Vacancy is a very important class of phonon scattering center to reduce thermal conductivity for the development of highly efficient thermoelectric materials. However, conventional monovacancy may also act as an electron or hole acceptor, thereby modifying the electrical transport properties and even worsening the thermoelectric performance. This issue urges researchers to create new types of vacancies that scatter phonons effectively while not deteriorating the electrical transport.

Recently, center member Prof. Yi Xie first reported the successful synergistic optimization of electrical and thermal parameters through Bi/Cu dual vacancies. As compared to its pristine and monovacancy samples, these dual vacancies further increase the phonon scattering. Most importantly, the clear-cut evidence in positron annihilation unambiguously confirms the interlayer charge transfer between these Bi/Cu dual vacancies, which results in the significant increase of electrical conductivity with relatively high Seebeck coefficient. As a result, BiCuSeO with Bi/Cu dual vacancies shows a high ZT value of 0.84 at 750 K. These findings undoubtedly elucidate a new strategy and direction for rational design of high performance thermoelectric materials.

The result was published in Journal of the American Chemical Society as “Dual Vacancies: an Effective Strategy Realizing Synergistic Optimization of Thermoelectric Property in BiCuSeO.” (J. Am. Chem. Soc., 2015, 137 (20), 6587–6593)