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New materials based on multicomponent chalcogenides of (Cu, Ag), DIV(Si, Ge, Sn), DII (Fe, Mn, Co, Ni) and REM: crystal structure and properties

Work number - M 23 FILED

Presented Ukrainka Volyn National University.

Smitiukh Oleksandr Viktorovich – PhD (Candidate of Chemical Science), senior lecturer of Lesya Ukrainka Volyn National University

The work utilizes a new concept for evaluating synthesized materials, specifically examining the influence of the second coordination environment on material properties. It was found that understanding the metal-nonmetal relationship is insufficient for predicting material characteristics such as thermoelectric properties. By considering specific structural units (for instance, [3Co0.25X0.75]CuS12 – cubooctahedron), the behavior of substances under various factors (temperature, pressure, etc.) can be predicted. It was determined that materials with low-coordinated atoms have low thermal conductivity, while those with rare-earth metal inclusions exhibit significantly better properties due to an increase in the first coordination shell and a large distortion factor in the second. The presence of heavy metals in voids enhances thermoelectric characteristics. The presence of dopants in a specific structural segment is also important. For example, the best electronic transport characteristics are observed when a position contains a mixture of atoms with the same number of electrons in the d-sublevel (for instance, 1Ni:3Hf, crystal structure of Cu2NiHf3S8). Substitution in the anionic sublattice and increased symmetry lead to high charge carrier mobility and significant improvement in thermoelectric parameters. The presence of different cations results in bond heterogeneity and structural disorder, leading to low lattice thermal conductivity (solid solution of Cu2CoSnS4−xSex(х = 0-1)) It makes the opportunity of effective prediction of properties of new materials. The use of the first coordination environment for structure analysis is known in world practice. In the work (Svitlana V. Shishkina, Stuart J McElhany and others) the analysis of first coordination environment is presented. However, there are few works considering the impact of the second coordination environment. Filling a position with atoms of different charges not only increases distortion within the primary shell of neighboring atoms but also creates point defects in all directions, enhancing nonlinear optical properties due to structural non-centrosymmetry.