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首页> 外文期刊>Physical review >Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites
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Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites

机译：氟锰酸盐冰晶石中压力诱导的等对称转变的微观起源

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Using first-principles density functional theory calculations, we investigate the hydrostatic pressure-induced reorientation of the Mn-F Jahn-Teller bond axis in the fluoride cryolite Na_3MnF_6. We find that a first-order isosymmetric phase transition (IPT) occurs between crystallographically equivalent monoclinic structures at approximately 2.15 GPa, consistent with earlier experimental studies. Mode-crystallography analyses of the pressure-dependent structures in the vicinity of the transition reveal a clear evolution of the Jahn-Teller bond distortions in cooperation with an asymmetrical stretching of the equatorial fluorine atoms in the MnF_6 octahedral units. We identify a significant (70%) change in the orbital occupancy of the e_8 manifold of the 3d~4 Mn(Ⅲ) to be responsible for the transition, stabilizing one monoclinic P2_1 variant over the other. The orbital reconstruction as a driving force for the transition is confirmed by analogous calculations of isostructural 3d~0 Na_3ScF_6, which shows no evidence of an IPT up to 6.82 GPa.
机译：使用第一原理密度泛函理论计算，我们研究了在氟化冰晶石Na_3MnF_6中静水压力引起的Mn-F Jahn-Teller键轴的重新定向。我们发现一阶等对称相变（IPT）发生在大约2.15 GPa的晶体学等效单斜晶结构之间，与早期的实验研究一致。过渡附近压力依赖结构的模式晶体学分析表明，与MnF_6八面体单元中的赤道氟原子的不对称伸展相配合，Jahn-Teller键畸变有了明显的发展。我们发现3d〜4 Mn（Ⅲ）的e_8流形的轨道占有率发生显着变化（70％），这是过渡的原因，使一个单斜P2_1 / n变体稳定于另一个变体。轨道重建是过渡的驱动力，通过等构3d〜0 Na_3ScF_6的类似计算得到了证实，没有显示IPT高达6.82 GPa的证据。

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