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In this work, the formation of the orthorhombic phase of ZrO 2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO 2 through oxygen scavenging. The ferroelectric properties of the W/ZrO 2 /W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarization-voltage measurements. A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie–Weiss temperature of 130 °C, significantly lower than the theoretical value for the bulk. • Dielectric properties of ferroelectric orthorhombic ZrO 2 films were investigated. • An activation energy of 0.48 eV was estimated which can be associated to oxygen vacancies. • DFT calculations suggest that oxygen vacancies are responsible for lowering the Curie–Weiss temperature. [ABSTRACT FROM AUTHOR]