Measuring Radiation Enhanced Diffusion Through in situ Ion Radiation Induced Sintering of Oxide Nanoparticles

Radiation enhanced diffusion often contributes significantly to the evolution of microstructures subject to radiation but can be challenging to predict in complex nonmetallic material systems. Here, microstructural evolution in the presence of ion radiation was leveraged to explore the underlying transport phenomenon. Specifically, in situ ion irradiation of nanoparticles reveal rapid densification at room temperature for nanoparticles of cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) but not for magnesium oxide (MgO) or silicon carbide (SiC). This is attributed to rapid diffusion of radiation induced interstitial defects to the high density of free surfaces in the nanoparticle agglomerates. When these observations are combined with image processing and application of a simple two-sphere sintering model, radiation enhanced diffusivity values can be calculated. In situ irradiation of YSZ nanoparticles over a broader temperature range, 50 K to 1073 K, clearly revealed a transition between three distinct rate limiting regimes: (i) low temperature, sink-limited kinetics, (ii) intermediate temperature, recombination-limited kinetics, and (iii) at high-temperature the densification is consistent with thermally activated diffusion kinetics. The high spatial and temporal resolution provided by the in situ methodology is critical to confidently distinguishing these regimes in nonmetallic oxides. While only four nonmetallic nanoparticle systems are presented here (YSZ, CeO2, SiC, and MgO), application of this methodology to the readily accessible, diverse catalog of nanoparticle chemistries and morphologies will allow for rapid exploration of radiation-enhanced diffusion behavior in a broader range of complex nonmetallic systems without the need for tracers.