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WO3 thin films have outstanding chromogenic and catalytic properties arising from the functional defects of an n-type semiconductor with a perovskite-like structure, useful to fabricate electronic devices. We report a piezoresponse related to the presence of oxygen vacancies and ionic charge dynamics [1], rather than to the presence of a non-centrosymmetric structure. WO3 thin films (~200–250 nm) were fabricated by RF-sputtering at 225 W in Ar-rich atmosphere and subjected to an annealing treatments post-deposit under a forming gas (3% H2 in N2). The film process at 400 °C shows piezoelectric domains (Fig. 1a) and hysteresis loops (d33 = 35±5 pm/V) by switching spectroscopy – piezoresponse force microscopy (SS-PFM) technique (Fig. 1b) [2], while after treatment with 500 °C no piezoresponse was found. The characterization with X-ray diffraction (XRD) and transmission electron microscopy (TEM) show a mixture of cubic and tetragonal WO3 phases [3]. Furthermore, atomprobe tomography (Fig. 1c) reveals nanovoids filled with constituents of the forming gas, indirectly causing the piezoresponse due to ionic charge dynamics during the measurement.