Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films

A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in - 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb: SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of -14.3 mu C/cm2, remnant polarization of -9.3 mu C/cm2 and coercive field -1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m) and o-phases causing an inferior remnant polarization of -4.8 mu C/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.

Automated summary

A new method for stabilizing ferroelectric o-ZrO2 films with negative piezoelectric coefficient is demonstrated by growing -8nm thick films using ion-beam sputtering. The films on (011)-Nb:SrTiO3 showed oriented o-phase and exhibited ferroelectric behavior, while films on (001)-Nb:SrTiO3 showed mixed m and o-phases with inferior ferroelectric properties. Density functional theory calculations support the experimental findings and explain the negative piezoelectric coefficient.