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 Yb_0.75Ba_0.25Mg₂Bi_1.98 achieves 1.21 W m⁻¹ K⁻1 with a decrease of 46% compared to that of pristine YbMg₂Bi_1.98 at room temperature. Ultimately, for nontoxic Yb_0.75Ba_0.25Mg₂Bi_1.98, a significantly improved ZT value of ∼1.04 at 823 K is achieved. More importantly, the ZT_eng value noticeably increases to ∼0.64 when T_h = 873 K and T_c = 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.