Thermoelectric properties of Bi2O2Se single crystals

Bismuth oxyselenide (Bi2O2Se) attracts great interest as a potential n-type complement to p-type thermoelectric oxides in practical applications. Previous investigations were generally focused on polycrystals. Here, we performed a study on the thermoelectric properties of Bi2O2Se single crystals. Our samples exhibit electron mobility as high as 250 cm2 V−1 s−1 and thermal conductivity as low as 2 W m−1 K−1 near room temperature. The maximized figure of merit is yielded to be 0.188 at 390 K, higher than that of polycrystals. Consequently, a rough estimation of the phonon mean free path (ℓph) from the kinetic model amounts to 12 Å at 390 K and follows a T−1 behavior. An extrapolation of ℓph to higher temperatures indicates that this system approaches the Ioffe–Regel limit at about 1100 K. In light of the phonon dispersions, we argue that the ultralow ℓph is attributed to intense anharmonic phonon–phonon scattering, including the Umklapp process and acoustic to optical phonon scattering. Our results suggest that single crystals provide a further improvement of thermoelectric performance of Bi2O2Se.