Origin of Pyroelectricity in Ferroelectric HfO2

The emergent pyroelectricity in the ferroelectric (orthorhombic $P\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}a{2}_{1}$) phase of CMOS-compatible hafnia offers great potential for future infrared-sensing and energy-harvesting applications, but an understanding of the phenomenon in this particular compound is still lacking. The authors use first-principles calculations to show that pyroelectricity arises unexpectedly from the $s\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}y$ effect in ferroelectric HfO${}_{2}$, due to the peculiarity of its piezoelectricity. They also find an orthorhombic-to-tetragonal structural phase transition associated with a giant pyroelectric response, which can be further enhanced by doping with Si.