Grain-size-dependent thermal transport properties in nanocrystalline yttria-stabilized zirconia

Understanding the role of grain boundaries in controlling heat flow is critical to the success of many envisioned applications of nanocrystalline materials. This study focuses on the effect of grain boundaries on thermal transport behavior in nanocrystalline yttria-stabilized zirconia (YSZ) coatings prepared by metal-organic chemical vapor deposition. A strong grain-size-dependent reduction in thermal conductivity is observed at all temperatures from 6-480 K. The behavior is due primarily to the effect of interfacial (Kapitza) resistance on thermal transport. In response to the application of heat to a material, interfacial resistance results in a small temperature discontinuity at every grain boundary, an effect that is magnified in nanocrystalline materials because of the large number of grain boundaries. The observed behavior in YSZ is compared with predictions derived from a diffuse-mismatch model. Implications for the possible development of improved thermal barriers based on nano-layered structures with large interfacial thermal resistance are discussed.