Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation.

We present a detailed analysis of the ferroelectric domain structure of K0.70Na0.30NbO3 thin films on (110) TbScO3 grown by metal-organic chemical vapor deposition. Upon piezoresponse force microscopy and nanofocus x-ray diffraction measurements we derive a domain model revealing monoclinic MC 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.