title: Phase transformation of colloidal In2O3 nanocrystals driven by the interface nucleation mechanism: a kinetic study.
abstract: The kinetics of phase transformation of colloidal In(2)O(3) nanocrystals (NCs) during their synthesis in solution was explored by a combination of structural and spectroscopic methods, including X-ray diffraction, transmission electron microscopy, and extended X-ray absorption fine structure spectroscopy. Johnson-Mehl-Avrami-Erofeyev-Kholmogorov (JMAEK) and the interface nucleation models were used to analyze the isothermal kinetic data for the phase transformation of NCs in the temperature range of 210-260 °C. The results show that NCs are initially stabilized in the metastable corundum (rh-In(2)O(3)) phase. The phase transformation occurs via nucleation of cubic bixbyite (bcc-In(2)O(3)) phase at the interface between contacting rh-In(2)O(3) NCs, and propagates rapidly throughout the NC volume. The activation energy of the phase transformation was determined from the Arrhenius expression to be 152 ± 60 kJ/mol. The interface nucleation rate is maximal at the beginning of the phase transformation process, and decreases over the course of the reaction due to a decrease in the concentration of rh-In(2)O(3) NCs in the reaction mixture. In situ high-temperature XRD patterns collected during nonisothermal treatment of In(2)O(3) NCs reveal that phase transformation of smaller NCs occurs at a faster rate and lower temperature, which is associated with their higher packing density and contact formation probability. Because NC surfaces and interfaces play a key role in phase transformation, their control through the synthesis conditions and reaction kinetics is an effective route to manipulate NC structure and properties.
authors.affiliation: Department of Chemistry and Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Shokouh S
authors.initials: SS
authors.lastname: Farvid
authors.forename: Pavle V
authors.initials: PV
authors.lastname: Radovanovic
mesh_terms: D003102:Colloids / Q000737:chemistry; D007204:Indium / Q000737:chemistry*; D007700:Kinetics; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D044367:Phase Transition
chemical_list: D003102:Colloids; D007204:Indium; C047711:indium oxide