We propose to investigate ferroelectric switching in lead-free monoclinic (K,Na)NbO3 strained thin films. In order to correlate the inversion of spontaneous polarization with changes in atomic structure and domain morphology, operando (scanning) X-ray nano-diffraction shall be performed during/after application of an electric field intended for polarization switching. We plan to use a focused X-ray beam of typically 100 x 100 nm2 size which allows to visualize the temporal evolution of polarization domains and corresponding domain walls with high spatial resolution. These experiments will help correlate switching of spontaneous polarization with changes in atomic structure and domain morphology.