Structural Peculiarities and Thermoelectric Study of Iron Indium Thiospinel

Abstract

The homogeneity range of ternary iron indium thiospinela t8 73 Kw as investigated. Ad etailed study was focused on two distinct series (y = z): 1) ap reviously reported charge-balanced (In 0.67 + 0.33y & 0.33À0.33y ) tetr [In 2Àz Fe z ] oct S 4 (A1series; & stands for vacancy;t he abbreviations "tetr" and "oct" indicate atoms occupying tetrahedral 8a and octahedral 16d sites, respectively)a nd 2) an ew charge-unbalanced (In 0.67 + y & 0.33Ày ) tetr [In 2Àz Fe z ] oct S 4 (A2-series). Fe atoms were confirmed to exclusively occupy an octahedral positioni nb oth series. An unusualr eduction of the unit cell parameter with increasing Fe contenti se xplained 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 studiedc ompound is an n-type semiconductor,a nd its charge carrier concentration increases or decreases for larger Fe content withint he A1-and A2-series, respectively.T he thermal conductivity k tot is significantly reducedu pon increasing vacancy concentration, whereas the changeo fp ower factor is insufficientt od rastically improve the thermoelectric figure of merit.

Ternary MIn2S4 (M = Mn, Fe, Co, Ni) Thiospinels – Crystal Structure and Thermoelectric Properties

“…a) Crystal structure refinement was performed on additional sample with FeIn 2 S 4 nominal composition. The specimen was proven to be singlephase with unit-cell parameter and magnetic properties close to the FeIn 2 S 4 sample [16] discussed here. b) Given unit-cell parameters were refined separately with LaB 6 as an internal standard (values are also shown in Figure 4).…”

“…The UCPs are also smaller than the value of a ≈ 10.77 Å determined for the binary In 0.67 ᮀ 0.33 In 2 S 4 pristine compound due to smaller ionic radii of M 2+ ions than that of In 3+ . [16,34] UCPs remain unchanged after SPS treatment and LFA measurement thus indicating thermal stability of these materials. Rietveld refinements were performed on HR PXRD patterns and crystallographic parameters are summarized in Table 2.…”

“…We observed differences in temperature dependences of ρ(T) and α(T) between heating-and cooling-curve, as for previously discussed binary In-S and ternary Fe-In-S thiospinels. [15,16] Since DSC analysis does not reveal any thermal effects up to 873 K, the reason for the change of electrical trans-ARTICLE port properties remains unclear. Thus, the following discussion is based on data from heating-mode only.…”

“…[27,28] An increase of the inversion parameter i from Mn to Ni was reported, however, without a simple correlation to the bandgap. Both MnIn 2 S 4 [29] and FeIn 2 S 4 [16] compounds revealed high electrical resistivity ρ ≈ 10 3 -10 5 Ω•m at room temperature, which decreases from Mnto Fe-thiospinel. This would suggest further reduction of ρ for the subsequent M elements (i.e.…”

“…Besides intensively studied tetrahedrites, [1][2][3] chalcosite [4][5][6] or colusites, [7][8][9] there is an increasing interest in electronic and thermal transport properties of AB 2 S 4 thiospinels. [10][11][12][13][14][15][16] The reason for that is the ability of the spinel-type structure to accommodate different metal elements, [17,18] which results in tunability of physical properties e.g., from insulator to metal. [19] Interestingly, many thiospinels reveal n-type semiconducting behavior, [10][11][12]15,16] in contrast to the majority of state of the art sulfides, [20,21] which makes them good candidates for n-type counterparts in TE devices.…”