TiNiSi Type Research Articles

The high-temperature modification of ScRuSi – Structure, 29Si and 45Sc solid state NMR spectroscopy

A polycrystalline sample of the TiNiSi type low-temperature (LT) modification of ScRuSi was synthesized by arc-melting. Longer annealing in a sealed silica tube (6 weeks at 1270 K) followed by quenching led to the high-temperature (HT) phase. HT-ScRuSi adopts the ZrNiAl structure type: P6¯2m, a = 688.27(9), c = 336.72(5) pm, wR2 = 0.0861, 260 F2 values, 14 variables. The striking structural building units are regular, tricapped trigonal prisms Si1@Ru3Sc6 and Si2@Ru6Sc3. Both polymorphs have been characterized by 29Si and 45Sc MAS-NMR spectroscopy. The local scandium environments in the two polymorphs are easily distinguished by their electric field gradient tensor values, in agreement with theoretically calculated values.

Structural Characterization of Intermetallic Compounds by 27Al Solid State NMR Spectroscopy.

Intermetallic compounds are of broad interest for solid state chemists, condensed matter physicists, and material scientists due to their intriguing crystal chemistry, their physical properties, and their potential applications, ranging from lab curiosities to everyday objects. To characterize and understand the properties of new compounds and novel materials, the availability of structural information, particularly single-crystal X-ray diffraction data, is a mandatory prerequisite. Especially when it comes to the formation of compounds with deficient or mixed site occupancies, superstructures, or representatives crystallizing in other, thus far unknown structure types, a complementary method for structural analysis is of great value. Solid state nuclear magnetic resonance spectroscopy has been a valuable tool in many areas of chemistry, being an element-selective, site-specific, and inherently quantitative tool for detailed structural characterization. Magic-angle spinning conditions eliminate or reduce the effect of anisotropic interactions in the solid state, producing high-resolution spectra. Until recently, 27Al NMR studies of intermetallic aluminum compounds have been relatively sparse and mostly limited to binary systems. In this Account, we will summarize the current state of the art of high-resolution 27Al NMR in intermetallic compounds focusing on recent research efforts in our laboratories and the interpretation of NMR parameters in terms of the structural details of the compounds investigated. Besides theoretical aspects of 27Al NMR spectroscopy, short paragraphs on experimental details and the crystal chemistry of the discussed compounds are given. In the main part of this Account, we focus on three key aspects: (i) crystal structure validation, (ii) structural disorder and mixed site occupancies, and (iii) the electronic structure, all of which can be investigated by spectroscopic means. For the first part, we have chosen the ternary equiatomic compounds CaAuAl (TiNiSi type), BaAuAl (LaIrSi type), and Ba3Pt4Al4 (own type). Structural disorder and mixed site occupancies have been probed in the ScTAl series (T = Cr, Ru, Ag, Re) crystallizing in the TiNiSi, HfRhSn, and MgZn2-type structures. Also Na2Au3Al and the Heusler compounds, Sc(T0.5T'0.5)2Al (T = T' = Ni, Pd, Pt, Cu, Ag, Au), have been used for structure validation purposes, based on the number and signal area ratios of the resonances observed and on the comparison between experimental and theoretically calculated nuclear electric quadrupolar interaction parameters. Electronic structure information available from 27Al magnetic shielding will be discussed based on experimental data obtained for the RET5Al2 series (RE = Y, Lu; T = Pd, Pt), the extended RE10TAl3 series (RE = Y, Lu; T = Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt), and the ordered Heusler compounds ScT2Al (T = Ni, Pd, Pt, Cu, Ag, Au).

Equiatomic compounds REIrMg (RE = Y, La-Nd, Sm, Gd-Tm) and RERhMg (RE = Y, Sm, Gd-Tm)

The equiatomic intermetallic compounds REIrMg (RE = Y, La-Nd, Sm, Gd-Tm) and RERhMg (RE = Y, Sm, Gd-Tm) were synthesized from the elements in sealed niobium ampoules in a high-frequency furnace and characterized based on X-ray powder data. LaIrMg and CeIrMg crystallize with the orthorhombic LaNiAl type structure (Pnma), while all other compounds adopt the TiNiSi type. The structures of YRhMg, GdRh1.190(4)Mg0.810(4), DyRh1.126(5)Mg0.874(5), LaIrMg, NdIr1.033(2)Mg0.967(2) and ErIr1.059(3)Mg0.941(3) were refined from single-crystal X-ray diffractometer data. The striking structural motifs of these phases are tricapped trigonal prisms around the transition metal atoms formed by RE and Mg. The two structure types differ in the connectivity pattern of the trigonal prisms. The rhodium (iridium) atoms build up three-dimensional [RhMg] and [IrMg] networks in which cavities are filled by the rare earth atoms. Temperature dependent magnetic susceptibility measurements on X-ray pure samples of NdIrMg, SmRhMg, GdRhMg, TbRhMg and DyRhMg show Curie-Weiss paramagnetism of the trivalent rare earth ions and magnetic ordering at low temperatures: TC = 9.5K for NdIrMg and Néel temperatures of 10.0, 16.7, 10.6 and 11.3K for SmRhMg, GdRhMg, TbRhMg and DyRhMg. TbRhMg and DyRhMg exhibit field-induced spin reorientations (metamagnetism).

NbOsSi and TaOsSi – Two new superconducting ternary osmium silicides

The new equiatomic silicides NbOsSi and TaOsSi as well as ZrOsSi, TIrSi (T = Zr, Hf, Nb, Ta) and TPtSi (T = Nb, Ta) were prepared from the elements by arc-melting. These silicides crystallize with the orthorhombic TiNiSi type structure, space group Pnma. Irregularly shaped crystals of ZrOsSi, NbOsSi, TaOsSi, ZrIrSi and HfIrSi were separated from the annealed samples and investigated by single-crystal X-ray diffraction (a = 640.46(7), b = 404.07(5), c = 743.66(8) pm, wR2 = 0.0285, 390 F2 values, 20 variables for ZrOsSi; a = 629.78(6), b = 388.72(4), c = 727.48(7) pm, wR2 = 0.0350, 397 F2 values, 20 variables for NbOsSi, a = 626.80(6), b = 389.36(4), c = 726.22(7) pm, wR2 = 0.0501, 385 F2 values, 20 variables for TaOsSi, a = 653.48(8), b = 395.35(4), c = 739.19(8) pm, wR2 = 0.0427, 413 F2 values, 20 variables for ZrIrSi and a = 646.34(12), b = 393.57(7), c = 736.8(14) pm, wR2 = 0.0582, 371 F2 values, 20 variables for HfIrSi). The striking structural motifs in the new osmium compounds are three-dimensional [OsSi] networks (Os–Si: 240–251 pm) in which the osmium atoms have strongly distorted tetrahedral silicon coordination. High-pressure/high-temperature experiments (9.5 GPa/1520 K) on TaOsSi gave no hint for a structural phase transition. Temperature dependent measurements of the magnetic susceptibility and the electrical conductivity of NbOsSi and TaOsSi showed superconductivity below TC = 3.5 and 5.5 K, respectively. 29Si solid state MAS NMR investigations of the prepared silicides approved the structural models and showed a correlation between the observed 29Si resonance shifts and the electronegativity of the involved refractory metal.

Equiatomic intermetallic compounds REPtMg (RE = Y, Eu, Tb-Tm, Lu) – Structure and magnetism

Eight new equiatomic REPtMg intermetallics with RE = Y, Eu, Tb-Tm, Lu were synthesized from the elements in sealed niobium ampoules (induction melting followed by different annealing sequences). All samples were characterized through X-ray powder patterns and the structures of YPtMg, EuPtMg, DyPtMg, HoPtMg and TmPtMg were refined from single crystal X-ray diffractometer data. The REPtMg phases crystallize with two different structure types. The representatives with RE = Y, Tb-Ho crystallize with the hexagonal ZrNiAl type, space group P6¯2m, while those with RE = Eu, Yb and Lu adopt the orthorhombic TiNiSi type, space group Pnma. ErPtMg and TmPtMg are dimorphic with a ZrNiAl type high and a TiNiSi type low-temperature modification. Temperature-dependent magnetic susceptibility measurements indicate Pauli paramagnetism for YPtMg and LuPtMg while EuPtMg, TbPtMg, DyPtMg and HoPtMg are Curie-Weiss paramagnets. Antiferromagnetic (TN = 12.6 K for EuPtMg) respectively ferromagnetic ordering (TC = 56.3 K for TbPtMg, 28.8 K for DyPtMg and 19.9 K for HoPtMg) occurs in the low-temperature regime. 151Eu Mössbauer spectra confirm divalent europium (δ = −8.03 mm s−1 at 78 K) in EuPtMg and show strong magnetic hyperfine field splitting below the Néel temperature.

Crystal Structure, Magnetism, 89Y Solid State NMR, and 121Sb Mössbauer Spectroscopic Investigations of YIrSb

The ternary antimonide YIrSb was synthesized from the binary precursor YIr and elemental antimony by a diffusion controlled solid‐state reaction. Single crystals were obtained by a flux technique with elemental bismuth as an inert solvent. The YIrSb structure (TiNiSi type, space group Pnma) was refined from single‐crystal X‐ray diffractometer data: a = 711.06(9), b = 447.74(5), c = 784.20(8) pm, wR2 = 0.0455, 535 F2 values, 20 variables. 89Y solid state MAS NMR and 121Sb Mössbauer spectra show single resonance lines in agreement with single‐crystal X‐ray data. YIrSb is a Pauli paramagnet.

Cerium intermetallics CeTX– review III

AbstractThe structure–property relationships of CeTXintermetallics with structures other than the ZrNiAl and TiNiSi type are systematically reviewed. These CeTXphases form with electron-poor and electron-rich transition metals (T) andX= Mg, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb, and Bi. The review focusses on the crystal chemistry, the chemical bonding peculiarities, and the magnetic and transport properties. Furthermore119Sn Mössbauer spectroscopic data, high-pressure studies, hydrogenation reactions and the formation of solid solutions are reviewed. This paper is the third of a series of four reviews on equiatomic intermetallic cerium compounds [Part I: R. Pöttgen, B. Chevalier,Z. Naturforsch.2015,70b, 289; Part II: R. Pöttgen, B. Chevalier,Z. Naturforsch.2015,70b, 695].

29Si,47Ti,49Ti and195Pt solid state MAS NMR spectroscopic investigations of ternary silicides TPtSi, germanides TPtGe (T = Ti, Zr, Hf) and stannide TiPtSn

Eight ternary tetrelides TPtX (T = Ti, Zr, Hf; X = Si, Ge, Sn) were synthesized from the elements by arc-melting and subsequent annealing. TiPtSi, ZrPtSi, ZrPtGe, HfPtSi and HfPtGe crystallize with the orthorhombic TiNiSi type structure, in the space group Pnma. The structures of HfPtSi (a = 654.44(9), b = 387.97(6), c = 750.0(1) pm, wR2 = 0.0592, 411 F(2) values, 20 variables) and HfPtGe (a = 660.36(7), b = 395.18(4), c = 763.05(8) pm, wR2 = 0.0495, 430 F(2) values, 20 variables) were refined from single crystal X-ray diffractometer data. TiPtSn adopts the cubic MgAgAs type. TiPtGe is dimorphic with a TiNiSi type high-temperature modification which transforms to cubic LT-TiPtGe (MgAgAs type). All phases were investigated by high resolution (29)Si, (47)Ti, (49)Ti and (195)Pt solid state MAS NMR spectroscopy. In the cubic compounds, the (47/49)Ti NMR signals are easily detected owing to the absence of quadrupolar broadening effects. The (195)Pt resonances of the orthorhombic compounds are characterized by strongly negative isotropic Knight shifts and large Knight shift anisotropies, whereas positive isotropic Knight shifts and no anisotropies are observed for the cubic compounds. These results indicate that the phase transition in TiPtGe is associated with dramatic changes in the electronic properties. Within each group of isotypic compounds the isotropic (29)Si, (47/49)Ti and (195)Pt Knight shifts show systematic dependences on the transition metal or tetrel atomic number, suggesting that the numerical values are influenced by the electronegativities of the metallic (or metalloid) neighbours.

The solid solutions CeRu1–x Pd x Sn and CeRh1–x Pd x Sn – Applicability of the ICF model to determine intermediate cerium valencies by comparison with XANES data

Abstract Several samples of the solid solutions CeRu1–x Pd x Sn and CeRh1–x Pd x Sn have been synthesized by arc-melting and characterized by X-ray powder diffraction. Guinier powder patterns prove that the ZrNiAl-type structure is the dominating one, besides the CeRuSn and TiNiSi type structures. The structures of CeRu0.28Pd0.72Sn (ZrNiAl type, P6̅2m, a = 751.95(3), c = 418.70(2) pm, wR2 = 0.0274, 332 F 2 values, 14 variables) and CeRh0.66Pd0.34Sn (ZrNiAl type, P6̅2m, a = 750.26(3), c = 411.59(2) pm, wR2 = 0.0533, 358 F 2 values, 14 variables) were refined from single crystal diffractometer data. Magnetic measurements in combination with XANES (X-Ray Absorption Near Edge Structure) clearly proved intermediate cerium valencies for most compounds and revealed the best fitting parameters for those with the ICF model (Interconfiguration fluctuation). The electrical resistivity is also influenced by the substitutions. At low and high valence electron counts (VECs) metallic character is present, while around the VEC of CeRhSn the typical resistivity behavior for valence fluctuating compounds is observed.

The equiatomic intermetallics REPtCd (RE = La, Ce, Pr, Nd, Eu) and magnetic properties of CeAuCd

Abstract 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.

Three structure types and intermediate cerium valence in the solid solution CeRu1–xNixSn

Detailed analytical studies of the solid solutions CeRu1–xNixSn revealed a sequence of three different structure types, CeRuSn, ZrNiAl, and TiNiSi, with increasing x value. All compounds have been synthesized and characterized by X-ray powder diffraction. The structures of CeRu0.68Ni0.32Sn, CeRu0.38Ni0.62Sn and CeRu0.14Ni0.86Sn have been refined from single crystal X-ray diffractometer data. The former one exhibits the ZrNiAl type, P6¯2m, a = 737.9, c = 406.2 pm, wR2 = 0.0436, 345 F2 values, 17 variables. The two latter ones crystallize with the TiNiSi type, Pnma, a = 736.9, b = 468.5, c = 760.5 pm, wR2 = 0.0389, 631 F2 values, and a = 750.8, b = 461.8, c = 761.3 pm, wR2 = 0.0520, 632 F2 values, 21 variables for CeRu0.38Ni0.62Sn and CeRu0.14Ni0.86Sn, respectively. In accordance with magnetic susceptibility and Ce LIII-edge XANES measurements, cerium valence fluctuation has been proven for all samples that exhibit the hexagonal ZrNiAl type structure, while samples with the TiNiSi type show stable trivalent cerium. DFT calculations indicate that the CeRu0.5Ni0.5Sn composition should be thermodynamically stable in the hexagonal ZrNiAl type structure, while the unstable orthorhombic structure becomes monoclinic after structure relaxation.

The germanides ScTGe (T = Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au) – Structure and 45Sc solid state NMR spectroscopy

The germanides ScTGe (T = Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au) were obtained in X-ray pure form by arc-melting of the elements. The structures of the members with T = Co, Ni, Cu, Rh, Pd, Ag, Ir, and Pt were refined on the basis of single crystal X-ray diffractometer data. The germanides with T = Cu, Ru, Pd, Ag crystallize with the hexagonal ZrNiAl type structure, space group P6¯2m and those with T = Co, Ni, Rh, Ir, Pt adopt the orthorhombic TiNiSi type. ScAuGe is isotypic with NdPtSb. All germanides exhibit single scandium sites. A simple systematization of the structure type according to the valence electron concentration is not possible. The 45Sc solid state NMR parameters (Knight shifts and nuclear electric quadrupole coupling constants) of those members crystallizing in the TiNiSi structure show systematic trends as a function of valence electron concentration number. Furthermore, within each T-group the Knight shift decreases with increasing atomic number; this correlation also includes previously published results on the isotypic silicide family. The 45Sc quadrupolar interaction tensor components are generally well-reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code.

The Stannides Nd3Pd5Sn5, Gd3Pd4.96(1)Sn5, and GdPdSn

Abstract The stannides Nd3Pd5Sn5 and Gd3Pd4.96(1)Sn5 were obtained by arc‐melting of the elements. Nd3Pd5Sn5 and Gd3Pd4.96(1)Sn5 crystallize with the monoclinic Sm3Pd4.95Sn5 type structure, space group C2/m. Both structures were refined from single crystal diffractometer data: a = 1729.5(4), b = 454.51(8), c = 1428.2(3) pm, β = 99.71(2)°, wR2 = 0.0689, 2220 F2 values, 82 variables for Nd3Pd5Sn5 and a = 1712.2(2), b = 450.36(9) c = 1412.0(3) pm, β = 99.804(2)°, wR2 = 0.0526, 1834 F2 values, 83 variables for Gd3Pd4.96(1)Sn5. The Pd2 site of the gadolinium compound showed site occupancy of only 95.8(7) %. The palladium and tin atoms in these monoclinic stannides build up complex three‐dimensional [Pd5Sn5]δ– polyanionic networks, which leave cavities for the three crystallographically independent rare earth sites: RE1@Pd6Sn8, RE2@Pd7Sn8, and RE3@Pd6Sn9. The networks are stabilized by Pd–Sn, Pd–Pd as well as Sn–Sn bonding. The rare earth atoms bind to the networks via shorter RE–Pd contacts. The Gd3Pd4.96(1)Sn5 crystal showed an adherent second domain, which consisted of GdPdSn: TiNiSi type, Pnma, a = 725.6(3), b = 461.3(3), c = 790.6(3) pm, wR2 = 0.0973, 431 F2 values, 20 variables.

High-pressure phases of Tb2Ni2Sn and Dy2Ni2Sn

The W2B2Co-type ternary stannides Tb2Ni2Sn and Dy2Ni2Sn (space group Immm) show pressure-induced reconstructive phase transitions. Under high-pressure (8 GPa) and high-temperature (1,470 K) treatment they transform to the tetragonal Mo2B2Fe-type high-pressure (HP) modifications: P4/mbm, a = 732.6(1) pm, c = 371.71(9) pm, wR2 = 0.0319, 225 F 2 values for HP-Tb2Ni2Sn and a = 730.3(2) pm, c = 369.1(2) pm, wR2 = 0.0221, 230 F 2 values for HP-Dy2Ni2Sn, with 12 variables per refinement. At 8 GPa HP-Tb2Ni2Sn and HP-Dy2Ni2Sn started to decompose into the equiatomic stannides TbNiSn and DyNiSn and a yet unknown phase. Single-crystal diffractometry revealed the following data: TiNiSi type, Pnma, a = 714.9(1) pm, b = 445.9(1) pm, c = 766.4(1) pm, wR2 = 0.0558, 575 F 2 values, 20 parameters for TbNiSn and a = 710.5(1) pm, b = 445.31(9) pm, c = 765.7(1) pm for DyNiSn. The cell volumes of HP-Tb2Ni2Sn and HP-Dy2Ni2Sn nicely fit into the Iandelli plot of the whole RE2Ni2Sn (RE = rare earth) series of compounds. The polyanionic networks [NiSn] and [Ni2Sn] of the investigated ternary stannides show covalent Ni–Sn bonding with distorted tetrahedral SnNi4/4 coordination (259−279 pm Ni–Sn) in the RENiSn compounds and a square-planar SnNi4/4 arrangement (291−292 pm Ni–Sn) in HP-Tb2Ni2Sn and HP-Dy2Ni2Sn. The nickel atoms form Ni2 pairs with Ni–Ni distances of 250 pm.

Equiatomic intermetallic compounds YTX (T = Ni, Ir; X = Si, Ge, Sn, Pb): a systematic study by89Y solid state NMR and119Sn Mössbauer spectroscopy

The equiatomic TiNiSi type tetrelides YTX (space group Pnma) with T = Ni, Ir and X = Si, Ge, Sn, Pb were synthesized from the elements by arc-melting or via high-frequency-melting of the elements in sealed niobium ampoules. All samples were characterized by powder X-ray diffraction using the Guinier technique. The structures of YNiGe, YNiPb, YIrSi, YIrGe, and YIrSn were refined from single crystal X-ray diffractometer data. The YTX tetrelides are characterized by a three-dimensional [TX] network that consists of puckered T3X3 hexagons with T-X distances in the order of the sums of the covalent radii. YIrSi and YIrGe show a reverse occupancy of the T and X sites with respect to the remaining YTX compounds, which is most likely a size effect. Solid state NMR studies reveal the sensitivity of (89)Y Knight shifts to electronic structure details. A monotonic dependence on the tetrelide Pauling electronegativity is observed in addition. The stannides YTSn (T = Ni, Rh, Ir, Pt) were further characterized by (119)Sn Mössbauer spectroscopy. They show single signals that are subjected to quadrupole splitting. Comparison of the isomer shifts with the whole series of YTSn stannides gives no hint of obvious correlations as a consequence of the valence electron count but reveals a systematic decrease with atomic number within a given group.

Magnesium and cadmium in covalently bonded networks: synthesis and structure of AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) with TiNiSi type structure and the solid solution Yb2–xPtMgx

The equiatomic intermetallic compounds AETMg and AETCd (AE = Ca, Sr; T = Pd, Ag, Pt, Au) and the whole solid solution Yb2-xPtMgx were synthesized from the elements in sealed niobium tubes in a high-frequency or a muffle furnace. All samples were characterized on the basis of their powder X-ray diffraction patterns. The structures of SrAuCd, CaPdCd, CaPtCd, CaPdMg, SrPtMg, CaAg1.017Mg0.983, SrAg1.032Mg0.968, and Yb1.792PtMg0.208 were refined on the basis of single-crystal X-ray diffractometer data. Some of the crystals showed small homogeneity ranges. All compounds crystallize with the orthorhombic TiNiSi type structure, space group Pnma. The crystal chemistry is briefly discussed and variations in chemical bonding as a result of the electronegativity of the transition metal are described.

YPdSn and YPd2Sn: Structure, 89Y solid state NMR and 119Sn Mössbauer spectroscopy

The stannides YPdSn and YPd2Sn were synthesized by high-frequency melting of the elements in sealed tantalum tubes. Both structures were refined on the basis of single crystal X-ray diffractometer data: TiNiSi type, Pnma, a=715.4(1), b=458.8(1), c=789.1(1)pm, wR2=0.0461, 510F2 values, 20 variables for YPdSn and MnCu2Al type, Fm3¯m, a=671.44(8), wR2=0.0740, 55 F2 values, 5 parameters for YPd2Sn. The yttrium atoms in the new stannide YPdSn are coordinated by two tilted Pd3Sn3 hexagons (ordered AlB2 superstructure). In the Heusler phase YPd2Sn each yttrium atom has octahedral tin coordination and additionally eight palladium neighbors. The cubic site symmetry of yttrium is reflected in the 119Sn Mössbauer spectrum which shows no quadrupole splitting. In contrast, YPdSn shows a single signal at δ=1.82(1)mm/s subjected to quadrupole splitting of ΔEQ=0.93(1)mm/s. Both compounds have been characterized by high-resolution 89Y solid state NMR spectroscopy, which indicates the presence of strong Knight shifts. The spectrum of YPd2Sn is characterized by an unusually large linewidth, suggesting the presence of a Knight shift distribution reflecting local disordering effects. The range of 89Y Knight shifts of several binary and ternary intermetallic yttrium compounds is briefly discussed.

45Sc Solid State NMR studies of the silicides Sc TSi ( T=Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt)

The silicides Sc TSi ( T=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) were synthesized by arc-melting and characterized by X-ray powder diffraction. The structures of ScCoSi, ScRuSi, ScPdSi, and ScIrSi were refined from single crystal diffractometer data. These silicides crystallize with the TiNiSi type, space group Pnma. No systematic influences of the 45Sc isotropic magnetic shift and nuclear electric quadrupolar coupling parameters on various structural distortion parameters calculated from the crystal structure data can be detected. 45Sc MAS-NMR data suggest systematic trends in the local electronic structure probed by the scandium atoms: both the electric field gradients and the isotropic magnetic shifts relative to a 0.2 M aqueous Sc(NO 3) 3 solution decrease with increasing valence electron concentration and within each T group the isotropic magnetic shift decreases monotonically with increasing atomic number. The 45Sc nuclear electric quadrupolar coupling constants are generally well reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code.

Dimorphism in the REPdZn series

The intermetallic compounds REPdZn ( RE = Y, La, Pr, Nd, Sm, Gd–Tm, Lu) were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. They were characterized by powder and single crystal X-ray diffraction. The REPdZn phases crystallize with an orthorhombic TiNiSi type high- and a hexagonal ZrNiAl type low-temperature modification. The crystal chemical details are discussed for α- and β-YPdZn. High-pressure high-temperature studies (up to 11.5 GPa, 1570 K) on the structurally closely related intermetallic compounds GdAuZn and TbAuZn gave no hint for pressure-induced phase transitions.

Dimorphic LaPdSn and ErAgSn – A first principles study

The stannides LaPdSn (orthorhombic TiNiSi type, Pnma) and ErAgSn (hexagonal NdPtSb type, P6 3 mc) both transform to ZrNiAl type ( P – 6 ¯ 2 m ) high-pressure phases with different transition metal-tin ordering. The electronic structure and the chemical bonding of all four modifications have been studied by quantum theoretical DFT methodologies. Geometry optimizations are in good agreement with the experimentally determined structures. Strongest bonding interactions were observed for Pd–Sn (LaPdSn) and Er–Sn (ErAgSn). These findings result from different site occupancies and the chemical natures and electronegativities of the interacting species forming the prevailing chemical bonds in the NP/HP varieties of the two compounds.