Fig. 6.

BCC$\leftrightarrow$SC solid–solid phase transition is a continuous (i.e., second- or higher-order) thermodynamic phase transition. (A) Order parameter $\overline{Q_4}$ vs. shape suggests the derivative of the order parameter changes discontinuously near ${\alpha }_{a\text{,}c}=0.6$. (B) $P({\alpha }_a\text{,}{\alpha }_c)$ also indicates a discontinuous derivative near ${\alpha }_{a\text{,}c}$ also consistent with a continuous phase transition.