Diverse Defects in Alkali Niobate Thin Films: Understanding at Atomic Scales and Their Implications on Properties

Abstract

Defects in ferroelectric materials have many implications on the material properties which, in most cases, are detrimental. However, engineering these defects can also create opportunities for property enhancement as well as for tailoring novel functionalities. To purposely manipulate these defects, a thorough knowledge of their spatial atomic arrangement, as well as elastic and electrostatic interactions with the surrounding lattice, is highly crucial. In this work, analytical scanning transmission electron microscopy (STEM) is used to reveal a diverse range of multidimensional crystalline defects (point, line, planar, and secondary phase) in (K,Na)NbO3 (KNN) ferroelectric thin films. The atomic‐scale analyses of the defect‐lattice interactions suggest strong elastic and electrostatic couplings which vary among the individual defects and correspondingly affect the electric polarization. In particular, the observed polarization orientations are correlated with lattice relaxations as well as strain gradients and can strongly impact the properties of the ferroelectric films. The knowledge and understanding obtained in this study open a new avenue for the improvement of properties as well as the discovery of defect‐based functionalities in alkali niobate thin films.

A multiscale generative model to understand disorder in domain boundaries

“…S5) and are thus ignored in model construction. These dissimilar regions can be regarded as islands of secondary phases precipitating in a KNN grain ( 40 ).…”

Large Electromechanical Response in a Polycrystalline Alkali-Deficient (K,Na)NbO3 Thin Film on Silicon

“…High-performance piezoelectric thin films are crucial for advanced applications like microsensors and actuators for microelectromechanical systems (MEMS). , Typically, lead-based solid solutions with chemically driven morphotropic phase boundaries (MPBs) are dominantly used for such applications due to their remarkable piezoelectric properties, despite their environmental concerns. Efforts to replace lead with viable alternatives have led to phase boundary engineering using multielement dopants, resulting in large piezoelectric responses in bulk ceramics, but this is much more challenging in thin films due to chemical control issues during deposition , and substrate clamping affecting phase stability. , Hence, new approaches are needed for outstanding electromechanical responses in thin films with simple, lead-free chemical compositions. While strain engineering enhances piezoelectric response and high-temperature stability in compositionally simple ferroelectric thin films, , its effectiveness is limited to epitaxial thin films on single-crystal substrates with a suitable lattice matching, and their piezoelectric properties remain far behind those of lead-based counterparts.…”

“…1,2 Typically, lead-based solid solutions with chemically driven morphotropic phase boundaries (MPBs) are dominantly used for such applications due to their remarkable piezoelectric properties, despite their environmental concerns. Efforts to replace lead with viable alternatives have led to phase boundary engineering using multielement dopants, resulting in large piezoelectric responses in bulk ceramics, but this is much more challenging in thin films 3 due to chemical control issues during deposition 4,5 and substrate clamping affecting phase stability. 6,7 Hence, new approaches are needed for outstanding electromechanical responses in thin films with simple, lead-free chemical compositions.…”