Copper-based chalcogenides have emerged as promising thermoelectric materials due to their high thermoelectric performance, tunable transport properties, earth abundance and low toxicity. We have presented an overview of experimental results and first-principal calculations investigating the thermoelectric properties of various polymorphs of Cu₂SnS₃ (CTS), Cu₂ZnSnS₄ (CZTS), and Cu₂ZnSnSe₄ (CZTSe) synthesized by high-energy reactive mechanical alloying (ball milling). Of particular interest are the disordered polymorphs of these materials, which exhibit phonon-glass–electron-crystal behavior—a decoupling of electron and phonon transport properties. The interplay of cationic disorder and nanostructuring leads to ultra-low thermal conductivities while enhancing electronic transport. These beneficial transport properties are the consequence of a plethora of features, including trap states, anharmonicity, rattling, and conductive surface states, both topologically trivial and non-trivial. Based on experimental results and computational methods, this report aims to elucidate the details of the electronic and lattice transport properties, thereby confirming that the higher thermoelectric (TE) performance of disordered polymorphs is essentially due to their complex crystallographic structures. In addition, we have presented synchrotron X-ray diffraction (SR-XRD) measurements and ab initio molecular dynamics (AIMD) simulations of the root-mean-square displacement (RMSD) in these materials, confirming anharmonicity and bond inhomogeneity for disordered polymorphs.

CuFeS₂ (CFS) stands out as a promising narrow band-gap semiconductor for thermoelectric (TE) applications. However, its high lattice thermal conductivity is one of the factors hampering its potential for TE generation. A common strategy for tackling this problem is to produce this material in thin film form. Thus, this study aims to practically understand and optimize the synthesis of CFS 2D materials using a simple three-step approach of ball-milling, thermal evaporation, and sulfurization of the CuFe metallic precursors. The tools for thin film characterization employ X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDXS), and Hall-effect measurements. DFT phase diagrams are also used to understand the energy of formation of the secondary phases present in the film. Here, we highlight that the ball-milling mechanisms, allied with high vacuum and high energy density during evaporation, are essential for the interdiffusion of Cu and Fe during the evaporation process. The film presented a flower-like morphology and p-type semiconducting behavior. A proof-of-concept Thermoelectric Generator (TEG) was designed in an in-plane geometry, showing a power output per unit active area of 114 nW cm⁻² (ΔT = 180 °C), comparable to other Cu-based materials, thus demonstrating the feasibility of this method of synthesis for TE applications.

Diffuse scattering is a component of the powder pattern bearing information on the local atomic structure and disorder of crystalline materials. It is visible in the X-ray diffraction patterns of binary structures like Ag₂O, which has a large mean squared displacement for its constituent elements. Pair distribution function (PDF) analysis is widely employed to extract this local structural information, embedded in the widths of PDF peaks. However, obtaining the PDF from experimental data requires a Fourier transform, which introduces aberrations in the transformed data due to instrument resolution, complicating the distinction between its static and dynamic components. In this work, the analysis of thermal diffuse scattering is performed directly on the X-ray powder pattern, using the traditional Rietveld method integrated with a correlated displacement model for atomic pairs. The Ag₂O case study data were collected using synchrotron radiation at room temperature, supplemented by laboratory experiments up to 200°C. An Einstein model was used to obtain the harmonic and anharmonic force constants of the system. The force constants were also obtained via density functional theory and ab initio molecular dynamics simulations and showed similar values to the experiments. The analysis reveals the complex dynamic structure of Ag₂O, characterized by high anisotropy in phonon dispersion relations and the presence of soft phonon modes, which explain the significant displacement parameters observed. The proposed approach can be easily employed for other binary or more complex systems to understand the dynamics of local forces through X-ray diffraction analysis.