Rainer Kraft

Intermetallic rare earth (RE) magnesium compounds REPdMg and RE2Pd2Mg

Abstract The intermetallic rare earth metal compounds REPdMg (RE=Nd, Eu, Tb, Ho, Tm, Yb) and RE2Pd2Mg (RE=Y, Pr, Nd, Sm, Gd, Tb, Dy, Ho) were synthesized from the elements by reactions in sealed tantalum tubes in a high-frequency furnace. All compounds were investigated by X-ray powder diffraction. With a trivalent rare earth element, the REPdMg intermetallics adopt the hexagonal ZrNiAl structure, while those with a divalent rare earth metal crystallize with the orthorhombic TiNiSi type. The structures of EuPdMg and YbPdMg have been refined on the basis of single-crystal diffractometer data: Pnma, a=753.85(9), b=440.27(4), c=866.27(9) pm, wR2=0.0770, 366 Fo2 values, 20 variables for EuPdMg and a=729.4(2), b=424.3(2), c=850.5(3) pm, wR2=0.0622, 546 Fo2 values, 20 variables for YbPdMg. In both structure types, the palladium and magnesium atoms build a three-dimensional [PdMg] network in which the rare earth metal atoms fill distorted hexagonal channels. With a lower magnesium content the compounds RE2Pd2Mg with the tetragonal Mo2FeB2 structure, space group P4/mbm were obtained. Single crystal data yielded a=774.4(2), c=393.37(8) pm, wR2=0.0556, 216 Fo2 values, 13 variables for Nd2Pd2Mg and a=762.56(8), c=380.55(7) pm, wR2=0.0476, 298 Fo2 values, 12 variables for Tb2Pd2Mg. The magnesium position of the neodymium compound shows a small magnesium/palladium mixed occupancy leading to the refined composition Nd2Pd2.11Mg0.89. The compounds may be considered as intergrowths of CsCl and AlB2 related slabs of compositions REMg and REPd2. The crystal chemistry and chemical bonding in these intermetallics is briefly discussed. The magnetic properties of YbPdMg, Pr2Pd2Mg and Sm2Pd2Mg were investigated with a SQUID magnetometer. YbPdMg is Pauli paramagnetic with a room temperature susceptibility of 246(5)×10−6 cm3/mol. Pr2Pd2Mg is Curie–Weiss paramagnetic above 100 K with an experimental magnetic moment of 3.86(5) μB/Pr atom. Antiferromagnetic ordering occurs at 15(1) K. Pr2Pd2Mg is a metamagnet with a critical field of 0.8(1) T. The saturation magnetization at 2 K and 5 T is 2.65(5) μB/Pr atom. Sm2Pd2Mg shows Van Vleck paramagnetism.

Syntheses and Crystal Structures of LaRhMg, CeRhMg, PrRhMg, and NdRhMg

New intermetallic rare earth compounds LaRhMg, CeRhMg, PrRhMg, and NdRhMg were prepared by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. LaRhMg crystallizes with the LaNiAl type structure, space group Pnma, Z = 8, a = 760.1(2), b = 419.92(8), c = 1702.6(2) pm, wR2 = 0.0482, 740 F2 values and 38 variable parameters. The cerium compound adopts the ZrNiAl structure: P6¯2m, Z = 3, a = 752.3(1), c = 417.6(1) pm, wR2 = 0.0497, 250 F22 values and 17 variable parameters. PrRhMg and NdRhMg crystallize with the TiNiSi type: Pnma, Z = 4, a = 721.62(7), b = 415.98(4), c = 869.47(8) pm, wR2 = 0.1864, 440 F2 values, 20 variables for PrRhMg and a = 720.6(1), b = 417.6(1), c = 868.8(1) pm, wR2 = 0.0779, 425 F2 values, 22 variables for NdRhMg. Refinements of the occupancy parameters revealed mixed Mg/Rh occupancy for the magnesium sites of the cerium and the neodymium compound leading to the compositions CeRh1.262(8)Mg0.738(8) and NdRh1.114(9)Mg0.886(9) for the investigated single crystals. From a geometrical point of view, the four crystal structures are built up from different rhodium centered trigonal prisms. The rhodium and magnesium atoms form three-dimensional [RhMg] networks in which the rare earth metal atoms are located in different types of channels. The networks show Rh—Mg and Mg—Mg bonding. Synthese und Kristallstrukturen von LaRhMg, CeRhMg, PrRhMg und NdRhMg Die neuen intermetallischen Seltenerdverbindun-gen LaRhMg, CeRhMg, PrRhMg und NdRhMg wurden durch Reaktion der Elemente in geschlossenen Tantalampullen in einem Hochfrequenzofen synthetisiert. Die Verbindungen wurden uber Rontgen-Pulver- und Einkristalluntersuchungen charakterisiert. LaRhMg kristallisiert im LaNiAl-Typ, Raumgruppe Pnma, Z = 8, a = 760, 1(2); b = 419, 92(8); c = 1702, 6(2) pm; wR2 = 0, 0482; 740 F2-Werte und 38 variable Parameter. Die Cerverbindung ist isotyp zu ZrNiAl: P6¯2m, Z = 3, a = 752, 3(1); c = 417, 6(1) pm; wR2 = 0, 0497; 250 F2-Werte und 17 variable Parameter. PrRhMg und NdRhMg kristallisieren im TiNiSi-Typ: Pnma, Z = 4, a = 721, 62(7); b = 415, 98(4); c = 869, 47(8) pm; wR2 = 0, 1864; 440 F2-Introduction Werte, 20 Variable fur PrRhMg und a = 720, 6(1); b = 417, 6(1); c = 868, 8(1) pm; wR2 = 0, 0779; 425 F2-Werte; 22 Variable fur NdRhMg. Verfeinerungen der Besetzungsparameter ergaben eine gemischte Mg/Rh-Besetzung fur die Magnesium-Positionen der Cer- und Neodymverbindung, was zu den Zusammensetzungen CeRh1.262(8)Mg0.738(8) und NdRh1.114(9)Mg0.886(9) fur die untersuchten Einkristalle fuhrte. Rein geometrisch betrachtet sind die vier Strukturen aus unterschiedlichen, rhodium-zentrierten trigonalen Prismen aufgebaut. Die Rhodium- und Magnesiumatome bilden dreidimensionale [RhMg] Netzwerke aus, in denen die Seltenerdmetallatome zwei unterschiedliche Arten von Kanalen besetzen. Innerhalb der Netzwerke findet man Rh—Mg- und Mg—Mg-Bindungen.

Ternary Thallides REMgTl (RE = Y, La - Nd, Sm, Gd - Tm, Lu)

The rare earth metal (RE)-magnesium-thallides REMgTl (RE = Y, La-Nd, Sm, Gd-Tm, Lu) were prepared from the elements in sealed tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. The thallides were characterized through their X-ray powder patterns. They crystallize with the hexagonal ZrNiAl type structure, space group P62m, with three formula units per cell. Four structures were refined from X-ray single crystal diffractometer data: α = 750.5(1), c = 459.85(8) pm, wR2 = 0.0491, 364 F2 values, 14 variables for YMgTl; α = 781.3(1), c = 477.84(8) pm, wR2 = 0.0640, BASF = 0.09(2), 425 F2 values, 15 variables for LaMgTl; α = 774.1(1), c = 473.75(7) pm, wR2 = 0.0405, 295 F2 values, 14 variables for CeMgTl; a = 760.3(1), c = 465.93(8) pm, wR2 = 0.0262, 287 F2 values, 14 variables for SmMgTl. The PrMgTl, NdMgTl, GdMgTl, TbMgTl, and DyMgTl structures have been analyzed using the Rietveld technique. The REMgTl structures contain two cystallographically independent thallium sites, both with tri-capped trigonal prismatic coordination: Tl1Mg3RE6 and Tl2Mg6RE3. Together the magnesium and thallium atoms form three-dimensional [MgTl] networks with Mg-Mg distances of 327 and Mg-Tl distances in the range 299 - 303 pm (data for CeMgTl)

Ternary Indides REMgIn (RE = Y, La-Nd, Sm, Gd-Tm, Lu). Synthesis, Structure and Magnetic Properties

Abstract The equiatomic rare earth-magnesium-indium compounds REMgIn (RE = Y, La-Nd, Sm, Gd- Tm, Lu) were prepared from the elements in sealed tantalum tubes inside a water-cooled sample chamber of an induction furnace. All compounds were characterized through their X-ray powder patterns. They crystallize with the hexagonal ZrNiAl type structure, space group P6̄̄2m, with three formula units per cell. The structure of SmMgIn was refined from X-ray single crystal diffractometer data: a = 761.3(2), c = 470.3(1) pm, wR2 = 0.0429, 380 F2 values and 14 variable parameters. The DyMgIn, HoMgIn, and TmMgIn structures have been analyzed using the Rietveld technique. The REMgIn structures contain two cystallographically independent indium sites, both with tri-capped trigonal prismatic coordination: In1Sm6Mg3 and In2Mg6Sm3. Together the magnesium and indium atoms form a three-dimensional [MgIn] network with Mg-Mg distances of 320 and Mg-In distances in the range 294 - 299 pm. Temperature dependent magnetic susceptibility data show Curie-Weiss behavior for DyMgIn, HoMgIn, and TmMgIn with experimental magnetic moments of 11.0(1) μB/Dy atom, 10.9(1) μB/Ho atom, and 7.5(1) μB/Tm atom. The three compounds order antiferromagnetically at TN = 22(2) K (DyMgIn), 12(1) K (HoMgIn), and 3(1) K (TmMgIn).

Ternary gallides REMgGa (RE = Y, La, Pr, Nd, Sm-Tm, Lu): Synthesis and crystal chemistry

The title compounds have been synthesized by reacting the elements in sealed niobium or tantalum tubes in a high-frequency furnace. They crystallize with the hexagonal ZrNiAl type structure, space group P62m. All gallides have been characterized through their X-ray powder diffractogram. The cell volume decreases from the lanthanum to the lutetium compound as expected from the lanthanoid contraction. The structures of LaMgGa, PrMgGa, NdMgGa, SmMgGa and TmMgGa have been refined from single crystal diffractometer data. The structures contain two crystallographically independent gallium sites which both have a trigonal prismatic coordination: Ga1 by six RE and Ga2 by six Mg atoms. These trigonal prisms are capped on the rectangular sites by three Mg (RE) atoms, leading to coordination number 9 for each gallium atom. Together, the gallium and magnesium atoms form a three-dimensional [MgGa] network in which the rare earth atoms fill distorted hexagonal channels. Within the network the magnesium atoms have short Mg-Mg contacts, i. e. 312 pm in SmMgGa. The Mg-Ga distances in that gallide range from 284 to 287 pm. Bonding in the network is thus governed by strong Mg-Ga and Mg-Mg bonding. EuMgGa crystallizes with the orthorhombic TiNiSi type: Pnma, a = 783.1(2), b = 472.8(1), c = 829.8(2) pm.

Ferromagnetic Ordering in the Thallide EuPdTl2

Abstract The new thallide EuPdTl2, synthesized from the elements in a sealed tantalum tube in a highfrequency furnace, was investigated by X-ray diffraction on powders and single crystals: MgCuAl2 type, Cmcm, Z = 4, a = 446.6(1), b = 1076.7(2), c = 812.0(2) pm, wR2 = 0.0632, 336 F2 values, 16 variables. The structure can be considered as an orthorhombically distorted, palladium-filled variant of the binary Zintl phase EuTl2. The palladium and thallium atoms build up a three-dimensional [PdTl2] polyanion with significant Pd-Tl (286 - 287 pm) and Tl-Tl (323 - 329 pm) interactions. The europium atoms fill distorted hexagonal channels of the [PdTl2] polyanion. Susceptibility measurements show a magnetic moment of 7.46(5) μB/Eu atom, indicative of divalent europium. EuPdTl2 is a soft ferromagnet with a Curie temperature of TC = 12.5(5) K.

Structure and magnetism of REPtMg (RE = Pr, Nd, Sm)

New magnesium based intermetallic compounds PrPtMg, NdPtMg and SmPtMg were synthesized from the elements by reaction in sealed tantalum tubes in a high-frequency furnace. The three compounds were investigated by X-ray powder and single crystal diffraction: ZrNiAl type, space group P6̄2m, a = 752.34(8), c = 412.66(4) pm, wR2 = 0.0668, 341 F2 values, 14 variables for PrPtMg, a = 748.80(8), c = 411.52(4) pm, wR2 = 0.0521, 196 F2 values, 14 variables for NdPtMg and a = 743.90(5), c = 409.80(3) pm, wR2 = 0.0489, 248 F2 values, 12 variables for SmPtMg. From a geometrical point of view these structures are composed of two types of platinum centered trigonal prisms, i. e. [Pt1Mg3RE6] and [Pt2Mg6RE3]. These prisms are condensed via common edges and faces. Together the platinum and magnesium atoms build three-dimensional [PtMg] networks in which the rare earth atoms are located in distorted pentagonal channels. Magnetic susceptibility data of PrPtMg show Curie-Weiss behaviour with an experimentalmagnetic moment of 3.59(2) μB and a paramagnetic Curie temperature of 7.5(5) K. Ferromagnetic ordering is detected at TC = 8.0(5) K with a magnetic moment of 1.75(5) μB/Pr at 4.5 K and 5 T. SmPtMg orders ferromagnetically below 52(1) K with a presumably complex spin structure in the ordered state.