skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}: Crystal structure and electronic properties

Abstract

The praseodymium cobalt aluminides, PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}, were prepared by reaction of the elemental components in an arc-melting furnace, followed by heat treatment at 900 deg. C for several days. Their chemical composition was checked by scanning electron microscopy and energy dispersive spectroscopy, and their crystal structure was refined from single crystal X-ray diffraction data. PrCo{sub 2}Al{sub 8} adopts the CaCo{sub 2}Al{sub 8} type of structure, crystallizing with the orthorhombic space group Pbam, with four formula units in a cell of dimensions at room temperature: a=12.4623(3)A, b=14.3700(4)A, c=4.0117(1)A. Pr{sub 2}Co{sub 6}Al{sub 19} crystallizes in the monoclinic space group C2/m, with four formula units in a cell of dimensions at room temperature: a=17.6031(4)A, b=12.1052(4)A, c=8.2399(2)A and {beta}=103.903(1){sup o}. Its structure belongs to the U{sub 2}Co{sub 6}Al{sub 19} type. The crystal structures of both compounds studied can be viewed as three-dimensional structures resulting from the packing of Al polyhedra centred by the transition elements. Along the c-axis, the coordination polyhedra around the Pr atoms pack by face sharing to form strands, which are separated one from another by an extended Co-Al network. Magnetic measurements have revealed that PrCo{sub 2}Al{sub 8} orders antiferromagnetically at T{sub N}=5K, with amore » clear metamagnetic transition occurring at a critical field H{sub c}=0.9(1)T. The temperature dependence of the susceptibility of Pr{sub 2}Co{sub 6}Al{sub 19} does not provide any evidence for long-range magnetic ordering in the temperature domain 1.7-300K. At low temperatures (T<10K), the susceptibility saturates in a manner characteristic of a non-magnetic singlet ground state. At high temperatures, the magnetic susceptibility of each compound follows a Curie-Weiss law, with the effective magnetic moment per Pr atom of 3.48(5){mu}{sub B} and 3.41(2){mu}{sub B} for PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}, respectively. These values are close to the theoretical value of 3.58{mu}{sub B} expected for a free Pr{sup 3+} ion and exclude any contribution due to the Co atoms. Both compounds exhibit in the temperature range 5-300K metallic-like electrical conductivity, and their Seebeck coefficient is of the order of several {mu}V/K. several {mu}V/K.« less

Authors:
 [1];  [2];  [3]
  1. Laboratoire de Chimie du Solide et Inorganique Moleculaire, Universite de Rennes1, LCSIM, UMR CNRS 6511, 263 avenue du General Leclerc, 35042 Rennes (France). E-mail: tougait@univ-rennes1.fr
  2. Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw (Poland)
  3. Laboratoire de Chimie du Solide et Inorganique Moleculaire, Universite de Rennes1, LCSIM, UMR CNRS 6511, 263 avenue du General Leclerc, 35042 Rennes (France)
Publication Date:
OSTI Identifier:
20784808
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 178; Journal Issue: 12; Other Information: DOI: 10.1016/j.jssc.2005.09.019; PII: S0022-4596(05)00416-0; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALUMINIUM COMPOUNDS; CHEMICAL COMPOSITION; COBALT COMPOUNDS; CURIE-WEISS LAW; ELECTRIC CONDUCTIVITY; ELECTRONIC STRUCTURE; INTERMETALLIC COMPOUNDS; MAGNETIC SUSCEPTIBILITY; MONOCLINIC LATTICES; MONOCRYSTALS; ORTHORHOMBIC LATTICES; PRASEODYMIUM COMPOUNDS; PRASEODYMIUM IONS; SCANNING ELECTRON MICROSCOPY; SPACE GROUPS; TEMPERATURE RANGE 0065-0273 K; TEMPERATURE RANGE 0273-0400 K; X-RAY DIFFRACTION

Citation Formats

Tougait, O., Kaczorowski, D., and Noel, H.. PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}: Crystal structure and electronic properties. United States: N. p., 2005. Web. doi:10.1016/j.jssc.2005.09.019.
Tougait, O., Kaczorowski, D., & Noel, H.. PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}: Crystal structure and electronic properties. United States. doi:10.1016/j.jssc.2005.09.019.
Tougait, O., Kaczorowski, D., and Noel, H.. Thu . "PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}: Crystal structure and electronic properties". United States. doi:10.1016/j.jssc.2005.09.019.
@article{osti_20784808,
title = {PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}: Crystal structure and electronic properties},
author = {Tougait, O. and Kaczorowski, D. and Noel, H.},
abstractNote = {The praseodymium cobalt aluminides, PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}, were prepared by reaction of the elemental components in an arc-melting furnace, followed by heat treatment at 900 deg. C for several days. Their chemical composition was checked by scanning electron microscopy and energy dispersive spectroscopy, and their crystal structure was refined from single crystal X-ray diffraction data. PrCo{sub 2}Al{sub 8} adopts the CaCo{sub 2}Al{sub 8} type of structure, crystallizing with the orthorhombic space group Pbam, with four formula units in a cell of dimensions at room temperature: a=12.4623(3)A, b=14.3700(4)A, c=4.0117(1)A. Pr{sub 2}Co{sub 6}Al{sub 19} crystallizes in the monoclinic space group C2/m, with four formula units in a cell of dimensions at room temperature: a=17.6031(4)A, b=12.1052(4)A, c=8.2399(2)A and {beta}=103.903(1){sup o}. Its structure belongs to the U{sub 2}Co{sub 6}Al{sub 19} type. The crystal structures of both compounds studied can be viewed as three-dimensional structures resulting from the packing of Al polyhedra centred by the transition elements. Along the c-axis, the coordination polyhedra around the Pr atoms pack by face sharing to form strands, which are separated one from another by an extended Co-Al network. Magnetic measurements have revealed that PrCo{sub 2}Al{sub 8} orders antiferromagnetically at T{sub N}=5K, with a clear metamagnetic transition occurring at a critical field H{sub c}=0.9(1)T. The temperature dependence of the susceptibility of Pr{sub 2}Co{sub 6}Al{sub 19} does not provide any evidence for long-range magnetic ordering in the temperature domain 1.7-300K. At low temperatures (T<10K), the susceptibility saturates in a manner characteristic of a non-magnetic singlet ground state. At high temperatures, the magnetic susceptibility of each compound follows a Curie-Weiss law, with the effective magnetic moment per Pr atom of 3.48(5){mu}{sub B} and 3.41(2){mu}{sub B} for PrCo{sub 2}Al{sub 8} and Pr{sub 2}Co{sub 6}Al{sub 19}, respectively. These values are close to the theoretical value of 3.58{mu}{sub B} expected for a free Pr{sup 3+} ion and exclude any contribution due to the Co atoms. Both compounds exhibit in the temperature range 5-300K metallic-like electrical conductivity, and their Seebeck coefficient is of the order of several {mu}V/K. several {mu}V/K.},
doi = {10.1016/j.jssc.2005.09.019},
journal = {Journal of Solid State Chemistry},
number = 12,
volume = 178,
place = {United States},
year = {Thu Dec 15 00:00:00 EST 2005},
month = {Thu Dec 15 00:00:00 EST 2005}
}
  • The crystal structure, electronic structure, and photoluminescence properties of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} (x=0-0.1, 0<z<1) and Eu{sub x}M{sub y}Si{sub 6-z}Al{sub z-x-y}O{sub z+x+y}N{sub 8-z-x-y} (M=2Li, Mg, Ca, Sr, Ba) have been studied. Single-phase Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} can be obtained in very narrow ranges of x{<=}0.06 (z=0.15) and z<0.5 (x=0.3), indicating that limited Eu{sup 2+} ions can be incorporated into nitrogen-rich Si{sub 6-z}Al{sub z}O{sub z}N{sub 8-z}. The Eu{sup 2+} ion is found to occupy the 2b site in a hexagonal unit cell (P6{sub 3}/m) and directly connected by six adjacent nitrogen/oxygen atoms ranging 2.4850-2.5089 A. The calculatedmore » host band gaps by the relativistic DV-X{alpha} method are about 5.55 and 5.45 eV (without Eu{sup 2+} 4f5d levels) for x=0 and 0.013 in Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} (z=0.15), in which the top of the 5d orbitals overlap with the Si-3s3p and N-2p orbitals within the bottom of the conduction band of the host. Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} shows a strong green emission with a broad Eu{sup 2+} band centered at about 530 nm under UV to near-UV excitation range. The excitation and emission spectra are hardly modified by Eu concentration and dual-doping ions of Li and other alkaline-earth ions with Eu. Higher Eu concentrations can significantly quench the luminescence of Eu{sup 2+} and decrease the thermal quenching temperature. In addition, the emission spectrum can only be slightly tuned to the longer wavelengths ({approx}529-545 nm) by increasing z within the solid solution range of z<0.5. Furthermore, the luminescence intensity of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} can be improved by increasing z and the dual-doping of Li and Ba. - Graphical abstract: Excitation and emission spectra of Eu{sub x}Si{sub 6-z}Al{sub z-x}O{sub z+x}N{sub 8-z-x} with the project of a 2x2x2 supercell crystal structure viewed along (001), in which red spheres are the Eu atoms.« less
  • A novel polyoxometalate-based organic-inorganic hybrid compound, [Co(bpy){sub 3}]{sub 2} [Mo{sub 6}O{sub 19}] [{beta}-(H{sub 2}Mo{sub 8}O{sub 26})].4H{sub 2}O (1), have been hydrothermally synthesized and structurally characterized by elemental analysis, single-crystal X-ray diffraction, IR and X-ray photoelectron spectra. Compound 1 represents the first example that racemic complexes coexisting with two kinds of polyoxomolybdate anions in the same crystal architecture, which should be of rare chance that four kinds of complexes crystallizes into a compound.
  • The bis(dinitrogen) molybdenum complexes trans-Mo(N{sub 2}){sub 2}((ArCH{sub 2}){sub 2}PC{sub 2}H{sub 4}P(CH{sub 2}Ar){sub 2}){sub 2} (Ar = C{sub 6}H{sub 5} (1a), C{sub 6}H{sub 4-} m-Me (1b), C{sub 6}H{sub 4}-o-Me (1c), C{sub 6}H{sub 4}-p-Me (1d), C{sub 6}H{sub 4}-o-F (1e), C{sub 6}H{sub 4}-m-F (1f) C{sub 6}H{sub 4}-p-F (1g), C{sub 6}H{sub 4}-m-OMe (1h), C{sub 6}H{sub 4}-p-OMe (1i)) are prepared by reduction of MoCl{sub 5} with magnesium under a dinitrogen atmosphere in the presence of the appropriate diphosphine ligand. Treatment of 1a and 1b with ethyl acetate in refluxing benzene under argon affords the formally 16-electron complexes MoCl{sub 5} with magnesium under a dinitrogen atmospheremore » in the presence of the appropriate diphosphine ligand. Treatment of 1a and 1b with ethyl acetate in refluxing benzene under argon affords the formally 16-electron complexes Mo(CO)((ArCH{sub 2}){sub 2}PC{sub 2}H{sub 4}P(CH{sub 2}Ar){sub 2}){sub 2} (Ar = C{sub 6}H{sub 5} (2a), C{sub 6}H{sub 4}-m-Me (2b)), which are shown by {sup 1}H NMR spectroscopy to contain an agostic Mo{hor_ellipsis}H-C interaction between the molybdenum and an ortho aryl hydrogen atom. The {eta}{sup 2}-H{sub 2} coordination in 3a and 3b is unambiguously established by IR, NMR, and neutron scattering spectroscopies and a single-crystal X-ray diffraction analysis of 3b. The predisposition toward hydrogen dissociation in these complexes is discussed.« less
  • New complexes, mer,trans,M(CO)/sub 3/(PR/sub 3/)/sub 2/(SO/sub 2/) (M = Mo,W; R = Ph,Cy,i-Pr) (I), cis,trans-Mo(CO)/sub 2/-(PPh/sub 3/)/sub 2/(SO/sub 2/)(L) (L = NCMe,py,CNCy,CN-t-Bu and CN(p-tolyl))(II), and (Mo(CO)/sub 2/(py)(PPh/sub 3/)(..mu..-SO/sub 2/))/sub 2/, have been prepared and characterized by infrared spectroscopy, /sup 17/O and /sup 31/P NMR spectroscopy, and X-ray crystallography. Syntheses for fac-Mo(CO)/sub 3/(n/sup 2/-SO/sub 2/)(LL) (LL = dppe,bpy,phen,2 py) have also been developed. Depending upon L, II has been found to coordinate SO/sub 2/ either in the S-bonded (n/sup 1/ planar) or O,S-bonded (n/sup 2/) geometries. Remarkably, for L = CNCy or CN-t-Bu, II has been found to contain, in themore » solid state, an apparent equimixture of both coordination types. Isomerization of fac-M(CO)/sub 3/(dppe)(n/sup 2/-SO/sub 2/) (M=Mo,w; dppe = 1,2-bis(diphenylphosphino)ethane) to an n/sup 1/-planar SO/sub 2/ form, mer-M(CO)/sub 3/(dppe)(SO/sub 2/), has also been found to occur. Thus, control of the SO/sub 2/ coordination geometry has been achieved by varying either the electronic properties of the ancillary ligands or their disposition with respect to the SO/sub 2/. The X-ray crystal structure of mer,trans-Mo(CO)/sub 3/(P-i-Pr/sub 3/)/sub 2/(SO/sub 2/) revealed n/sup 1/-planar SO/sub 2/ binding, the first example of this geometry for group 6 metals. The M-S distance, 2.239 (3) angstrom, is the longest such distance for this geometry recorded to date. Crystal data: Pbca, Z=8, a=24.712(8) angstrom, b=16.033(6) angstrom, c=14.058(5) angstrom, R=0.079 for 2934 reflections with Igreater than or equal to2sigma(I). The structure of (Mo(CO)/sub 2/(py)(PPh/sub 3/)(..mu..-SO/sub 2/))/sub 2/ showed a novel SO/sub 2/ bridging geometry in which all three atoms of SO/sub 2/ are metal coordinated. Crystal data: P1, Z=1, a=14.883(4) angstrom, b=9.264(2) angstrom, c=10.808(2) angstrom, R=0.039 for 3282 reflections with Igreater than or equal to2sigma(I).« less