Giant Domain Walls and Intrinsic Heterogeneity in 214 Cuprate Superconductors
Structural phase transitions generate complex microstructures that often govern material functionality, yet directly resolving their three-dimensional organisation in bulk samples remains challenging. Here we employ scanning three-dimensional X-ray diffraction to resolve the bulk microstructure of La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_{4}$, a prototypical 1/8-doped cuprate in which structural and electronic heterogeneity is well established. We reveal remarkably broad tetragonal-like domain wall regions within the nominally orthorhombic crystal structure, and, upon cooling to 100 K, a fine microstructure of orthorhombic-like stripes embedded within the tetragonal matrix that has significant consequences for interpreting the interplay between structural and electronic heterogeneity in this class of materials. More broadly, this work establishes 3DXRD as a powerful approach for resolving bulk microstructures and understanding their role in emergent functionality.