Determination of the magnetic contribution to the heat capacity of cobalt oxide nanoparticles and the thermodynamic properties of the hydration layers

Journal Article · Fri Dec 31 23:00:00 EST 2010 · Journal of Physics: Condensed Matter

DOI:https://doi.org/10.1088/0953-8984/23/20/205303· OSTI ID:1081787

Spencer, Elinor ^[1]; Ross, Dr. Nancy ^[1]; Parker, Stewart F. ^[2]; Woodfield, Brian ^[3]; Boerio-Goates, Juliana ^[3]; Smith, S. J. ^[3]; Olsen, R. E. ^[3]; Kolesnikov, Alexander I ^[4]; Navrotsky, Alexandra ^[5]; Ma, C ^[5]

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1. Virginia Polytechnic Institute and State University (Virginia Tech)
2. ISIS Facility, Rutherford Appleton Laboratory
3. Brigham Young University
4. ORNL
5. University of California, Davis

We present low temperature (11 K) inelastic neutron scattering (INS) data on four hydrated nanoparticle systems: 10 nm CoO 0.10H2O (1), 16 nmCo3O4 0.40H2O (2), 25 nm Co3O4 0.30H2O (3) and 40 nmCo3O4 0.026H2O (4). The vibrational densities of states were obtained for all samples and from these the isochoric heat capacity and vibrational energy for the hydration layers confined to the surfaces of these nanoparticle systems have been elucidated. The results show that water on the surface of CoO nanoparticles is more tightly bound than water confined to the surface of Co3O4, and this is reflected in the reduced heat capacity and vibrational entropy for water on CoO relative to water on Co3O4 nanoparticles. This supports the trend, seen previously, for water to be more tightly bound in materials with higher surface energies. The INS spectra for the antiferromagnetic Co3O4 particles (2 4) also show sharp and intense magnetic excitation peaks at 5 meV, and from this the magnetic contribution to the heat capacity of Co3O4 nanoparticles has been calculated; this represents the first example of use of INS data for determining the magnetic contribution to the heat capacity of any magnetic nanoparticle system.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1081787
• Journal Information: Journal of Physics: Condensed Matter, Journal Name: Journal of Physics: Condensed Matter Journal Issue: 20 Vol. 23; ISSN 0953-8984
• Country of Publication: United States
• Language: English