Reduced activation energy and crystalline size for yttria-stabilized zirconia nano-crystals: an experimental and theoretical study

摘要

Pure and 2mol% yttria-doped zirconia nano-powders were synthesized via the precipitation method, using ZrOCl_2-8H_2O with fixed concentration of 0.1 M [Zr~(4+) ] as the starting material. The very lower activation energy (～34.029kJ/mol) related to the bulk counterpart is observed for the grain growth in nano-2YSZ powders within the calcination temperature range of 600-1000℃. Experimental results show that two factors were contributed to the lower activation energy of grain growth. Firstly, the introduction of oxygen vacancies in nano-2YSZ grain surface reduces the activation energy of the formation of necks between grains. Secondly, the rotation process between coherent grains has very lower activation energy or even a zero-kinetic barrier. Moreover, several models of zirconium and yttrium complexes were applied to simulate the structural monomers and the condensation productions of aqueous precursor solution using the density functional theory (DFT/B3LYP). Theoretical results show that the condensation reaction between [Zr(OH)_6]~(2-) and [Zr(OH)_6]~(2-) will preferentially occur along the apical directions while the condensation reaction between [Zr(OH)_6]~(2-) and [Y(OH)_6]~(3-) will occur along the edge directions during the oxolation process of grain growth. And the smaller crystallite size of doped-zirconia powders was attributed to the reduced intergranular attraction force between nano-particles because of the lower charge of separate surface yttrium ions.