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Enhanced thermoelectric performance in topological crystalline insulator n-type Pb₀.₆Sn₀.₄Te by simultaneous tuning of the band gap and chemical potential

Roychowdhury, Subhajit, Dutta, Moinak, Biswas, Kanishka
Journal of materials chemistry A 2018 v.6 no.47 pp. 24216-24223
chemistry, iodides, iodine, temperature, topology
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.