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Strong Antibonding I (p)–Cu (d) States Lead to Intrinsically Low Thermal Conductivity in CuBiI4
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-01-03 , DOI: 10.1021/jacs.2c11908 Anustoop Das 1 , Koushik Pal 2 , Paribesh Acharyya 1 , Subarna Das 1 , Krishnendu Maji 1 , Kanishka Biswas 1
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2023-01-03 , DOI: 10.1021/jacs.2c11908 Anustoop Das 1 , Koushik Pal 2 , Paribesh Acharyya 1 , Subarna Das 1 , Krishnendu Maji 1 , Kanishka Biswas 1
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Chemical bonding present in crystalline solids has a significant impact on how heat moves through a lattice, and with the right chemical tuning, one can achieve extremely low thermal conductivity. The desire for intrinsically low lattice thermal conductivity (κlat) has gained widespread attention in thermoelectrics, in refractories, and nowadays in photovoltaics and optoelectronics. Here we have synthesized a high-quality crystalline ingot of cubic metal halide CuBiI4 and explored its chemical bonding and thermal transport properties. It exhibits an intrinsically ultralow κlat of ∼0.34–0.28 W m–1 K–1 in the temperature range 4–423 K with an Umklapp crystalline peak of 1.82 W m–1 K–1 at 20 K, which is surprisingly lower than other copper-based halide or chalcogenide materials. The crystal orbital Hamilton population analysis shows that antibonding states generated just below the Fermi level (Ef), which arise from robust copper 3d and iodine 5p interactions, cause copper–iodide bond weakening, which leads to reduction of the elastic moduli and softens the lattice, finally to produce extremely low κlat in CuBiI4. The chemical bonding hierarchy with mixed covalent and ionic interactions present in the complex crystal structure generates significant lattice anharmonicity and a low participation ratio in low-lying optical phonon modes originating mostly from localized copper–iodide bond vibrations. We have obtained experimental evidence of these low-lying modes by low-temperature specific heat capacity measurement as well as Raman spectroscopy. The presence of strong p–d antibonding interactions between copper and iodine leads to anharmonic soft crystal lattice which gives rise to low-energy localized optical phonon bands, suppressing the heat-carrying acoustic phonons to steer intrinsically ultralow κlat in CuBiI4.
中文翻译：
强反键合 I (p)–Cu (d) 态导致 CuBiI4 中固有的低热导率
结晶固体中存在的化学键对热量如何通过晶格移动具有重大影响，并且通过正确的化学调整，可以实现极低的热导率。对本质上低晶格热导率 (κ lat ) 的需求在热电学、耐火材料以及当今的光伏和光电子学领域得到了广泛关注。在这里，我们合成了立方金属卤化物 CuBiI 4的高质量结晶锭，并探索了其化学键合和热传输特性。它在 4–423 K 的温度范围内表现出∼0.34–0.28 W m –1 K –1的固有超低 κ lat ，具有 1.82 W m –1 K的 Umklapp 结晶峰–1在 20 K 时，这比其他铜基卤化物或硫族化物材料低得惊人。晶体轨道汉密尔顿布居分析表明，刚好在费米能级 (Ef) 以下产生的反键态由铜 3d 和碘 5p 相互作用引起，导致铜-碘化物键减弱，从而导致弹性模量降低并软化晶格，最终在 CuBiI 4中产生极低的 κ lat. 复杂晶体结构中存在的具有混合共价和离子相互作用的化学键合层次产生显着的晶格非谐性和低位光学声子模式的低参与率，主要源于局部铜 - 碘化物键振动。我们通过低温比热容测量和拉曼光谱获得了这些低洼模式的实验证据。铜和碘之间强 p – d 反键相互作用的存在导致非谐软晶格产生低能局部光学声子带，抑制载热声学声子以引导CuBiI 4中固有的超低 κ lat。
更新日期：2023-01-03
中文翻译：
强反键合 I (p)–Cu (d) 态导致 CuBiI4 中固有的低热导率
结晶固体中存在的化学键对热量如何通过晶格移动具有重大影响，并且通过正确的化学调整，可以实现极低的热导率。对本质上低晶格热导率 (κ lat ) 的需求在热电学、耐火材料以及当今的光伏和光电子学领域得到了广泛关注。在这里，我们合成了立方金属卤化物 CuBiI 4的高质量结晶锭，并探索了其化学键合和热传输特性。它在 4–423 K 的温度范围内表现出∼0.34–0.28 W m –1 K –1的固有超低 κ lat ，具有 1.82 W m –1 K的 Umklapp 结晶峰–1在 20 K 时，这比其他铜基卤化物或硫族化物材料低得惊人。晶体轨道汉密尔顿布居分析表明，刚好在费米能级 (Ef) 以下产生的反键态由铜 3d 和碘 5p 相互作用引起，导致铜-碘化物键减弱，从而导致弹性模量降低并软化晶格，最终在 CuBiI 4中产生极低的 κ lat. 复杂晶体结构中存在的具有混合共价和离子相互作用的化学键合层次产生显着的晶格非谐性和低位光学声子模式的低参与率，主要源于局部铜 - 碘化物键振动。我们通过低温比热容测量和拉曼光谱获得了这些低洼模式的实验证据。铜和碘之间强 p – d 反键相互作用的存在导致非谐软晶格产生低能局部光学声子带，抑制载热声学声子以引导CuBiI 4中固有的超低 κ lat。
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