Enhanced piezoelectricity in twinned ferroelastics with nanocavities

GM Lu and SZ Li and XD Ding and J Sun and EKH Salje, PHYSICAL REVIEW MATERIALS, 4, 074410 (2020).

DOI: 10.1103/PhysRevMaterials.4.074410

Enhancing the electromechanical response by engineering domain boundaries in multiferroics has become a highly active research field in recent years. The starting point is the discovery that ferroelastic twin walls are polar inside a nonpolar matrix. The density of such twin walls is then greatly enhanced by forming complex twin patterns. Our computer simulations show that the interaction of nanocavities with differently charged configurations with twin boundaries generates strong piezoelectricity in ferroelastic (nonferroelectric) crystals. Cavity- induced domain patterns statistically break the inversion symmetry of a sample even when the cavities themselves obey inversion symmetry with relatively weak emerging piezoelectricity (d similar to 10(-3) pm/V). Stronger piezoelectricity occurs in noncentrosymmetric charged cavity arrangements with a coefficient of d similar to 10(-1) pm/V. Structurally, the electric field polarizes and shifts the nanocavities by the displacement of trapped surface charges. The related strain fields interact with the ferroelastic domains, which act as soft bridges between the nanocavities. This leads to a significant deformation of the entire sample and hence to enhanced piezoelectricity. Our simulation results point to new directions for designing and enhancing electromechanical nanodevices based on ferroelastic templates even when the bulk material is structurally centrosymmetric.

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