Thermal formation of vacancies inFe3Si

The formation of thermal vacancies in the intermetallic compound ${\mathrm{Fe}}_3$Si was studied below and at the ferromagnetic-paramagnetic phase transition by means of positron-lifetime spectroscopy. Low values of the vacancy formation enthalpies ${\mathit{H}}_{\mathit{V},\mathit{f}}^{\mathit{F}}$=0.77 eV in the ferromagnetic state and ${\mathit{H}}_{\mathit{V},\mathit{p}}^{\mathit{F}}$=0.74 eV in the paramagnetic state are derived in the case of stoichiometric ${\mathrm{Fe}}_{75}$ ${\mathrm{Si}}_{25}$. These values substantially increase to ${\mathit{H}}_{\mathit{V},\mathit{f}}^{\mathit{F}}$=1.11 eV and ${\mathit{H}}_{\mathit{V},\mathit{p}}^{\mathit{F}}$=1.07 eV in the case of Fe-rich ${\mathrm{Fe}}_{79}$ ${\mathrm{Si}}_{21}$. In addition, an upper limit of the vacancy migration enthalpy was derived from measurements after fast temperature changes. The results are discussed with respect to recent tracer diffusion measurements in ${\mathrm{Fe}}_3$Si.