1990 Fiscal Year Final Research Report Summary
Dependence of Valence Fluctuation and Physical Anomalies on the Degree of Order in Pd-Ce Ordering Alloys
| Project/Area Number |
01550511
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Physical properties of metals
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| Research Institution | Kyushu University |
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Principal Investigator |
OKI Kensuke Kyushu University, Graduate School of Engineering Sciences, Professor, 総合理工学研究科, 教授 (70037860)
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| Co-Investigator(Kenkyū-buntansha) |
ITAKURA Masaru Kyushu University, Graduate School of Engineering Sciences, Research Associate, 総合理工学研究科, 助手 (20203078)
MATSUMURA Syo Kyushu University, Graduate School of Engineering Sciences, Research Associate, 総合理工学研究科, 助手 (60150520)
KUWANO Noriyuki Kyushu University, Graduate School of Engineering Sciences, Associate Professor, 総合理工学研究科, 助教授 (50038022)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Palladium Cerium alloy / Concentrated Kondo effect / 4f-electron / Valenece fluctuation / Annealing temperature effect / Ordering alloy / Physical anomaly |
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| Research Abstract |
The physical anomalies of Pd_7Ce, L-Pd_5Ce and Pd_3Ce alloys were studied by means of X-ray powder diffraction, electron microscopy, electrical resistivity measurement at low temperatures (10-300 K) and L_3-XANES (X-ray absorption near edge structure). Special attention was paid to the relationship of the physical anomalies with the state of atomic ordering in the alloys. The following results were obtained.
1. The degree of order in the Pd-Ce alloys decreases with annealing temperature and with the degree of off-stoichiometry. The changes in the degree of order are associated with small changes in the atomic volume in the alloys. The small change in atomic volume, however, has no significant effect on the valence of Ce.
2. In Pd_7Ce and L-Pd_5Ce, the electrical resistivity at room temperature and the temperature coefficient of the resistivity show a strong dependence upon the annealing temperature. This suggests that the decrease in the degree of order enhances the concentrated Kondo effect (scatterings of conduction electrons by isolated spins of 4f electrons in Ce) of the alloys.
3. For Pd_3Ce, the electrical resistivity is almost independent of annealing temperature, except for the absolute value of resistivity at room temperature for the alloy with the stoichiometric composition.
From these experimental results, the effects of stomic disordering on the valence fluctuation were discussed in terms of the changes in atomic volume and in the configurations of Ce in the alloys. In the latter, the correlation between the configurations of Ce atoms and of Ce^<3+> was taken into account.
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