Fluctuation-dominated regime in the second-order antiferrodistortive transition of the layered perovskite
Laboratoire Physique de l'Etat Condensé, UPRES-A 6087, Université du Maine, Avenue Olivier Messiaen - 72085 Le Mans cedex 9, France
Accepted: 27 October 1998
By EPR spectroscopy, the two components (n=2) of the order parameter are monitored near Tc in the second-order structural phase transition of the layered compound from P4/mbm to Pmmn. The direction of the spontaneous displacements is not fixed by symmetry but depends on the ratio between two quartic anisotropies. In the never before probed range , a sharp crossover is evidenced as well as in (). The order parameter amplitude accurately follows an exponent law of index , at most slightly increased in the random-bond–like solid solution.
PACS: 64.60.Fr – Equilibrium properties near critical points, critical exponents / 63.70.+h – Statistical mechanics of lattice vibrations and displacive phase transitions / 76.30.Fc – Iron group (3d) ions and impurities (Ti-Cu)
© EDP Sciences, 1998