依赖环境的氢化钛相稳定性:第一性原理预测

Environment-dependent phase stabilities of titanium hydrides:First-principles prediction

在充分考虑所有可能的H原子构型的条件下,构建各种TiH_(x)(x=1-2)相结构,并基于第一性原理能量学,计算评估各相的形成能力及其力学和热力学稳定性,进而构建稳定和亚稳TiH_(x)的相稳定性图。结果显示,很多稳定和亚稳TiH_(x)相具有非常接近的形成能,可能同时共存。这些相的相对稳定性强烈依赖于环境温度(T)和氢分压(p(H_(2)))。在整个感兴趣的T和p(H_(2))范围内,只可能存在γ-TiH和γ-TiH_(2)2种稳定相,以及ε-TiH、γ-TiH_(1.5)、ε-TiH_(1.75)、δ-TiH_(1.75)和ε-TiH_(2)5种亚稳相。这些亚稳相均满足力学稳定性,且在热力学上具有不断吸收或释放H,向平衡相γ-TiH_(2)或γ-TiH发生转化的趋势。

Various phases of TiHx(x=1−2)were constructed,with all possible H-atom configurations being considered.The first-principles energetics calculations were performed to evaluate their formation preference and mechanical and thermodynamic stabilities.All the results were then combined to construct the stable and metastable phase stability diagrams of TiHx.It is suggested that many stable and metastable TiHx phases have very comparable formation energies and thus are likely to co-exist.Their relative stabilities are strongly depended on temperature(T)and the partial pressure of hydrogen(p(H_(2))).Over the entire T and p(H_(2))range of interest,γ-TiH andγ-TiH_(2) are the only two stable phases.ε-TiH,γ-TiH_(1.5),ε-andδ-TiH_(1.75),andε-TiH_(2) can possibly present as metastable phases.These metastable phases are all mechanically stable,and have a thermodynamic tendency to continuously absorb or release H until reaching the equilibrium phases ofγ-TiH_(2) orγ-TiH.