Ferroelectric monoclinic phases in strained K 0.70 Na 0.30 NbO ₃ thin films promoting selective surface acoustic wave propagation

We present a detailed analysis of the ferroelectric domain structure of K 0.70 Na 0.30 NbO 3 thin films on (110) TbScO 3 grown by metal–organic chemical vapor deposition. Upon piezoresponse force microscopy and nanofocus x-ray diffraction measurements we derive a domain model revealing monoclinic M C domains. The complex domain pattern is formed out of four co-existing in-plane orientations of the shearing direction of the monoclinic unit cell resulting in four types of superdomains each being composed of well-ordered stripe domains. Finally, we present surface acoustic wave (SAW) experiments that exhibit extraordinary signal intensities given the low thickness of the tested film. Moreover, the SAW propagation is found to occur selectively along the identified shearing directions.