[论文解读] Structural, elastic, electronic, bonding, thermo-mechanical and optical properties of predicted NbAlB MAB phase in comparison to MoAlB: DFT based ab-initio insights

Mst. Bina Aktar, F. Parvin+2 more|arXiv (Cornell University)|May 22, 2023

MXene and MAX Phase Materials被引用 6

一句话总结

这项基于第一性原理的DFT研究预测了新型NbAlB MAB相的结构、弹性、电子、化学键合、热机械及光学性质，并与MoAlB进行比较。结果表明，NbAlB化学稳定，机械硬度高（19.0 GPa），因费米能级处态密度高而具有优异导电性，且在紫外吸收和太阳能反射方面性能优于MoAlB，展现出更优的可加工性和电导率。

ABSTRACT

In this study, we have used density functional theory (DFT) based first-principles investigation of the physical properties of prospective NbAlB compound for the first time. From the analysis of the cohesive energy and enthalpy of formation, it was found that NbAlB is chemically stable. The physical properties of NbAlB have been compared and contrasted with those obtained for MoAlB. Both these MAB phases are elastically anisotropic, mechanically stable, machinable and brittle materials. Structural and elastic features reflect the layered features. The estimated hardness of NbAlB is 19.0 GPa comparable to that of MoAlB (20.8 GPa) suggesting that predicted NbAlB is a hard compound and is suitable for heavy duty industrial applications. NbAlB is more machinable than MoAlB. Electronic band structure calculations reveal conventional metallic behavior with the electronic density of states at the Fermi level arising mainly due to the Nb 4d orbitals in NbAlB. The electronic density of states at the Fermi level is significantly higher in NbAlB in comparison to MoAlB, indicating that NbAlB is expected to exhibit higher level of electrical conductivity. Electronic dispersion is highly anisotropic for both MoAlB and NbAlB with substantially large electronic effective masses in the out-of-plane directions. The bonding features have been elucidated via the analysis of the band structure and charge density distribution. Both the compounds have mixed covalent, ionic and metallic bonding characteristics. The Fermi surfaces of MoAlB and NbAlB consists of electron and hole like sheets. The Debye temperatures of MoAlB and NbAlB are comparable. The estimated melting temperature of NbAlB is somewhat lower than that of MoAlB. NbAlB shows excellent reflection characteristics suitable to be used as an efficient solar reflector. NbAlB is also expected to absorb ultraviolet radiation very effectively.

研究动机与目标

• 预测并分析新型NbAlB MAB相的结构与热力学稳定性。
• 比较NbAlB与已知MoAlB相的机械、电子及化学键合特性。
• 评估NbAlB的热机械与光学性质，以探索其在工业和光电应用中的潜力。
• 基于电子结构分析，评估两种MAB相的电导率与各向异性。
• 确定NbAlB在重载涂层和太阳能反射器等高性能应用中的适用性。

提出的方法

• 采用密度泛函理论（DFT）结合广义梯度近似（GGA）进行电子结构计算。
• 通过晶格能和生成焓计算评估NbAlB的热力学稳定性。
• 利用弹性常数张量计算评估机械稳定性、各向异性和硬度（基于Pugh规则计算维氏硬度）。
• 通过电子能带结构、态密度（DOS）及费米面拓扑结构分析，确定电子行为与有效质量。
• 通过电子结构分析评估电荷密度分布与化学键合特征，识别共价、离子与金属键合贡献。
• 利用声子与热力学模型计算德拜温度与熔点；基于介电函数评估光学反射率与紫外吸收性能。

实验结果

研究问题

• RQ1 NbAlB MAB相是否具有热力学稳定性？其稳定性与MoAlB相比如何？
• RQ2 NbAlB的机械性能如何？其硬度、脆性与可加工性与MoAlB相比有何差异？
• RQ3 NbAlB的电子结构与MoAlB有何不同，特别是在费米能级处的态密度与电导率方面？
• RQ4 NbAlB中的化学键合性质如何？其共价、离子与金属键合贡献与MoAlB相比有何差异？
• RQ5 NbAlB的光学与热机械性能如何？其是否可作为高效的太阳能反射器或紫外吸收材料？

主要发现

• NbAlB具有热力学稳定性，负的生成焓与有利的结合能证实其化学稳定性。
• 计算得到的NbAlB维氏硬度为19.0 GPa，与MoAlB（20.8 GPa）相近，表明其在工业应用中具有优异的机械耐久性。
• NbAlB在费米能级处的电子态密度显著高于MoAlB，表明其具有更优的电导率。
• NbAlB与MoAlB均表现出强烈的电子各向异性，且在垂直方向具有较大的有效质量。
• NbAlB与MoAlB的德拜温度相近，表明其晶格振动行为相似。
• NbAlB展现出优异的太阳能反射率与强紫外吸收性能，是太阳能反射器与紫外屏蔽应用的有力候选材料。