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We present an extended X-ray absorption fine structure (EXAFS) study of the NdOs4Sb12 system at the Nd and Os L III edges. Nd is expected to be a 'rattler' atom in this skutterudite crystal and we obtain a low Einstein temperature (61 K) as expected. However, although ultrasonic measurements have suggested a large off-center displacement of Nd, the EXAFS data are inconsistent with such a model. An analysis of the first two Os-Sb peaks in the Os L III data also shows no evidence for unusual disorder. In contrast the Nd-Os peak in the Nd L III data and the Os-Os peak in the Os L III data both show significant disorder at 4 K, with the largest disorder found for the Nd-Os pair. This suggests that a distortion of the structure that involves mainly the Os atoms is present; it is likely that this distortion - which may also be dynamic - also causes the anomalies in the ultrasonic data (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

When the well know thermoelectric PbTe is doped with a few percent Tl, the figure of merit, ZT = S2 σ / κ, is dramatically improved (here S is the Seebeck coefficient, σ the electrical conductivity and κ the thermal conductivity). Tl is a valence skipper with valences of +1 and +3 and replaces Pb(+2) in PbTe. Further Tl(+1) has a lone electron pair; consequently, the atom is asymmetric and large local distortions are expected if Tl(+1) is present. Here we we present Extended X-ray Absorption Fine Structure (EXAFS) data for 1% Tl doped PbTe at the Tl and Pb L3 edges and at the Te K edge, to probe the local structure about the dopant, and host atoms. At 10 K the local structure about Pb and Te is well ordered, although disorder of the Pb-Te (Te-Pb) pair distribution function (PDF) increases rapidly with increasing T. In contrast the environment around Tl is more disordered even at 10 K within the well ordered host material. This indicates a large variation of the Tl-Te bond lengths presumably as a result of the presence of some Tl(+1). This increased local disorder will result in additional electron and phonon scattering. We discuss possible models for the disorder about Tl and for PbTe at higher temperature for which neutron PDF measurements suggest Pb moves off-center (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We present an extended X-ray absorption fine structure (EXAFS) study of the NdOs4Sb12 system at the Nd and Os L III edges. Nd is expected to be a 'rattler' atom in this skutterudite crystal and we obtain a low Einstein temperature (61 K) as expected. However, although ultrasonic measurements have suggested a large off-center displacement of Nd, the EXAFS data are inconsistent with such a model. An analysis of the first two Os-Sb peaks in the Os L III data also shows no evidence for unusual disorder. In contrast the Nd-Os peak in the Nd L III data and the Os-Os peak in the Os L III data both show significant disorder at 4 K, with the largest disorder found for the Nd-Os pair. This suggests that a distortion of the structure that involves mainly the Os atoms is present; it is likely that this distortion - which may also be dynamic - also causes the anomalies in the ultrasonic data (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]