Cation site disorder provides a degree of freedom in the growth of ternary nitrides for tuning the technologically relevant properties of a material system. For example, the band gap of ZnGeN$_2$ changes when the ordering of the structure deviates from that of its ground state. By combining the perspectives of carrier localization and defect states, we analyze the impact of different degrees of disordering on electronic properties in ZnGeN$_2$, addressing a gap in current studies which focus on dilute or fully disordered systems. The present study demonstrates changes in the density of states and localization of carriers in ZnGeN$_2$ calculated using band gap-corrected density functional theory and hybrid calculations on partially disordered supercells generated using the Monte Carlo method. We use localization and density of states to discuss the ill-defined nature of a band gap in a disordered material, comparing multiple definitions of the energy gap in the context of theory and experiment. Decreasing the order parameter results in a large reduction of the band gap in disordered cases. The reduction in band gap is due in part to isolated, localized states that form above the valence band continuum and are associated with nitrogen coordinated by more zinc than germanium. The prevalence of defect states in all but the perfectly ordered structure creates challenges for incorporating disordered ZnGeN$_2$ into optical devices, but the localization associated with these defects provides insight into mechanisms of electron/hole recombination in the material.
Blue-Green Emission from Epitaxial Yet Cation-Disordered ZnGeN$_{2-x}$O$_x$
ZnGeN $_2$提供了InGaN的低成本替代品，具有使用阳离子位点排序进行带隙调谐以跨越绿色带隙的潜力。在阴离子位点上添加氧产生额外程度的电子可调谐性。在这里，我们研究的结构和光电性能的外延ZnGeN $_{2-x}$ O $_{x}$薄膜库的组合共溅射生长的c-Al $_2$ O $_3$。样品表现出X射线衍射图案和X射线极图特征的纤锌矿（阳离子无序）结构与预期的6倍面内对称性。透射电子显微镜揭示了一个半相干界面与周期性位错，缓解应变从大的晶格失配，并确认了面内和面外的晶体取向。室温下的光致发光表现出2.4和2.8 eV之间的峰，这是一致的尖锐的吸收开始观察到的紫外-可见光谱。这些结果证明了光学活性但阳离子无序的ZnGeN $_{2-x}$ O $_{x}$的低成本合成，表明了作为蓝绿色发光体的应用途径。
Evidence for percolation diffusion of cations and material recovery in disordered pyrochlore from accelerated molecular dynamics simulations
我们使用经典和加速分子动力学模拟来表征空位介导的扩散的阳离子在Gd $_2$ Ti $_2$ O $_7$烧绿石作为一个功能的微秒时间尺度上的无序。我们发现，在低水平的无序材料中，阳离子空位扩散是缓慢的。然而，更高水平的无序允许快速的阳离子扩散，然后还伴随着快速的反位湮灭和阳离子的有序化。因此，阳离子扩散率不是恒定的，而是随着材料重新排序而降低。结果表明，快速阳离子扩散是由反位的渗流网络的存在触发的。这与氧扩散形成鲜明对比，氧扩散显示出随着同一化合物中无序度的增加，离子扩散率平稳增加。无序的阳离子扩散系数的增加也与其他复杂氧化物和无序介质模型的观察相反，这表明无序和质量传输之间存在根本不同的关系。这些结果突出了快速阳离子扩散和无序恢复之间的动态相互作用，并具有重要的意义，了解辐射损伤的演变，烧结和老化，以及扩散的无序氧化物更普遍。
Multi-scale model for disordered hybrid perovskites: the concept of organic cation pair modes
我们利用相对论密度泛函理论（DFT）研究了有机-无机杂化钙钛矿$\text{CH}_3^{}\text{NH}_3^{}\text{PbI}_3^{}$的性质。为了我们的分析，我们引入了$\text{CH}_3^{}\text{NH}_3^+$“对模式”的概念，即两个相邻的$\text{CH}_3^{}\text{NH}_3^+$阳离子的特征相对取向。在我们之前的工作[Phys. Rev. B \textbf{94}，045201（2016）]中，我们确定了单个$\text{CH}_3^{}\text{NH}_3^+$阳离子在晶胞中采用的两个优先取向。通过应用对称操作，相关对的总数可以从产生的196个组合减少到仅25个。对几种$2\!\times\!2\!\times\!2$超原胞模型的DFT计算结果揭示了总能量、带隙和能带结构与$\text{CH}_3^{}\text{NH}_3^+$阳离子分布和对模的关系。然后，我们分析了一系列的$4\!\times\!4\!\times\!4$超原胞模型与无序$\text{CH}_3^{}\text{NH}_3^+$阳离子的对模式分布。我们的研究结果表明，对角取向的$\text{CH}_3^{}\text{NH}_3^+$阳离子是罕见的优化$\text{CH}_3^{}\text{NH}_3^{}\text{PbI}_3^{}$超晶胞结构。在…
Coupling Lattice Distortion and Cation Disorder to Control Li-ion Transport in Cation-Disordered Rocksalt Oxides
School of Materials Science and Engineering, Peking University（北京大学材料科学与工程学院）；Zhejiang Key Laboratory of All-Solid-State Battery, Eastern Institute of Technology（宁波东方理工大学全固态电池浙江省重点实验室）；Beijing Key Laboratory of Theory and Technology for Advanced Batteries Materials, Peking University（北京大学先进电池材料理论与技术北京市重点实验室）
Band-Like Transport and Cation Off-Centring in Ag/Bi-Based Solar Absorbers
Inorganic Chemistry Laboratory, University of Oxford（牛津大学无机化学实验室）；Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University（台湾大学光电子学研究所及电气工程系）；Department of Materials, University of Oxford（牛津大学材料系）；Department of Chemistry, University of Manchester（曼彻斯特大学化学系）；Centre for Nano Science and Engineering, Indian Institute of Science（印度科学学院纳米科学与工程中心）；Department of Physics, University of Warwick（华威大学物理系）；Warwick Centre for Ultrafast Spectroscopy, University of Warwick（华威大学超快光谱学中心）；Catalonia Institute for Energy Research (IREC)（加泰罗尼亚能源研究所）；Facultat de Fisica, Universitat de Barcelona（巴塞罗那大学物理学院）；Cavendish Laboratory, University of Cambridge（剑桥大学卡文迪许实验室）；ISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory（科学和技术设施委员会卢瑟福阿普尔顿实验室ISIS中子和缪子源）；Institut Laue-Langevin（朗之万研究所）；School of Chemistry, University of Birmingham（伯明翰大学化学学院）；Departament d'Enginyeria Electrònica i Biomèdica, IN2UB, Universitat de Barcelona（巴塞罗那大学电子与生物医学工程系）；Institute for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH（柏林亥姆霍兹材料与能源研究所太阳能燃料研究所）；Yusuf Hamied Department of Chemistry, University of Cambridge（剑桥大学优素福·哈米德化学系）
Bi-S network origin of cation-disorder stability and dispersive band edges in AgBiS2
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences（中国科学院宁波材料技术与工程研究所）；The Hong Kong University of Science and Technology (Guangzhou)（香港科技大学（广州））；Eastern Institute of Technology（东方理工大学）；Beijing Computational Science Research Center（北京计算科学研究中心）
Anomalous Crystallinity and Magnetism in Chemically Disordered Coherent Heterostructures
The Pennsylvania State University（宾夕法尼亚州立大学）；University of Michigan（密歇根大学）；Virginia Polytechnic Institute and State University（弗吉尼亚理工大学）；Oak Ridge National Laboratory（橡树岭国家实验室）
