Abstract
A micromechanics-based thermodynamics model is developed to predict the effects of internal stress, microstructures, porosity, and external hydrostatic pressure, on the phase transition of ferroelectric ceramics, with a special reference to the cubic→tetragonal transformation. The development makes use of the 3-D randomly oriented ellipsoidal inclusions containing an eigenstrain and eigen-polarization to represent the morphology of the transformed domains in the polycrystalline ceramic. The change of Gibbs free energy under a thermo-electro-mechanical loading is then derived at a finite volume concentration of new domains f p and porosity f v. This free energy serves to determine the thermodynamic driving force for domain growth, and, together with the resistance force associated with the energy dissipation due to domain wall motion, a kinetic equation is established. This kinetic equation provides the evolution of the tetragonal domains as the temperature passes through the Curie point. The build-up of internal stress in the parent phase is then calculated, and found to increase linearly at the initial stage but becomes nonlinear at the end. This internal stress plays a significant role in hindering the domain growth process. Consistent with some experimental observations, porosity is found to raise the transition temperature, but for BaTiO3 ceramic external pressure is found to lower it. Applications of the theory to a BaTiO3 single crystal for the evolution of overall polarization is found to give results that are in good accord with the test data.
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Li, W., Weng, G.J. Effects of Microstructures, Porosity and External Pressure on the Phase Transition of Ferroelectric Ceramics Upon Cooling. Mechanics and Materials in Design 1, 17–32 (2004). https://doi.org/10.1023/B:MAMD.0000035455.71448.82
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DOI: https://doi.org/10.1023/B:MAMD.0000035455.71448.82