Strain modulation of TaO4 planarity in tantalates ultrathin films: surface states engineering

Abstract

Ultrathin films of perovskites have attracted considerable attention once they fit in numerous applications. Over the years, controlling and tuning their properties have been attainable when biaxial strain is applied. Through ab initio DFT calculations, (110) ultrathin (Na,K)TaO 3 films were submitted to biaxial tensile and compressive strain. Intrinsically, surface Ta shallow states emerge into the bandgap since the (110) cleavage breaks its octahedral symmetry to create TaO 4 units. Removal of ligands along the x-y plane stabilizes d x 2-y 2 orbitals, which decrease in energy due to lower electrostatic repulsion. Such stabilization is maximized when biaxial tensile increases the TaO 4 planarity towards a square planar symmetry. Accordingly, the corresponding electronic levels move further into the bandgap. Conversely, compressive biaxial strain intensifies electrostatic repulsion, closing the TaO 4 tetrahedra, and surface states move to higher energy zones. The reported strain-driven modulation might be applied in different applications, as photocatalysis, ferroelectricity, and spintronics.

Predicting the structural, electronic and magnetic properties of few atomic-layer polar perovskite

“…This could be explained by the "polar catastrophe" of perovskite materials when an electrostatic instability happens as layer thickness is accumulated to certain threshold. Further, there are many compensation mechanisms to stabilize such as electrostatic shielding by 2DEG, charge transfer, surface reconstruction, chemical doping and adsorption [15][16][17]19,29]. As displayed in Fig.…”

Hybrid Functional-Based Scissors Operator for Perovskite Oxide Nanostructures: A NaTaO3 Case Study

“…Such TaO 4 groups accommodate most of the distortions triggered by polarity-induced surface reconstruction 56. The more planar geometry and the rotation of these tetrahedra stabilize surface Ta 5d states (hybridized with O 2p), now occupied within the bandgap region 66. Consequently, besides the energy difference between E HOS (surface defect state) and E LUS (conduction band minimum) that provides the absolute bandgap (E gap ), both slabs also present a bulk-like bandgap (E B−gap ).…”