中子粉末衍射鉴定 CsCuBr3 卤化物的新型高温物相和晶体结构演化,CrystEngComm

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中子粉末衍射鉴定 CsCuBr3 卤化物的新型高温物相和晶体结构演化
CrystEngComm ( IF 2.6 ) Pub Date : 2023-05-29 , DOI: 10.1039/d3ce00432e
Carmen Abia _{1,

2} , Carlos A. López _{1,

3} , Javier Gainza ₁ , João Elias F. S. Rodrigues ₄ , María T. Fernández-Díaz ₂ , Eva Céspedes ₁ , José Luis Martínez ₁ , José Antonio Alonso ₁

Affiliation

寻找具有潜在光电应用的新型无铅材料是当今环境友好型能源转型的主要研究课题。基于有前途的全无机CsPbBr ₃钙钛矿，我们在这里测试了用Cu ²⁺替代有毒的Pb ²⁺，并探索了正在研究的CsCuBr ₃卤化物。我们提出了机械合成的 CsCuBr ₃通过球磨获得的样品，由结晶良好且纯净的样品组成。量热测量揭示了热事件，表明在 422 K 左右发生结构相变，紧邻样品因 Br 损失而分解的温度。使用20至420 K的中子粉末衍射数据进行了详细的结构分析，重点关注斜方相（空间群：C 222 ₁）直至400 K的演化；这种晶体排列由共面 [CuBr ₆ ] 八面体的二聚体单元组成，其中包含 Cu-Cu 二聚体，其距离明显较短，这说明了 Cu ^{2+之间的磁耦合}之前描述过的旋转。此外，在 420 K 下，我们发现了一种新的高温相，如六边形P 6 ₅ 22 空间群中所述，其中观察到无限链的 [CuBr ₄ ] 方形平面单元。另一项考虑德拜模型的研究进行了，提供了有关 Cs-Br 和 Cu-Br 化学键的相关信息。根据漫反射紫外-可见光测量，估计室温下斜方相的光学间隙为~1.8 eV。磁性测量表明，有效磁化行为与温度的关系似乎接近线性，并且似乎可以外推到零（小于 10 ^-5 μ _B/Cu 原子）在 420 K 以上的温度下，与相变的开始同时发生。

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Novel high-temperature phase and crystal structure evolution of CsCuBr3 halide identified by neutron powder diffraction

The search for novel lead-free materials with potential optoelectronic applications is a main research topic nowadays for an environment-friendly energy transition. Based on promising all-inorganic CsPbBr₃ perovskite, we tested here the substitution of toxic Pb²⁺ with Cu²⁺ and explored the understudied CsCuBr₃ halide. We present a mechanically-synthesized CsCuBr₃ specimen obtained by ball milling, consisting of a well-crystallized and pure sample. Calorimetric measurements revealed a thermal event suggesting a structural phase transition around 422 K, immediately below the decomposition of the sample due to Br loss. A detailed structural analysis was carried out using neutron powder diffraction data from 20 to 420 K, focusing on the evolution of the orthorhombic phase (space-group: C222₁) up to 400 K; this crystal arrangement consists of dimer units of face-sharing [CuBr₆] octahedra containing Cu–Cu dimers with conspicuously short distances that account for the magnetic coupling between Cu²⁺ spins described before. Additionally, at 420 K, we identified a novel high-temperature phase as described in the hexagonal P6₅22 space group, where infinite chains of [CuBr₄] square-planar units were observed. An additional study considering the Debye model was carried out, providing information on the relative Cs–Br and Cu–Br chemical bonds. From diffuse reflectance UV-Vis measurements, an optical gap of ∼1.8 eV was estimated for the orthorhombic phase at room temperature. Magnetic measurements indicate that the effective magnetization behavior versus temperature appears close to linear and seems to extrapolate to zero (smaller than 10⁻⁵ μ_B/Cu atom) at temperatures above 420 K, coinciding with onset of phase transition.

更新日期：2023-05-29

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