Dependence of Valence Fluctuation and Physical Anomalies on the Degree of Order in Pd-Ce Ordering Alloys

用X射线粉末衍射、电子显微镜、低温电阻率测量和L_3-XANES（X射线吸收近边结构）等方法研究了Pd_7Ce、L-Pd_5Ce和Pd_3Ce合金的物理异常。特别注意的是合金中的原子有序状态的物理异常的关系。得到以下结果. Pd-Ce合金的有序度随退火温度和偏离化学计量的程度而降低。有序度的变化与合金中原子体积的微小变化有关。原子体积的微小变化，但是，没有显着的影响Ce的化合价。在Pd_7Ce和L-Pd_5Ce中，室温电阻率和电阻率的温度系数与退火温度有很强的依赖关系。这表明有序度的降低增强了合金的集中近藤效应（传导电子被Ce中孤立的4f电子自旋散射）。对于Pd_3Ce合金，除了化学计量比的合金室温电阻率的绝对值与退火温度无关外，其电阻率几乎与退火温度无关.根据这些实验结果，从Ce在合金中的原子体积变化和组态变化讨论了无序对价态涨落的影响.在后者中，考虑了Ce原子和Ce^<3+>的构型之间的相关性。

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.