Quadrupole-quadrupole forces in cerium metal

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1953
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Koenigsberg, Ernest
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Physics and Astronomy
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The specific heat of cerium shows an anomalous peak at about 12°K. The peak is too sharp to be accounted for by the splitting of the ground level by the electrostatic field of the crystal. In this thesis an attempt has been made to explain the peak by proposing a model which approximates the metal as a hexagonal close packed array of multipoles superimposed on a uniform negative charge density. This model contains strong quadrupole-quadrupole couplings between the ions of the lattice. The Q-Q energies are of the order of magnitude of the crystal field energies, and the effect of these Q-Q couplings on the filling of the various states is considerable;The simple approach, based on an approximate partition function, approximate wave functions and the assumption that the ions of the various kinds are randomly distributed throughout the lattice, is evidently inadequate to explain the anomaly in the specific heat;An attempt to improve the wave functions shows that the crystal field wave functions are not suitable, but the improved wave functions do not appreciably change the specific heat, (Stated more carefully, wave functions obtained by neglecting Q-Q interactions are not appropriate at very low temperatures.

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Thu Jan 01 00:00:00 UTC 1953