Nanostructural Maze, Phase Diversity, and Coherent Growth in PbS-NaSbS₂ Semiconductors

We present findings from an electron diffraction and high-resolution transmission electron microscopy (HRTEM) study of composites mPbS + NaSbS2 (m = 10, 18). The study reveals that these materials exhibit a nanostructured nature. The dominant observed structure corresponds to the NaCl type, characterized by numerous inhomogeneities. Interestingly, nanocrystals with a cubic structure, but possessing distinct lattice parameters (i.e., different compositions) compared to their surroundings, were observed. Additionally, some nanocrystals exhibited an orthorhombic structure distortion and some nanocrystals with a modulated structure resulting from long-range ordering effects were observed. All types of nanocrystals were observed to grow endotaxially within the matrix. Evidence was also found, suggesting a remarkable phenomenon where, in some areas, S atoms migrate from octahedral to tetrahedral sites, thereby validating previous predictions. These findings significantly contribute to our understanding of these semiconductors and motivate future studies of the thermoelectric properties in PbS-NaSbS2 materials.