Structural transformation and bandgap engineering by doping Pr in HfO2 nanoparticles

Abstract

Here, we have stabilized the high-temperature cubic phase of HfO2 at room temperature (RT) with doping Pr up to 15 at%. While monoclinic phase remains stable below 7 at%, coexistence of monoclinic and cubic phases is observed between 7 and 13 at% of Pr. Such transformation is confirmed from Raman spectroscopy and transmission electron microscopy. With doping, while particle size is reduced from 35 to 10 nm accompanied with enhanced strain estimated from Williamson-Hall plots, the bandgap decreases from 5.42 to 5.06 eV due to non-stoichiometric HfO2−x and formation of sub-bands near conduction band. Such exciting results are discussed on the basis of enhanced oxygen vacancies inducing 8-fold oxygen coordinated Pr3+ ions in lattice that stabilize cubic phase of HfO2. © 2021 Elsevier B.V.