The stability of nanoparticles is strongly dependent on the thermodynamics of interfaces. Providing reliable data on surface and grain boundary energies is therefore of key importance for predicting and improving nanostability. In this work, we used a combination of high-temperature oxide melt drop solution calorimetry and water adsorption microcalorimetry to demonstrate the effect of a dopant (manganese) on both surface and grain boundary energies of SnO 2 , and discussed the impacts on the average particle size at a given temperature. The results show a significant decrease in the grain boundary energy with increasing manganese content and a concomitant moderate decrease in the surface energy, consistently with segregation enthalpy values acquired from an analytical fitting model. The results explain the measured increase in stability with increasing dopant content (smaller sizes) and suggest the grain boundary energy has a much more important role in defining particle stability than previously supposed.

Highly stable ceria nanoparticles (< 11 nm) with different manganese contents were prepared by a co-precipitation method. The powders were studied by x-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy, and water adsorption microcalorimetry. The data show that only a small fraction of the manganese ions dissolved into ceria fluorite structure as solid solution, and most segregated on the particles' surface, causing decrease of the average surface energy of the particles with increasing dopant concentration. This was confirmed by direct surface energy measurements using water adsorption microcalorimetry, and has consequences on particle coarsening behavior. That is, the results explain why manganese doped ceria nanoparticles show stronger resistance to coarsening as compared to undoped ceria. The enthalpy of surface segregation of manganese was calculated and discussed as an important parameter to design highly metastable ceria nanoparticles on a thermodynamic basis.

Nanocrystalline ceramics offer interesting and useful physical properties attributed to their inherent large volume fraction of grain boundaries. At the same time, these materials are highly unstable, being subjected to severe coarsening when exposed at moderate to high temperatures, limiting operating temperatures and disabling processing conditions. In this work, we designed highly stable nanocrystalline yttria stabilized zirconia (YSZ) by targeting a decrease of average grain boundary (GB) energy, affecting both driving force for growth and mobility of the boundaries. The design was based on fundamental equations governing thermodynamics of nanocrystals, and enabled the selection of lanthanum as an effective dopant which segregates to grain boundaries and lowers the average energy of YSZ boundaries to half. While this would be already responsible for significant coarsening reduction, we further experimentally demonstrate that the GB energy decreases continuously during grain growth caused by the enrichment of boundaries with dopant, enhancing further the stability of the boundaries. The designed composition showed impressive resistance to grain growth at 1100°C as compared to the undoped YSZ and opens the perspective for similar design in other ceramics.