Delocalization and phase transitions in Pr: Theory
Delocalization and phase transitions in Pr: Theory
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Pr 中的离域和相变：理论
DOI：
10.1103/physrevb.65.115105
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发表时间：
2002
影响因子：
3.7
通讯作者：
P. Söderlind
中科院分区：
文献类型：
--
作者：
P. Söderlind
用密度泛函电子结构计算方法研究了Pr在低温下的高压行为。通过这些计算提出了几种相变，它们与现有的实验数据吻合得很好。在低压下，dhcp（Pr-I）→ fcc（Pr-II）转变发生在60 kbar。不考虑计算要求太高的Pr-III相，Pr-II在165 kbar时转变为α-U（Pr-IV）相。后者的转变是伴随着约10%的体积崩溃，并驱动的4f电子在Pr。的轴比（B/a和c/a）和内部参数的Pr-IV的计算作为一个函数的压缩，y和c/a是相当不敏感的压缩，而B/a随压力的增加显着下降。在约1毫巴的一个新的相预测，即体心四轴（bct）结构与c/a轴比为1.78。这个新的阶段是稳定的，以非常高的压力，但在六倍压缩的最终六方密堆积（hep）结构的预测。计算的Pr的高压行为与早锕系元素Pa的高压行为相似。压力引起的4f-轨道重叠、占据和带宽的增加以及与压力的静电库仑相互作用的增加是稳定Pr的高压相的关键组成部分。
Density-functional electronic structure calculations have been used to investigate the high pressure behavior of Pr at low temperature. Several phase transitions are suggested by these calculations and they agree well with available experimental data. At low pressure, a dhcp (Pr-I)→fcc (Pr-II) transition is calculated to occur at 60 kbar. Not considering the Pr-III phase, which is computationally too demanding, Pr-II transforms to the α-U (Pr-IV) phase at 165 kbar. This latter transition is accompanied by a volume collapse of about 10% and is driven by delocalization of the 4f electrons in Pr. The axial ratios (b/a and c/a) and the internal parameter y of Pr-IV were calculated as a function of compression, y and c/a are rather insensitive to the compression whereas b/a decreases significantly with increasing pressure. At about I Mbar a new phase is predicted, namely a body-centered-tetragonal (bct) structure with a c/a axial ratio of 1.78. This new phase is stable up to very high pressures but at a sixfold compression an ultimate hexagonal close-packed (hep) structure is predicted. The calculated high pressure behavior of Pr is similar to that of the early actinide Pa. Pressure induced increase in 4f-orbital overlap, occupation and band width together with an increased electrostatic Coulomb interaction with pressure are the key components in stabilizing the high pressure phases of Pr.