High Bi-ratio ternary sulfides have been recently reported as superior thermoelectric materials. However, the synthesis of high Bi-ratio Cu-Bi-S nanocrystal remains a challenge. Reported here are the synthesis and characterization of three-phase Cu-Bi-S nanocrystals with the nominal chemical formulae of Cu1.57 Bi4.57 S8 , Cu2.93 Bi4.89 S9 and Cu3 BiS3 . The samples were prepared using a Bi2 S3 precursor by varying the amount and type of Cu2-x S (i. e. Cu2 S or Cu7.2 S4 ) reactants. TEM images reveal that two new samples crystalized having nanorod morphology with radii of approximately 50 nm and lengths of 200 nm. XPS results indicate that the valence states of Bi in both the two new phases are +3 with viable oxidation states for Cu. UV-Vis-NIR absorption spectroscopy reveals that narrow direct bandgaps are 1.12 and 1.27 eV for Cu1.57 Bi4.57 S8 and Cu2.93 Bi4.89 S9 , respectively. Besides, this method could also be applied to synthesize the Cu3 BiS3 phase with a new nanoplate morphology. The as-synthesized Cu-Bi-S samples show Cu/Bi ratio-dependent photoresponsive properties. This study not only reports the structure and bandgap of two ternary sulfides, which have only been discovered in the mineral previously, but also provides an efficient method for synthesizing Bi-rich ternary chalcogenide nanocrystals.

中文翻译：

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Cu1.57 Bi4.57 S8和Cu2.93 Bi4.89 S9的高双比例三元硫化物纳米晶体的相控合成。

最近已经报道了高双比例三元硫化物是优良的热电材料。然而，高Bi比率的Cu-Bi-S纳米晶体的合成仍然是一个挑战。这里报道的是具有标称化学式为Cu1.57 Bi4.57 S8，Cu2.93 Bi4.89 S9和Cu3 BiS3的三相Cu-Bi-S纳米晶体的合成和表征。通过改变Cu2-x S（即Cu2 S或Cu7.2 S4）反应物的数量和类型，使用Bi2 S3前体制备样品。TEM图像显示，两个新样品结晶后具有纳米棒形态，半径约为50 nm，长度为200 nm。XPS结果表明，两个新相中Bi的化合价态均为+3，而Cu的氧化态可行。UV-Vis-NIR吸收光谱显示，Cu1.57 Bi4的窄直接带隙为1.12和1.27 eV。分别为57 S8和Cu2.93 Bi4.89 S9。此外，该方法还可用于合成具有新的纳米板形态的Cu3 BiS3相。合成后的Cu-Bi-S样品显示出Cu / Bi比率依赖性的光响应特性。这项研究不仅报告了以前仅在矿物中发现的两种三元硫化物的结构和带隙，而且为合成富含Bi的三元硫属元素化物纳米晶体提供了一种有效的方法。