We present an experimental study of the high-pressure, high-temperature behaviour of cerium up to $\sim$22 GPa and 820 K using angle-dispersive x-ray diffraction and external resistive heating. Studies above 820 K were prevented by chemical reactions between the samples and the diamond anvils of the pressure cells. We unambiguously measure the stability region of the orthorhombic \textit{oC}4 phase and find it reaches its apex at 7.1 GPa and 650 K. We locate the $\alpha$-\textit{cF}4 -- \textit{oC}4 -- \textit{tI}2 triple point at 6.1 GPa and 640 K, 1 GPa below the location of the apex of the \textit{oC}4 phase, and 1-2 GPa lower than previously reported. We find the $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 phase boundary to have a positive gradient of 280 K/GPa, less steep than the 670 K/GPa reported previously, and find the \textit{oC}4 $\rightarrow$ \textit{tI}2 phase boundary to lie at higher temperatures than previously found. We also find variations as large as 2-3 GPa in the transition pressures at which the \textit{oC}4 $\rightarrow$ \textit{tI}2 transition takes place at a given temperature, the reasons for which remain unclear. Finally, we find no evidence that the $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 is not second order at all temperatures up to 820 K.

中文翻译：

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铈的高压、高温相图

我们使用角色散 X 射线衍射和外部电阻加热，对高达 $\sim$22 GPa 和 820 K 的铈的高压、高温行为进行了实验研究。超过 820 K 的研究因样品与压力单元的金刚石砧之间的化学反应而被阻止。我们明确地测量正交\textit{oC}4 相的稳定区域，发现它在 7.1 GPa 和 650 K 处达到顶点。我们找到 $\alpha$-\textit{cF}4 -- \textit{oC} 4 -- \textit{tI}2 三相点在 6.1 GPa 和 640 K，低于 \textit{oC}4 相顶点位置 1 GPa，比之前报道的低 1-2 GPa。我们发现 $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 相界具有 280 K/GPa 的正梯度，比之前报道的 670 K/GPa 更小，并找到 \textit{oC}4 $\rightarrow$ \textit{tI}2 相边界位于比以前发现的更高的温度。我们还发现 \textit{oC}4 $\rightarrow$ \textit{tI}2 转变在给定温度下发生的转变压力变化高达 2-3 GPa，其原因尚不清楚。最后，我们没有发现任何证据表明 $\alpha$-\textit{cF}4 $\rightarrow$ \textit{tI}2 在高达 820 K 的所有温度下都不是二阶的。