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Page 2 of 21 Duparchy et al. Energy Mater. 2025, 5, 500134 https://dx.doi.org/10.20517/energymater.2025.51

boundaries for the performance of TE materials and the successful application of thermodynamic degrees of
freedom to address fundamental challenges in TE material systems while retaining promising TE performance.

Keywords: Mg Si Sn , thermoelectric transport properties, single parabolic band model, Mg-related defects,
1-x
2
x
material stoichiometry

INTRODUCTION
As the global energy crisis escalates, the need for sustainable and efficient energy sources is becoming
[1,2]
increasingly important . Current methods of power generation, such as coal and gas combustion,
contribute significantly to environmental degradation and resource depletion. By converting (waste) heat
into usable electrical energy, thermoelectric technology offers a promising solution to ease energy demand
while reducing our carbon footprint . Thermoelectric (TE) generators are competitive solutions due to
[3]
their high reliability, absence of mechanical components, extended operation lifespan and low maintenance
demands. They have been used mainly in the aerospace field for space probes such as Voyager 1 and 2 (after
decades of operation) or in Mars missions with Perseverance and Curiosity rovers .
[4-6]

The efficiency of TE devices depends on the properties of the employed TE material, evaluated by the
thermoelectric figure of merit at an absolute temperature T. Here, S represents the Seebeck
coefficient, σ the electrical conductivity and κ the thermal conductivity . Maximizing the figure of merit is
[7]
essential for the development of thermoelectric technologies, as it indicates the material’s ability to
[8,9]
efficiently convert heat into electricity at a given temperature gradient. However, the value of zT is
limited by the interdependence of the three essential transport properties: S, σ and κ, where κ should be low
and the TE power factor PF = S σ should be high. The Seebeck coefficient and electrical conductivity are
2
largely governed by the charge carrier concentration (n) and the charge carrier mobility (µ). The charge
carrier concentration depends on the defect types and concentrations of the semiconducting base material
and can be adjusted by doping the material . Generally, TE materials achieve maximum zT for relatively
[7]
high carrier concentrations (10 -10 cm ) and the addition of a well-chosen foreign atom will modify the
19
-3
20
[7]
Fermi level, resulting in higher carrier concentration .
So far, significant advancements have been made in developing TE materials suitable for intermediate
temperatures ranging from 500 K to 900 K, resulting in high figures of merit up to zT > 2. Noteworthy
[10]
examples include PbTe , Skutterudites , half-Heusler compounds and Mg-based materials such as
[11]
[12]
MgAgSb [13,14] , Mg Sb 2 [15,16] or Mg Si Sn solid solutions [17,18] . The latter meet several criteria for large scale
1-x
x
3
2
applicability, including the utilization of lightweight and abundant raw elements (Mg, Si and Sn), low cost,
environmental compatibility and excellent thermoelectric performance [19,20] . N-type Mg Si Sn solid
x
1-x
2
solutions doped with antimony have been optimized showing excellent TE properties (zT ~ 1.4) arising
max
from a degeneracy of the conduction bands (CB) for the composition range x = 0.6 to 0.7 and reduced
lattice thermal conductivity due to alloying [18,21,22] . The application potential has been demonstrated by the
[23]
successful fabrication of prototypes by Kaibe et al. using a two-stage BiTe-silicide module, followed by the
[24]
development of the first full Mg (Si,Sn) (used as both p- and n-type) device by Camut et al. which
2
achieved conversion efficiencies of 12% with T = 550 °C and T = 30 °C and 3.6% with T = 400 °C and T =
c
h
h
c
25 °C, respectively. Later on, Wieder et al. developed a module combining p-type MgAgSb and n-type
[25]
Mg (Si,Sn) leading to an improved efficiency of 6.4%.
2