Giant Volume Change and Topological Gaps in Temperature- and Pressure-Induced Phase Transitions: Experimental and Computational Study of ThMo2 O8.
Giant Volume Change and Topological Gaps in Temperature- and Pressure-Induced Phase Transitions: Experimental and Computational Study of ThMo2 O8.
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DOI：
10.1002/chem.201503839
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发表时间：
2016-01
期刊：
影响因子：
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通讯作者：
B. Xiao;P. Kegler;T. Gesing;L. Robben;A. Blanca-Romero;P. Kowalski;Yan Li;V. Klepov;D. Bosbach;E. Alekseev
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文献类型：
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作者：
B. Xiao;P. Kegler;T. Gesing;L. Robben;A. Blanca-Romero;P. Kowalski;Yan Li;V. Klepov;D. Bosbach;E. Alekseev
通过施加高温（1270 K）和高压（3.5 GPa），ThMo 2 O 8的结构体积和晶体拓扑发生了显著变化，从而形成了意想不到的新ThMo 2 O 8多晶型物（高温/高压（HT/HP）正交ThMo 2 O 8）。与在环境压力下制备的其他三种ThMo 2 O 8多晶型物（单斜晶、斜方晶和六方晶相）相比，猝灭的HT/HP-斜方晶ThMo 2 O 8的摩尔体积减少了近20%。由于这种剧烈的结构转变，当压力释放时，能够维持永久的高压可淬火状态。三个环境ThMo 2 O 8相的晶体结构是基于从角共享ThOx（x=6，8或9）多面体和MoO 4四面体构建的三维（3D）框架。HT/HP-正交相ThMo 2 O 8，然而，结晶在一个新的结构拓扑结构，表现出非常密集的安排ThO 11和MoO 4 +1多面体连接沿着晶体学c轴。这些ThMo 2 O 8多晶型物的所有四个之间的相变被揭开，并充分表征的结构转变，热稳定性，和振动性能。吉布斯自由能的互补第一性原理计算揭示了相变的基本能量学，支持了实验结果。
By applying high temperature (1270 K) and high pressure (3.5 GPa), significant changes occur in the structural volume and crystal topology of ThMo2 O8 , allowing the formation of an unexpected new ThMo2 O8 polymorph (high-temperature/high-pressure (HT/HP) orthorhombic ThMo2 O8 ). Compared with the other three ThMo2 O8 polymorphs prepared at the ambient pressure (monoclinic, orthorhombic, and hexagonal phases), the molar volume for the quenched HT/HP-orthorhombic ThMo2 O8 is decreased by almost 20 %. As a result of such a dramatic structural transformation, a permanent high-pressure quenchable state is able to be sustained when the pressure is released. The crystal structures of the three ambient ThMo2 O8 phases are based on three-dimensional (3D) frameworks constructed from corner-sharing ThOx (x=6, 8, or 9) polyhedra and MoO4 tetrahedra. The HT/HP-orthorhombic ThMo2 O8 , however, crystallizes in a novel structural topology, exhibiting very dense arrangements of ThO11 and MoO4+1 polyhedra connecting along the crystallographic c axis. The phase transitions among all four of these ThMo2 O8 polymorphs are unveiled and fully characterized with regard to the structural transformation, thermal stability, and vibrational properties. The complementary first principles calculations of Gibbs free energies reveal the underlying energetics of the phase transition, which support the experimental findings.