Crystal structure and high temperature X-ray diffraction study of thermoelectric chimney-ladder FeGe (γ ≈ 1.52)

Abstract

The crystal structure of Nowotny chimney-ladder phase FeGe γ with γ ≈ 1.52 was studied by X-ray diffractometry from 300 K to 850 K. The diffraction patterns were fitted by Rietveld refinement considering an incommensurate composite crystal structure. The refined crystal structure of FeGe γ is described in details and compared to MnSi γ , a thermoelectric material with γ ≈ 1.74. The lattice parameters a, c Fe and c Ge were found to increase with the temperature following a polynomial law, while the modulation vector component γ remained constant up to the peritectoid decomposition into FeGe and FeGe 2 . Within the temperature range considered, the linear and volumetric thermal expansion parameters increased from about 3×10 −6 K −1 to 10×10 −6 K −1 and from 9.6×10 −6

Electronic Configurations of 3d Transition-Metal Compounds Using Local Structure and Neural Networks

“…It should be pointed out that these compounds share some common features of the disruption of long-range ordering that might influence their physical properties. For example, Mn 4 Si 7 and Mn 3 Ge 5 are examples of Nowotny chimney-ladder structures which consist of the interpenetration of [Si/Ge] and [Mn] subsystems with an incommensurate c parameter. ,− Similarly, Fe 7 Se 8 and its counterpart Fe 7 S 8 are well-known examples of compounds with a superstructure due to ordered intrinsic vacancies. , The difference between ideal input structures and experimental ones must contribute to prediction deviations. Furthermore, some of these compounds may show strong itinerant magnetic behavior, as exhibited by Mn 4 Si 7 , for instance; therefore, a local description of the magnetic moment may not be valid.…”

Influence of Stoichiometry and Aging at Operating Temperature on Thermoelectric Higher Manganese Silicides

“…Important research efforts have been undertaken during the past two decades to increase ZT of numerous materials such as Bi 2 Te 3 , GeTe, or PdTe to enable a more extensive development of the TE technology. However, many other factors must be taken into account when selecting materials for the TE generator, such as the raw material costs and toxicity, mechanical properties, chemical and thermal stability, and thermal expansion coefficients . For all these reasons, higher manganese silicides (HMSs) with the composition MnSi x (1.725 < x < 1.75) are considered as promising p -type thermoelectric materials for the mid-temperature applications (600–800 K), despite a moderate ZT of 0.4 …”

“…However, many other factors must be taken into account when selecting materials for the TE generator, such as the raw material costs and toxicity, 4 mechanical properties, chemical and thermal stability, and thermal expansion coefficients. 5 For all these reasons, higher manganese silicides (HMSs) with the composition MnSi x (1.725 < x < 1.75) are considered as promising p-type thermoelectric materials for the mid-temperature applications (600−800 K), despite a moderate ZT of 0.4. 6 According to Miyazaki et al, 7 HMSs crystallize in a tetragonal composite crystal Nowotny chimney-ladder structure type, as shown in Figure 1.…”

Itinerant ferromagnet Re4−xMnxGe7−δ (x = 0.9–1.5, δ = 0.42–0.44) with incommensurate chimney-ladder structure stabilised at ambient pressure

“…Nowotny chimney-ladder phases represent a large family of T-E intermetallic compounds (Ttransition metal, Emain group element) with a general formula of T n E m (1 < m/n ≤ 2). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Their crystal structures present an interesting case of composite structures, with p-element atoms forming a nested n-fold spiral ("ladder") inside a β-Sn-type spiral of d-element atoms ("chimney"). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The transition metal spiral has a short period c T of 4-6 Å and remains virtually identical between various phases, while the period of a full rotation for the main group element helix varies significantly and can sometimes reach hundreds of ångströms leading to an incommensurate structure.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Their crystal structures present an interesting case of composite structures, with p-element atoms forming a nested n-fold spiral ("ladder") inside a β-Sn-type spiral of d-element atoms ("chimney"). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The transition metal spiral has a short period c T of 4-6 Å and remains virtually identical between various phases, while the period of a full rotation for the main group element helix varies significantly and can sometimes reach hundreds of ångströms leading to an incommensurate structure. [6][7][8][9][10] Therefore, the main group substructure is usually described using a much smaller subcell containing two "steps" of the "ladder" with the c parameter of 2.5-3.5 Å denoted as c E .…”