Nanostructures and defects in nonequilibrium-synthesized filled skutterudite CeFe₄Sb₁₂

We studied nanoprecipitates (NPs) and defects in p-type filled skutterudite CeFe₄Sb₁₂ prepared by a nonequilibrium melt spinning plus spark plasma sintering method using transmission electron microscopy. NPs with mostly spherical shapes and different sizes (from several nanometers to several tens of nanometers) have been observed. Among these, two types of NPs were most commonly observed, Sb-rich superlattices and CeSb₂. The Sb-rich superlattices with a periodicity of about 3.6 nm were induced by the ordering of excessive Sb atoms along the c-direction. These NPs typically share coherent interfaces with the surrounding matrix and induce anisotropic strain fields in the matrix. NPs with compositions close to CeSb₂, on the other hand, have been shown to be much larger in size (∼30 nm) and have orthorhombic structures. Various defects were typically observed on the interfaces between these NPs and the matrix. The strain fields induced by these NPs are less distinct, possibly because part of the strain has been released by defect formation.