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 cm(2) 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 ( l ph) from the kinetic model amounts to 12 angstrom at 390 K and follows a T - 1 behavior. An extrapolation of l ph 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 l ph 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.