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Tailoring the electronic structure of topological crystalline insulators (TCIs) is necessary to enhance their thermoelectric (TE) performance. p-Type chemical doping in a TCI such as Pb0.6Sn0.4Te exhibited a significantly high TE figure of merit (zT), but the n-type Pb0.6Sn0.4Te is still elusive and is urgently needed for thermoelectric applications. Herein, we report enhanced thermoelectric performance in n-type iodine (I) doped Pb0.6Sn0.4Te. Aliovalent I− doping in the Te2− sublattice of Pb0.6Sn0.4Te widens the band gap via breaking of local crystal mirror symmetry, which decreases the bipolar conduction and pushes the Seebeck maxima towards high temperatures. Iodine doping in Pb0.6Sn0.4Te significantly increases the n-type carrier concentration and shifts the chemical potential (Fermi level) inside the conduction band of Pb0.6Sn0.4Te, thus improving the electrical transport properties. We report a maximum zT of 1.05 in the n-type Pb0.60Sn0.40Te0.995I0.005 sample at 620 K, which is 483% higher than pristine Pb0.6Sn0.4Te. [ABSTRACT FROM AUTHOR]

Lead chalcogenides and their alloys belong at the heart of thermoelectrics due to their large thermoelectric figure of merit (zT). However, recent research has shown a limitation in the use of lead (Pb)-based materials due to their toxicity and efforts have been made to produce non-toxic analogues of lead chalcogenides. Tin chalcogenides have been predicted to be promising for this purpose due to their unique electronic structure and phonon dispersion properties. Here, we discuss the journey of tin chalcogenides in the field of thermoelectrics and topological materials with the main emphasis on the bonding, crystal structures, electronic band structures, phonon dispersion and thermoelectric properties. The thermal transport properties of tin chalcogenides are explained based on lattice dynamics, where resonant bonding and local structural distortion play an important role in creating lattice anharmonicity, thereby lowering the lattice thermal conductivity. Since thermoelectric and topological materials, especially topological insulators and topological crystalline insulators, share similar material features, such as a narrow band gap, heavy constituent elements and significant spin–orbit coupling, we have discussed the thermoelectric properties of several topological tin chalcogenides from a chemistry perspective. This feature article serves as a useful reference for researchers who strive to improve the properties of tin chalcogenides and advance the field of thermoelectric and topological materials. [ABSTRACT FROM AUTHOR]

Recently, tin telluride (SnTe) has drawn much attention as a potential candidate for thermoelectric power generation. Herein, we report the high thermoelectric performance in SnTe achieved through a two-step design (a) reduction in lattice thermal conductivity via solid solution alloying and (b) enhancement of the Seebeck coefficient (S) via the modification of the electronic structure through co-doping. First, we demonstrate that the introduction of Pb into the position of Sn in SnTe decreases the excess of p-type carrier concentration in SnTe. Notably, the Sn0.70Pb0.30Te sample exhibits a κlatt value of ∼0.67 W m−1 K−1 at 300 K, which is close to the theoretical minimum limit of the κlatt in SnTe, which results mainly from scattering of heat carrying phonons by solid solution point defects. Secondly, we achieve an S value of 121 μV K−1 at 300 K, which increases to ∼241 μV K−1 at 710 K for In and Mg co-doped Sn0.70Pb0.30Te, which is the highest Seebeck coefficient among all the state-of-the-art SnTe based materials known so far. Indium acts as a resonant dopant, leading to a remarkable enhancement in the Seebeck coefficient mainly near room temperature, whereas Mg doping enables the valence band convergence in Sn0.70Pb0.30Te, which is confirmed by density functional theory (DFT) calculations of its electronic structure. As a result of co-doping, a remarkable enhancement in the Seebeck coefficient over a wide range of temperatures is achieved due to the synergistic effect of resonance level formation and valence band convergence. Hence, we have achieved a maximum zT of 1 at 710 K for In and Mg co-doped Sn0.70Pb0.30Te. Notably, an average zT (zTavg) of ∼0.6 is achieved in the temperature range of 300–710 K for the Sn0.655Mg0.04In0.005Pb0.30Te sample. [ABSTRACT FROM AUTHOR]

Thermoelectric materials have received recent attention due to their ability to convert waste heat to electrical energy directly and reversibly. Inorganic materials, especially Bi2Te3, PbTe and Si–Ge based alloys, have been investigated in the temperature range of 300–1000 K, among which PbTe based materials have been extensively studied, and reported to be the leading thermoelectric materials for mid-temperature power generation. However, environmental concern limits their large scale production due to the toxic nature of Pb. As an alternative, GeTe-rich alloys such as TAGS (GeTe–AgSbTe2) have been largely investigated since the 1960s. Most recently, some of the new materials in the GeTe family have been introduced such as Ge0.87Pb0.13Te, the homologous series of Sb2Te3(GeTe)n and Ge0.9Sb0.1Te, and are reported to exhibit high thermoelectric performance, inherently formed nano and microstructure modulations, and high thermal and mechanical stability. These collective enhanced properties of GeTe-rich alloys have generated great interest in investigating further new GeTe based alloys for intermediate temperature thermoelectric applications. In order to provide the fundamental understanding, technological insights, and to further promote the GeTe based alloys, we hereby present a review on (i) the crystal structure, nano/microstructure, phase transition, electronic structure, and thermoelectric properties of GeTe, (ii) correlation of compositional and microstructure modulations and thermoelectric properties of doped GeTe, TAGS based alloys, Ge–Pb–Te materials, and Ge–Sb–Te materials, (iii) mechanical properties, (iv) past and present devices based on GeTe materials and (v) future directions. [ABSTRACT FROM AUTHOR]