Local distortions about Nd in NdOs4Sb12

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. (c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim