Equation of state for the Ce/sub 1-x/Th/sub x/ valence transition
The valence transition in Ce/sub 1 - x/Th/sub x/ is isomorphic, and, hence, analogous to a liquid-vapor transition (the order parameter being the volume V); and it exhibits mean-field behavior. It is found that in the critical region the x - T phase boundary is nearly parallel to the x-axis, and that the data for resistivity R (which couples linearly to the order parameter) fits a Landau equation of state of the approximate form 0.35 (..delta..R/R/sub 0/)/sup 3/ + 0.67 (..delta..x/x/sub 0/)(..delta..R/R/sub 0/) = ..delta..T/T/sub 0/ - 0.07 ..delta..x/x/sub 0/. This is in analogy to a mean-field ferromagnet with (M,H,T) approximately (V,T,x); consequently dR/dT parallel/sub max/ approximately (..delta..x)/sup ..gamma../ with ..gamma.. = 1, as demonstrated by the data. The mean field nature is due to the electroelastic coupling associated with the large volume change. This coupling enters the free energy as the ..delta..x(..delta..V)/sup 2/ term, which may reflect the dominance of anharmonic strain with increased alloying. Magnetic susceptibility and specific heat measurements reveal that both the average magnetic moment and entropy couple linearly to the order parameter. The latter finding is consistent with the existence of the term -..delta..V..delta..T in the free energy as implied by the above equation of state.
- Research Organization:
- Univ. of Rochester, NY
- OSTI ID:
- 7269509
- Journal Information:
- AIP (Am. Inst. Phys.) Conf. Proc.; (United States), Vol. 29; Conference: 21. annual conference on magnetism and magnetic materials, Philadelphia, PA, USA, 9 Dec 1975; Other Information: See CONF-751209--
- Country of Publication:
- United States
- Language:
- English
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