Systematic studies on polycrystalline Hf1-xZrxO2 films varying Zr content show that HfO2 films are paraelectric (monoclinic). If Zr content is increased films become ferroelectric (orthorhombic) and after antiferroelectric (tetragonal). Whereas HfO2 shows very good insulating properties and it is used in metaloxide-semiconductor field-effect devices, ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at expenses of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively. Here, we explore ferroelectric, insulating and piezoelectric properties of a series of epitaxial films of Hf1-xZrxO2 with different composition. We show that epitaxial growth enhances the stabilization of the ferroelectric behaviour compared with polycrystalline films in a wider compositional range and up to around 1000 K. This allows, in epitaxial ZrO2 films ferroelectricity coexists with better piezoelectric and insulating properties than Hf0.5Zr0.5O2 and in HfO2 epitaxial films ferroelectricity coexists with better insulating properties than Hf0.5Zr0.5O2. In both cases, the ferroelectric endurance is poorer than for Hf0.5Zr0.5O2.

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