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Electronic properties of CeNi4Si compound

Falkowski M., Kowalczyk A., Toliński T., Chełkowska G.

Materials Science Poland

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2007

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Vol. 25, No. 2

321--326

EN

Temperature dependence of the specific heat for CeNi4Si was analyzed. These studies were supported by magnetic susceptibility, electrical resistivity and X-ray photoemission spectroscopy measurements.CeNi4Si is paramagnetic and follows the Curie-Weiss. This effective paramagnetic moment is lower than that for the free Ce3+. The f-occupancy nf and coupling between the f level and the conduction state are derived to be about 0.91 and 36 meV, respectively. Both the susceptibility data and the XPS spectra have shown that Ce ions are in intermediate valence state. The specific heat has been analyzed considering the electronic contribution, the Schottky anomaly, and the lattice contributions within the Debye model. The scheme of the energy levels created by the crystal electric field split is determined from the Schottky contribution to the specific heat.

2

Study of valence state of U ion in the quasi-two dimensional ternary uranium compounds

Troć R.

Materials Science Poland

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2006

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Vol. 24, No. 3

585--589

EN

The valence states and thermoelectric properties of two Ru-based uranium ternaries, namely U2Ru2Sn and U2RuGa8, have been studied. Intermediate-valence behaviour manifests themselves in broad peaks in the susceptibility, largely negative values of the paramagnetic Curie temperature and in the occurrence of maxima in the thermoelectric power. At the same time the specific heat data show no transition at low temperatures for both the compounds studied. The experimental results are fitted to the equations given in the literature relevant to a valence fluctuating state. The studied compounds are unique examples of such a state found for the first time among the huge family of known up to know uranium compounds usually being magnetically ordered at low temperatures.

3

Spin-entropy driven charge transfer phase transition in iron mixed-valence system

Kojima N., Itoi M., Ono Y., Okubo M., Enmoto M.

Materials Science

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2003

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Vol. 21, No. 2

181-189

EN

We have synthesized iron mixed-valence complexes, (n-CnH2n+1)4N[FeIIFeIIIX3] (X = mto(C2O3S), dto(C2O2S2), tto(C2OS3)) and have investigated their physical properties by means of 57Fe Mössbauer spectroscopy, magnetic susceptibility and electrical resistivity measurements. From the analysis of 57Fe Mössbauer spectra, magnetic susceptibility and electrical resistivity, we have discovered a new type of first order phase transition around 120°K for (n-CnH2n+1)4N[FeIIFeIII(dto)3](n = 3, 4), where the charge transfer transition between FeII and FeIII occurs reversibly. In the higher temperature phase, the FeIII (S = 1/2) and FeII (S = 2) sites are coordinated by six S atoms and six O atoms, respectively. In the lower temperature phase, on the other hand, the FeIII (S = 5/2) and FeII (S = 0) sites are coordinated by six O atoms and six S atoms, respectively. Moreover, we have found the ferromagnetic phase transition in this system. The ferromagnetic order is induced by the charge transfer interaction between the FeIII and FeII sites. Moreover, we propose various multifunctional properties for (n-CnH2n+1)4N[FeIIFeIII(mto)3] and (n-CnH2n+1)4N[FeIIFeIII(tto)3].

4

Intramolecular electron transfer on the vibrational timescale in mixed valence ruthenium clusters

Imai N., Hamaguchi T., Yamaguchi T., Ito T.

Materials Science

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2003

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Vol. 21, No. 2

207-214

EN

The thermodynamic stability of the mixed valence (one electron reduced) state between linked Ru3 units was studied by means of electrochemistry for the series of the ligand bridged triruthenium cluster dimers, [Ru3(ž3-O)(ž-CH3CO2)6(CO)(L)(ž-BL)Ru3(ž3-O)-(ž-CH3CO2)6(CO)(L)] (BL = pyrazine: L = 4-dimethyl-aminopyridine (dmap) (1a), pyridine (py) (1b), 4-cyanopyridine (cpy) (1c), 1-azabicyclo[2.2.2]octane (1d); BL = 4,4'-bipyridine: L = dmap (2a), py (2b), cpy (2c); BL = 2,7-diazapyrene: L = dmap (3a); BL = 1,4-diazabicyclo-[2.2.2]octane: L = dmap (4a), py (4b), cpy (4c)). The mixed valence states undergoing rapid intramolecular electron transfers were observed by IR spectroelectrochemistry. By simulating dynamical effects on the observed ?(CO) absorption bandshapes, the rate constants, ke, for electron transfer in the mixed valence states of 1a, 1b, 1c and 1d were estimated to be 9 x 1011 s-1 (at room temperature (rt)), 5 x 1011 s-1 (at rt), ca. 1 x 1011 s-1 (at rt), and 1 x 1012 s-1 (at -18°C), respectively. Possible applications of this approach to asymmetric mixed valence systems were discussed.