The Piezoresponse in WO(3) Thin Films Due to N(2)-Filled Nanovoids Enrichment by Atom Probe Tomography

Tungsten trioxide (WO(3)) is a versatile n-type semiconductor with outstanding chromogenic properties highly used to fabricate sensors and electrochromic devices. We present a comprehensive experimental study related to piezoresponse with piezoelectric coefficient d(33) = 35 pmV(−1) on WO(3) thin films ~200 nm deposited using RF-sputtering onto alumina (Al(2)O(3)) substrate with post-deposit annealing treatment of 400 °C in a 3% H(2)/N(2)-forming gas environment. X-ray diffraction (XRD) confirms a mixture of orthorhombic and tetragonal phases of WO(3) with domains with different polarization orientations and hysteresis behavior as observed by piezoresponse force microscopy (PFM). Furthermore, using atom probe tomography (APT), the microstructure reveals the formation of N(2)-filled nanovoids that acts as strain centers producing a local deformation of the WO(3) lattice into a non-centrosymmetric structure, which is related to piezoresponse observations.