Contribution of unstable valence states of europium to the electronic transport properties of EuPd_2-xSi_2+x

Chem. Met. Alloys 3 (2010) 83-89

https://doi.org/10.30970/cma3.0123

B. KUZHEL, B. BELAN, V. KUZHEL, I. STETS’, R. SERKIZ

The intermetallic alloy system EuPd_2-xSi_2+x (-0.2 ≤ х ≤ 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 L_III-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 (x = -0.2) to almost 2.00 (x = 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 EuPd_2-xSi_2+x alloys:

1 – EuPd_1.25Si_2.75 5 – EuPd_1.9Si_2.1

2 – EuPd_1.5Si_2.5 6 – EuPd₂Si₂

3 – EuPd_1.7Si_2.3 7 – EuPd_2.1Si_1.9

4 – EuPd_1.8Si_2.2 8 – EuPd_2.2Si_1.8.

Keywords

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