Static Critical Exponents at Structural Phase Transitions

Abstract

The temperature dependence of the rotational displacement parameters below the second-order phase transitions in SrTi${\mathrm{O}}_{3}$ and LaAl${\mathrm{O}}_{3}$ at ${T}_{a}=105.5 \mathrm{and} 797$\ifmmode^\circ\else\textdegree\fi{}K is described by an exponent $\ensuremath{\beta}=0.33\ifmmode\pm\else\textpm\fi{}0.02$ down to $t=\frac{T}{{T}_{a}}=0.95$. For smaller $t$'s there occurs a change to Landau behavior approximately followed between $t=0.9 \mathrm{and} 0.7$. The observation of static critical exponents near displacive phase transitions confirms now the notion of universality in this field.