Layer structured MAB phases (M=transition metal, A=III_A or IV_A group element, B is boron) are promising ternary borides for high and ultrahigh‐temperature applications. Herein, a new MAB phase Y₅Si₂B₈ consisting of alternative stacking of YB₄ and Y₃Si₂ slabs along the [001] direction is investigated. Density functional theory (DFT) calculations on the electronic structure and chemical bonding reveal that this new MAB phase has diverse chemical bonding and properties similar to MAX phases. The strong covalent bonds in the two‐dimensional B network on (001) plane in the YB₄ slab and between Si atoms on (002) plane in the Y₃Si₂‐slab warrant the high stiffness (E_x=288 GPa) of Y₅Si₂B₈ in the ab plane and the weak Y2‐Si and Y1‐B2 bonds that connecting the YB₄ and Y₃Si₂ slabs underpin the low Young's modulus in [001] direction (E_z=200 GPa). The low shear deformation resistance is due to the presence of the metallic bond and the weak bond within the B₆ octahedral. The possible slip systems are {001}< 100> and {110}< 111> . Based on the low shear modulus (G = 104 GPa) and Pugh's ratio G/B, Y₅Si₂B₈ is predicted as a damage tolerant MAB phase. Y₅Si₂B₈ is also predicted electrically conductive and the conductivity is higher in directions parallel to ab plane. In addition, temperature‐dependent phonon and electron heat capacity are predicted based on the electron and phonon density of states analysis.

中文翻译：

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Y5Si2B8：理论上预测的具有层状晶体结构的新的耐损伤MAB相

层状MAB相（M =过渡金属，A = III _A或IV _A族元素，B是硼）是用于高温和超高温应用的三元硼化物。在此，研究了一种新的MAB相Y ₅ Si ₂ B ₈，该相由YB ₄和Y ₃ Si ₂板沿[001]方向的交替堆叠组成。对电子结构和化学键合的密度泛函理论（DFT）计算表明，这种新的MAB相具有多种化学键合和与MAX相相似的性质。YB _4中（001）平面上二维B网络中的强共价键板和Y ₃ Si ₂板中（002）平面上的Si原子之间，保证了a 5平面中Y ₅ Si ₂ B ₈的高刚度（E _x = 288 GPa）以及较弱的Y2-Si和Y1-B2连接YB ₄和Y ₃ Si ₂平板的键在[001]方向（E _z = 200 GPa）上支撑了低杨氏模量。较低的抗剪切变形性是由于在B ₆八面体中存在金属键和弱键。可能的滑动系统为{001} <100>和{110} <111>。基于低剪切模量（G＝ 104GPa）和Pugh比G / B，Y ₅ Si ₂ B ₈被预测为耐损伤的MAB相。还预测Y ₅ Si ₂ B ₈具有导电性，并且在平行于ab平面的方向上的电导率较高。另外，基于状态分析的电子和声子密度，可以预测与温度有关的声子和电子的热容。