Abstract
The microstructures of a series of Cu2ZnxSn1-xS3 (x = 0, 0.05, 0.10, 0.15,0.20) ceramic samples are investigated by a combination of selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field imaging (HAADF) and X-ray energy dispersive spectroscopy (EDS) techniques. The pure Cu2SnS3 sample takes the monoclinic structure with the ordering of eight 3Cu-Sn and four 2Cu-2Sn clusters, which obey the octet rule. With the increase of Zn substitution, unique mosaic-type nanostructures comprising well-defined cation-disordered domains coherently bonded to a surrounding network phase with semi-ordered cations are formed in the matrix grains. The atomic structures of the semi-ordered phases are revealed as CuInS2–like phase (Zn < 5 atom%), Cu6ZnSn3S10 (Cu2SnS3: ZnS = 3:1) and Cu4ZnSn2S7 (Cu2SnS3: ZnS = 2:1), respectively. These ordered structures derive from the zinc blende structure (201) superlattice of -(Cu−S)2(Zn−S)(Sn−S)- in the kesterite Cu2ZnSnS4 (Cu2SnS3:ZnS = 1:1). Meanwhile, point defects, dislocations, stacking faults, and finally Cu2-xS nanoprecipitates are formed sequentially to compromise the excessive Cu ions when the Zn contents increase from 5 atom% to 20 atom%. Understanding of the concurrence and evolution of the cation ordering and crystal defects are important to tailor their microstructures and physical properties in the Cu-Zn-Sn-S quaternary system.
Highlights
Multiple chalcogenide including I-II-IV-VI system and I-III-VI system (I= Cu or Ag; II=Zn, Cd, Ni, Co, Fe, or Mn; III= In or Ga; IV= Si, Ge, or Sn; and VI= S, Se, or Te), are an extraordinarily interesting class of materials with many advantages, such as their abundance, low cost, and reduced environmental and health impact, compared with cadmium-and lead-based compounds.[1,2] These materials possess excellent intrinsic functional properties, including appropriate direct band gaps for solar light absorption, plasmonic properties, notable charge carrier mobilities, potential high carrier concentrations, and low thermal conductivity.[1]
From the viewpoint of experiment, despite X-ray diffraction (XRD) being the most prevalent technique used for crystal phase identification, it is not sensitive to the metal cation arrangement in Cu-Zn-Sn-S compounds because the occupation of the atomic sites by Cu, Zn, and Sn results in similar X-ray scattering factors, which makes the CZTS, ZnS, Cu2SnS3 and related ordered structures difficult to be distinguished.[15]
high-resolution TEM (HRTEM) and high-angle annular dark-field imaging (HAADF) observations were carried out using a field emission microscope (JEM-2100F, JEOL, Co., Tokyo, Japan) operated at 200 kV equipped with an X-ray energy dispersive spectrometer (EDS: X-Max 80T, Oxford, UK) for chemical composition analyses
Summary
Multiple chalcogenide including I-II-IV-VI system and I-III-VI system (I= Cu or Ag; II=Zn, Cd, Ni, Co, Fe, or Mn; III= In or Ga; IV= Si, Ge, or Sn; and VI= S, Se, or Te), are an extraordinarily interesting class of materials with many advantages, such as their abundance, low cost, and reduced environmental and health impact, compared with cadmium-and lead-based compounds.[1,2] These materials possess excellent intrinsic functional properties, including appropriate direct band gaps for solar light absorption, plasmonic properties, notable charge carrier mobilities, potential high carrier concentrations, and low thermal conductivity.[1]. We reported the discovery of a mosaic-type domain nanostructure comprising welldefined cation-disordered domains coherently bonded to a surrounding network Cu4ZnSn2S7 phase with semi-ordered cations in a Cu2Zn0.2Sn0.8S3 ceramic sample by a combination of high-angle annular dark-field (HAADF) imaging and atomic resolved EDS mapping techniques in a spherical aberration (Cs) corrected STEM.[26] the crystalline phase of Cu2-xS nanoprecipitate, their orientation relationships with the matrix and the interface structures were revealed by HRTEM.[27]. The evolution of cation ordering and crystal defects with the increase of Zn content were revealed
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