In order to systematize the knowledge on thermodynamic stability and thermoelectric properties of AgSbTe₂-based alloys, several experiments examining the influence of thermal treatment on their structural and thermoelectric properties were performed. Samples with a nominal composition of AgSbTe₂ and AgSbTe_1.98Se_0.02 were prepared and then annealed in various temperature conditions. It was confirmed that Ag_1−xSb_1+xTe_2+x (β phase) is the only thermodynamically stable ternary compound in the Ag₂Te-Sb₂Te₃ pseudobinary system. It was also proved that thermal stability of β phase is limited—it slowly decomposes below 633 K. In contrast to some reports, it was also indicated that a small amount of Se does not lead to stabilisation of AgSbTe₂ crystal structure. Despite slow kinetics of the decomposition processes, thermoelectric properties of the material are notably affected by thermal treatment and amount of Ag₂Te precipitations. Maximal ZT value of prepared materials varies from 0.65 at 575 K to 1.07 at 563 K.

A combined structural, magnetic and thermoelectric study of polycrystalline ternary MIn₂S₄ (M = Mn, Fe, Co, Ni) thiospinels is presented. All compounds crystallize with MgAl₂O₄‐type structure. Rietveld refinement analysis confirmed that the preferred crystallographic position of transition metal element changes from mainly tetrahedral 8a for Mn to exclusively octahedral 16d for Ni (i.e. increase of the inversion parameter). Magnetic susceptibility measurements revealed M‐elements to possess 2+ oxidation state in MIn₂S₄. All these compounds order antiferromagnetically with Néel temperatures T_N ranging from 5–13 K. The studied thiospinels are n‐type semiconductors with large values of electrical resistivity ρ > 0.6 Ω·m at room temperature. An increase of the inversion parameter leads to a reduction of the determined activation energies, as well as to a more disorder‐like behavior of thermal conductivity. The highest thermoelectric Figure of merit ZT was observed for MIn₂S₄ with M = Fe, Ni, which adopt inverse spinel structure.

This report presents studies of crystal structures of α- and β-In ₂ S ₃ as well as a mechanism of the 1st order α–β phase transition. The structural part is supported by an analysis of thermoelectric properties and by DFT calculations.

A detailed study of polycrystalline indium-based In_1−x□_xIn₂S₄ (x = 0.16, 0.22, 0.28, and 0.33) thiospinel is presented (□ – vacancy). Comprehensive investigation of synthesis conditions, phase composition and thermoelectric properties was performed by means of various diffraction, microscopic and spectroscopic methods. Single-phase α- and β-In_1−x□_xIn₂S₄ were found in samples with 0.16 ≤ x ≤ 0.22 and x = 0.33 (In₂S₃), respectively. In contrast, it is shown that In_0.72□_0.28In₂S₄ contains both α- and β-polymorphic modifications. Consequently, the thermoelectric characterization of well-defined α- and β-In_1−x□_xIn₂S₄ is conducted for the first time. α-In_1−x□_xIn₂S₄ (x = 0.16 and 0.22) revealed n-type semiconducting behavior, a large Seebeck coefficient (>|200| μV K⁻¹) and moderate charge carrier mobility on the level of ∼20 cm² V⁻¹ s⁻¹ at room temperature (RT). Decreases in charge carrier concentration (increase of electrical resistivity) and thermal conductivity (even below 0.6 W m⁻¹ K⁻¹ at 760 K) for larger In-content are observed. Although β-In_0.67□_0.33In₂S₄ (β-In₂S₃) is a distinct polymorphic modification, it followed the abovementioned trend in thermal conductivity and displayed significantly higher charge carrier mobility (∼10⁴ cm² V⁻¹ s⁻¹ at RT). These findings indicate that structural disorder in the α-modification affects both electronic and thermal properties in this thiospinel. The reduction of thermal conductivity counterbalances a lowered power factor and, thus, the thermoelectric figure of merit ZT_max = 0.2 at 760 K is nearly the same for both α- and β-In_1−x□_xIn₂S₄.

The homogeneity range of ternary iron indium thiospinel at 873 K was investigated. A detailed study was focused on two distinct series (y=z): 1) a previously reported charge‐balanced (In_0.67+0.33y□_0.33−0.33y)_tetr[In_2−zFe_z]_octS₄ (A1‐series; □ stands for vacancy; the abbreviations “tetr” and “oct” indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively) and 2) a new charge‐unbalanced (In_0.67+y□_0.33−y)_tetr[In_2−zFe_z]_octS₄ (A2‐series). Fe atoms were confirmed to exclusively occupy an octahedral position in both series. An unusual reduction of the unit cell parameter with increasing Fe content is explained by differences in the ionic radii between Fe and In, as well as by an additional electrostatic attraction originating from charge imbalance (latter only in A2‐series). The studied compound is an n‐type semiconductor, and its charge carrier concentration increases or decreases for larger Fe content within the A1‐ and A2‐series, respectively. The thermal conductivity κ_tot is significantly reduced upon increasing vacancy concentration, whereas the change of power factor is insufficient to drastically improve the thermoelectric figure of merit.