Influence of Critical Polarization Fluctuations on the Photoelastic Behavior of BaTiO3

Measurements of the temperature dependence of the $p_{11}$ and $p_{12}$ elasto-optic tensor coefficients of BaTi${\mathrm{O}}_3$ in the cubic phase confirm the previously predicted anomalous $\frac{T}{{(T-T_0)}^2}$ enhancement caused by critical polarization fluctuations ($T_0$ is the Curie-Weiss temperature). The $p_{11}$ and $p_{12}$ data provide an estimate of the polarization-fluctuation correlation volume of $V_c=4.5\mathrm{}\pm 1.2\times {10}^4$ ${\mathrm{\AA }}^3$, and lend strong support to the view that $V_c$ is at most weakly temperature-dependent and does not display critical behavior.