Monoclinic M_A domains in anisotropically strained ferroelectric K_0.75Na_0.25NbO₃ films on (110) TbScO₃ grown by MOCVD

Abstract

A highly regular one-dimensional domain pattern is formed in ferroelectric K 0.75 Na 0.25 NbO 3 thin films grown on (110) TbScO 3 substrates using metalorganic chemical vapour deposition (MOCVD). The domain pattern exhibits a lateral periodicity of about 50 nm and extends over several micrometres. The monoclinic symmetry of the domains is controlled by the elastic anisotropy of K 0.75 Na 0.25 NbO 3 and the anisotropic lattice strain, which is highly compressive in one in-plane direction and weakly tensile in the corresponding orthogonal direction. Using piezoresponse force microscopy and X-ray diffraction, the monoclinic M A phase is identified, which is associated with both a strong vertical and a lateral electric polarization component. The lateral component of the polarization vector is collinear with the AE[110] pc shear direction of the pseudocubic unit cell of the film and changes periodically by 180 in adjacent domains. A structural variant of a 90 rotated M A domain pattern, where the monoclinic distortion of the pseudocubic unit cells occurs along AE[110] pc , is also observed. However, this variant appears with significantly lower probability, in agreement with energy considerations based on linear elasticity theory. Thus, the incorporation of highly anisotropic lattice strain provides the opportunity to grow one-dimensional nanostructures with high ferroelectric properties.

Monoclinic (K,Na)NbO3 Ferroelectric Phase in Epitaxial Films

“…PZT exhibits a maximum piezoelectric coefficient at a morphotropic phase boundary (MPB) close to Zr/Ti = 52/48, where rhombohedral and tetragonal phases coexist. [26][27][28][29] In this work, KNN epitaxial thin films were prepared by a sol-gel method on (001)-oriented Nb:SrTiO 3 (STO) substrate. [5] Those boundary in KNN-based ceramics.…”

Potassium‐Sodium‐Niobate‐Based Thin Films: Lead Free for Micro‐Piezoelectrics

“…However, it is always challenging to fabricate high‐quality and uniform KNN‐based films with stoichiometric compositions due to the complexity of the film composition and the volatilization of K and Na elements at high temperatures. Nevertheless, several techniques have been utilized to overcome the initial difficulties to prepare the KNN‐based epitaxial films, for example, PLD, RF magnetron sputtering, sol–gel, HT, and metal organic chemical vapor deposition (MOCVD) …”

“…Schwarzkopf et al. have investigated (K 0.75 ,Na 0.25 )NbO 3 films with a thickness of 29 nm on (110) TbScO 3 substrates . (110) TbScO 3 substrate is orthorhombic, and the anisotropic lattice strain induced by the orthorhombic substrate resulted in monoclinic M A phase, showing 180 o stripe domain structures and a 90 o rotated domain pattern.…”

“…Motivated by excellent properties of KNN‐based ceramics, KNN‐based films have also drawn increasing attention due to the potential applications for miniaturized devices in microelectromechanical systems (MEMS) . However, prior to this, the piezoelectric properties of KNN‐based films were not the primary consideration .…”

Phase transition and piezoelectricity of BaZrO3‐modified (K,Na)NbO3 lead‐free piezoelectric thin films

“…Additionally, the research of KNN‐based thin films has also gained increasing attention due to the promising properties of their bulk counterparts as well as their potential applications in miniaturized sensors, actuators, energy harvesting systems, and microelectromechanical systems (MEMS) . However, the thin films suffered from the limited thickness and the substrate clamping effect.…”