻. These anionic species are separated by Eu²⁺ and Yb²⁺ cations, which occupy the empty space between them and counterbalance the formal charges. Temperature-dependent magnetic susceptibility and resistivity measurements corroborate such analysis and indicate divalent Eu and Yb, as well as poorly metallic behavior for both Eu₁₁InSb₉ and Yb₁₁InSb₉. The close relationships between these structures and those of the monoclinic α-Ca₂₁Mn₄Sb₁₈ and Ca₂₁Mn₄Bi₁₈ are also discussed.     

Magnetic transitions in the Gd5Si4−xPx (x = 0.5, 0.75, 1.25) phases. Magnetocaloric effect of the Gd5Si2.75P1.25 phase

The Gd₅Si_2.75P_1.25 phase with all interslab Si/P–Si/P dimers broken (Sm₅Ge₄-type structure) undergoes a ferromagnetic transition at 184 K. For this phase, the magnetocaloric effect in terms of the magnetic entropy change, ΔS, reaches the maximum value of −7.8 J/kg K at 177 K. Absence of a temperature-dependant structural transition, as confirmed by the low-temperature single crystal diffraction studies, together with the moderate value of ΔS points to the presence of a conventional magnetocaloric effect. Gd₅Si_3.5P_0.5 and Gd₅Si_3.25P_0.75, which are composites of the Gd₅Si₄- (all Si/P–Si/P dimers intact) and Sm₅Ge₄-type phases, possess two magnetic transitions associated with the two-phases. Introduction of P into Gd₅Si₄ lowers the Curie temperature from 336 K to 332 K in Gd₅Si_3.25P_0.75.     

Yb5Ni4Sn10 and Yb7Ni4Sn13: New polar intermetallics with 3D framework structures

The title compounds have been obtained by solid state reactions of the corresponding pure elements at high temperature, and structurally characterized by single-crystal X-ray diffraction studies. Yb₅Ni₄Sn₁₀ adopts the Sc₅Co₄Si₁₀ structure type and crystallizes in the tetragonal space group P4/mbm (No. 127) with cell parameters of a=13.785(4) Å, c=4.492 (2) Å, V=853.7(5) Å³, and Z=2. Yb₇Ni₄Sn₁₃ is isostructural with Yb₇Co₄InGe₁₂ and crystallizes in the tetragonal space group P4/m (No. 83) with cell parameters of a=11.1429(6) Å, c=4.5318(4) Å, V=562.69(7) Å³, and Z=1. Both structures feature three-dimensional (3D) frameworks based on three different types of one-dimensional (1D) channels, which are occupied by the Yb atoms. Electronic structure calculations based on density functional theory (DFT) indicate that both compounds are metallic. These results are in agreement with those from temperature-dependent resistivity and magnetic susceptibility measurements.     

Electron spin resonance of diluted solid solutions of Gd2O3 in CeO2

Electron spin resonance spectra of Gd³⁺ in diluted solid solutions of Gd₂O₃ in CeO₂ have been studied at room temperature for Gd concentrations between 0.01 and 1.00 mol%. While in the case of Mn²⁺:CeO₂ samples, both the linewidth and the line intensity go through a maximum between 0.2 and 0.4% Mn and then start to decrease, in the case of Gd³⁺:CeO₂ samples the linewidth and the line intensity increase monotonically with the dopant concentration. This as taken as evidence that in Gd₂O₃-CeO₂ diluted solid solutions there are no clustering effects similar to the ones observed in Mn:CeO₂ solid solutions. It is not clear why clustering effects are present in Mn:CeO₂ solid solutions and not in Gd:CeO₂ solid solutions; however, it seems reasonable to assume that this is due to the fact that the ionic radius of Mn²⁺ (81 pm) is about 25% smaller that that of Gd³⁺ (107.8 pm). In any case, the fact that Gd:CeO₂ solid solutions do not exhibit clustering effects means that ESR linewidth data can be used to estimate the concentration of Gd in CeO₂ samples, as it is possible to do in several solid solutions of paramagnetic ions in ceramic materials. The results also suggest that the range of the exchange interaction between Gd³⁺ ions in CeO₂ is about 0.89 nm.     

High-temperature X-ray diffraction and specific heat studies on GdAlO3, Gd3Al5O12 and Gd4Al2O9

Gadolinium aluminates, GdAlO₃, Gd₃Al₅O₁₂ and Gd₄Al₂O₉ were synthesized by the solution combustion method. Very fine particles in the nanoparticle range of ∼10-20 nm could be prepared by this method as evidenced by surface area measurement by multipoint BET method. Thermal studies on these compounds were carried out using high-temperature X-ray diffraction (HT-XRD) and differential scanning calorimetry (DSC) methods. The thermal expansion coefficients of GdAlO₃, Gd₃Al₅O₁₂ and Gd₄Al₂O₉ were calculated from the lattice parameter data and specific heats were calculated from DSC data. The lattice parameters of GdAlO₃ and Gd₃Al₅O₁₂ were found to increase linearly with temperature whereas Gd₄Al₂O₉ did not show a linear trend. The specific heats of these compounds show an increasing trend with increase in aluminum atom fraction. Based on the thermodynamic data available in the literature and the specific heat data obtained in this study, oxygen potential diagram was constructed at 1000 K.     

Crystal structure and physical properties of the quaternary manganese-bearing pavonite homologue Mn1.34Sn6.66Bi8Se20

The quaternary manganese tin bismuth selenide, Mn_1.34Sn_6.66Bi₈Se₂₀ was synthesized by combining constituent elements at 723 K. Single crystal structure determination revealed that Mn_1.34Sn_6.66Bi₈Se₂₀ is isostructural to the mineral pavonite, AgBi₃S₅, crystallizing in the monoclinic space group C2/m (#12) with a=13.648(3) Å; b=4.175(1) Å; c=17.463(4) Å; β=93.42(3)°. In the structure, two kinds of layered modules, denoted A and B, alternate along [0 0 1]. Module A consists of paired chains of face-sharing monocapped trigonal prisms (around Bi/Sn) separated by a single chain of edge-sharing octahedra (around Mn/Sn). Module B represents a NaCl-type fragment of edge-sharing [(Bi/Sn)Se₆] octahedra. Mn_1.34Sn_6.66Bi₈Se₂₀ is an n-type narrow gap semiconductor with E_g∼0.29 eV. At 300 K, thermopower, electrical conductivity and lattice thermal conductivity values are −123 μV/K, 47 S/cm and 0.6 W/m K, respectively. Mn_1.34Sn_6.66Bi₈Se₂₀ is paramagnetic at high temperatures and undergoes antiferromagnetic transition at T_N=10 K.     

Syntheses, structures, optical properties, and theoretical calculations of Cs2Bi2ZnS5, Cs2Bi2CdS5, and Cs2Bi2MnS5

Three new compounds, Cs₂Bi₂ZnS₅, Cs₂Bi₂CdS₅, and Cs₂Bi₂MnS₅, have been synthesized from the respective elements and a reactive flux Cs₂S₃ at 973 K. The compounds are isostructural and crystallize in a new structure type in space group Pnma of the orthorhombic system with four formula units in cells of dimensions at 153 K of a=15.763(3), b=4.0965(9), c=18.197(4) Å, V=1175.0(4) Å³ for Cs₂Bi₂ZnS₅; a=15.817(2), b=4.1782(6), c=18.473(3)  Å, V=1220.8(3)  ų for Cs₂Bi₂CdS₅; and a=15.830(2), b=4.1515(5), c=18.372(2) Å, V=1207.4(2) Å³ for Cs₂Bi₂MnS₅. The structure is composed of two-dimensional _∞²[Bi₂MS₅²⁻] (M=Zn, Cd, Mn) layers that stack perpendicular to the [100] axis and are separated by Cs⁺ cations. The layers consist of edge-sharing _∞¹[Bi₂S₆⁶⁻] and _∞¹[MS₃⁴⁻] chains built from BiS₆ octahedral and MS₄ tetrahedral units. Two crystallographically unique Cs atoms are coordinated to S atoms in octahedral and monocapped trigonal prismatic environments. The structure of Cs₂Bi₂MS₅, is related to that of Na₂ZrCu₂S₄ and those of the AMM′Q₃ materials (A=alkali metal, M=rare-earth or Group 4 element, M′= Group 11 or 12 element, Q=chalcogen). First-principles theoretical calculations indicate that Cs₂Bi₂ZnS₅ and Cs₂Bi₂CdS₅ are semiconductors with indirect band gaps of 1.85 and 1.75 eV, respectively. The experimental band gap for Cs₂Bi₂CdS₅ is ≈1.7 eV, as derived from its optical absorption spectrum.     

On the structural and magnetic properties of the ternary silicides Ce6M1.67Si3 (M=Co, Ni) and Ce5Ni1.85Si3

Contrary to that reported previously, the ternary silicide “Ce₆Ni₂Si₃” does not exist. The melting of this alloy, followed or not by annealing, leads to the existence of the two new ternary compounds, Ce₆Ni_1.67Si₃ and Ce₅Ni_1.85Si₃. The investigation of these ternary silicides based on nickel and Ce₆Co_1.67Si₃ by X-ray diffraction on single crystal reveals an ordered distribution between Ni (or Co) and Si atoms. The nickel or cobalt positions in the chains of face-shared octahedra of cerium are not fully occupied with a strong delocalisation of their electron density. The structural investigations of these compounds confirm that the “Ce₆Ni₂Si₃” and “Ce₅Ni₂Si₃” structural type have to be rewritten as Ce₆Ni_2−xSi₃ and Ce₅Ni_2−xSi₃. Magnetisation and specific heat measurements evidence a magnetic ordering at 3.8(2) K for Ce₆Ni_1.67Si₃ and a heavy fermion behaviour for Ce₆Co_1.67Si₃.     

The new ternary pnictides Er12Ni30P21 and Er13Ni25As19: Crystal structures and magnetic properties

The new ternary pnictides Er₁₂Ni₃₀P₂₁ and Er₁₃Ni₂₅As₁₉ have been synthesized from the elements. They crystallize with hexagonal structures determined from single-crystal X-ray data for Er₁₂Ni₃₀P₂₁ (space group P6₃/m, a=1.63900(3) nm, c=0.37573(1) nm, Z=1, R_F=0.062 for 1574 F-values and 74 variable parameters), and for Er₁₃Ni₂₅As₁₉ (Tm₁₃Ni₂₅As₁₉-type structure, space group P6?, a=1.6208(1) nm, c=0.38847(2) nm, Z=1, R_F=0.026 for 1549 F-values and 116 variable parameters). These compounds belong to a large family of hexagonal structures with a metal-metalloid ratio of 2:1. HRTEM investigations were conducted to probe for local ordering of the disordered structure at the nanoscale. The magnetic properties of the phosphide Er₁₂Ni₃₀P₂₁ have been studied in the temperature of range 2<T<300 K and with applied fields up to 5 T. The magnetic susceptibility follows the Curie-Weiss law from 4 to 300 K. The measured value of μ_eff=9.59 μ_B corresponds to the theoretical value of Er³⁺.     

Solvothermal synthesis and luminescence properties of monodisperse Gd2O3:Eu and Gd2O3:Eu@SiO2 nanospheres

A series of uniform, monodispersed Gd(OH)³:Eu³⁺ nanospheres less than 100 nm were successfully synthesized with iron ions as catalyst and DMF as solvent under the solvothermal condition. Cetyltrimethyl ammonium bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as co-surfactant during this facile procedure should be changed as A series of uniform, monodisperse Gd(OH)³:Eu³⁺ nanospheres less than 100 nm in diameter were successfully synthesized with solvothermal method. Iron ion was used as catalyst and Dimethylformamide (DMF) as solvent, Cetyltrimethyl Ammonium Bromide (CTAB) and Polyvinylpyrrolidone (PVP) were performed as surfactants. Further calcination process was applied to prepare Gd₂O₃:Eu³⁺ nanoshpheres during this facile procedure.     

Yb3CoSn6 and Yb4Mn2Sn5: New polar intermetallics with 3D open-framework structures

Two new ternary ytterbium transition metal stannides, namely, Yb₃CoSn₆ and Yb₄Mn₂Sn₅, have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Yb₃CoSn₆ crystallizes in the orthorhombic space group Cmcm (no. 63) with cell parameters of a=4.662(2), b=15.964(6), c=13.140(5) Å, V=978.0(6) Å³, and Z=4. Its structure features a three-dimensional (3D) open-framework composed of unusual [CoSn₃] layers interconnected by zigzag Sn chains, forming large tunnels along the c-axis which are occupied by the ytterbium cations. Yb₄Mn₂Sn₅ is monoclinic space group C2/m (no. 12) with cell parameters of a=16.937(2), b=4.5949(3), c=7.6489(7) Å, β=106.176(4)°, V=571.70(8) Å³, and Z=2. It belongs to the Mg₅Si₆ structure type and its anionic substructure is composed of parallel [Mn₂Sn₂] ladders interconnected by unusual zigzag [Sn₃] chains, forming large tunnels along the c-axis, which are filled by the ytterbium cations. Band structure calculations based on density function theory methods were also made for both compounds.     

Structure and physical properties of ternary W5Si3-type antimonides and bismuthides Zr5M1-xPn2+x (M=Cr, Mn; Pn=Sb, Bi)

Four new ternary compounds Zr₅M_1-xPn_2+x (M=Cr, Mn; Pn=Sb, Bi) were synthesized by arc-melting and annealing at 800 °C. They crystallize in the tetragonal W₅Si₃-type structure. The crystal structure of Zr₅Cr_0.49(2)Sb_2.51(2) was refined from powder X-ray diffraction data by the Rietveld method (Pearson symbol tI32, tetragonal, space group I4/mcm, Z=4, a=11.1027(6) Å, c=5.5600(3) Å). Four-probe electrical resistivity measurements on sintered polycrystalline samples indicated metallic behavior. Magnetic susceptibility measurements between 2 and 300 K revealed temperature-independent Pauli paramagnetism for Zr₅Cr_1-xSb_2+x and Zr₅Cr_1-xBi_2+x, but a strong temperature dependence for Zr₅Mn_1-xSb_2+x and Zr₅Mn_1-xBi_2+x which was fit to the Curie-Weiss law for the latter with θ=-11.3 K and μ_eff=1.81(1) μ_B. Band structure calculations for Zr₅Cr_0.5Sb_2.5 support a structural model in which Cr and Sb atoms alternate within the chain of interstitial sites formed at the centers of square antiprismatic Zr₈ clusters.     

Structural, magnetic, and thermal characteristics of the phase transitions in Gd5GaxGe4−x magnetocaloric materials

Temperature-dependent, single crystal and powder X-ray diffraction studies as well as magnetization, and heat capacity measurements were carried out on two phases of the Gd₅Ga_xGe_4−x system: for x=0.7 and 1.0. Gd₅Ga_0.7Ge_3.3 shows three structure types as a function of temperature: (i) from 165 K to room temperature, the orthorhombic Sm₅Ge₄-type structure exists; (ii) below 150 K, it transforms to a orthorhombic Gd₅Si₄-type structure; and (iii) a monoclinic Gd₅Si₂Ge₂-type component is observed for the intermediate temperature range of 150 K≤T≤165 K. This is the first time that all these three structure types have been observed for the same composition. For Gd₅Ga_1.0Ge_3.0, the room temperature phase belongs to the orthorhombic Pu₅Rh₄-type structure with interslab contacts between main group atoms of 2.837(4) Å. Upon heating above 523 K, it transforms to a Gd₅Si₄-type structure with this distance decreasing to 2.521(7) Å before decomposing above 573 K.     

Synthesis and characterization of quaternary chalcogenides InSn2Bi3Se8 and In0.2Sn6Bi1.8Se9

Quaternary chalcogenides InSn₂Bi₃Se₈ and In_0.2Sn₆Bi_1.8Se₉ were synthesized on direct combination of their elements in stoichiometric ratios at T>800 °C under vacuum. Their structures were determined with X-ray diffraction of single crystals. InSn₂Bi₃Se₈ crystallizes in monoclinic space group C2/m (No. 12) with a=13.557(3) Å, b=4.1299(8) Å, c=15.252(3) Å, β=115.73(3)°, V=769.3(3) Å³, Z=2, and R₁/wR₂/GOF=0.0206/0.0497/1.092; In_0.2Sn₆Bi_1.8Se₉ crystallizes in orthorhombic space group Cmc2₁ (No. 36) with a=4.1810(8) Å, b=13.799(3) Å, c=31.953(6) Å, V=1843.4(6) Å³, Z=4, and R₁/wR₂/GOF=0.0966/0.2327/1.12. InSn₂Bi₃Se₈ and In_0.2Sn₆Bi_1.8Se₉ are isostructural with CuBi₅S₈ and Bi₂Pb₆S₉ phases, respectively. The structures of InSn₂Bi₃Se₈ and In_0.2Sn₆Bi_1.8Se₉ feature a three-dimensional framework containing slabs of NaCl-(311) type with varied thicknesses. Calculations of the electronic structure and measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps. Both compounds show n-type semiconducting properties with Seebeck coefficients −270 and −230 μV/K at 300 K for InSn₂Bi₃Se₈ and In_0.2Sn₆Bi_1.8Se₉, respectively.     

Neutron powder diffraction study of the crystal and magnetic structures of BiNiO3 at low temperature

The crystal and magnetic structures of the charge ordered perovskite BiNiO₃ have been studied at temperatures from 5 to 300 K using neutron diffraction. Rietveld analysis of the data shows that the structure remains triclinic (space group ) throughout the whole temperature range. Bond-valence sum calculations based on the Bi-O and Ni-O bond distances confirm that the charge distribution is Bi³⁺_0.5Bi⁵⁺_0.5Ni²⁺O₃ down to 5 K. The magnetic cell is identical to that of the triclinic superstructure and a G-type antiferromagnetic model gives a good fit to the magnetic intensities, with an ordered Ni²⁺ moment of 1.76(3) μ_B at 5 K. However, BiNiO₃ is ferrimagnetic due to the inexact cancellation of opposing, inequivalent moments in the low symmetry cell.     

Thermoelectric properties of p-type pseudo-binary (Ag0.365Sb0.558Te)x-(Bi0.5Sb1.5Te3)1−x (x=0-1.0) alloys prepared by spark plasma sintering

In this paper, pseudo-binary (Ag_0.365Sb_0.558Te)_x-(Bi_0.5Sb_1.5Te₃)_1−x (x=0-1.0) alloys were prepared using spark plasma sintering technique, and the composition-dependent thermoelectric properties were evaluated. Electrical conductivities range from 7.9×10⁴ to 15.6×10⁴ Ω⁻¹ m⁻¹ at temperatures of 507 and 318 K, respectively, being about 3.0 and 8.5 times those of Bi_0.5Sb_1.5Te₃ alloy at the corresponding temperatures. The optimal dimensionless figure of merit (ZT) of the sample with molar fraction x=0.025 reaches 1.1 at 478 K, whereas that of the ternary Bi_0.5Sb_1.5Te₃ alloy is 0.58 near room temperature. The results also reveal that a direct introduction of Ag_0.365Sb_0.558Te in the Bi-Sb-Te system is much more effective to the property improvement than naturally precipitated Ag_0.365Sb_0.558Te in the Ag-doped Ag-Bi-Sb-Te system.     

Yb3Cu6Sn5, Yb5Cu11Sn8 and Yb3Cu8Sn4: crystal structure of three ordered compounds

Yb₃Cu₆Sn₅, Yb₅Cu₁₁Sn₈ and Yb₃Cu₈Sn₄ compounds were prepared in sealed Ta crucibles by induction melting and subsequent annealing. The crystal structures of Yb₃Cu₆Sn₅ and Yb₅Cu₁₁Sn₈ were determined from single crystal diffractometer data: Yb₃Cu₆Sn₅, isotypic with Dy₃Co₆Sn₅, orthorhombic, Immm, oI28, a=4.365(1) Å, b=9.834(3) Å, c=12.827(3) Å, Z=2, R=0.019, 490 independent reflections, 28 parameters; Yb₅Cu₁₁Sn₈ with its own structure, orthorhombic, Pmmn, oP48, a=4.4267(6) Å, b=22.657(8) Å, c=9.321(4) Å, Z=2, R=0.047, 1553 independent reflections, 78 parameters. Both compounds belong to the BaAl₄-derived defective structures, and are closely related to Ce₃Pd₆Sb₅ (oP28, Pmmn). The crystal structure of Yb₃Cu₈Sn₄, isotypic with Nd₃Co₈Sn₄, was refined from powder data by the Rietveld method: hexagonal, P6₃mc, hP30, a=9.080(1) Å, c=7.685(1) Å, Z=2, R_wp=0.040. It is an ordered substitution derivative of the BaLi₄ type (hP30, P6₃/mmc). All compounds show strong Cu-Sn bonds with a length reaching 2.553(3) Å in Yb₅Cu₁₁Sn₈.