Experimental observation of multicritical points with TGB phases on a pure compound

Abstract

Abstract High pressure studies for the n = 12 homologues of the 3-fluoro-4((R) or (S)-methylheptyloxy)-4′-(4-alkyloxy-3-fluorobenzoyloxy) tolanes series have been performed by thermobarometric analysis. The phase sequence presents two Twist Grain Boundary phases denoted TGBA and TGBC. The pressure-temperature phase diagram has been determined; it exhibits a SC∗ phase, and an induced phase identified as SA which does not exist under atmospheric pressure. The TGBA temperature stability domain versus pressure first increases, then rises to a maximum and finally disappears. Such phase behaviour leads to an experimental observation of two multicritical points SC∗-SA-TGBA and SA-TGBA-N∗ for the pure compound under high pressures. This result confirms the existence of singular points previously predicted by the Renn-Lubensky theory.