发表机构
National Institute for Materials Science（物质材料研究机构）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过X射线衍射和第一性原理计算，发现钛的α相在低温下呈现较小的c轴负热膨胀，而ω相近似各向同性膨胀，并获得了精确的德拜温度和Grüneisen参数。
AI 中文摘要
我们通过从约5 K到300 K的X射线衍射测量，并结合第一性原理计算，研究了钛的α相和高压多形体ω相的低温热膨胀。在7.7 GPa和500 °C条件下合成了单相块体多晶ω-Ti，并将其回收至环境压力。尽管这两个相表现出非常相似的体积热膨胀，但其轴向响应却显著不同。在α-Ti中，c轴热膨胀系数在约50 K以下变为负值，并在20 K时达到最小值-0.71 × 10⁻⁶ K⁻¹。实验和理论均表明，c轴负热膨胀明显小于先前从单晶长度测量中报道的值。相比之下，ω-Ti沿a轴和c轴几乎各向同性地膨胀，其c/a比几乎与温度无关，且接近理想的体心立方衍生值。α-Ti的c/a比随温度升高而减小。Debye-Grüneisen分析得出α-Ti和ω-Ti的德拜温度分别为427 ± 5 K和409 ± 12 K，有效Grüneisen参数分别为1.33 ± 0.04和1.23 ± 0.04。第一性原理计算重现了这两个相的体积热膨胀，并捕捉了其轴向响应的总体趋势。
英文摘要
We investigated the low-temperature thermal expansion of the $α$ phase and the $ω$ phase, a high-pressure polymorph of titanium, by X-ray diffraction measurements from approximately 5 to 300 K, together with first-principles calculations. Single-phase bulk polycrystalline $ω$-Ti was synthesized at 7.7 GPa and 500 $^\circ$C and recovered to ambient pressure. Although the two phases exhibit very similar volumetric thermal expansion, their axial responses are markedly different. In $α$-Ti, the $c$-axis thermal expansion coefficient becomes negative below approximately 50 K and reaches a minimum of $-0.71 \times 10^{-6}$ K$^{-1}$ at 20 K. Both experiment and theory indicate substantially smaller $c$-axis negative thermal expansion than previously reported from single-crystal length measurements. In contrast, $ω$-Ti expands nearly isotropically along the $a$ and $c$ axes, and its $c/a$ ratio remains nearly temperature independent and close to the ideal bcc-derived value. The $c$/$a$ ratio of $α$-Ti decreases with increasing temperature. Debye-Grüneisen analysis yielded Debye temperatures of $427 \pm 5$ K and $409 \pm 12$ K and effective Grüneisen parameters of $1.33 \pm 0.04$ and $1.23 \pm 0.04$ for $α$-Ti and $ω$-Ti, respectively. The first-principles calculations reproduce the volumetric thermal expansion of both phases and capture the overall trends of their axial responses.
Comments28 pages, 2 tables, 6 Figures
