Formation of tetragonal and monoclinic-HfO 2 nanoparticles in the oil/water interface

Abstract

Abstract Pure tetragonal hafnium oxide (t-HfO 2 , ca. 4.5 nm) and monoclinic hafnium oxide (m-HfO 2 , ca. 105 nm × 45 nm) possessing a narrow size-distribution were synthesized with an oil/water interface approach by adjusting various reaction parameters such as aging temperature, reaction time, and concentration of sodium hydroxide. The t-HfO 2 and m-HfO 2 were spherical and spindle-like, respectively. The formation and transformation mechanisms of HfO 2 have been proposed from both of aspects of energy and time. Low temperature, appropriate reaction time and high concentration of sodium hydroxide are kinetically beneficial for the formation of t-HfO 2 . The hafnium oxide transformation from small spherical tetragonal nanoparticles to large spindle-like monoclinic nanoparticles happened due to the decline of their total surface energy with the increases of temperature and reaction time. Moreover, by the use of seeds, formation of HfO 2 nanoparticles was obviously promoted and the size was reduced, suggesting the non-aggregation and surface-deposition growth of nanoparticles.