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Title: Thermodynamic Nature of the Antiferromagnetic Transition in Na xCoO 2

Abstract

High-resolution thermal expansion measurements of single-crystalline Na0.80CoO2 reveal continuous behavior of the paramagnetic-antiferromagnetic phase transition at TM=21.7(1) K with critical exponent a=0.18(2). The thermal expansion is found to be highly anisotropic. Thermodynamic analysis provides the hydrostatic pressure derivative dTM/dP=+4.6(2) K/GPa. Similar measurements and analysis are presented for Na0.75CoO2.

Authors:
 [1];  [1];  [1];  [2];  [3];  [3];  [3]
  1. Montana State University
  2. National Center for Biotechnology Information
  3. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1003682
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 74; Journal Issue: 13
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; HYDROSTATICS; THERMAL EXPANSION; THERMODYNAMICS

Citation Formats

dos Santos, C. A. M., Neumeier, J. J., Bollinger, R. K., Yu, Yi-Kuo, Jin, Rongying, Mandrus, David, and Sales, Brian C. Thermodynamic Nature of the Antiferromagnetic Transition in NaxCoO2. United States: N. p., 2006. Web. doi:10.1103/PhysRevB.74.132402.
dos Santos, C. A. M., Neumeier, J. J., Bollinger, R. K., Yu, Yi-Kuo, Jin, Rongying, Mandrus, David, & Sales, Brian C. Thermodynamic Nature of the Antiferromagnetic Transition in NaxCoO2. United States. doi:10.1103/PhysRevB.74.132402.
dos Santos, C. A. M., Neumeier, J. J., Bollinger, R. K., Yu, Yi-Kuo, Jin, Rongying, Mandrus, David, and Sales, Brian C. Sun . "Thermodynamic Nature of the Antiferromagnetic Transition in NaxCoO2". United States. doi:10.1103/PhysRevB.74.132402.
@article{osti_1003682,
title = {Thermodynamic Nature of the Antiferromagnetic Transition in NaxCoO2},
author = {dos Santos, C. A. M. and Neumeier, J. J. and Bollinger, R. K. and Yu, Yi-Kuo and Jin, Rongying and Mandrus, David and Sales, Brian C},
abstractNote = {High-resolution thermal expansion measurements of single-crystalline Na0.80CoO2 reveal continuous behavior of the paramagnetic-antiferromagnetic phase transition at TM=21.7(1) K with critical exponent a=0.18(2). The thermal expansion is found to be highly anisotropic. Thermodynamic analysis provides the hydrostatic pressure derivative dTM/dP=+4.6(2) K/GPa. Similar measurements and analysis are presented for Na0.75CoO2.},
doi = {10.1103/PhysRevB.74.132402},
journal = {Physical Review B},
number = 13,
volume = 74,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Cells using polyethylene oxide as a sodium ion conducting electrolyte, P2 phase Na[sub x]CoO[sub 2] as the positive electrode and either sodium or sodium/lead alloy as the negative electrode were assembled, discharged, and cycled. Na[sub x]CoO[sub 2] intercalates sodium over a range of x = 0.3--0.9, giving theoretical energy densities of 1,600 Wh/liter (for sodium) or 1,470 Wh/liter (for sodium/lead alloy). Cells could be discharged at rates up to 2.5 mA/cm[sup 2] corresponding to 25% depth of discharge and typically were discharged and charged at 0.5 mA/cm[sup 2] (100% depth of discharge) or approximately 1--2 C rate. Over one hundredmore » cycles to 60% utilization or more, and two hundred shallower cycles at this rate have been obtained in this laboratory. Experimental evidence suggests that the cathode is the limiting factor in determining cycle life and not the Na/PEO interface as previously thought. Estimates of practical energy and power densities based on the cell performance and the following configuration are presented: 30--45 w/o electroactive material in the positive electrode, a twofold excess of sodium, 10 [mu]m separators, and 5 [mu]m current collectors composed of metal coated plastic. On the basis of these calculations, practical power densities of 335 W/liter for continuous discharge at 0.5 mA/cm[sup 2] and up to 2.7 kW/liter for short periods of time should be attainable. This level of performance approaches or exceeds that seen for some lithium/polymer systems under consideration for electric vehicle applications, but with a lower anticipated cost.« less
  • The Raman spectra of the parent compound Na{sub x}CoO{sub 2} (x = 0.75) and the superconducting oxyhydrates Na{sub x}CoO{sub 2} {center_dot} yH{sub 2}O with different superconducting temperatures (T{sub c}) have been measured. Five Raman active phonons around 195 cm{sup -1} (E{sub 1g}), 482 cm{sup -1}, 522 cm{sup -1}, 616 cm{sup -1} (3E{sub 2g}), and 663 cm{sup -1} (A{sub 1g}) appear in all spectra. These spectra change systematically along with the intercalation of H{sub 2}O and superconducting properties. In particular, the Raman active phonons (A{sub 1g} and E{sub 1g}) involving the oxygen motions within the Co-O layers show up monotonous decreasemore » in frequency along with superconducting temperature T{sub c}. The fundamental properties and alternations of other active Raman phonons in the superconducting materials have also been discussed.« less
  • We have studied the electronic nature of the layered oxysulfide Sr{sub 2-x}Ca{sub x}Cu{sub 2}CoO{sub 2}S{sub 2} which has strongly correlated CoO{sub 2} square planes. These materials exhibit narrow-gap semiconducting behavior and the conduction mechanism depends on the temperature. Valence band x-ray photoemission spectroscopy spectra show that Ca doping and the production of Sr defects cause the generation of a quasiparticle band near the Fermi level. These phenomena suggest that the materials are changing from correlated semiconductors to bad metals.
  • A comparative study on the oxidation and charge compensation in the A{sub x} CoO{sub 2-} {sub {delta}} systems, A=Na (x=0.75, 0.47, 0.36, 0.12) and Li (x=1, 0.49, 0.05), using X-ray absorption spectroscopy at O 1s and Co 2p edges is reported. Both the O 1s and Co 2p XANES results show that upon removal of alkali metal from A{sub x} CoO{sub 2-} {sub {delta}} the valence of cobalt increases more in Li {sub x} CoO{sub 2-} {sub {delta}} than in Na {sub x} CoO{sub 2-} {sub {delta}} . In addition, the data of O 1s XANES indicate that charge compensationmore » by oxygen is more pronounced in Na {sub x} CoO{sub 2-} {sub {delta}} than in Li {sub x} CoO{sub 2-} {sub {delta}} . - Graphical abstract: The valence of cobalt increases more upon removal of alkali metal from Li {sub x} CoO{sub 2} than from Na {sub x} CoO{sub 2}.« less
  • The crystal and magnetic structures of polycrystalline samples of the cobalt oxyhalides Sr{sub 2}CoO{sub 2}X{sub 2}, X=Cl and Br, have been studied using variable temperature neutron diffraction. The materials are isostructural with the K{sub 2}NiF{sub 4}-type square lattice Heisenberg antiferromagnet Sr{sub 2}CuO{sub 2}Cl{sub 2} and contain two-dimensional CoO{sub 2} sheets separated along z by double rocksalt SrX layers. Both materials exhibit magnetic Bragg scattering indicative of long range antiferromagnetic order at T{<=}20 K. The thermal evolution of magnetic reflections has allowed a T{sub N}=215(10) K to be determined for Sr{sub 2}CoO{sub 2}Cl{sub 2}. No evidence of a lowering of crystalmore » symmetry at the onset of magnetic order within Sr{sub 2}CoO{sub 2}Cl{sub 2} is found and the crystal structure of both materials in their antiferromagnetically ordered states is well described with I4/mmm symmetry. The coexistence of domains with the La{sub 2}CuO{sub 4}-type and La{sub 2}NiO{sub 4}-type spin structures is proposed to account for the observed magnetic scattering. The ordered moments of Sr{sub 2}CoO{sub 2}Cl{sub 2} and Sr{sub 2}CoO{sub 2}Br{sub 2} obtained at 20 K and 2 K, respectively, are 3.22(4){mu}{sub B} and 3.52(7){mu}{sub B} indicating the presence of a significant orbital contribution in these high spin (S=3/2) cobalt (II) systems.« less