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Title: Synthesis, structure and magnetic properties of R-W-O-N (R=Nd and Eu) oxynitrides

Abstract

Neodymium and europium tungsten oxynitrides have been synthesized by the nitridation of corresponding R{sub 2}W{sub 2}O{sub 9} precursor oxides, in ammonia flow at 1173K during 24h. The obtained polycrystalline neodymium oxynitride phase, with NdWO{sub 3.05}N{sub 0.95} composition, crystallizes with the tetragonal symmetry of the scheelite-type structure, space group S.G. I4{sub 1}/a (no. 88). The analogous europium derivative, with formula EuWO{sub 1.58}N{sub 1.42}, presents the cubic perovskite-type structure, S.G. Pm3-bar m (no. 221). Unit-cell parameters, a=5.255(1)A, c=11.399(3)A, and a=3.976(3)A, have been established from Rietveld refinements of collected X-ray powder diffraction patterns for the Nd and Eu- oxynitrides, respectively. Magnetic susceptibility measurements show that NdWO{sub 3.05}N{sub 0.95} behaves as paramagnetic in a wide range of temperature T {approx}50-300K. The downwards deviation from the Curie-Weiss law below 40K reflects the splitting of the {sup 4}I{sub 9/2} ground state of Nd{sup 3+} experienced under the influence of a S{sub 4} crystal field CF potential, as the successful reproduction of the magnetic susceptibility {chi}{sup -1}{sub m} vs. T, using semi-empirical structure-derived CF parameters, indicates. EuWO{sub 1.58}N{sub 1.42} is paramagnetic down to 20K, and the measured effective magnetic moment 8.01{mu}{sub B} is indicative of the presence of Eu{sup 2+} in this oxynitride. The observed sudden jumpmore » in the magnetic susceptibility at 20K and the value of 6{mu}{sub B} for the saturation moment is attributed to the onset of ferrimagnetic interactions in which the Eu{sup 2+} and W{sup 5+} sublattices appear to be involved.« less

Authors:
 [1];  [1];  [2];  [3]
  1. Department of Quimica Inorganica I, Facultad de Ciencias Quimicas, Universidad Complutense, 28040 Madrid (Spain)
  2. Instituto de Ciencia de Materiales de Madrid ICMM, Consejo Superior de Investigaciones Cientificas CSIC, C/ Sor Juana Ines de la Cruz, 3. Cantoblanco, 28040 Madrid (Spain)
  3. Department of Quimica Inorganica I, Facultad de Ciencias Quimicas, Universidad Complutense, 28040 Madrid (Spain), E-mail: rsp92@quim.ucm.es
Publication Date:
OSTI Identifier:
21015623
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 1; Other Information: DOI: 10.1016/j.jssc.2006.09.025; PII: S0022-4596(06)00535-4; Copyright (c) 2006 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; AMMONIA; CRYSTAL FIELD; CUBIC LATTICES; CURIE-WEISS LAW; EUROPIUM COMPOUNDS; EUROPIUM IONS; FERRIMAGNETISM; MAGNETIC MOMENTS; MAGNETIC SUSCEPTIBILITY; NEODYMIUM COMPOUNDS; NEODYMIUM IONS; NITRIDATION; NITRIDES; OXIDES; PARAMAGNETISM; PEROVSKITE; POLYCRYSTALS; SPACE GROUPS; SYNTHESIS; TEMPERATURE RANGE 1000-4000 K; TETRAGONAL LATTICES; TUNGSTEN COMPOUNDS; TUNGSTEN IONS; X-RAY DIFFRACTION

Citation Formats

Pastrana-Fabregas, R., Isasi-Marin, J., Cascales, C., and Saez-Puche, R. Synthesis, structure and magnetic properties of R-W-O-N (R=Nd and Eu) oxynitrides. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.09.025.
Pastrana-Fabregas, R., Isasi-Marin, J., Cascales, C., & Saez-Puche, R. Synthesis, structure and magnetic properties of R-W-O-N (R=Nd and Eu) oxynitrides. United States. doi:10.1016/j.jssc.2006.09.025.
Pastrana-Fabregas, R., Isasi-Marin, J., Cascales, C., and Saez-Puche, R. Mon . "Synthesis, structure and magnetic properties of R-W-O-N (R=Nd and Eu) oxynitrides". United States. doi:10.1016/j.jssc.2006.09.025.
@article{osti_21015623,
title = {Synthesis, structure and magnetic properties of R-W-O-N (R=Nd and Eu) oxynitrides},
author = {Pastrana-Fabregas, R. and Isasi-Marin, J. and Cascales, C. and Saez-Puche, R.},
abstractNote = {Neodymium and europium tungsten oxynitrides have been synthesized by the nitridation of corresponding R{sub 2}W{sub 2}O{sub 9} precursor oxides, in ammonia flow at 1173K during 24h. The obtained polycrystalline neodymium oxynitride phase, with NdWO{sub 3.05}N{sub 0.95} composition, crystallizes with the tetragonal symmetry of the scheelite-type structure, space group S.G. I4{sub 1}/a (no. 88). The analogous europium derivative, with formula EuWO{sub 1.58}N{sub 1.42}, presents the cubic perovskite-type structure, S.G. Pm3-bar m (no. 221). Unit-cell parameters, a=5.255(1)A, c=11.399(3)A, and a=3.976(3)A, have been established from Rietveld refinements of collected X-ray powder diffraction patterns for the Nd and Eu- oxynitrides, respectively. Magnetic susceptibility measurements show that NdWO{sub 3.05}N{sub 0.95} behaves as paramagnetic in a wide range of temperature T {approx}50-300K. The downwards deviation from the Curie-Weiss law below 40K reflects the splitting of the {sup 4}I{sub 9/2} ground state of Nd{sup 3+} experienced under the influence of a S{sub 4} crystal field CF potential, as the successful reproduction of the magnetic susceptibility {chi}{sup -1}{sub m} vs. T, using semi-empirical structure-derived CF parameters, indicates. EuWO{sub 1.58}N{sub 1.42} is paramagnetic down to 20K, and the measured effective magnetic moment 8.01{mu}{sub B} is indicative of the presence of Eu{sup 2+} in this oxynitride. The observed sudden jump in the magnetic susceptibility at 20K and the value of 6{mu}{sub B} for the saturation moment is attributed to the onset of ferrimagnetic interactions in which the Eu{sup 2+} and W{sup 5+} sublattices appear to be involved.},
doi = {10.1016/j.jssc.2006.09.025},
journal = {Journal of Solid State Chemistry},
number = 1,
volume = 180,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Graphical abstract: Ammonolysis of LnNbO{sub 4} (Ln = rare earth or Y) leads to the formation of oxynitrides of different structures depending on the size of the rare earth. Highlights: {yields} We have carried out ammonolysis of LnNbO{sub 4} (Ln = rare earth and Y) to form oxynitrides of different structures depending on the size of the rare earth. {yields} Infrared spectroscopy shows the marked difference between oxides and the corresponding oxynitrides. {yields} The oxynitrides are stable in air upto {approx}400 {sup o}C above which an intermediate phase with nitrogen molecules attached to the oxide lattice forms. {yields} Gadolinium niobiummore » oxynitride shows paramagnetism. -- Abstract: Ammonolysis of rare earth niobates of the type LnNbO{sub 4} (Ln = Y, La, Pr, Nd, Gd, Dy) yields oxynitrides of different structures. When Ln = La, Nd and Pr, the structure is that of an orthorhombic perovskite of the general formula LnNbON{sub 2}. As the size of the rare earth decreases, the oxynitride has a nitrogen-deficient defect fluorite (Ln = Pr, Nd, Gd), or pyrochlore (Ln = Y) structure. The IR spectra of the oxynitrides and the corresponding oxides are significantly different. Thermogravimetric analysis suggests the formation of an intermediate phase wherein the N{sub 2} molecule is attached to the oxide lattice above 400 {sup o}C and decomposes to give the oxide on heating in an oxygen atmosphere. Raman spectra of the intermediate phases show evidence for the N{identical_to}N stretching vibration. Gadolinium niobium oxynitride is found to be paramagnetic.« less
  • Transition metal carbides and nitrides have attracted attention as possible replacements for platinum group catalysts. Most of the work has been carried out with single-metal compounds. The authors report the preparation of two new bimetallic compounds, V-Mo and V-W oxynitrides, obtained by nitriding oxide precursors with ammonia gas via a temperature-programmed reaction. The bimetallic oxide precursors are prepared by conventional solid state reaction using commercial V, Mo, and W oxides. The oxynitrides thus obtained adopt a face-centered cubic crystal structure. They have high specific surface areas (74 and 62 m{sup 2} g{sup {minus}1}), and their pyrophoricity suggests high surface activity.
  • Although R{sub 2}O{sub 3}:MoO{sub 3}=1:6 (R=rare earth) compounds are known in the R{sub 2}O{sub 3}-MoO{sub 3} phase diagrams since a long time, no structural characterization has been achieved because a conventional solid-state reaction yields powder samples. We obtained single crystals of R{sub 2}Mo{sub 6}O{sub 21}.H{sub 2}O (R=Pr, Nd, Sm, and Eu) by thermal decomposition of [R{sub 2}(H{sub 2}O){sub 12}Mo{sub 8}O{sub 27}].nH{sub 2}O at around 685-715{sup o}C for 2h, and determined their crystal structures. The simulated XRD patterns of R{sub 2}Mo{sub 6}O{sub 21}.H{sub 2}O were consistent with those of previously reported R{sub 2}O{sub 3}:MoO{sub 3}=1:6 compounds. All R{sub 2}Mo{sub 6}O{sub 21}.H{submore » 2}O compounds crystallize isostructurally in tetragonal, P4/ncc (No. 130), a=8.9962(5), 8.9689(6), 8.9207(4), and 8.875(2)A; c=26.521(2), 26.519(2), 26.304(2), and 26.15(1)A; Z=4; R{sub 1}=0.026, 0.024, 0.024, and 0.021, for R=Pr, Nd, Sm, and Eu, respectively. The crystal structure of R{sub 2}Mo{sub 6}O{sub 21}.H{sub 2}O consists of two [Mo{sub 2}O{sub 7}]{sup 2-}-containing layers (A and B layers) and two interstitial R(1){sup 3+} and R(2){sup 3+} cations. Each [Mo{sub 2}O{sub 7}]{sup 2-} group is composed of two corner-sharing [MoO{sub 4}] tetrahedra. The [Mo{sub 2}O{sub 7}]{sup 2-} in the B layer exhibits a disorder to form a pseudo-[Mo{sub 4}O{sub 9}] group, in which four Mo and four O sites are half occupied. R(1){sup 3+} achieves 8-fold coordination by O{sup 2-} to form a [R(1)O{sub 8}] square antiprism, while R(2){sup 3+} achieves 9-fold coordination by O{sup 2-} and H{sub 2}O to form a [R(2)(H{sub 2}O)O{sub 8}] monocapped square antiprism. The disorder of the [Mo{sub 2}O{sub 7}]{sup 2-} group in the B layer induces a large displacement of the O atoms in another [Mo{sub 2}O{sub 7}]{sup 2-} group (in the A layer) and in the [R(1)O{sub 8}] and [R(2)(H{sub 2}O)O{sub 8}] polyhedra. A remarkable broadening of the photoluminescence spectrum of Eu{sub 2}Mo{sub 6}O{sub 21}.H{sub 2}O supported the large displacement of O ligands coordinating Eu(1) and Eu(2)« less
  • New oxynitrides corresponding to the general formulation Ln[sub 2]W(O,N)[sub 6[minus]x](Ln = Nd to Yb, Y) have been prepared by reaction at 800[degrees]C between ammonia and Ln[sub 2]WO[sub 6] tungstates, and characterized as defect fluorite type compounds. Their general composition A[sub 4]X[sub 6.6] is intermediate between the CaF[sub 2](A[sub 4]X[sub 8]) fluorite and Mn[sub 2]O[sub 3](A[sub 4]X[sub 6]) bixbyite stoichiometries. The parameter of the cubic unit cell comprised between 5.16 and 5.39 [angstrom], depends on the size of the lanthanide. Ln and W atoms occupy a same crystallographic position.
  • Two oxynitrides, SrWO{sub 2}N and SrMoO{sub 2.5}N{sub 0.5}, were synthesized by the ammonolysis of SrMO{sub 4} (M = W, Mo) at 900 and 800 C, respectively. Both oxynitrides adopt the cubic perovskite structure (space group Pm3m) with a = 3.97951(9) {angstrom} for SrWO{sub 2}N and a = 3.9773(1) {angstrom} for a SrMoO{sub 2.5}N{sub 0.5}. The M-(O,N) and Sr-(O,N) bond lengths, determined form the Rietveld refinement of the powder X-ray diffraction data, are in good agreement with those reported for other oxynitrides with the perovskite structure. Nearly temperature independent electrical resistivities were observed for both compounds. The magnetic susceptibility measurements indicatedmore » Pauli-paramagnetic behavior in both cases. A sharp anomaly observed in the magnetization data of SrMoO{sub 2.5}N{sub 0.5} at {approximately} 50 K has been attributed to a spin-glass-like transition.« less