Polarization states and dielectric responses of elastically clamped ferroelectric nanocrystals

Polarization states and physicalproperties of ferroelectrics depend on the mechanical boundary conditions due to electrostrictive coupling between electricpolarization and lattice strains. Here, we describe theoretically both equilibrium thermodynamic states and electric permittivities of ferroelectricnanocrystals subjected to theelastic three-dimensional (3D) clamping by a surroundingdielectric material. The problem is solved by the minimization of a special thermodynamic potential that describes the case of an ellipsoidal ferroelectricinclusion embedded into a linearelastic matrix. Numerical calculations are performed for BaTiO3, PbTiO3, and Pb(Zr0.5Ti0.5)O3 nanoparticles surrounded bysilica glass. It is shown that, in the case of BaTiO3 and PbTiO3,elastic 3D clamping may change the order of aferroelectric phase transition from first to second. Furthermore, the mechanical inclusion –matrix interaction shifts the temperatures of structuraltransitions between different ferroelectric states and even eliminates some ferroelectric phases existing in stress-free BaTiO3 and Pb(Zr0.5Ti0.5)O3 crystals. Another important effect ofelastic clamping is the lowering of the symmetry of ferroelectric states in ellipsoidalinclusions, where orthorhombic and monoclinic phases may form instead of the tetragonal and rhombohedral bulk counterparts. Finally, our thermodynamic calculations show that thedielectric responses of studied perovskite ferroelectrics are sensitive to matrix-induced clam...

Source: Journal of Applied Physics - December 2, 2016 Category: Physics Authors: A. V. Azovtsev and N. A. Pertsev Source Type: research