LAUSR

HfO2 and ZrO2 have increasingly drawn the interest of researchers as lead-free and silicon-technology-compatible materials for ferroelectric, pyroelectric, piezoelectric applications in thin films like ferroelectric field-effect transistors, ferroelectric random access memory, nanoscale sensors and energy harvesters. Owing to the environmental regulations against lead-containing electronic components, HfO2 and ZrO2 offer, along with AlN, (K,Na)NbO3 and (Bi0.5Na0.5)TiO3-based materials, an alternative to Pb(ZrxTi1-x)O3-based materials, which are the overwhelmingly used ceramics in industry. HfO2 and ZrO2 thin films may show field-induced phase transformation from the paraelectric tetragonal to the ferroelectric orthorhombic phase, leading to a change in crystal volume, and thus strain. These field-induced strains have already been measured experimentally in pure and doped systems, however no systematical optimization of the piezoelectric activity was performed, neither experimentally nor theoretically. In this screening study we calculate the ultimate size of this effect for 58 dopants, depending on oxygen supply and the defect incorporation type: substitutional or interstitial. The largest piezoelectric strain values are achieved with Yb, Li and Na in ZrO2 and exceed 40 pm V-1 or 0.8% maximal strain, which exceeds the best experimental findings by a factor of two. Furthermore, we discovered that Mo, W, and Hg makes the polar-orthorhombic phase in ZrO2 bulk stable under certain circumstances, which would count in favor of these systems for the ceramic crystallization process. Our work guides the development of the performance of a promising material system by rational design of the essential mechanisms, so as to apply it to unforeseen applications.