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A2AgCrCl6 (A = Li, Na, K, Rb, Cs) halide double perovskites: a transition metal-based semiconducting material series with appreciable optical characteristics
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-08-31 , DOI: 10.1039/d0cp01896a Pradeep R. Varadwaj 1, 2, 3, 4, 5
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-08-31 , DOI: 10.1039/d0cp01896a Pradeep R. Varadwaj 1, 2, 3, 4, 5
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We have theoretically examined the geometries, electronic density of states and band structures of cubic and hexagonal A2AgCrCl6 (A = Cs, Rb, K, Na, Li) using meta-GGA SCAN-rVV10. The optimized lattice density was found to vary between 2.68 and 4.08 g cm−3 for cubic-A2AgCrCl6, with the fundamental electronic bandgap (direct) in the range of 0.66–0.69 eV. The cell density of hexagonal A2AgCrCl6 was between 2.97 and 3.93 g cm−3, but with an indirect bandgap of 0.93–1.02 eV. The valence band maximum and the conduction band minimum of A2AgCrCl6 were confirmed to be essentially of Cr(3d) character, but the contributions from the orbital states of Cl(3p) to the VBM were also appreciable. Cubic A2AgCrCl6 (A = Cs, Rb, K) was identified to possess genuine perovskite stoichiometry, evaluated using various geometry-based indices (viz. octahedral factor, tolerance factor, and global instability index). This was not so for A2AgCrCl6 (A = Na, Li), and was due to the small size of Na and Li cations that caused the critical strain of CrCl6 octahedra and a significant decrease in the cell volume. However, all the five A2AgCrCl6 displayed nearly similar optical properties, including the nature of the oscillator peaks in the dielectric function, absorption coefficient, photoconductivity, reflectivity, and Tauc spectra. The zero-limit of the refractive index was calculated around 2.25 and 2.00 for cubic and hexagonal A2AgCrCl6, respectively, and the extinction coefficient was very small for all cases. The nature of the optical bandgap and transition peaks discussed in this study of cubic and hexagonal Cs2AgCrCl6 agreed well with the experiment. The examination of phonon band dispersion led to the conclusion that cubic-A2AgCrCl6 (A = Cs, Rb) are the only halide double perovskites of the entire series that are dynamically stable.
中文翻译：
A2AgCrCl6（A = Li，Na，K，Rb，Cs）卤化物双钙钛矿：一种过渡金属基半导体材料系列，具有明显的光学特性
我们已经从理论上研究了几何形状，立方和六方A的状态和带结构的电子密度2 AgCrCl 6使用元GGA SCAN-（A = CS，RB，钾，钠，锂）痘苗病毒10.优化格密度，发现对于立方A 2 AgCrCl 6，在2.68到4.08 g cm -3之间变化，基本电子带隙（直接）在0.66-0.69 eV的范围内。六角形的A 2 AgCrCl 6的细胞密度在2.97至3.93 g cm -3之间，但间接带隙为0.93–1.02 eV。A 2 AgCrCl 6的价带最大值和导带最小值被证实是本质上具有Cr（3d）特征，但Cl（3p）轨道状态对VBM的贡献也很可观。立方A 2 AgCrCl 6（A = Cs，Rb，K）经鉴定具有真正的钙钛矿化学计量，并使用各种基于几何的指标（即八面体因子，公差因子和整体不稳定性指数）进行了评估。对于A 2 AgCrCl 6（A = Na，Li）并非如此，这是由于Na和Li阳离子的尺寸小，导致CrCl 6八面体的临界应变和细胞体积的显着减少。但是，所有五个A 2 AgCrCl 6显示出几乎相似的光学特性，包括介电函数，吸收系数，光电导率，反射率和Tauc光谱中振荡器峰的性质。立方和六角形的A 2 AgCrCl 6的折射率的零极限分别约为2.25和2.00 ，并且在所有情况下消光系数都非常小。在本研究中，立方和六方Cs 2 AgCrCl 6讨论的光学带隙和跃迁峰的性质与实验非常吻合。对声子带色散的研究得出结论，即立方A 2 AgCrCl 6 （A = Cs，Rb）是整个系列中唯一动态稳定的卤化物双钙钛矿。
更新日期：2020-10-17
中文翻译：
A2AgCrCl6（A = Li，Na，K，Rb，Cs）卤化物双钙钛矿：一种过渡金属基半导体材料系列，具有明显的光学特性
我们已经从理论上研究了几何形状，立方和六方A的状态和带结构的电子密度2 AgCrCl 6使用元GGA SCAN-（A = CS，RB，钾，钠，锂）痘苗病毒10.优化格密度，发现对于立方A 2 AgCrCl 6，在2.68到4.08 g cm -3之间变化，基本电子带隙（直接）在0.66-0.69 eV的范围内。六角形的A 2 AgCrCl 6的细胞密度在2.97至3.93 g cm -3之间，但间接带隙为0.93–1.02 eV。A 2 AgCrCl 6的价带最大值和导带最小值被证实是本质上具有Cr（3d）特征，但Cl（3p）轨道状态对VBM的贡献也很可观。立方A 2 AgCrCl 6（A = Cs，Rb，K）经鉴定具有真正的钙钛矿化学计量，并使用各种基于几何的指标（即八面体因子，公差因子和整体不稳定性指数）进行了评估。对于A 2 AgCrCl 6（A = Na，Li）并非如此，这是由于Na和Li阳离子的尺寸小，导致CrCl 6八面体的临界应变和细胞体积的显着减少。但是，所有五个A 2 AgCrCl 6显示出几乎相似的光学特性，包括介电函数，吸收系数，光电导率，反射率和Tauc光谱中振荡器峰的性质。立方和六角形的A 2 AgCrCl 6的折射率的零极限分别约为2.25和2.00 ，并且在所有情况下消光系数都非常小。在本研究中，立方和六方Cs 2 AgCrCl 6讨论的光学带隙和跃迁峰的性质与实验非常吻合。对声子带色散的研究得出结论，即立方A 2 AgCrCl 6 （A = Cs，Rb）是整个系列中唯一动态稳定的卤化物双钙钛矿。
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