Ternary rare earth-rich nickel cadmium compounds RE 14 Ni 3 Cd 3 ( RE = Dy–Tm, Lu)

Eighteen new rare earth-rich intermetallic phases RE 10 TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) were obtained by induction melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. All samples were characterized by X-ray powder diffraction. The structures of four representatives were refined from single-crystal X-ray diffractometer data: ordered Co2Al5 type, P63/mmc, a=951.2(1), c=962.9(2) pm, wR=0.0460, 595 F 2 values, 20 parameters for Er10RhCd3; a=945.17(4), c=943.33(4), wR=0.0395, 582 F 2 values, 21 parameters for Lu9.89PdCd3.11; a=964.16(6), c=974.93(6) pm, wR=0.0463, 614 F 2 values, 21 parameters for Y10Ir1.09Cd2.91; a=955.33(3), c=974.56(3) pm, wR=0.0508, 607 F 2 values, 22 refined parameters for Dy9.92IrCd3.08. Refinements of the occupancy parameters revealed small homogeneity ranges resulting from RE/Cd, respectively T/Cd mixing. The basic building units of the RE 10 TCd3 phases are transition metal-centered RE 6 trigonal prisms (TP) that are condensed with double-pairs of empty RE 6 octahedra via common triangular faces. A second type of rods is formed by slightly distorted RE3@Cd6 RE 6 icosahedra which are condensed via Cd3 triangular faces. The shortest interatomic distances occur for RE–T, compatible with strong covalent bonding interactions. Temperature dependent magnetic susceptibility measurements were performed for RE 10RhCd3 (RE=Dy–Tm, Lu), RE 10IrCd3 (RE=Er, Tm, Lu) and RE 10PtCd3 (RE=Y, Lu). While Y10PtCd3 and Lu10 TCd3 (T=Rh, Ir, Pt) show Pauli paramagnetic behavior, the compounds containing paramagnetic rare earth elements show Curie-Weiss behavior (the experimental magnetic moments indicate stable trivalent RE 3+) and magnetic ordering at low temperatures: T C=80.5 K for Dy10RhCd3 and Neél temperatures of 42.1, 23.3, 12.6, 5.9, 10.0 K for Ho10RhCd3, Er10RhCd3, Er10IrCd3, Tm10RhCd3, Tm10IrCd3, respectively.

The rare earth intermetallic compounds RE 2Ga2Mg with RE = Tb–Tm and Lu were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. These rare earth-rich phases crystallize with the tetragonal Mo2B2Fe-type structure, space group P4/mbm and Z = 2. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of Er2Ga2.092(1)Mg0.908(1), Tm2Ga2.037(1)Mg0.963(1) and Lu2Ga2.176(1)Mg0.824(1) have been refined from single crystal X-ray diffractometer data. The refinements revealed small homogeneity ranges (small degrees of Mg/Ga mixing on the 2a sites). The magnesium atoms show square planar coordination by Ga2 dumbbells (282 pm Mg–Ga and 257 pm Ga–Ga in the lutetium compound). Geometrically one can describe the RE 2Ga2Mg phases as 1:1 intergrowth structures of CsCl and AlB2-related slabs of compositions REMg and REGa2. From DFT based calculations, charge transfer from the rare earth and magnesium atoms towards gallium can be illustrated in electron localization function ELF slice planes showing strong localization around gallium in the basal plane as well as along the tetragonal c axis signaling Ga–Ga pair interactions. The site-projected density of states DOS and COOP data further quantify this observation. Temperature dependent magnetic susceptibility measurements show Pauli paramagnetism for Sc2Ga2Mg and Lu2Ga2Mg with low room temperature susceptibility values of 2.1(1) × 10−4 and 1.1(1) × 10−4 emu mol−1, respectively. Ho2Ga2Mg, Er2Ga2Mg and Tm2Ga2Mg are Curie-Weiss paramagnets with stable trivalent rare earth ground states. Antiferromagnetic ordering was detected below the Néel temperatures of T N = 18.6(1) (RE = Ho), 11.9(1) (RE = Er) and 6.4(1) K (RE = Tm). The three compounds show metamagnetic transitions in their 3 K magnetization isotherms. Tm2Ga2Mg exhibits a square loop behavior with small hysteresis.

The ternary rare earth transition metal-indides RE 3 T 2In4 (RE=Dy–Tm; T=Pd, Ir) were obtained from high-temperature reactions in sealed niobium ampoules. These indides adopt a hexagonal structure of the Lu3Co1.87In4 type (space group P6̅), a ternary ordered superstructure of the aristotype Fe2P. The structures of three different compounds were refined from single-crystal X-ray diffractometer data: a=768.20(6), c=381.97(3) pm, 1441 F 2 values, 24 parameters, wR2=0.0338 (Ho3Pd1.90In4); a=774.98(3), c=378.51(2) pm, 577 F 2 values, 23 parameters, wR2=0.0742 (Ho3Ir1.69In4.31) and a=780.3(1), c=369.4(1) pm, 573 F 2 values, 22 parameters, wR2=0.0403 (Tm3Ir1.51In4.49). Refinements of the occupancies revealed homogeneity ranges in case of the iridium-based crystals resulting from Ir/In mixing. The refined composition of the palladium compound was Ho3Pd1.90In4 resulting from defects on the Wyckoff position 1d, which was already reported for the prototype Lu3Co1.87In4. The geometrical motifs of the RE 3 T 2In4 structures are three different types of tricapped trigonal prisms around the transition metal and indium atoms which are condensed via common edges and triangular faces. Temperature dependent magnetic susceptibility measurements of Dy3Ir2In4 and Tm3Ir2In4 showed Curie-Weiss behavior and the experimental magnetic moments of 10.59(2) μB (Dy3Ir2In4) and 7.40(2) μB (Tm3Ir2In4) confirming stable trivalent RE 3+ states. Dy3Ir2In4 and Tm3Ir2In4 order antiferromagnetically with Néel temperatures of T N=13.6(5) and 5.4(5) K, respectively.

The intermetallic calcium compounds CaTMg2 and CaTCd2 (T =Rh, Pd, Pt) were obtained by high-frequency melting of the elements in sealed niobium ampoules or through reactions in muffle furnaces. The polycrystalline samples were characterized by powder X-ray diffraction. They crystallize with a site occupancy variant of YPd2Si, a ternary ordered version of Fe3C. The structures of CaPdMg2 and CaPdCd2 were refined from single-crystal diffractometer data: Pnma, a=792.2(2), b=803.4(2), c=572.0(1) pm, wR2=0.0663, 1621 F2 values, 24 variables for Ca0:94PdMg2:06 and a=794.6(2), b=809.5(3), c=554.7(2) pm, wR2=0.0301, 819 F2 values, 23 variables for CaPdCd2. A small range of homogeneity was observed for Ca1-xPdMg2+x. The magnesium and cadmium atoms build up three-dimensional tetrahedral substructures (306 - 327 pm Mg-Mg and 307 - 317 pm Cd-Cd) that resemble hexagonal diamond, lonsdaleite. Together with the palladium atoms one obtains three-dimensional, covalently bonded [PdMg2] and [PdCd2] networks which leave cages for the calcium atoms. The latter are bonded to these networks via shorter Ca-Pd contacts (298 - 319 pm in Ca0:94PdMg2:06 and 295 - 312 pm in CaPdCd2). The course of the interatomic distances is in line with calculated overlap populations. The CaPdMg2, SrPdMg2 and CaRhIn2 structures are all derived from a CaIn2-related subcell by an ordered filling of transition metal atoms into trigonal prisms. This leads to different herringbone patterns for the networks of puckered and elongated hexagons of magnesium and indium atoms.

The REPt2Al3 compounds of the late rare-earth metals (RE = Y, Dy–Tm) were found to crystallize isostructural. Single-crystal X-ray investigations of YPt2Al3 revealed an orthorhombic unit cell (a = 1080.73(6), b = 1871.96(9), c = 413.04(2) pm, wR2 = 0.0780, 942 F2 values, 46 variables) with space group Cmmm (oC48; q2pji2hedb). A comparison with the Pearson database indicated that YPt2Al3 forms a new structure type, in which the Pt and Al atoms form a [Pt2Al3]δ− polyanion and the Y atoms reside in the cavities within the framework. Via a group-subgroup scheme, the relationship between the PrNi2Al3-type structure and the new YPt2Al3-type structure was illustrated. The compounds with RE = Dy–Tm were characterized by powder X-ray diffraction experiments. While YPt2Al3 is a Pauli-paramagnet, the other REPt2Al3 (RE = Dy–Tm) compounds exhibit paramagnetic behavior, which is in line with the rare-earth atoms being in the trivalent oxidation state. DyPt2Al3 and TmPt2Al3 exhibit ferromagnetic ordering at TC = 10.8(1) and 4.7(1) K and HoPt2Al3 antiferromagnetic ordering at TN = 5.5(1) K, respectively. Attempts to synthesize the isostructural lutetium compound resulted in the formation of Lu2Pt3Al4 (Ce2Ir3Sb4-type, Pnma, a = 1343.4(2), b = 416.41(8), c = 1141.1(2) pm), which could also be realized with thulium. The structure was refined from single-crystal data (wR2 = 0.0940, 1605 F2 values, 56 variables). Again, a polyanion with bonding Pt–Al interactions was found, and the two distinct Lu atoms were residing in the cavities of the [Pt3Al4]δ– framework. X-ray photoelectron spectroscopy (XPS) measurements were conducted to examine the electron transfer from the rare-earth atoms onto the polyanionic framework.

Rare earth-rich compounds RE9TMg4 (RE = Y, Dy-Tm, Lu; T = Ru, Rh, Os, Ir) with an ordered Co2Al5-type structure

Structure and homogeneity ranges of the REAuZn series

Samples of the solid solutions EuAu4Cd2−x Mg x were synthesized from the elements in sealed tantalum ampoules. The elements were reacted at a maximum temperature of 1273 K followed by slow cooling. For crystal growth, the polycrystalline samples were ground to powders, pressed to pellets and annealed again. All samples crystallize with the tetragonal YbAl4Mo2-type structure, space group I4/mmm. The solid solution extends up to x = 1 and the Cd/Mg substitution has only a minor influence on the lattice parameters. The samples have been characterized by powder X-ray diffraction and the structure of EuAu4Cd1.58(2)Mg0.42(2) was refined from single crystal X-ray diffractometer data: a = 715.46(14), c = 549.96(11) pm, wR2 = 0.0334, 180 F 2 values and 11 variables. The striking crystal chemical motifs of the EuAu4Cd2−x Mg x structures are Eu@Au12 and (Cd/Mg)@Au8(Cd/Mg)2 polyhedra and linear Cd/Mg chains in form of a tetragonal rod packing with distances of 275 pm for Cd/Mg–Cd/Mg. Temperature dependent magnetic susceptibility measurements of all samples from the solid solutions EuAu4Cd2−x Mg x revealed Curie–Weiss behavior and stable divalent europium. All samples are ordered ferromagnetically around T = 16 K, and magnetization isotherms at 3 K classify these materials as soft ferromagnets. It is remarkable that the structural Cd/Mg disorder within the chains does not influence the ferromagnetic ground state. The divalent nature of europium in these intermetallics was exemplarily studied for the EuAu4Cd1.4Mg0.6 sample by 151Eu Mössbauer spectroscopy. At 6 K the isomer shift is −9.95(4) mm s−1 and one observes full magnetic hyperfine field splitting with B hf = 27.1(1) T.

The magnesium- and cadmium-rich intermetallic phases EuTMg2 (T = Rh, Pd, Ag, Ir, Pt, Au), EuTCd2 (T = Pd, Pt, Au) and CaRhMg2 were synthesized from the elements in sealed niobium or tantalum ampoules and with heat treatments in muffle or induction furnaces. The samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data. EuTMg2 (T = Pd, Ag, Pt, Au) and EuTCd2 (T = Pd, Pt, Au) crystallize with the MgCuAl2 type, space group Cmcm, while EuRhMg2, EuIrMg2 and CaRhMg2 adopt the YSiPd2 type, space group Pnma. The striking crystal chemical motif of both series of compounds are networks of puckered Mg(Cd) hexagons in ABAB stacking sequence that derive from the aristotype AlB2; however, with different tiling. Temperature dependent magnetic susceptibility and 151Eu Mössbauer spectroscopic measurements indicate stable divalent europium. Antiferromagnetic ordering sets in at 20.2 (EuIrMg2), 22.3 (EuPdMg2), 21.3 (EuAgMg2), 10.9 (EuPdCd2) and 15.5 K (EuPtCd2), respectively. The stable antiferromagnetic ground states are substantiated by metamagnetic transitions. The 151Eu isomer shifts show a linear correlation with the valence electron count for the whole series of EuTMg2, EuTCd2, EuTIn2 and EuTSn2 phases.

The stannide Li4Rh3Sn5 was synthesized by induction-melting of the elements in a sealed tantalum ampoule. The sample was characterized by powder X-ray diffraction and the Li4Rh3Sn5 structure was refined from single-crystal X-ray diffractometer data: new type, orthorhombic space group Pnnm, a = 813.27(11), b = 2,259.6(3), c = 449.94(6) pm, wR2 = 0.0486, 1577 F 2 values and 64 variables. The rhodium and tin atoms form a rigid covalently bonded three-dimensional [Rh3Sn5] network with Rh–Sn distances ranging from 263 to 277 pm. Within this network, the tin atoms form two different substructures, i. e., angled Sn1–Sn4–Sn5 units and isolated Sn2 and Sn3 atoms. The lithium atoms fill cages within the [Rh3Sn5] network. They have coordination numbers 11, 12 and 13. Based on their different 7Li resonance shifts two groups of distinct local environments can be identified in an intensity ratio of 3:1, namely the 4g Wyckoff sites Li1, Li2, and Li5, and the 2c Wyckoff sites Li3 and Li4. The whole Li4Rh3Sn5 structure can be described by condensation of the Li1@LiRh4Sn6, Li2@Li2Rh4Sn6, Li3@Li2Rh4Sn6, and Li4@Li2Rh4Sn6 polyhedra, including the Li5 atoms which are within the Li1 coordination sphere. The 119Sn Mössbauer spectrum of Li4Rh3Sn5 shows a superposition of two sub-signals in a ratio of 60:40. The two sub-signals with similar isomer shift are discernable through their quadrupole splitting parameters: ∼1.93 mm s−1 for the tin atoms of the angled Sn3 unit, and ∼1.20 mm s−1 for the isolated tin atoms with a more symmetric electron density distribution.

The stannides AuTSn2 (T = Ni, Cu, Pd) were synthesized by reacting the elements in sealed silica ampoules at 1300 K and subsequent annealing sequences. The compounds were studied by X‐ray powder diffraction. The structure of the new stannide AuPdSn2 was refined from single crystal diffractometer data: P63/mmc, a = 415.8(2), c = 557.1(2) pm, wR2 = 0.0400, 88 F2 values, and 6 variable parameters. These ternary stannides derive from the NiAs structure. For AuPdSn2 only a disordered structure with a random distribution of gold and palladium on the nickel site was observed. AuNiSn2 and AuCuSn2, however, are ordered superstructures, space group $P{\bar 3}m{\rm 1}$. 119Sn Mössbauer spectra show single signals at isomer shifts of 2.00(1) (Ni), 2.10(1) (Pd), and 2.26(1) mm/s (Cu), indicating the highest s electron density at the tin nuclei of AuCuSn2. AuNiSn2, where the tin atoms show the strongest displacement from the subcell mirror plane reveals the largest quadrupole splitting of 0.60(1) mm/s. Chemical bonding in AuSn and AuNiSn2 was compared on the basis of TB–LMTO–ASA electronic structure calculations. The latter reveal strong Au–Ni and Ni–Sn bonding in the ordered structure of AuNiSn2.

This paper reports for the first time on the new laminar quaternary orthorhombic heterometallic quaternary tellurides SrLnCuTe3, the fabrication of which has been a challenge until this work. Data on the crystal structure of tellurides complete the series of quaternary strontium chalcogenides SrLnCuCh3 (Ch = S, Se, Te). Single crystals of the compounds were synthesized from the elements by the halogenide-flux method at 1070 K. The compounds are crystallizing in two space groups Pnma (Ln = Sm, Gd and Tb) and Cmcm (Ln = Dy–Tm and Lu). For SrSmCuTe3 (a = 11.4592(7), b = 4.3706(3), c = 14.4425(9) Å, space group: Pnma) with the largest lanthanoid cation, Sr2+ shows C.N. = 7, whereas Sm3+ reveals a diminished coordination number C.N. = 6. For SrLuCuTe3 (a = 4.3064(3), b = 14.3879(9), c = 11.1408(7) Å, space group: Cmcm) with the smallest lanthanoid cation, coordination numbers of six are realized for both high-charged cations (Sr2+ and Lu3+: C.N. = 6). The cations Sr2+, Ln3+, Cu+ each take independent positions. The structures are built by distorted [CuTe4]7– tetrahedra, forming the infinite chains {∞1[Cu(Te1)1/1t(Te2)1/1t(Te3)2/2e]5−} along [010] in SrLnCuTe3 (Ln = Sm, Gd and Tb) and [100] in SrLnCuTe3 (Ln = Dy–Tm and Lu). The distortion of the polyhedra [CuTe4]7– was compared for the whole series SrLnCuTe3 by means of τ4-descriptor for the four coordinating Te2– anions, which revealed a decrease in the degree of distortion with a decreasing radius at Ln3+. The distorted octahedra [LnTe6]9– form layers {∞2[Ln(Te1)2/2(Te2)2/2(Te3)2/2]3−}. The distorted octahedra and tetrahedra fuse to form parallel layers {∞2[CuLnTe3]2−} and between them, the Sr2+ cations providing three-dimensionality of the structure are located. In the SrLnCuTe3 (Ln = Sm, Gd and Tb) structures, the Sr2+ cations center capped the trigonal prisms [SrTe6+1]12−, united in infinite chains {∞1[Sr(Te1)2/2(Te2)3/3(Te3)2/2]4−} along the [100] direction. The domains of existence of the Ba2MnS3, BaLaCuS3, Eu2CuS3 and KZrCuS3 structure types are defined in the series of orthorhombic chalcogenides SrLnCuCh3 (Ch = S, Se and Te). The tellurides SrLnCuTe3 (Ln = Tb–Er) of both structure types in the temperature range from 2 up to 300 K are paramagnetic, without showing clear signs of a magnetic phase transition.

The cadmium intermetallics REPtCd (RE = La, Ce, Pr, Nd, Eu) and CeAuCd were synthesized by induction-melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. The samples were characterized by powder X-ray diffraction. The structures of CePtCd (ZrNiAl type, P 6 ¯ 2 m , $P\bar 62m,$ a = 763.8(6), c = 409.1(4) pm, wR2 = 0.0195, 298 F 2 values, 14 variables) and EuPtCd (TiNiSi type, Pnma, a = 741.3(2), b = 436.4(1), c = 858.0(4) pm, wR2 = 0.0385, 440 F 2 values, 20 variables) were refined from single-crystal data. The REPtCd structures exhibit three-dimensional networks of corner- and edge-sharing Cd@Pt2/6Pt2/3 and Cd@Pt4/4 tetrahedra, which leave cages for the rare earth atoms. Temperature-dependent magnetic susceptibility data of CeAuCd reveal a paramagnetic to antiferromagnetic phase transition at T N = 3.7(5) K.

The cadmium-rich intermetallic cage compounds A Ir 2 Cd 20 ( A = Sr, La–Nd, Sm, Eu) were synthesized by induction-melting of the elements in sealed tantalum ampoules followed by annealing in muffle furnaces. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of LaIr 2 Cd 20 and EuIr 2 Cd 20 were refined from single crystal X-ray diffractometer data: CeCr 2 Al 20 -type, Fd 3 ‾ $\overline{3}$ m , a = 1,566.26(4) pm, w R = 0.0438, 514 F 2 values, 17 variables for LaIr 2 Cd 20 and a = 1,567.58(3) pm, w R = 0.0645, 438 F 2 values, 17 variables for EuIr 2 Cd 20 . The structures derive from a MgCu 2 -type A Ir 2 substructure where the A atoms are surrounded by 16 Cd atoms in form of a Frank-Kasper polyhedron and the Ir atoms have 12 Cd neighbors in icosahedral coordination. Temperature dependent magnetic susceptibility studies show diamagnetism for SrIr 2 Cd 20 and LaIr 2 Cd 20 . CeIr 2 Cd 20 , PrIr 2 Cd 20 and NdIr 2 Cd 20 are Curie-Weiss paramagnets without any sign for magnetic ordering down to 2 K. EuIr 2 Cd 20 contains stable divalent europium (7.85(1) µ B Eu atom −1 ) and orders ferromagnetically at T C = 17.2(1) K. The stable divalent ground state is corroborated by 151 Eu Mössbauer spectroscopy with an isomer shift value of δ = −10.66(1) mm s −1 .

Polycrystalline samples of the stannides Ca1.692Pt2Sn3.308, SrPtSn2 and EuAuSn2 were synthesized directly from the elements, using sealed tantalum ampoules as crucible material. The reactions were performed in muffle or induction furnaces. The phase purity of the samples was studied by X-ray powder diffraction (Guinier technique). The structures of Ca1.692Pt2Sn3.308 and SrPtSn2 were refined from single-crystal X-ray diffractometer data: NdRh2Sn4 type, Pnma, a = 1887.22(13), b = 441.22(3), c = 742.89(4) pm, wR = 0.0626, 1325 F 2 values, 45 variables for Ca1.692(8) Pt2Sn3.308(8) and CeNiSi2 type, Cmcm, a = 462.59(5), b = 1932.8(2), c = 458.00(5) pm, wR = 0.0549, 481 F 2 values, 18 variables for SrPtSn2. The calcium compound shows a homogeneity range Ca1+x Pt2Sn4−x with substantial Sn4/Ca2 mixing on one of the 4c Wyckoff positions. The [PtSn2] network is characterized by Pt–Sn (269–281 pm) and Sn–Sn (306–336 pm) bonding interactions. SrPtSn2 contains two different tin substructures: (i) Sn1–Sn1 zig-zag chains (282 pm) and (ii) orthorhombically distorted Sn2 squares (326 pm) with stronger and weaker Sn–Sn bonding. Together, the platinum and tin atoms build up a three-dimensional [PtSn2] network in which the platinum atoms have a distorted square-pyramidal tin coordination with Pt–Sn distances ranging from 261–270 pm. EuAuSn2 also crystallizes with the CeNiSi2-type structure with the lattice parameters a = 453.9(1), b = 2018.9(5) and c = 456.8(1) pm. Temperature dependent magnetic susceptibility studies indicate europium(II) with an experimental magnetic moment of 8.28(2) µB per Eu atom. EuAuSn2 is ordered antiferromagnetically at T N = 14.8(2) K. 151Eu Mössbauer spectra confirm the oxidation state +2 for europium (isomer shift δ = −11.17(2) mm s−1) and the magnetic ordering at low temperature (21.8 T magnetic hyperfine field at 6 K).