Size-Induced Structural Disorder Enables Ultrahard Oxides

作者：Muche Dereck N F; Marple Maxwell A T; Hung Ivan; Gan Zhehong; Castro Ricardo H R; Sen Sabyasachi^*

来源：Journal of Physical Chemistry C, 2017, 121(25): 13898-13905.

DOI：10.1021/acs.jpcc.7b03323

It has been empirically observed that decreasing grain size in polycrystalline materials leads to an increase in hardness following a linear dependence with the inverse square root of the size. This so-called Hall-Petch relationship was originally observed in metals and was attributed to the blocking effect of grain boundaries on dislocation motion. However, the Hall Fetch theory is not tenable for explaining similar phenomena in oxide ceramics, where dislocations are virtually immobile at ambient temperature. In this study, multinuclear (Al-27, (25) Mg) magnetic resonance spectroscopy is utilized to demonstrate that a reduction in the grain size of MgAl2O4 spinel nanoceramics induces structural disorder in the form of cation site inversion in the grain boundary region, which leads to an increase in the average bond density and bond strength. The rapid increase in the volume fraction of such structurally disordered and strong grain boundary regions with decreasing grain size of the nanoceramics is responsible for the corresponding remarkable increase in the hardness.

• 出版日期2017-6-29