Thermodynamic properties of a quasi-harmonic model for ferroelectric transitions

• Published in: Journal of physics. Condensed matter Vol. 23; no. 12; pp. 125902 - 12
• Main Authors: Mkam Tchouobiap, S E, Mashiyama, H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 30.03.2011; Institute of Physics
• Subjects: Barriers; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Entropy; Exact sciences and technology; Ferroelectric materials; Ferroelectricity and antiferroelectricity; Mathematical analysis; Mathematical models; Phase transformations; Phase transitions and curie point; Physics; Thermodynamic properties; Thermodynamics; Specific heat; Ferroelectric transitions; Mean field approximation; Ferroelectricity; Phase transformations; Particle interactions; Numerical method; Thermodynamic properties; Quantum theory; Quantum fluctuation
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/23/12/125902

Within a framework of a quasi-harmonic model for quantum particles in a local potential of the double Morse type and within the mean-field approximation for interactions between particles, we investigate the thermodynamic properties of ferroelectric materials. A quantum thermodynamic treatment gives analytic expressions for the internal energy, the entropy, the specific heat, and the static susceptibility. The calculated thermodynamic characteristics are studied as a function of temperature and energy barrier, where it is shown that at the proper choice of the theory parameters, particularly the energy barrier, the model system exhibits characteristic features of either second-order tricritical or first-order phase transitions. Our results indicate that the barrier energy seems to be an important criterion for the character of the structural phase transition. The influence of quantum fluctuations manifested on zero-point energy on the phase transition and thermodynamic properties is analyzed and discussed. This leads to several quantum effects, including the existence of a saturation regime at low temperatures, where the order parameter saturates giving thermodynamic saturation of the calculated thermodynamic quantities. It is found that both quantum effects and energy barrier magnitude have an important influence on the thermodynamic properties of the ferroelectric materials and on driving the phase transition at low temperatures. Also, the analytical parameters' effect on the transition temperature is discussed, which seems to give a general insight into the structural phase transition and its nature.