Zintl Phase Yb_1–xBa_xMg₂Bi_1.98 Compounds with Enhanced Thermoelectric Performance Caused by Cation Substitution

Contributing to the unique structural and chemical characteristics, AM2X2 Zintl compounds with the CaAl2Si2-type structure present advanced thermoelectric properties. In the present work, for YbMg2Bi2 compounds, the impact of Ba substitution on the Yb site is investigated. Owing to the changed electronegativity, the addition of Ba gives rise to the decline of carrier concentration and then induces the depressed power factor. However, fortunately, phonon scattering is dramatically intensified at the same time, which could be attributed to the obvious mass and strain fluctuation that originated from a visibly different mass/size between the Yb and Ba atoms. Typically, the lattice thermal conductivity of Yb0.75Ba0.25Mg2Bi1.98 achieves 1.21 W m–1 K–1 with a decrease of 46% compared to that of pristine YbMg2Bi1.98 at room temperature. Ultimately, for nontoxic Yb0.75Ba0.25Mg2Bi1.98, a significantly improved ZT value of ∼1.04 at 823 K is achieved. More importantly, the ZTeng value noticeably increases to ∼0.64 when Th = 873 K and Tc = 300 K, with an enhancement of ∼46% compared with the initial one. Meanwhile, the characteristic of nontoxicity would also enhance the possibility of YbMg2Bi2 to realize practical application.