Raman imaging of ferroelastically configurable Jahn–Teller domains in LaMnO3

The Jahn–Teller (JT) effect, through geometric deformation of molecules or local ionic lattices, lowers the overall energy of the system by removing electron degeneracy from partially occupied orbitals. Crystal symmetry lowered by JT distortion inevitably creates multiple variants of elastic and orbital-anisotropic states. Visualization and control of the domain/wall textures create a cornerstone to understand various correlated phenomena and explore wall properties. Here, we report the real-space observation of JT phonon and orbiton-related domains in a LaMnO3 thin film using confocal Raman spectromicroscopy. The characteristic symmetries of the JT-originated Raman modes allow us to detect and visualize the local population and orientation of the JT planes. Combined with a crystal structural analysis, we find that the formation of ferroelastic domains with W or W’ walls provides the basic framework for understanding JT domain textures. Furthermore, we demonstrate the JT domains can be manipulated by applying local external stress. Our findings provide a useful pathway for mechanically-tunable orbitronic applications.

Layer number dependent ferroelasticity in 2D Ruddlesden–Popper organic-inorganic hybrid perovskites

Ferroelasticity represents material domains possessing spontaneous strain that can be switched by external stress. Three-dimensional perovskites like methylammonium lead iodide are determined to be ferroelastic. Layered perovskites have been applied in optoelectronic devices with outstanding performance. However, the understanding of lattice strain and ferroelasticity in layered perovskites is still lacking. Here, using the in-situ observation of switching domains in layered perovskite single crystals under external strain, we discover the evidence of ferroelasticity in layered perovskites with layer number more than one, while the perovskites with single octahedra layer do not show ferroelasticity. Density functional theory calculation shows that ferroelasticity in layered perovskites originates from the distortion of inorganic octahedra resulting from the rotation of aspherical methylammonium cations. The absence of methylammonium cations in single layer perovskite accounts for the lack of ferroelasticity. These ferroelastic domains do not induce non-radiative recombination or reduce the photoluminescence quantum yield.

Mobile and immobile boundaries in ferroelectric films

The intrinsic mobile interfaces in ferroelectrics—the domain walls can drive and enhance diverse ferroelectric properties, essential for modern applications. Control over the motion of domain walls is of high practical importance. Here we analyse theoretically and show experimentally epitaxial ferroelectric films, where mobile domain walls coexist and interact with immobile growth-induced interfaces—columnar boundaries. Whereas these boundaries do not disturb the long-range crystal order, they affect the behaviour of domain walls in a peculiar selective manner. The columnar boundaries substantially modify the behaviour of non-ferroelastic domains walls, but have negligible impact on the ferroelastic ones. The results suggest that introduction of immobile boundaries into ferroelectric films is a viable method to modify domain structures and dynamic responses at nano-scale that may serve to functionalization of a broader range of ferroelectric films where columnar boundaries naturally appear as a result of the 3D growth.

Ferroelastic domains and phase transitions in organic–inorganic hybrid perovskite CH3NH3PbBr3

Polarized light microscopy reveals twin domains and symmetry of the phases in CH3NH3PbBr3 crystal; domain structure remains unresponsive to electric field but changes under external stress, confirming ferroelasticity while ruling out ferroelectricity.

Symmetry mismatch controlled ferroelastic domains ordering and functional properties of manganite films on cubic miscut substrates

We have studied the magnetotransport properties and strain release mechanisms in ferroelastic La0.9Sr0.1MnO3 (LSMO) epitaxial thin films on SrTiO3 (STO) (001) substrates with different miscut angles. The substrate miscut angle...