MAX phases have attracted increased attention due to their unique combination of ceramic and metallic properties. Point-defects are known to play a vital role in the structural, electronic and transport properties of alloys in general and this system in particular. As some MAX phases have been shown to be stable in non-stoichiometric compositions, it is likely that such alloying effects will affect the behavior of lattice point defects. This problem, however, remains relatively unexplored. In this work, we investigate the alloying effect on the structural-stability, energy-stability, electronic-structure, and diffusion barrier of point defects in MAX phase alloys within a first-principles density functional theory framework. The vacancy (V$_{M}$, V$_{A}$, V$_{X}$) and antisite (M-A; M-X) defects are considered with M and A site disorder in (Zr-M)$_{2}$(AA${'}$)C, where M=Cr,Nb,Ti and AA${'}$=Al, Al-Sn, Pb-Bi. Our calculations suggest that the chemical disorder helps lower the V$_{A}$ formation energies compared to V$_{M}$ and V$_{X}$. The V$_{A}$ diffusion barrier is also significantly reduced for M-site disorder compared to their ordered counterpart. This is very important finding because reduced barrier height will ease the Al diffusion at high-operating temperatures, which will help the formation of passivating oxide layer (i.e., Al$_{2}$O$_{3}$ in aluminum-based MAX phases) and will slow down or stop the material degradation. We believe that our study will provide a fundamental understanding and an approach to tailor the key properties that can lead to the discovery of new MAX phases.
Lattice vacancy migration barriers in Fe-Ni alloys, and why Ni atoms diffuse slowly: An ab initio study
United Kingdom Atomic Energy Authority（英国原子能管理局）；University of Warwick（华威大学）；H.H. Wills Physics Laboratory, University of Bristol（布里斯托大学H.H.威尔斯物理实验室）；Northeastern University（东北大学）
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）
Extreme Fermi surface smearing in a maximally disordered concentrated solid solution
我们发现，费米面可以生存的等原子合金Ni $_{0.25}$ Fe $_{0.25}$ Co $_{0.25}$ Cr $_{0.25}$中的极端成分无序的存在。我们的高分辨率康普顿散射实验揭示了一个费米表面，这是涂抹在一个显着的分数的布里渊区（高达40\%的$\frac{2π}{a}$）。这种涂抹的程度和它的变化上和之间的费米表面的不同片已被确定，和估计的电子平均自由程和剩余电阻率已通过连接这种涂抹与准粒子状态的相干长度。
