Phase Transitions, Domains Walls and Defects Dynamics of LaAlO3 via In Situ Heating in the Transmission Electron Microscope

Many materials processes are thermally activated, and a full understanding of the microscopic details often requires characterization on the nanoscale. In situ heating in the TEM is a powerful technique for observing temperature effects on the atomic scale. We use in situ TEM to study octahedral rotations, which play a key role in the strain-driven coupling of order parameters in multifunctional transition metal oxides. In LaAlO3 (LAO), these rotations drive a continuous improper ferroelastic phase transition from a rhombohedral (R-3c) to cubic (Pm-3m) perovskite structure (Tc ~ 540°C). This phase change is the result of distortions of the oxygen-sublattice, without changing the periodicity of the cation sublattice. Here we perform in situ heating of bulk LAO single crystals. We observe the phase transition with diffraction, and also observe twin-boundaries and defect motion by STEM at high temperatures.