Epitaxial TiC (001) layers: Phase formation and physical properties vs C-to-Ti ratio
Epitaxial TiC (001) layers: Phase formation and physical properties vs C-to-Ti ratio
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外延 TiC (001) 层：相形成和物理性能与 C/Ti 比率
DOI：
10.1016/j.actamat.2022.117643
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发表时间：
2022
期刊：
影响因子：
9.4
通讯作者：
Gall, Daniel
中科院分区：
文献类型：
--
作者：
Fang, Peijiao;Mulligan, C.P.;Jia, Ru;Shi, Jian;Khare, S.V.;Gall, Daniel
用反应磁控溅射法在1100℃的Ar/CH4混合气体中在MgO(001)衬底上沉积了碳化钛薄膜，其中CH4的质量分数fCH4=0.04-8%，C/Ti比为0.08-1.8。显微组织以外延岩盐结构TiCx(0 0 1)为主，基体中分别含有二次HCP Ti和石墨质/a-C：H，x≤=0.2 4，x≥=1.5。第一性原理计算表明，立方相中的间隙C可以忽略不计，立方结构的大的平衡相场x=0.50-1，并被熵稳定化扩展到约0.5，在1100℃时，预测的C-在hcp-TiOfx中的溶解度=0.06，测量的驰豫晶格常数从TiC0.5的mao=约0.4304 nm增加到TiC1.0的0.4325 nm，与预测的结果非常一致。然而，盐岩TiCx中C空位和间隙的Dao/dxforx<；0.5和x>；1.0分别比预测的要小得多，证实了第二相的形成，并表明立方相的最小x=100.46。TiC1.0相纯TiCx(001)的硬度和弹性模量值分别从H=24 GPA和H=631 GPA和De=0462 GPA增加，这归因于TiC1.0的成键离子数增加所致。由于二次相软化，硬度和弹性模量值分别随着x&t；0.5和x&>1.0的降低而降低，这可以用均匀应力的有效介质来描述。TiC0.5和TiC1.0的电阻率在298K时分别为168和83μΩ/cm，在77℃时分别为158和72μΩ/cm，这表明电子在x=0.5时的随机阴离子空位上散射，但对于化学计量比的TiC1.0来说，也是主要的缺陷散射。
Titanium carbide films are deposited onto MgO(001) by reactive magnetron sputtering in Ar/CH4mixtures at 1100 °C with a varying CH4fractionfCH4= 0.4–8%, yielding C-to-Ti ratiosx= 0.08–1.8. The microstructure is dominated by an epitaxial rock-salt structure TiCx(001) matrix which contains secondary hcp Ti and graphitic/a-C:H forx≤ 0.24 andx≥ 1.5, respectively. First-principles calculations indicate negligible interstitial C in the cubic phase, a large equilibrium phase-fieldx= 0.5–1 for the cubic structure which is extended tox< 0.5 by entropic stabilization, and a predicted C-solubility in hcp Ti ofx= 0.06 at 1100 °C. The measured relaxed lattice constant increases fromao= 0.4304 nm for TiC0.5to 0.4325 nm for TiC1.0, in excellent agreement with predictions. However, dao/dxforx< 0.5 andx> 1.0 is much smaller than predicted for C vacancies and interstitials in rock-salt TiCx, respectively, confirming secondary phase formation and indicating a minimumx= 0.46 in the cubic phase. The hardness and elastic modulus of phase-pure TiCx(001) increases fromH =24 GPa andE= 304 GPa for TiC0.5toH= 31 GPa andE= 462 GPa for TiC1.0, which is attributed to an increasing bonding ionicity.HandEdecrease withx< 0.5 andx> 1.0 due to secondary phase softening which is well described by an effective medium with homogenous stress. The electrical resistivities for TiC0.5and TiC1.0are 168 and 83 μΩ cm at 298 K, and 158 and 72 μΩ cm at 77 K, indicating electron scattering at random anion vacancies forx= 0.5 but also dominant defect scattering for stoichiometric TiC1.0.