Tantalum Tubes Research Articles

Na–Sb–Sn ternary phase diagram at room temperature for potential anode materials in sodium-ion batteries

A first attempt to build an experimental Na–Sb–Sn ternary phase diagram at room temperature is presented. Different compositions of NaxSbySn100-x-y were melted in sealed tantalum tubes. The powders formed are polycrystalline according to X-ray diffraction studies and their patterns were refined by Rietveld method. The ternary phase diagram Na–Sb–Sn is, at first sight, complex. We have observed unidentified stable phases which do not correspond to known phases of the individual constituents or their alloys. The unidentified phases are therefore most likely ternary. A layered-type structure was observed in the powders in which an unidentified phase was grown as major compound. The ternary phase diagram will be a useful tool to understand the possible phases formed electrochemically when SbSn alloys are used as anode materials in room temperature sodium ion batteries. Indeed, some groups have recently reported promising results of this unconventional anode electrode material, bringing to light new interest in intermetallic electrode materials for sodium ion batteries.

Crystal Structure and Magnetic Ordering Transitions in CeNiIn4, EuNiIn4 and EuCuIn4

Abstract Polycrystalline CeNiIn4 was prepared by arc-melting of the elements and subsequent annealing at 970 K in vacuum. EuNiIn4 and EuCuIn4 were synthesized from the elements by reactions in sealed tantalum tubes. These indium-rich compounds crystallize with the YNiAl4-type structure which was refined for EuCuIn4 from single-crystal X-ray diffraction data: Cmcm, a=450:04(9), b=1698:7(4), c = 740:2(2) pm, wR2 = 0:0606, 495 F2 values, 24 variables. The EuCuIn4 structure is built up from a complex three-dimensional [CuIn4] polyanion (265 - 279 pm Cu-In and 296 - 331 pm In- In) in which the europium atoms occupy distorted hexagonal channels. The Eu-Eu distances within these channels (450 pm) are significantly shorter than the distances between Eu atoms in neighboring channels (552 pm). The magnetic properties and the specific heats of the europium compounds have been investigated. Both europium compounds show the magnetism of divalent Eu ions and antiferromagnetic ordering at low temperatures. EuCuIn4 is magnetically ordered via a surprisingly complex sequence of three transitions

A simple and clean source of low-energy atomic carbon

A carbon source emitting low-energy carbon atoms from a thin-walled, sealed tantalum tube via thermal evaporation has been constructed. The tube is made from a 0.05 mm thick tantalum foil and filled with 12C or 13C carbon powder. After being sealed, it is heated by direct electric current. The solvated carbon atoms diffuse to the outer surface of the tube and, when the temperature rises over 2200 K, the evaporation of atomic carbon from the surface of the tantalum tube is observed. As the evaporated species have low energy they are well-suited for the incorporation into liquid helium droplets by the pick-up technique. Mass analysis of the incorporated species reveals the dominant presence of atomic carbon and very low abundances of C2 and C3 molecules (<1%). This is in striking contrast to the thermal evaporation of pure carbon, where C3 molecules are found to be the dominant species in the gas phase. Due to the thermal evaporation and the absence of high-energy application required for the dissociation of C2 and C3 molecules, the present source provides carbon atoms with rather low energy.

Pronounced matrix effect in YbMo2Al4-type Ca(AuxZn2−x)Au4 (x=0.09–0.89)

Electron-poor polar intermetallics Ca(AuxZn2−x)Au4 have been synthesized through fusion of stoichiometric metals in sealed tantalum tubes at 800°C and annealing at 400°C for one week. Single crystal X-ray diffraction analyses reveal that this phase belongs to the YbMo2Al4-type structure (I4/mmm, Pearson symbol tI14), a≈6.943–7.017Å, c≈5.278–5.286Å, Z=2, with homogeneous composition range of x=0.09(1)–0.89(1). The structure exhibits a three-dimensional framework of (Au8)1/2 featuring square and octagonal channels extending in c, in which Ca and the infinite linear chains of [(Au,Zn)2]1/2 are located, respectively. Mulliken population analyses demonstrate that Zn prefers to form the linear chains in the whole homogeneous composition range, consistent with experimental observations. Crystal orbital Hamilton population (COHP) analyses reveal that the channel-to-chain Au–Zn contact has strong bonding interactions regardless of its large interatomic distance (~2.85Å), a signature of pronounced matrix effect. The last mentioned effect in YbMo2Al4-type structures is expected in case the linear chains are defined by small size atoms.

SrPdGa3 – An orthorhombic superstructure of the ThCr2 Si2 type

Abstract The gallide SrPdGa3 was synthesized by melting of the elements in a sealed tantalum tube in an induction furnace. SrPdGa3 crystallizes with a new structure type which was determined on the basis of single-crystal X-ray diffractometer data: Cmcm, a=643.7(1), b=1044.9(2), c=600.4(1) pm, wR=0.0283, 504 F 2 values, 19 variables. SrPdGa3 is a new ternary ordering variant of the aristotype BaAl4/ThCr2 Si2. The structural relation with ThCr2 Si2 and the closely related silicide BaNi2 Si2 is discussed on the basis of a group-subgroup relation. The three-dimensional [PdGa3]δ– network is dominated by Pd-Ga and Ga-Ga bonding interactions with 251–256 pm Pd-Ga and 267 pm Ga-Ga distances.

Ba@Sn10 and Ru@Sn7/Rh@Sn7 polyhedra as basic building units in the stannides BaT 5–x Sn9 (T = Ru, Rh)

The tin-rich stannides BaRh5–x Sn9 and BaRu5–x Sn9 were synthesized by direct reactions of the elements in sealed niobium or tantalum tubes in muffle furnaces. Their structures were refined from X-ray single-crystal diffractometer data: BaCo4.7Ge9 type, Pnma, Z = 4, a = 1,553.44(8) pm, b = 438.38(2) pm, c = 1,861.5(1) pm, wR = 0.0558, 2,787 F 2 values for BaRh4.43Sn9, a = 1,554.09(6) pm, b = 438.44(1) pm, c = 1,873.44(5) pm, wR = 0.0589, 2,184 F 2 values for BaRh4.68Sn9, and a = 1,560.7(2) pm, b = 440.24(4) pm, c = 1,869.0(3) pm, wR = 0.0674, 2,197 F 2 values for BaRu4.57Sn9 with 93 variables per refinement. The Rh5 and Ru5 sites show small defects. The shortest interatomic distances occur for Ru–Sn and Rh–Sn, leading to Ru@Sn7 and Rh@Sn7 building units that derive from an octahedron by replacing one apex by a pair of tin atoms. These units condense by common triangular and rectangular faces forming a three-dimensional network in which the barium atoms fill slightly distorted pentagonal prismatic voids.

SrAu4Ga3: a further example with Ga3 units and a Lonsdaleite-related gold substructure

The gallide SrAu4Ga3 was obtained by induction melting of the elements in a sealed tantalum tube and subsequent annealing in a muffle furnace. SrAu4Ga3 is isotypic with Ba3Ag14.6Al6.4. Its structure was refined from single crystal X-ray diffractometer data: $${P}{\bar{6}}$$ 2m, a = 860.9(3) pm, c = 720.4(2) pm, wR = 0.0342, 678 F values, and 30 variables. The gold atoms build a distorted lonsdaleite-related (hexagonal diamond) substructure and the cavities left by this network are filled in an ordered manner by the strontium atoms as well as Ga3 and (Ga,Au)3 triangles. The latter have Ga–Ga and Ga/Au–Ga/Au distances of 305 and 262 pm, respectively. Consequently one can topologically describe the SrAu4Ga3 structure as an ordered substitution variant of the Zintl phase CaIn2. This structural relationship is discussed on the basis of a group–subgroup scheme.

BaRu3Sn6 – A Tin-rich Stannide with Ba@Sn8 and Ru@Sn7 Building Units

BaRh3Sn6 has been prepared by melting of the elements in a sealed tantalum tube and subsequent annealing. It crystallizes in the BaRh3Pb6-type structure: Cmcm, a = 807.4(2), b = 2615.3(6), c = 444.0(1) pm, wR = 0.0535, 957 F2 values, 36 variables. The structure is composed of Ba@Sn8 trapezoids (349 and 353 pm Ba-Sn) and Ru@Sn7 units (255- 284 pm Ru-Sn) which can be derived from an octahedron by replacement of one apex by a pair of tin atoms. The Ru@Sn7 units are condensed to strands via the trapezoidal faces, and these strands are connected to the Ba@Sn8 trapezoids via common edges. The tin substructure of BaRu3Sn6 exhibits a broad range of Sn-Sn distances (310 - 354 pm).

Nd3Ge1.18In0.82 and Sm3Ge1.33In0.67 – New ternary indides with La3GeIn type structure

New indides, Nd3Ge1.18In0.82 and Sm3Ge1.33In0.67, were synthesized from the elements by arc-melting and subsequent annealing at 870 K. Single crystals were grown through special annealing procedures in sealed tantalum tubes in a resistance furnace. Both compounds were investigated on the basis of X-ray powder and single crystal data: La3GeIn type structure, Pearson code tI80, space group I4/mcm; a = 1200.1(1), c = 1562.8(1) pm, wR2 = 0.0781, 716 F2 values, 34 variables for Nd3Ge1.18In0.82 and a = 1184.7(2), c = 1537.0(3) pm, wR2 = 0.0305, 911 F2 values, 34 variables for Sm3Ge1.33In0.67. The crystal chemistry in Nd3Ge1.18In0.82 is discussed from a geometrical point of view and in terms of LMTO band structure calculations.

ChemInform Abstract: NdNiMg5, a New Magnesium‐Rich Phase with an Unusual Structural Type.

AbstractNdNiMg5 is identified during a study of the Mg‐rich part of the Mg—Nd—Ni system and can be synthesized by melting of the elements (sealed tantalum tube, 973 K, 10 d).

ChemInform Abstract: From REZnSn to REZnSnH1.5 (RE: Pr, Nd) — Inducing Ferromagnetism Through Hydrogenation.

AbstractPolycrystalline PrZnSn (I) and NdZnSn (II) are prepared by induction melting of the elements in sealed tantalum tubes (1.

Sr2Au6Al3 and Eu2Au6Al3 – First Representatives of the Sr2Au6Zn3 Type with Aluminum Triangles

The aluminides Sr2Au6Al3 and Eu2Au6Al3 were synthesized by melting the elements in sealed tantalum tubes in a muffle or induction furnace. The samples were characterized by powder and single-crystal X-ray diffraction: Sr2Au6Zn3 type, R3̄c, a = 845.1(1), c = 2177.2(3) pm, wR2=0.0263, 520 F2 values, 20 variables for Sr2Au6.18(1)Al2.82(1), and a = 838.0(1), c = 2177.1(7) pm, wR2 = 0.0276, 510 F2 values, 19 variables for Eu2Au6Al3. The gold atoms build up diamond-related networks of slightly distorted tetrahedra in the stacking sequence of the 6R polytype (289 - 296 pm Au-Au in Eu2Au6Al3). The voids left by this network are filled in an ordered manner by strontium (europium) atoms and the rare motif of Al3 triangles (286 pm Al-Al in Eu2Au6Al3). The Al3 triangles in Sr2Au6.18(1)Al2.82(1) show a small degree of Al/Au mixing.

NdNiMg5, a New Magnesium-Rich Phase with an Unusual Structural Type

The new intermetallic NdNiMg5 was discovered during the study of the Mg-rich part of the Mg-Nd-Ni system. It was synthetized by melting of the constituent elements in a sealed tantalum tube with subsequent annealing. Its structure was determined by X-ray diffraction on a single crystal. Crystal data: orthorhombic system, Cmcm, Z = 4, a = 4.4799(2) Å, b = 9.9827(3) Å, c = 13.7854(10) Å, d(calc) = 3.49 g·cm(-3). Its structure is made of infinite layers of Mg atoms that form blocks stacked along the c axis. These blocks, with a close-packed array of Mg atoms, are separated by infinite NiNd layers and connected through short Mg-Mg bonds. In the NiNd layer, the Ni and Nd atoms form an ordered graphite-type network. Antiferromagnetic ordering is observed with T(N) = 12 K, and the effective magnetic moment μeff is equal to 3.89(1) μB.

From REZnSn to REZnSnH1:5 (RE = Pr, Nd) – Inducing Ferromagnetism through Hydrogenation

The ternary stannides PrZnSn and NdZnSn were synthesized by induction-melting of the elements in sealed tantalum tubes. They were characterized by powder and single-crystal X-ray diffraction: YPtAs-type structure, P63=mmc, a = 455:4(1) and c = 1650:3(2) pm, wR2=0.0266, 297 F2 for PrZnSn and a = 453:7(1) and c = 1637:0(4) pm, wR2=0.1558, 234 F2 for NdZnSn with 12 variables per refinement. PrZnSn and NdZnSn are AlB2 superstructures with slightly puckered and ordered [Zn3Sn3] hexagons in AA´BB´ stacking sequence along the crystallographic c axis. Hydrogenation results in the new hexagonal hydrides PrZnSnH1:5 (a = 447:98(8) and c = 1707:5(5) pm) and NdZnSnH1:5 (a = 448:28(8) and c = 1689:8(2) pm). Filling of RE3Zn tetrahedra by hydrogen leads to anisotropic changes of the lattice parameters and a drastic flattening of the [Zn3Sn3] layers. Temperature-dependent magnetic susceptibility measurements show Curie-Weiss behavior for PrZnSn and NdZnSn with experimental magnetic moments close to the free-ion values of RE3+. Magnetic ordering is detected at 4.7 (PrZnSn) and 6:5 K (NdZnSn). Hydrogenation induces ferromagnetism with increased ordering temperatures of 12.0 (PrZnSnH1:5) and 14:5 K (NdZnSnH1:5).

Zn3 and Ga3 Triangles as Building Units in Sr2Au6Zn3 and Sr2Au6Ga3

AbstractThe intermetallic compounds Sr2Au6.52Zn2.48, Sr2Au6Zn3, and Sr2Au6Ga3 were obtained by induction melting of the elements in sealed tantalum tubes. Their structures were studied by X‐ray diffraction on powders and refined from single crystal diffraction data: R$\bar{3}$c, a = 844.5(2), c = 2187.7(5) pm, wR2 = 0.0411, 936 F2 values and 20 variables for Sr2Au6.52Zn2.48; a = 841.6(2), c = 2191.5(7) pm, wR2 = 0.0126, 587 F2 values and 19 variables for Sr2Au6Zn3; and a = 841.9(2), c = 2191.1(7) pm, wR2 = 0.0199, 660 F2 values and 19 variables for Sr2Au6Ga3. The gold substructures of Sr2Au6Zn3 and Sr2Au6Ga3 can be considered as diamond polytypes with 6R stacking sequences (287–304 pm Au–Au in Sr2Au6Zn3). The cavities formed by this network are filled in an ordered manner by strontium atoms and Zn3 (281 pm Zn–Zn), respectively Ga3 (286 pm Ga–Ga) triangles in a 2:1 ratio. Consequently one can describe the Sr2Au6Zn3 and Sr2Au6Ga3 structures as ordered substitution variants of the Zintl phase CaIn2. This structural relationship is discussed on the basis of a group‐subgroup Scheme. Sr2Au6.52Zn2.48 shows Zn/Au mixing on the triangle.

Thermoelectric properties of Sb-doped Mg2 Si0.59 Sn0.41 solid solutions

N-type Mg2Si0.59 − xSn0.41Sbx (0 ≤ x ≤ 0.01) solid solutions were prepared by melting elemental metals in sealed tantalum tubes followed by hot pressing. The electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured as a function of temperature from 300 to 770 K. The electron effective mass and electron concentration increase with increasing Sb doping amount. The Sb doping enhances the concentration of Mg vacancies, which reduces the electron concentration. The maximum dimensionless figure of merit is 0.68 at 693 K for the x = 0.005 sample.

Infinite Linear Zinc Chains in AAu4Zn2 (A = Ca, Ce, Pr, Nd) with YbAl4Mo2 Type Structure

AbstractThe intermetallic zinc compounds AAu4Zn2 (A = Ca, Ce, Pr, Nd) were obtained by induction melting of the elements in sealed tantalum tubes. The samples were studied by X‐ray diffraction on powders. The structures of the calcium and the cerium compound were refined from single crystal diffraction data: YbAl4Mo2 type, I4/mmm, a = 692.8(1), c = 527.6(1) pm, wR2 = 0.0304, 244 F2 values and 11 variables for CaAu4.08Zn1.92 and a = 699.6(1), c = 531.2(1) pm, wR2 = 0.1152, 186 F2 values and 10 variables for CeAu4Zn2. The 4d site of the calcium compound shows small mixed Zn/Au occupancy. The AAu4Zn2 structures consist of three‐dimensional gold networks (272–286 pm Au–Au in CeAu4Zn2), which are penetrated by linear infinite zinc chains (266 pm Zn–Zn in CeAu4Zn2) that extend along the c axis. The calcium or rare earth atoms fill Au12 cavities within the networks. Temperature dependent magnetic susceptibility measurements reveal Pauli paramagnetism for CaAu4Zn2 and Curie‐Weiss paramagnetism for the cerium, praseodymium, and neodymium compound, respectively. No magnetic ordering was evident down to 2.5 K. The static intermediate‐valent compound Ce2RuZn4 crystallizes with a superstructure of CeAu4Zn2 (klassengleiche subgroup P4/nmm) with a different but fully ordered substitution on the transition metal sites. This structural relationship is discussed on the basis of a group‐subgroup scheme.

From One to Three Dimensions: Corrugated ∞1[NiGe] Ribbons as a Building Block in Alkaline Earth Metal Ae/Ni/Ge Phases with Crystal Structure and Chemical Bonding in AeNiGe (Ae = Mg, Sr, Ba)

The new equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been synthesized from the elements in sealed tantalum tubes using a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. MgNiGe crystallizes with TiNiSi-type structure, space group Pnma, Z = 4, a = 6.4742(2) Å, b = 4.0716(1) Å, c = 6.9426(2) Å, wR2 = 0.033, 305 F(2) values, 20 variable parameters. SrNiGe and BaNiGe are isotypic and crystallize with anti-SnFCl-type structure (Z = 4, Pnma) with a = 5.727(1) Å, b = 4.174(1) Å, c = 11.400(3) Å, wR2 = 0.078, 354 F(2) values, 20 variable parameters for SrNiGe, and a = 5.969(4) Å, b = 4.195(1) Å, c = 11.993(5) Å, wR2 = 0.048, 393 F(2) values, 20 variable parameters for BaNiGe. The increase of the cation size leads to a reduction of the dimensionality of the [NiGe] polyanions. In the MgNiGe structure the nickel and germanium atoms build a ∞(3)[NiGe] network with magnesium atoms in the channels. In SrNiGe and BaNiGe the ∞(1)[NiGe] ribbons are separated by strontium/barium atoms, whereas in the known CaNiGe structure the ribbons are fused to two-dimmensional atom slabs. The crystal chemistry and chemical bonding in AeNiGe (Ae = Mg, Ca, Sr, Ba) are discussed. The experimental results are reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method.

Linear infinite cadmium chains in CaAu4Cd2 and other intermetallics with YbMo2Al4-type structure

New YbMo2Al4-type cadmium compounds CaAu4Cd2, SrAu4Cd2, and EuAu4Cd2 were synthesized from the elements in sealed tantalum tubes. The structures of CaAu4Cd2 (I4/mmm, a = 710.7(1), c = 550.2(3) pm, wR2 = 0.026, 168 F 2 values, 10 variables) and EuAu4.80Cd1.20 (a = 716.6(1), c = 545.9(1) pm, wR2 = 0.024, 167 F 2 values, 11 variables) were refined from X-ray single-crystal diffractometry data. The gold and cadmium atoms show different substructures: Au4 squares (279 pm Au–Au in CaAu4Cd2) and cadmium chains (275 pm Cd–Cd in CaAu4Cd2). EuAu4Cd2 forms a solid solution EuAu4+x Cd2−x up to x ≈ 1, where almost every other cadmium atom within the chains is substituted by gold. Chemical bonding analyses on CaAu4Cd2 shows almost complete charge transfer from calcium to the [Au4Cd2] network. Bader charge analysis classifies CaAu4Cd2 as an auride. EuAu4Cd2 shows Curie–Weiss behavior above 25 K with an experimental magnetic moment of 7.86 μB/Eu atom, near to the free ion value of 7.94 μB for Eu2+ and orders ferromagnetically at T C = 16.3(5) K. 151Eu Mossbauer spectra show a single signal at an isomer shift of about −10 mm/s, compatible with divalent europium. At 5 K, and therefore clearly below T C, magnetic hyperfine splitting is observed.

SrCo2Sn8 and BaCo2Sn8: Tin-rich Stannides with Distorted SnSn6 Octahedra within Three-dimensional [Co2Sn8] Networks

Abstract The tin-rich stannides SrCo2Sn8 and BaCo2Sn8 were synthesized from the elements in sealed tantalum tubes. They crystallize with a new structure type, space group Cccm with a=1006.0(3), b=1514.4(6), c=1385.0(6) pm for SrCo2Sn8 and a=1032.8(2), b=1516.8(3), c=1405.1(3) pm for BaCo2Sn8. The structure of the barium compound was refined on the basis of single-crystal Xray diffractometer data: wR2=0.0450, 1715 F2 values, 57 variables. The cobalt atoms have seven nearest tin neighbors with Co-Sn distances ranging from 257 to 273 pm. These CoSn7 units are condensed via common rectangular faces to [Co2Sn10] double units which build up a covalently bonded three-dimensional network through Sn-Co-Sn bridges. Larger voids left by this network are filled by the barium and the Sn2 atoms. The latter have distorted octahedral tin coordination with Sn2- Sn distances of 311 - 315 pm. The barium atoms have 13 nearest tin neighbors (352 - 399 pm Ba-Sn). Temperature-dependent magnetic susceptibility data of BaCo2Sn8 show Pauli paramagnetism.