Structural phase transition behaviour of Zn₄Sb₃ and its substitutional compounds (Zn_1.98M_0.02)₄Sb₃ (M= Al, Ga and In) at low temperatures

Structural phase transitions of Zn₄Sb₃ and its substitutional compounds (Zn_1.98M_0.02)₄Sb₃ (M= Al, Ga and In) are investigated by electrical transport measurement and differential scanning calorimetry below room temperature. The results indicate that both \beta → \alpha and \alpha → \alpha' phase transitions of Zn₄Sb₃ are reversible and exothermic processes, which may be explained as that both the transitions originate from the ordering of the disordered interstitial Zn and vacancies in regular sizes. The derived activation energies of \beta → \alpha and \alpha → \alpha' phase transition processes for Zn₄Sb₃ are E_1=3.9 eV and E_2=4.1 eV, respectively. Although no remarkable influence on activation energy E_2 is observed after Al doping, Al substitution for Zn causes E_1 to increase to 4.6 eV, implying its suppression of \beta \leftrightarrow \alpha transition to a great extent. Moreover, it is found that both \beta \leftrightarrow \alpha and \alpha \leftrightarrow \alpha' transitions are completely prohibited by substitution of either In or Ga for Zn in Zn₄Sb₃. The underlying mechanisms for these phenomena are discussed.