氟锰氧化物晶体中压力诱导等对称相变的微观起源
Microscopic origin of pressure-induced isosymmetric transitions in fluoromanganate cryolites
摘要：
采用第一性原理密度泛函理论计算，研究了流体静压诱导的氟化物冰晶石Na $_3$ MnF $_6$中Mn-F Jahn-Teller键轴的重取向.我们发现一个一阶等对称过渡晶体学等效的单斜结构之间发生在约2.15 GPa，与早期的实验研究一致。对同构$3d^0$ Na $_3$ ScF $_6$的类似计算表明，在6.82 GPa以下没有跃迁的证据。模式晶体学分析的压力依赖的结构在附近的过渡揭示了一个明确的演变的Jahn-Teller键的扭曲与不对称的拉伸的赤道氟原子的MnF $_6$八面体单位的合作。我们确定的$3d^4$扬-泰勒活性锰（III）的$e_g$流形的轨道占有率的变化负责过渡，这稳定了一个单斜$P2_1/n$变体超过其他。
英文摘要：
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$_3$MnF$_6$. We find a first-order isosymmetric transition occurs between crystallographically equivalent monoclinic structures at approximately 2.15 GPa, consistent with earlier experimental studies. Analogous calculations for isostructural $3d^0$ Na$_3$ScF$_6$ show no evidence of a transition up to 6.82 GPa. Mode crystallography analyses of the pressure-dependent structures in the vicinity of the transition reveals 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 change in orbital occupancy of the $e_g$ manifold in the $3d^4$ Jahn-Teller active Mn(III) to be responsible for the transition, which stabilizes one monoclinic $P2_1/n$ variant over the other.
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