¹²⁵Te NMR and Seebeck Effect in Bi₂Te₃ Synthesized from Stoichiometric and Te-Rich Melts

Bi 2 Te 3 is a well-known thermoelectric material and, as a new form of quantum matter, a topological insulator. Variation of local chemical composition in Bi 2 Te 3 results in formation of several types of atomic defects, including Bi and Te vacancies and Bi and Te antisite defects; these defects can strongly affect material functionality via generation of free electrons and/or holes. Nonuniform distribution of atomic defects produces electronic inhomogeneity, which can be detected by 125 Te nuclear magnetic resonance (NMR). Here we report on 125 Te NMR and Seebeck effect (heat to electrical energy conversion) for two single crystalline samples: (#1) grown from stoichiometric composition by Bridgman technique and (#2) grown out of Te-rich, high temperature flux. The Seebeck coefficients of these samples show p- and n-type conductivity, respectively, arising from different atomic defects. 125 Te NMR spectra and spin–lattice relaxation measurements demonstrate that both Bi 2 Te 3 samples are electronically inhomogeneous at the atomic scale, which can be attributed to a different Te environment due to spatial variation of the Bi/Te ratio and formation of atomic defects. Correlations between 125 Te NMR spectra, spin–lattice relaxation times, the Seebeck coefficients, carrier concentrations, and atomic defects are discussed. Our data demonstrate that 125 Te NMR is an effective probe to study antisite defects in Bi 2 Te 3 .