Piezoelectric Response in WO3-x Thin Films by Aluminum Clustering

We report piezoelectric response of d 33  = 35 ± 5 pm V − 1 on aluminum doped tungsten trioxide thin films (Al-WO 3 −  x ), prepared by RF-sputtering and post annealing treatment in air atmosphere. Using XPS characterization indicate a stoichiometry of WO 2.7 and Raman a distorted octahedral tungsten vibration mode of monoclinic WO 3 at 236.9 cm − 1 , 691 cm − 1 and 803 cm − 1 corresponding to O-W-O chemical bonds. The grazing incidence X-ray diffraction revealed a non-centrosymmetric monoclinic (P2 1 /c) and tetragonal (P4/nmm) mixed phases of WO 3 − x with islands of piezoelectric domains as observed by atomic force microscope, additionally atom probe tomography revealed diffusion of aluminum ions from Al 2 O 3 substrate.