ZrNiAl Type Research Articles

Structure and Properties of CeNiZn and CeAuZn

Well crystallized samples of the intermetallic zinc compounds CeNiZn and CeAuZn were synthesized from the elements in sealed tantalum ampoules. They were investigated by X-ray diffraction on powders and single crystals. CeNiZn: ZrNiAl type, space group P6̅2m, Z = 3, a = 713.3(3), c = 388.7(1) pm, wR2 = 0.0422 for 14 refined variables and 286 F2 values; CeAuZn: TiNiSi type, space group Pnma, Z = 4, a = 719.2(2), b = 462.7(1), c = 796.5(2) pm, wR2 = 0.0403 for 20 refined variables and 467 F2 values. Magnetic susceptibility data reveal that CeNiZn is an intermediate-valent cerium compound with essentially tetravalent cerium. CeAuZn shows Curie-Weiss paramagnetism with an experimental magnetic moment of 2.51(1) μB per Ce atom and θP = −70(1) K. No magnetic ordering is observed down to 2.1 K.

Electronic structure and magnetic properties of the compound CeCuIn

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power and X-ray photoemission measurements were performed on a polycrystalline sample of CeCuIn. This compound crystallizes in a hexagonal structure of the ZrNiAl type. The magnetic data indicate that CeCuIn remains paramagnetic down to 1.9 K with a paramagnetic Curie temperature of −13 K and an effective magnetic moment equal to 2.5 μ B. The electrical resistivity has metallic character, yet in the entire temperature range studied here, it is a strongly nonlinear function of temperature. The temperature dependence of the thermoelectric power is dominated by a small positive maximum near 76 K and a deep negative minimum at about 16 K. Above 150 K the thermopower exhibits a Mott's type behavior. The positive sign of the Seebeck coefficient in this temperature region indicates that the holes are dominant charge and heat carriers. The structure of Ce 3d 5/2 and Ce 3d 3/2 XPS spectra has been interpreted in terms of the Gunnarsson–Schönhammer theory. Three final-state contributions f 0, f 1 and f 2 are clearly observed, which exhibit a spin–orbit splitting Δ SO≈18.7 eV. The appearance of the 3d 9f 0 component is a clear evidence of the intermediate valence behavior of Ce. From the intensity ratio I(f 0)/[ I(f 0)+ I(f 1)+ I(f 2)] the 4f-occupation number is estimated to be 0.95. In turn, the ratio I(f 2)/[ I(f 1)+ I(f 2)]=0.08 yields a measure of the hybridization energy that is equal to 45 meV.

Crystal and electronic structure and magnetic properties of CeRhPb

The new intermetallic cerium compound CeRhPb was synthesized by arc melting and studied by means of X-ray diffraction and magnetic measurements. The crystal structure determined from the single-crystal X-ray data is of the ZrNiAl type (space group P6¯2 m). The compound was found to be a Pauli paramagnet with 4 f 0 ground state of the Ce atoms. The ab-initio band structure calculations performed without and with spin polarization confirmed the nonmagnetic character of the plumbide studied.

YMgGa

The crystal structure of YMgGa, yttrium magnesium gallide, is isotypic with LaMgGa and crystallizes in the hexa­gonal ZrNiAl type structure. It consists of a three-dimensional network of Mg and Ga atoms, in which Y atoms fill channels. There are two crystallographically independent Ga sites. One Ga atom (Ga1) has three Mg atoms as near neighbours and six Y atoms at a slightly longer distance, giving rise to a [3 + 6] coordination. Another Ga atom (Ga2) is also nine-coordinate but has six near Mg neighbours and three Y at a somewhat longer distance in a [6 + 3] coordination. The Mg atom is tetra­hedrally coordinated by four Ga atoms and has two additional Mg neighbours at a slightly longer distance. The site symmetries for Y, Ga1, Ga2 and Mg are m2m, \overline{6}, \overline{6}2m and m2m, respectively. The crystal used was an inversion twin.

Dimorphic ErAgSn and TmAgSn – High‐Pressure and High‐Temperature Driven Phase Transitions

AbstractThe stannides ErAgSn and TmAgSn have been investigated under high‐temperature (HT) and high‐pressure (HP) conditions in order to investigate their structural chemistry. ErAgSn and TmAgSn are dimorphic: normal‐pressure (NP) ErAgSn and HT‐TmAgSn crystallize into the NdPtSb type structure, P63mc, a = 466.3(1), c = 729.0(2) pm for NP‐ErAgSn and a = 465.4(1), c = 726.6(2) pm for HT‐TmAgSn. NP‐ErAgSn was obtained via arc‐melting of the elements and subsequent annealing at 970 K, while HT‐TmAgSn crystallized directly from the melt by rapidly quenching the arc‐melted sample. HT‐TmAgSn transforms to the ZrNiAl type low‐temperature modification upon annealing at 970 K. The high‐pressure (HP) modification of ErAgSn was synthesized under multianvil high‐pressure (11.5 GPa) high‐temperature (1420 K) conditions from NP‐ErAgSn: ZrNiAl type, $P{\bar 6}{\rm 2}m$, a = 728.7(2), c = 445.6(1) pm. The silver and tin atoms in NP‐ErAgSn and HT‐TmAgSn build up two‐dimensional, puckered [Ag3Sn3] networks (277 pm intralayer Ag–Sn distance in NP‐ErAgSn) that are charge‐balanced and separated by the erbium and thulium atoms. The fourth neighbor in the adjacent layer has a longer Ag–Sn distance of 298 pm. The [AgSn] network in HP‐ErAgSn is three‐dimensional. Each silver atom has four tin neighbors (281–285 pm Ag–Sn). The [AgSn] network leaves distorted hexagonal channels, which are filled with the erbium atoms. The crystal chemistry of the three phases is discussed.

Hydrogenation of the Kondo compound CePtIn

CePtIn was synthesized from the elements via arc-melting and hydrogenated at 523 K and 4 MPa of hydrogen pressure leading to the hydride CePtInH 0.7. The metal positions of both indides were refined from single crystal X-ray diffractometer data: ZrNiAl type, P¯62 m, a = 765.3(2), c = 406.8(1) pm, wR2 = 0.0546, 276 F 2 values and 14 variables for CePtIn and a = 770.6(1), c = 409.7(1) pm, wR2 = 0.0491, 354 F 2 values and 14 variables for CePtInH 0.7. Hydrogenation leads to an isotropic increase of the unit cell through filling of tetrahedral Ce 3Pt sites. CePtInH 0.7 decomposes under ambient condition within some weeks leaving the parent CePtIn structure. Magnetization measurements performed on the hydride reveal a trivalent state for the cerium but no magnetic ordering occurs above 2 K.

The High‐Temperature Phases HT‐YPtSn, HT‐GdPtSn, and HT‐TbPtSn

AbstractThe TiNiSi type high‐temperature (HT) modifications of YPtSn, GdPtSn, and TbPtSn were obtained by rapidly quenching arc‐melted samples. They were investigated by X‐ray diffraction on powders and single crystals: Pnma, a = 716.0(1), b = 453.53(9), c = 795.1(1) pm, wR2 = 0.0432, 419 F2 values for HT‐YPtSn, a = 721.1(6), b = 455.6(4), c = 789.6(8) pm, wR2 = 0.0598, 802 F2 values for HT‐GdPtSn, and a = 716.4(2), b = 453.7(2), c = 794.1(3) pm, wR2 = 0.0390, 629 F2 values for HT‐TbPtSn, with 20 variables per refinement. HT‐YPtSn, HT‐GdPtSn, and HT‐TbPtSn transform to the ZrNiAl type low‐temperature modifications (space group $P{\bar 6}{\rm 2}m$; reconstructive phase transition) by annealing for five days at 800 °C. In all three compounds, the platinum and tin atoms build up three‐dimensional [PtSn] networks (267–284 pm Pt‐Sn in HT‐YPtSn) in which the rare earth metal atoms occupy distorted hexagonal channels.

New Stannide ScAgSn: Determination of the Superstructure via Two-Dimensional 45Sc Solid State NMR

The new stannide ScAgSn was synthesized by induction melting of the elements in a sealed tantalum tube and subsequent annealing. ScAgSn crystallizes with a pronounced subcell structure: ZrNiAl type, P2m, a = 708.2(2) pm, c = 433.9(1) pm, wR2 = 0.1264, 321 F2 values, and 14 variables. The Guinier powder pattern reveals weak superstructure reflections pointing to a TiFeSi-type structural arrangement: I2cm, a = 708.1(1) pm, b = 1225.2(2) pm, c = 869.9(1) pm, wR2 = 0.0787, 5556 F2 values, and 49 variables. So far the growth of high-quality single crystals failed. Determination of the superstructure was partly based on merohedral triplet X-ray data augmented by 119Sn Mössbauer spectroscopy and 119Sn and 45Sc solid-state NMR data. In particular, the observation of three crystallographically inequivalent sites in 45Sc NMR triple quantum magic-angle spinning (TQ-MAS) NMR spectra provided unambiguous proof of the superstructure proposed. The ScAgSn structure consists of a three-dimensional [AgSn] network (with Ag-Sn distances between 273 and 280 pm) in which the scandium atoms are located in distorted hexagonal channels, each having five tin and two silver nearest neighbors. Both crystallographically independent tin sites have a tricapped trigonal prismatic coordination, that is, [Sn1Sc6Ag3] and [Sn2Ag6Sc3] environments, which are well distinguished in the 119Sn NMR and Mössbauer spectra because of their different site symmetries.

Synthesis, Structure, and Properties of the High‐Pressure Modification of CePdSn – a 5 K Antiferromagnet

AbstractThe high‐pressure (HP) modification of CePdSn was synthesized under multianvil high‐pressure (10.5 GPa) high‐temperature (1100 °C) conditions from the normal‐pressure (NP) modification. The structures of both modifications were studied by X‐ray powder and single crystal diffraction: TiNiSi type, Pnma, a = 754.1(2), b = 470.6(1), c = 798.4(3) pm, wR2 = 0.0333, 945 F2 values, 20 variables for NP‐CePdSn and ZrNiAl type, $P{\bar 6}{\rm 2}m$, a = 760.03(5), c = 416.06(3) pm, wR2 = 0.0443, 248 F2 values, 13 variables for HP‐CePdSn. The structural chemistry of both modifications is goverened by platinum centered trigonal prisms. The platinum and tin atoms in NP‐CePdSn and HP‐CePdSn build up a three‐dimensional [PdSn] network in which the cerium atoms fill channels. Susceptibility measurements on HP‐CePdSn reveal an experimental magnetic moment of 2.55(1) μB/Ce atom in the paramagnetic region. At 5 K a paramagnetic‐to‐antiferromagnetic transition is evident from magnetization and specific heat measurements.

Synthesis, Structure and Properties of the High-pressure Modifications of the Ternary Compounds REPtSn (RE = La, Pr, Sm)

The hexagonal high-pressure (HP) modifications of the ternary compounds REPtSn (RE = La, Pr, Sm) were prepared under multianvil high-pressure (9 - 14 GPa) high-temperature (1050 - 1400 °C) conditions from the orthorhombic normal-pressure (NP) modifications. The HP-REPtSn stannides were investigated by X-ray diffraction on powders and single crystals: ZrNiAl type, space group P6̅2m, a = 762.6(2), c = 418.55(7) pm, wR2 = 0.1147, 256 F2 values and 14 variables for HP-LaPtSn, a = 754.97(7), c = 412.64(3) pm, wR2 = 0.0782, 252 F2 values and 14 variables for HP-PrPtSn, and a = 750.1(2), c = 407.6(1) pm, wR2 = 0.1060, 229 F2 values and 14 variables for HP-SmPtSn. The high-pressure modifications have two crystallographically independent platinum positions in trigonal prismatic coordination, Pt1Sn6RE3 and Pt2Sn3RE6. The shortest interatomic distances occur between the platinum and tin atoms with in the three-dimensional [PtSn] networks. The rare earth atoms fill distorted hexagonal channels within these networks and they are bound through short RE-Pt contacts. Susceptibility measurements of HP-PrPtSn reveal paramagnetic behaviour with an experimental magnetic moment of 3.31(2) μB/Pr atom. Low-temperature susceptibility and specific heat data point to inhomogeneous magnetism in HP-PrPtSn.

Magnetic order of CePdAl under pressure—neutron diffraction study

The heavy-fermion compound CePdAl adopting the hexagonal ZrNiAl type of structure (space group P-62m) orders at ambient pressure antiferromagnetically below 2.7 K with an incommensurate propagation vector q =(0.5 0 τ), τ≅0.35. Two, of the three Ce atoms in the hexagonal unit cell carry magnetic moment of about 1.6–1.8 μ B, while the remaining one remains frustrated down to at least 35 mK. The application of hydrostatic pressure leads to a suppression of the long-range magnetic order above the critical pressure P c. The results of neutron diffraction experiments under pressure suggest a value of P c=0.75 (5) GPa as compared with 0.95 GPa determined from the bulk measurements. At pressures lower than P c, the magnetic structure of CePdAl seems to be quite robust with a very little temperature-dependent propagation vector and unusual dependence of the magnetic moment. The P– T phase diagram has been constructed.

Spin glass anomalies in HP-NdPtSn—structural, magnetic and specific heat studies

The hexagonal high-pressure (HP) modification of NdPtSn was prepared under multianvil high-pressure (10.5 GPa) high-temperature (1425 K) conditions from the orthorhombic normal-pressure (NP) modification. NP- and HP-NdPtSn were studied by X-ray powder and single crystal diffraction: TiNiSi type, Pnma, a = 737.2 ( 1 ) , b = 460.0 ( 1 ) , c = 799.6 ( 2 ) pm , w R 2 = 0.0662 , 441 F 2 values, 20 variable parameters for NP-NdPtSn, and ZrNiAl type, P 6 2 ¯ m , a = 753.55 ( 5 ) , c = 410.55 ( 4 ) pm , w R 2 = 0.0709 , 248 F 2 values, 14 variable parameters for HP-NdPtSn. Temperature dependent susceptibility measurements reveal paramagnetism for HP-NdPtSn above 20 K with an experimental magnetic moment of 3.73(2) μ B / Nd mol and a paramagnetic Curie temperature θ P of − 5 ( 1 ) K. The low-temperature data indicate spin glass behavior with a freezing temperature around 4.5 K. The spin glass anomalies are also evident from specific heat measurements.

Melting of the antiferromagnetic structure in UNiAL near TN

UNiAl has the hexagonal ZrNiAl type of structure and below T N=19.3 K exhibits antiferromagnetic ordering of U moments with the propagation vector q=(0.1 0.1 0.5). In a sufficiently high magnetic field B c applied along the c-axis ( B c=11.4 T at 2 K), UNiAl undergoes a metamagnetic transition from an antiferromagnetic structure towards a ferromagnetic structure. In fields above ∼8 T (<11.4 T), a new antiferromagnetic structure is established in UNiAl with the in-plane modulation direction tilted to the [1 0 0] direction. The propagation vector of the new antiferromagnetic structure has the same length as in the original and also the direction of U moments along the c-axis is preserved. In this paper we show that the competition between the two indicated antiferromagnetic structures takes place even in zero field in the vicinity of T N. In a small temperature range around T N a diffuse ring of intensity can be observed, indicating that angular coherence is lost and the modulation of U moments exists in several directions.

Structural, magnetic, and spectroscopic studies of YAgSn, TmAgSn, and LuAgSn

The rare earth–silver–stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P6 3 mc, Z = 2 , a = 468.3 ( 1 ) , c = 737.2 ( 2 ) pm, w R 2 = 0.0343 , 353 F 2 values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a = 726.4 ( 2 ) , c = 443.7 ( 1 ) pm , w R 2 = 0.0399 , 659 F 2 values, 15 variables for TmAgSn, and a = 723.8 ( 2 ) , c = 442.47 ( 9 ) pm , w R 2 = 0.0674 , 364 F 2 values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with λ = 48.725 pm , in order to clarify the silver–tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag–Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag–Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie–Weiss paramagnet with an experimental magnetic moment of 7.2 μ B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by 119Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental 119Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag–Sn bonds and also significant Ag–Ag bonding in LuAgSn.

Hydrogenation of the intermediate valence ternary stannides CeRhSn and CeIrSn

CeRhSn and CeIrSn were synthesized from the elements via arc-melting. A single crystal from the CeIrSn sample was investigated on the basis of X-ray diffractometer data: ZrNiAl type, P 2 m , a = 743.8 ( 2 ) , c = 407.58 ( 7 ) pm , w R 2 = 0.0308 , 352 F 2 values and 14 variable parameters. An important structural feature of CeIrSn are relatively short Ce Ir distances ( 4 × 303 and 1 × 308 pm ). Hydrogenation of these ternary stannides leads to the formation of the new hydrides CeRhSnH 0.8 and CeIrSnH 0.7 which adopt the same crystal symmetry as the original compounds but a larger unit cell volume after hydrogen insertion. Magnetization, electrical resistivity and thermoelectric power measurements reveal a change of the ground state of the cerium from intermediate valence to the nearly trivalent state induced by hydrogenation. Moreover, 119Sn Mössbauer spectroscopic data of CeRhSn, CeIrSn and their hydrides at 4.2 and 78 K indicate only one tin site. The isomer shifts are slightly larger for the hydrogenated samples suggesting a slightly higher s electron density at the tin nuclei of the hydrides.

Hydrogenation and Crystal Structures of the Nd(Ni1‐xCux)(In1‐yAly) Intermetallics and Their Hydrides.

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Syntheses and Structure of Gd3Rh1.940(7)In4

The gadolinium–rhodium–indide Gd3Rh1.940(7)In4 was prepared by arc-melting of the elements and subsequent annealing in a corundum crucible in a sealed silica tube. Gd3Rh1.940(7)In4 adopts the hexagonal Lu3Co1.87In4 type, space group \(P{\bar 6}\), a = 781.4(5), c = 383.8(3) pm, wR2 = 0.0285, BASF = 0.375(1) (merohedric twinning via a twofold axis (xx0)), 648 F 2 values, 22 variables. The structure is derived from the well known ZrNiAl type through an ordering of rhodium and indium atoms on the Ni2 sites. The Rh/In ordering forces a reduction of the space group symmetry from \(P{\bar 6}62m\) to \(P{\bar 6}\), leading to merohedric twinning for the investigated crystal. The Rh1 site has an occupancy of only 94.0(7)%. The investigated crystal had a composition Gd3Rh1.940(7)In4. The main geometrical motif are three types of centered, tricapped trigonal prisms, i.e., [Rh1In26Gd3], [Rh2Gd6In23], and [In1Gd6In23]. The shortest interatomic distances occur for Rh–In (276–296 pm) followed by In–In (297 pm). Together, the rhodium and indium atoms build up a three-dimensional [Rh1.940(7)In4] network, in which the gadolinium atoms fill slightly distorted pentagonal channels. The crystal chemistry of Gd3Rh1.940(7)In4 is discussed on the basis of a group-subgroup scheme.

Structure, Chemical Bonding and 119Sn Mössbauer Spectroscopy of LaRhSn and CeRhSn

The rare earth (RE) stannides LaRhSn and CeRhSn were prepared from the elements by arcmelting or by reactions in sealed tantalum tubes in a high-frequency furnace. The structures have been refined from X-ray single crystal diffractometer data: ZrNiAl type, P6̅2̅m, a = 748.74(5), c = 422.16(3) pm, wR2 = 0.0307, 310 F2 values for LaRhSn and a = 745.8(1), c = 408.62(9) pm, wR2 = 0.0397, 354 F2 values for CeRhSn with 14 variables per refinement. The structures contain two crystallographically different rhodium sites which both have a tricapped trigonal prismatic coordination: [Rh1Sn3RE6] and [Rh2Sn6RE3]. Together the rhodium and tin atoms (280 - 288 pm Rh-Sn distances in LaRhSn and 277 - 285 pm in CeRhSn) build up three-dimensional [RhSn] networks in which the rare earth atoms fill distorted hexagonal channels. DFT band structure calculations reveal a large cerium 4 f contribution at the Fermi level and a strong mixing of cerium 5d/4 f with rhodium 4d orbitals. These results are in agreement with the short Ce-Rh bonds (304 and 309 pm) and also with the electronic and magnetic properties. 119Sn Mössbauer spectra of LaRhSn and CeRhSn show a single tin site at isomer shifts of δ = 1.98(2) (LaRhSn) and 1.79(1) mm/s (CeRhSn) subject to quadrupole splitting of Δ EQ = 0.79(4) (LaRhSn) and 1.12(3) mm/s (CeRhSn). The 1.8 K data show no transferred hyperfine field at the tin site for CeRhSn.

Structure, magnetic properties and 119Sn Mössbauer spectroscopy of PrRhSn

PrRhSn was synthesized in polycrystalline form by a reaction of praseodymium, rhodium, and tin in an arc-melting furnace. The sample was investigated by powder and single crystal X-ray diffraction: ZrNiAl type, space group P 6 ¯ 2 m , a = 742.49 ( 7 ) , c = 415.05 ( 5 ) pm, w R 2=0.0737, 353 F 2 values and 14 variables. The PrRhSn structure has two crystallographically independent rhodium sites with a tricapped trigonal prismatic coordination, i.e. [Rh1Sn 3Pr 6] and [Rh2Sn 6Pr 3]. The rhodium and tin atoms build up a three-dimensional [RhSn] network with short Rh–Sn contacts (278 and 285 pm), in which the praseodymium atoms fill distorted hexagonal channels. The magnetic and electronic properties of PrRhSn have been studied by means of AC and DC magnetic susceptibility measurements as well as 119Sn Mössbauer spectroscopy. A transition from a paramagnetic to a ferromagnetic state was found at T C = 3.0 K .

Magnetic ordering in NdRhSn

The stannide NdRhSn was synthesized from the elements in a sealed tantalum tube. The structure was investigated on the basis of X-ray powder and single crystal data: ZrNiAl type, P 6 ¯ 2 m , a = 741.3 ( 1 ) , c = 412.90 ( 9 ) pm , wR 2 = 0.0266 , 354 F 2 values and 14 variable parameters. The neodymium atoms fill distorted hexagonal channels within the three-dimensional [RhSn] network. The magnetic and electronic properties of NdRhSn have been studied by means of AC and DC magnetic susceptibility measurements as well as 119Sn Mössbauer spectroscopy. A transition from a paramagnetic to a ferromagnetic state was found at T C = 10.3 K .