The presence of an electric field and the dynamic formation of 3D ionic conduction network speeded up the mass diffusion process and the chemical reaction of Zn and Sb into β-Zn 4Sb 3 compared to the typical temperature-driven diffusion and chemical reactions. To overcome these two β-Zn 4Sb 3-specific obstacles and to answer the two aforementioned general questions, here we have utilized the fast migration of Zn 2+ ions under electrical field and a dynamical growth of three-dimensional (3D) ionic conduction network to attain ultra-fast synthesis of β-Zn 4Sb 3. However, broader commercial applications of β-Zn 4Sb 3 face two long-standing obstacles: developing time- and cost-efficient synthesis recipes and maintaining good phase stability 21, 22, 23, 24, 25, 26, 27, 28 while delivering outstanding TE performance. The weakly bonded Zn interstitials enable highly mobile Zn 2+ and also ultra-low thermal conductivity 17, 18, 19, 20. Unlike most state-of-the-art TE materials that are electron-based semiconductors or semimetals 14, 15, the mobile ions in β-Zn 4Sb 3 play a vital role in its promising TE performance in the context of the Electron-Crystal Phonon-Liquid paradigm 16. β-Zn 4Sb 3 is known for its complex crystal structure as well as the coexistence of mixed electronic and ionic conduction and promising thermoelectric (TE) performance in the low to intermediate temperature range (400–700 K) 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. Β-Zn 4Sb 3 is a perfect material template to address these questions. Second, whether the interplay between mobile ions, thermal, and electric fields can yield certain microstructures that stabilize the phase at a level beyond the aforementioned “threshold”. Mass transport mechanisms, different from the traditional thermal diffusion, are a frontier topic of materials science and engineering 3. First, whether the mass transport in the form of ionic migration can be utilized towards fast materials synthesis. For the sake of phase stability, the voltage across an ionic conductor needs to be lower than the material-specific temperature-dependent threshold 2.

On the other hand, ionic migration risks phase instability, for example, precipitation occurs when the mobile ion’s electrochemical potential is higher than its atomic counterpart. On the one hand, electric field-driven ionic migration enables a wide range of applications such as batteries, fuel cells, and sensors 1. Ionic migration is an important form of mass transport. Mass transport, along with energy and charge transfer, is ubiquitous in nature and underscores diverse phenomena in science, engineering, and technology.

E xs max the talos principle images