Contribution of unstable valence states of europium to the electronic transport properties of EuPd2-xSi2+x


Chem. Met. Alloys 3 (2010) 83-89




The intermetallic alloy system EuPd2-xSi2+x (-0.2 ≤ ≤ 0.75) (CeGa2Al2 structure type) was studied by microstructure and compositional homogeneity analysis, X-ray absorption and diffraction at room temperature. Electrical resistivity and thermopower measurements were performed in the temperature range 5.0-300 K. According to data obtained by X-ray LIII-absorption spectroscopy, resistivity and thermopower measurements, we can state that with increasing Si content there is a transition from an intermediate valence state (IV), through a Kondo type state (KS), to a stable Eu2+ europium ion. We can also state that an intermediate valence state and a Kondo type state coexist at specific Pd/Si ratios. The decrease of the effective valence of the europium ion from 2.30 (= -0.2) to almost 2.00 (= 0.75) is accompanied by a decrease of the lattice parameter a and the a/c ratio. The investigation was carried out in the context of questions discussed for some time in the scientific community, namely: How is the transition type (stable europium ion inter-configuration fluctuation state) related to the magnetic ordering state, Kondo type state, and to the intermediate valence state in this type of compound?



Temperature dependence of the reduced resistivity ρ/ρ300 of EuPd2-xSi2+x alloys:

1 EuPd1.25Si2.75 5 EuPd1.9Si2.1

2 EuPd1.5Si2.5 6 EuPd2Si2

3 EuPd1.7Si2.3 7 EuPd2.1Si1.9

4 EuPd1.8Si2.2 8 EuPd2.2Si1.8.



Intermetallics / Electron-electron interactions / Electronic transport / Kondo effect / Valence fluctuations