TY - JOUR
T1 - The magnetic transition, heat capacity, and thermodynamic properties of uranium dioxide from 5 to 350 K
AU - Huntzicker, James J.
AU - Westrum, Edgar F.
N1 - Funding Information:
Although the importance of UO2 in nuclear technology has been self-evident, it is only recently that this substance has come under the close scrutiny of solid-state physicists. Much of the increased interest concerns a striking magnetic-ordering transition in UO2 near 30 K. This transition was first detected in thermal capacity measurements by Jones, Gordon, and Long, °) who found a relatively blunt, ~.-type transformation at 28.7 K and suggested that the thermal anomaly was associated with a transition from a high-temperature paramagnetic state to a low-temperature anti-ferromagnetic state. This suggestion has been supported both by magnetic susceptibility studies (2-5) and by powder neutron diffraction measurements. (6) A preliminary report of this research in March 1964 (77 established that the heat capacities at the peak of the transition were at least 50 times as high as those previously reported and that the transition was a cooperative first-order one rather than a ~,-type anomaly. The N6el temperature TN ascertained was 30.44 K or 6 per cent higher than previous reports. These results were corroborated by a detailed diffraction study of the temperature dependence of ~he antiferromagnetism in single crystal UO2 reported in 1965 by Frazer eta/. (8) They found that TN was 30.80 K and that 50 per cent of the saturation magnetization was attained within 0.03 K below TN,
Funding Information:
t Supported in part by the Division of Research of the United States Atomic Energy Commission. Present Address: I Physikalisches Institut der Freien Universit[it Berlin, Berlin, Germany.
Funding Information:
We are grateful to the Division of Research of the United States Atomic Energy Commission for enabling financial support and to the National Science Foundation for research participation awards for one of us (J.J.H.). We would like to acknowledge the kind assistance of Dr Gerald Dolling (for a detailed tabulation of the heat capacity of UO 2 derived from the neutron scattering results of reference 14), that of Dr Ludmila Mich~elova Jake~ (who assisted in a preliminary endeavor to resolve the lattice heat capacity), that of Dr C. W. Kuhlman and the Mallinckrodt Chemical Works (for provision of the pressed and flame-fused calorimetric samples), and the interest and suggestions of Drs George H. Winslow and J. M. Leitnaker.
PY - 1971/1
Y1 - 1971/1
N2 - The heat capacity of high purity uranium dioxide has been re-examined over the low-temperature range especially in the vicinity of the λ-type anomaly reported to occur at 28·7 K as a consequence of magnetic ordering. The present study indicates a very sharp transition at 30·44 K with a maximum Cp of 391 cal mol-1 K-1. The heat capacity at constant pressure Cp, the entropy S°, the enthalpy (H° - H°0), and Gibbs energy function (G° - H°)/T are tabulated and at 298.15 K have the following values: 15.20 cal mol-1 K-1, 18.41 cal mol-1 K-1, 2696 cal mol-1 K-1, and -9.37 cal mol-1 K-1. The heat capacity results are compared with those derived from the neutron scattering work and also with the theory of Allen.
AB - The heat capacity of high purity uranium dioxide has been re-examined over the low-temperature range especially in the vicinity of the λ-type anomaly reported to occur at 28·7 K as a consequence of magnetic ordering. The present study indicates a very sharp transition at 30·44 K with a maximum Cp of 391 cal mol-1 K-1. The heat capacity at constant pressure Cp, the entropy S°, the enthalpy (H° - H°0), and Gibbs energy function (G° - H°)/T are tabulated and at 298.15 K have the following values: 15.20 cal mol-1 K-1, 18.41 cal mol-1 K-1, 2696 cal mol-1 K-1, and -9.37 cal mol-1 K-1. The heat capacity results are compared with those derived from the neutron scattering work and also with the theory of Allen.
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U2 - 10.1016/S0021-9614(71)80067-8
DO - 10.1016/S0021-9614(71)80067-8
M3 - Article
AN - SCOPUS:0006668954
VL - 3
SP - 61
EP - 76
JO - Journal of Chemical Thermodynamics
JF - Journal of Chemical Thermodynamics
SN - 0021-9614
IS - 1
ER -