Quantum Pinning-transition due to Charge Defects in Ferroelectrics

Abstract:

We investigate pinning of domain walls in ferroelectrics on the basis of two phonon bound state (TPBS) or discrete breather state due to impurity energy levels above the phonon continua in ferroelectrics such as LiNbO₃ to show pinning transition, which indicates the point of easiest switching. We predict with the help of our quantum calculations that every ferroelectric material has such a critical point of easy switching. Here we describe the quantum origin of pinning through the findings of analytical and numerical calculations, as interpreted by a TPBS concept by such impurity or nonlinearity induced modes, by plotting various TPBS parameters against the Landau coefficient and %impurity content. This new approach may lead to many interesting applications for device manufacture.

Keywords: Pinning Transition, Two-phonon Bound State, Ferroelectrics.

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Pinning is an important aspect in ferroelectric switching behavior. Pinning is ascribed to the presence of impurities in such systems that have been probed by various workers with DFT and other methods. Here, we use a micro level approach based on a detailed calculations of two-phonon bound state (TPBS) based on our discrete Hamiltonian. All the TPBS parameters (calculated through Fourier Grid Hamiltonian method) against impurities show a clear pinning transition in the system.

(J. Appl. Phys., Vol. 110 (2011) 024104)