Dislocation-induced local symmetry reduction in single-crystal KNbO3 observed by Raman spectroscopy

In recent years, dislocation-tuned functionalized ceramics have become one of the focal points of modern materials research due to their outstanding properties. These range from improved electrical conductivity and ferroelectric properties to dislocation-enhanced toughening and superconductivity, caused by local strain fields. The aim of this work is to investigate the dislocation-induced structural changes in single-crystal KNbO3 by micro-Raman spectroscopy. Dislocation-rich regions with tailored densities have been generated using the Brinell indenter scratching method. The influence of the dislocations on the single-crystal structure can be observed in the Raman spectra. The activation of additional Raman modes is observed, which does not occur in regions of low dislocation density. This observation is confirmed by DFT calculations of vibrational modes and is attributed to a reduction in the crystal symmetry due to increased defect densities in plastically deformed KNbO3. In addition, an increase in compressive stress at higher dislocation densities can be demonstrated by a blueshift in Raman mode positions.