Structural, Magnetic and Thermoelectric Properties of hp‐Mn₃Ge₅

Abstract

Mn3Ge5 was obtained by high‐pressure, high temperature synthesis. The compound adopts a Nowotny‐Chimney‐Ladder type crystal structure [tetragonal, space group P4n2, a = 5.7449(1) Å, c = 13.9096(4) Å, Z = 4]. Magnetic measurements reveal a ferromagnetic transition around 40 K and metallic conductivity in the temperature range from 3 K to 350 K. Despite a low thermal conductivity, the metallic character of the sample and the low Seebeck coefficient result in low values for the thermoelectric Figure of merit, ZT. Band‐structure calculations show that the Fermi level is located slightly below a pseudo‐gap in the electronic density of states. Chemical bonding analysis in position space discloses moderate charge transfer and two‐ as well as three‐atomic directed, heteroatomic bonding involving both the manganese and the germanium atoms.

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 .…”

“…1,4,5 The Nowotny phases can be observed at VEC = 12-15. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] At VEC = 14, the Fermi level usually lands in the band gap, which opens due to the covalent interactions, leading to semiconducting behaviour. 1,4,5,17,18 In some cases, valence and conduction bands overlap creating a pseudogap at the Fermi level.…”

“…1,4,5 Small deviations from VEC = 14 (e.g., 13.9 or 14.1) do not necessarily lead to the metallic state, as some compounds exhibit degenerate semiconducting behaviour, 1,9,12 whereas the larger VEC does result in metallic conductivity. 1,15,20,21 Due to the itinerant nature of magnetism in these compounds, the metallic state implies a possibility of magnetic ordering, which is experimentally observed for compounds with T = Cr and Mn. [13][14][15]22 The structural features of chimney-ladders make the latter property particularly interesting.…”

“…1,15,20,21 Due to the itinerant nature of magnetism in these compounds, the metallic state implies a possibility of magnetic ordering, which is experimentally observed for compounds with T = Cr and Mn. [13][14][15]22 The structural features of chimney-ladders make the latter property particularly interesting. While the complex crystal structure can give rise to similarly complex magnetic structure by itself, 23,24 the absence of the centre of inversion in a large number of chimney-ladder phases opens a possibility for a non-collinear magnetic structure, which was suggested in the case of Cr 11 Ge 19 .…”