Piezoelectricity in hafnia

HfO2 is a promising ferroelectric material for applications in electronics but knowledge on its ferroic and electromechanical response properties is still lacking. Here, the authors demonstrate the peculiar piezoresponse of HfO2, predicting on how to reverse its sign by means of a biaxial strain. Because of its compatibility with semiconductor-based technologies, hafnia (HfO2) is today's most promising ferroelectric material for applications in electronics. Yet, knowledge on the ferroic and electromechanical response properties of this all-important compound is still lacking. Interestingly, HfO2 has recently been predicted to display a negative longitudinal piezoelectric effect, which sets it apart from classic ferroelectrics (e.g., perovskite oxides like PbTiO3) and is reminiscent of the behavior of some organic compounds. The present work corroborates this behavior, by first-principles calculations and an experimental investigation of HfO2 thin films using piezoresponse force microscopy. Further, the simulations show how the chemical coordination of the active oxygen atoms is responsible for the negative longitudinal piezoelectric effect. Building on these insights, it is predicted that, by controlling the environment of such active oxygens (e.g., by means of an epitaxial strain), it is possible to change the sign of the piezoelectric response of the material.

Automated summary

Hafnia is a promising ferroelectric material in electronics due to its peculiar piezoresponse, which can be reversed by biaxial strain. The study demonstrates how controlling the environment of active oxygen atoms can change the sign of the piezoelectric response of the material.