Phase transitions in the ferroelectric crystals[CH3NH3]5Bi

Study of Order Parameters Coupling in Uniaxial Ferroelectrics on the Basis of Pyroelectric and Dilatometric Measurements

“…The symmetry relation is P cab → P ca2 1 in both cases [8,10,16]. The mechanism of the phase transitions involves ordering of one of three types of the methylammonium cations [8,10,12,13,16,[19][20][21].…”

“…Molecular ferroelectrics MAPCB and MAPBB undergo the second order phase transition at T C = 307.65 K [8,10,18] and at T C = 311.52 K [8,10], respectively. The symmetry relation is P cab → P ca2 1 in both cases [8,10,16].…”

“…Molecular ferroelectrics MAPCB and MAPBB undergo the second order phase transition at T C = 307.65 K [8,10,18] and at T C = 311.52 K [8,10], respectively. The symmetry relation is P cab → P ca2 1 in both cases [8,10,16]. The mechanism of the phase transitions involves ordering of one of three types of the methylammonium cations [8,10,12,13,16,[19][20][21].…”

“…and from the experimental conditions (as a finite temperature rate, a measuring frequency, a finite size of sample, etc.) [10,[13][14][15].…”

“…The present authors will show how to modify the mean field treatment to obtain a critical behaviour compatible with the scaling hypothesis [5][6][7][8] and at the same time the saturation at lower temperatures. The scaling equations of * corresponding author; e-mail: Miroslaw.Galazka@ifj.edu.pl state provide a correct description of real materials undergoing the second order phase transitions even if the full equilibrium is not attained because of a finite rate of temperature changes (for example see [8][9][10][11][12]). Then all of materials parameters, as, for example, the ratio of the inverse Curie-Weiss constants, Γ − /Γ + , the effective critical exponents, are a result of interplay between static and dynamical phenomena.…”