In cesium bismuth bromides comprising [BiBr₆]³⁻ octahedra, the octahedra behave as quantum dots and their interactions can be manipulated by tailoring their connectedness (e.g., corner-sharing, edge-sharing, or unconnected). Of the four compounds reported, CsBi₂Br₇, CsBiBr₄, Cs₃Bi₂Br₉, and Cs₃BiBr₆, there is only one publication each on CsBi₂Br₇ and CsBiBr₄. Here, we synthesize CsBi₂Br₇ and attempt to synthesize CsBiBr₄ using co-evaporation of CsBr and BiBr₃ where the precursor fluxes are controlled precisely. The structure, composition, morphology, and optical properties of the films are characterized using x-ray diffraction (XRD), scanning electron microscopy, energy dispersive x-ray spectroscopy, Raman scattering, and optical absorption as a function of time from hours to several months. When the CsBr:BiBr₃ flux ratio is 1:2, CsBi₂Br₇ forms but its XRD, Raman spectrum, and morphology change with time. CsBi₂Br₇ is ultimately unstable with respect to dissociation into Cs₃Bi₂Br₉ and BiBr₃ over a time period of weeks. Its optical absorption shows a peak at 407 nm, between that of Cs₃Bi₂Br₉ at 435 nm and Cs₃BiBr₆ at 386 nm, indicating that the interactions between the [BiBr₆]³⁻ octahedra in CsBi₂Br₇ is between those in Cs₃Bi₂Br₉, where the octahedra share corners, and Cs₃BiBr₆, where the octahedra are not connected. When the CsBr:BiBr₃ flux ratio is maintained at 1:1 to form CsBiBr₄, the XRD of the resulting film is consistent with a mixture of Cs₃Bi₂Br₉ and CsBi₂Br₇ suggesting that CsBiBr₄, if it exists and forms, is also unstable. We see remarkable fluidity and mobility of matter in the film with tens of micrometer size crystals growing or disappearing in thermodynamically frustrated films even at room temperature over a period of days to weeks.

中文翻译：

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卤化物钙钛矿CsBi2Br7的物理气相沉积

在包含[BiBr ₆ ] ^3-八面体的溴化铯铯中，八面体表现为量子点，可以通过调整它们的连接性（例如，角共享，边缘共享或不连接）来操纵它们的相互作用。在所报道的四种化合物CsBi ₂ Br ₇，CsBiBr ₄，Cs ₃ Bi ₂ Br ₉和Cs ₃ BiBr _6中，关于CsBi ₂ Br ₇和CsBiBr ₄各自只有一个出版物。在这里，我们合成CsBi ₂ Br ₇并尝试合成CsBiBr_{在图4中，}使用CsBr和BiBr _3的共蒸发，可精确控制前体通量。使用X射线衍射（XRD），扫描电子显微镜，能量色散X射线光谱，拉曼散射和光吸收随时间从几小时到几小时的函数来表征薄膜的结构，组成，形态和光学性质个月。当CsBr：BiBr _3的通量比为1：2时，形成CsBi ₂ Br _7，但其XRD，拉曼光谱和形态随时间变化。关于解离成Cs ₃ Bi ₂ Br ₉和BiBr _3， CsBi ₂ Br ₇最终是不稳定的。在数周的时间内。它的光吸收在407 nm处出现一个峰值，介于435 nm的Cs ₃ Bi ₂ Br ₉和386 nm的Cs ₃ BiBr ₆之间，表明CsBi ₂ Br _7中的[BiBr ₆ ] ^3-八面体之间的相互作用为介于八面体共享角的Cs ₃ Bi ₂ Br ₉和未连接八面体的Cs ₃ BiBr ₆之间。当CsBr：BiBr _3的通量比保持在1：1时形成CsBiBr ₄，所得膜的XRD与Cs ₃ Bi ₂ Br ₉和CsBi ₂ Br ₇的混合物一致，这表明CsBiBr ₄（如果存在并形成）也是不稳定的。我们看到薄膜中物质的流动性和流动性非常好，即使在室温下几天甚至几周的时间里，数十微米尺寸的晶体也会在热力学受阻的薄膜中生长或消失。