Das Anustoop, Debnath Koyendrila, Maria Ivy, Das Subarna, Dutta Prabir, Swain Diptikanta, Waghmare Umesh V, Biswas Kanishka
New Chemistry Unit, and School of Advanced Materials and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560064, India.
Theoretical Sciences Unit, and School of Advanced Materials and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore 560064, India.
J Am Chem Soc. 2024 Nov 6;146(44):30518-30528. doi: 10.1021/jacs.4c11738. Epub 2024 Oct 25.
Metal chalcohalides, owing to their higher stability over halides and greater tunability of electronic features over chalcogenides, open new avenues for investigating properties of materials. Complex metal chalcohalides can be a good choice for thermoelectric studies for their halide-like low thermal conductivity and chalcogenide-like high electrical conductivity. Here, we have investigated the thermoelectric properties of -type BiSBr and utilized the concept of Fajans' polarization to describe the formation of a dimer and explained how it can help achieve high thermoelectric figure of merit (zT) of ∼1.0 at 748 K. This zT value is so far the highest-reported value for pristine metal chalcohalides. The existence of subunit in BiSBr is experimentally verified by synchrotron X-ray pair distribution function (X-PDF) analysis. The complex structure of BiSBr having a large unit cell exhibits simultaneous dimer-cation rattler (i.e., "twin-rattler"), which decreases the lattice thermal conductivity drastically. We observed evidence of such low-energy rattling vibrations from DFT-calculated eigen mode visualizations of the phonon dispersion. The subvalent nature of accommodates an extra electron in () orbital, which helps form a weakly dispersed donor band just below the Fermi energy (), leading to a significant reduction in band gap (0.77 eV), which is favorable for high thermoelectric performance. Consequently, we obtained a semiconducting nature of -type BiSBr with moderate electrical conductivity, as well as a high Seebeck coefficient. Our investigation presents the importance of fundamental chemistry in thermoelectrics and demonstrates the influence of subvalent twin-rattler in triggering high thermoelectric performance in metal chalcohalides.
金属卤硫属化合物因其比卤化物具有更高的稳定性，且比硫属化合物具有更强的电子特性可调性，为材料性能研究开辟了新途径。复杂金属卤硫属化合物因其类似卤化物的低热导率和类似硫属化合物的高电导率，可能是热电研究的一个不错选择。在此，我们研究了n型BiSBr的热电性能，并利用法扬斯极化概念描述了二聚体的形成，并解释了它如何有助于在748 K时实现约1.0的高热电优值（zT）。这个zT值是迄今为止报道的原始金属卤硫属化合物的最高值。通过同步辐射X射线对分布函数（X-PDF）分析，实验验证了BiSBr中 亚基的存在。具有大晶胞的BiSBr复杂结构表现出同时存在二聚体-阳离子摇摆体（即“双摇摆体”），这极大地降低了晶格热导率。我们从声子色散的DFT计算本征模可视化中观察到了这种低能摇摆振动的证据。 的亚价性质在（）轨道中容纳了一个额外的电子，这有助于在费米能级（）下方形成一个弱色散的施主带，导致带隙显著减小（0.77 eV），这有利于高热电性能。因此，我们得到了具有中等电导率和高塞贝克系数的n型BiSBr的半导体性质。我们的研究揭示了基础化学在热电学中的重要性，并证明了亚价双摇摆体对触发金属卤硫属化合物高热电性能的影响。
