Time-differential perturbed-angular-correlation study of theIn2Se3crystal structure

The time-differential perturbed-angular-correlation technique has been used to investigate the temperature dependence of the electric-field gradient (EFG) at Cd impurities in the semiconducting compound ${\mathrm{In}}_2$ ${\mathrm{Se}}_3$. Between room temperature and the melting point, four different phases could be observed. Most crystal structures which have been proposed for the $\alpha$ and $\beta$ phases are shown to be incorrect. The ${\beta }^{\prime }$ phase (550-720°C) has not been reported previously. The data suggest that the $\beta$ phase may be a Peierls distortion of the ${\beta }^{\prime }$ phase. The EFG in the $\alpha$ phase is well described by a simple point-charge model suggesting that the electronic part of the EFG in $\alpha$-${\mathrm{In}}_2$ ${\mathrm{Se}}_3$ is small.