Probing Ferroelectric Phase Transitions in Barium Titanate Single Crystals via $\it{in-situ}$ Second Harmonic Generation Microscopy

TL;DR

This study uses in-situ second harmonic generation microscopy to visualize and analyze ferroelectric domain behavior and phase transitions in barium titanate single crystals, revealing detailed domain dynamics and transition characteristics.

Contribution

It introduces the application of SHGM for 3D in-situ mapping of ferroelectric domain switching and phase transitions in BTO, providing new insights into domain dynamics and transition types.

Findings

Direct visualization of FE domain switching in 3D

Local determination of transition temperatures and hysteresis

Identification of phase transition order (1st/2nd) from SHGM data

Abstract

Ferroelectric materials play a crucial role in a broad range of technologies due to their unique properties that are deeply connected to the pattern and behavior of their ferroelectric (FE) domains. Chief among them, barium titanate (BaTiO$_3$; BTO) sees widespread applications such as in electronics but equally is a ferroelectric model system for fundamental research, e.g., to study the interplay of such FE domains, the domain walls (DWs), and their macroscopic properties, owed to BTO's multiple and experimentally accessible phase transitions. Here, we employ Second Harmonic Generation Microscopy (SHGM) to $\it{in-situ}$ investigate the cubic-to-tetragonal (at $\sim$126$^\circ$C) and the tetragonal-to-orthorhombic (at $\sim$5$^\circ$C) phase transition in single-crystalline BTO via 3-dimensional (3D) DW mapping. We demonstrate that SHGM imaging provides the direct visualization of FE domain switching as well as the domain dynamics in 3D, shedding light on the interplay of the domain structure and the phase transition. These results allow us to extract the different transition temperatures locally, to unveil the hysteresis behavior, and to determine the type of phase transition at play (1st/2nd order) from the recorded SHGM data. The capabilities of SHGM in uncovering these crucial phenomena can easily be applied to other ferroelectrics to provide new possibilities for $\it{in-situ}$ engineering of advanced ferroic devices.