Structural transition of partially Ba-filled thermoelectric CoSb3 investigated by positron annihilation spectroscopy

Microstructure of unfilled and Ba-filled CoSb3 has been studied by positron lifetime measurements together with theoretical calculation. Positron trapping in intrinsic voids is observed in the CoSb3, which contributes a positron lifetime of 263 +/- 2 ps. After filling Ba atoms with content up to x=0.4, the positron lifetime shows continuous increase. By comparing the experimental results with calculation following the phase diagram of BaxCo4Sb12 with x in the range of 0-0.5, it is found that when the Ba content is lower than 0.16, the filling of Ba atoms is in a phase of solid solution. At x=0.2, gamma phase is formed, which is mixed with solid solution. At x > 0.25, transition from gamma phase to a mixture of gamma and alpha phases is confirmed. (C) 2015 AIP Publishing LLC.