Figure 1
(Lower Part) Temperature dependence of Δn(T) of ETO. The linear regime of the temperature dependence, as expected from, e.g., Landau theory, is observed below TS. The full vertical line at 282 K corresponds to the onset of symmetry lowering at TS. A dashed line is placed at the point where transition near 210 K is suggested, although conclusive evidence is discussed further in the text (see Fig. 2). (Upper Part) there are exemplary birefringence maps of ETO taken at temperatures T = 130 K (left), T = 170 K (middle), and T = 240 K (right). The white framed squares of size 200 µm × 200 µm are those regions for which Δn(T) has been determined. The colour code indicates the indicatrix angle φ.
