In Situ Exploration of Thermal-Induced Domain Evolution with Phase Transition in LiNbO3-Modified K0.5Na0.5NbO3 Single Crystal

Abstract

Temperature dependent domain evolution and domain-wall motion of ferroelectric materials have attracted dramatically increased interest due to the crucial influences on piezo- and dielectric properties and the performances of related nanoapplications. Here, the unambiguous evolutions of 90°/180° domain walls accompanied by phase transition have been discovered first in LiNbO3 doped (K0.5Na0.5)NbO3 single crystal during heating and cooling processes by in situ coupling characterizations of Raman spectra and piezoresponse force microscopy (PFM). Considering the vibrational modes of a NbO6 octahedron, the stretching modes of A1g(ν1), Eg(ν2), and the bending mode F2g(ν5) are sensitive to structural transition as well as the diversity of domain evolution. These modes are used to discuss the formation of 60° domain walls and the change of 90° domain-wall density. Under the precise control of the temperature gradient, homogeneous striped 90° domain boundaries movement and microscale out-of-plane polarization reversal can be observed. Simultaneously, as one of the most distinctive features from the ferroelectric first-order phase transition, a thermal hysteresis effect has been found in (K0.5Na0.5)NbO3–0.05LiNbO3 single crystal. The present study focuses on the correlation of crystal structural transformation and thermal domain evolution. It affords an effective opportunity to explore the stable performance in a broad temperature range for domain-wall dependent ferroelectric devices.