Abstract
Oxide interface engineering has attracted considerable attention since the discovery of its exotic properties induced by lattice strain, dislocation and composition change at the interface. In this paper, the atomic resolution structure and composition of the interface between the lead-free piezoelectric (K0.5Na0.5)NbO3 (KNN) thin films and single-crystalline SrTiO3 substrate were investigated by means of scanning transmission electron microscopy (STEM) combining with electron energy loss spectroscopy (EELS). A sharp epitaxial interface was observed to be a monolayer composed of Nb and Ti cations with a ratio of 3/1. The First-Principles Calculations indicated the interface monolayer showed different electronic structure and played the vital role in the asymmetric charge distribution of KNN thin films near the interface. We also observed the gradual relaxation process for the relatively large lattice strains near the KNN/STO interface, which remarks a good structure modulation behavior of KNN thin films via strain engineering.
Highlights
Potassium sodium niobate (K0.5Na0.5NbO3, KNN), as an environment-friendly lead-free piezoelectric material, has been extensively studied since the earlier pioneering works by Saito et al.[1]
Since the epitaxial or textured thin films are favorable for structural investigations using electron microscopy, the highly textured KNN thin films were prepared by spin-coating a KNN precursor solution on single crystal strontium titanate (SrTiO3, STO) substrate
The microstructure of KNN/STO interface was investigated by the atomic resolution scanning transmission electron microscopy (STEM)
Summary
Structure of Lead-free Ferroelectric received: 02 March 2016 accepted: 28 October 2016 Published: 25 November 2016. The First-Principles Calculations indicated the interface monolayer showed different electronic structure and played the vital role in the asymmetric charge distribution of KNN thin films near the interface. When the Nb5+ ions in the NbO2 layer bond directly to the oxygens in the SrO layer on the subsrate surface, the excessive Nb 4d-state valence electrons will stay in anti-bonding orbitals and act as interfacial carriers This would lead to a polar discontinuity at the KNN/STO interface and a higher leakage current density when an external electric field is applied. We investigated the interfacial lattice strains using GPA analysis and it was found that the interfacial strains can relax gradually at dislocation-free regions or abruptly via the dislocations
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