Defect structure of thermoelectric Zn4Sb3

Thermoelectric -Zn4Sb3 samples prepared by spark plasma sintering method have been studied by resistivity measurement, X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS). The existence of Zn vacancies in -Zn4Sb3 structure is confirmed by PAS, which contribute a positron lifetime component of 212 +/- 3ps. Positron lifetime calculation has been performed for different defect structural models of -Zn4Sb3. By comparing the calculated lifetime values with the experimental result, we find that each Zn vacancy must have at least two close interstitial Zn atoms in the crystal structure of -Zn4Sb3. Two separate phase transitions observed by resistivity measurement occur at about 232 and 252K, whereas the positron annihilation measurements indicate they are about 225 and 240K. Positron lifetime and Doppler broadening results reveal phase is a transition phase between and phases. The results also indicate the disordering of interstitial clusters into interstitial Zn sites during the to phase transition. The interstitial Zn clusters are found to act as shallow positron traps which apparently capture positrons below 200 K.