SCIENCE SPIN-OFFS

[dockzef]

Our model system can be extended in various ways. It is possible to consider a more complex unit cell that contains multiple ionic basis and extended neighbor interactions at the expense of rapidly increasing calculation complexity dealing with possible combinations of ions in a unit cell and its neighbors. On the other hand, to handle a system made of a single kind of atoms, it can be treated as a pseudo binary ion system by introducing imaginary ions that stands for the center of electron cloud [30]. Adopting anharmonic springs allows the model system to represent the e?ects of electrostriction and second order piezoelectricity [31–34]. The magnitudes of charges can be considered as the formal charges of the ions in a na¨ive sense. One may also interpret them as the Born e?ective charges taking electron redistribution into account [35] and the spring constants as the Born-von Karman force constants [36] beyond the classical picture. On the assumption that the charge is ten times larger than the elementary charge of electron and a is a few °A, the simulated result for the linear ?exoelectric coe?cient corresponds to ~1 nC/m which is comparable with the measured quantity in SrTiO3 [20]. This theoretical approach opens the door to a quantitative understanding of the electromechanical properties in crystals.

Nonlinear Flexoelectricity in Non-centrosymmetric Crystals
Kanghyun Chu, Chan-Ho Yang
(Submitted on 9 Feb 2017)
We analytically derive the elastic, dielectric, piezoelectric, and the flexoelectric phenomenological coefficients as functions of microscopic model parameters such as ionic positions and spring constants in the two-dimensional square-lattice model with rock-salt-type ionic arrangement. Monte-Carlo simulation reveals that a difference in the given elastic constants of the diagonal springs, each of which connects the same cations or anions, is responsible for the linear flexoelectric effect in the model. We show the quadratic flexoelectric effect is present only in non-centrosymmetric systems and it can overwhelm the linear effect in feasibly large strain gradients.

https://arxiv.org/abs/1702.02740

I would apply fig. 5 to the wing / feather construction power distribution to super capacitors