Experimental and theoretical investigations on high-pressure phase transition of Sr2Fe2O5
Experimental and theoretical investigations on high-pressure phase transition of Sr2Fe2O5
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DOI：
10.1007/s00269-013-0604-6
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发表时间：
2014-06
影响因子：
1.4
通讯作者：
Feng Zhu;Ye Wu;X. Lai;S. Qin;Ke Yang;Jing Liu;Xiang Wu
中科院分区：
文献类型：
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作者：
Feng Zhu;Ye Wu;X. Lai;S. Qin;Ke Yang;Jing Liu;Xiang Wu
sr2fe2o5是一种典型的缺氧钙钛矿，在常温条件下采用棕磨矿相（Ibm2，Z= 4）。利用同步辐射x射线衍射金刚石砧细胞技术和第一性原理计算对其高压结构行为进行了研究。实验结果清楚地表明，褐磨矿sr2fe2o5在12.0 GPa和室温下转变为四方钙钛矿型相，然后在23.3 GPa高温退火后转变为sr2mn2o5型相（Pbam，Z= 2）。sr2mn2o5型相在至少60 GPa时是稳定的，在79.1 GPa和~ 2000 K时，它进一步经历向低对称相的可逆转变。理论计算结果不仅证实了sr2fe2o5的四方相与Ba2In2O5（I4/mcm，Z= 4）的高温结构是同质的，而且预测了在6.9 GPa下从棕磨矿相到Ba2In2O5型相，再到19.7 GPa下的sr2mn2o5型相的一系列相变，与实验结果相吻合。Birch-Murnaghan状态方程可以很好地描述sr2mn2o5型相的等温压力-体积关系，实验条件为v0 = 111.6（10） Å3,B0= 122(9) GPa,B0′= 4（固定），理论条件为v0 = 115.8(3) Å3,B0= 92(4) GPa,B0′= 4（固定）。褐铁矿向ba2in2o5型相转变的机制是四配位Fe3+离子在压缩过程中向更高配位位置位移。此外，还预测了从褐铁矿到ba2in2o5型或sr2mn2o5型相的半导体-金属交叉。
Sr2Fe2O5is a typical oxygen-deficient perovskite and adopts brownmillerite phase (Ibm2,Z= 4) at ambient conditions. Its high-pressure structural behavior has been investigated by both synchrotron radiation X-ray diffraction with diamond anvil cell technique and first principles calculations. Experimental results clearly show that the brownmillerite Sr2Fe2O5transforms into a tetragonal perovskite-type phase at 12.0 GPa and room temperature, and then into a Sr2Mn2O5-type phase (Pbam,Z= 2) at 23.3 GPa after high-temperature annealing. The Sr2Mn2O5-type phase is stable up to at least 60 GPa and it further undergoes a reversible transition to a lower symmetry phase at 79.1 GPa and ~2,000 K. The results from theoretical calculation not only confirm that the tetragonal phase of Sr2Fe2O5is isostructural with the high-temperature structure of Ba2In2O5(I4/mcm,Z= 4), but also predict a series of phase transitions from brownmillerite phase to Ba2In2O5-type phase at 6.9 GPa, and then to Sr2Mn2O5-type phase at 19.7 GPa, which coincides with present experiment results. Isothermal pressure–volume relationship of the Sr2Mn2O5-type phase can be well described by the Birch–Murnaghan Equation of State withV0= 111.6(10) Å3,B0= 122(9) GPa,B0′= 4(fixed) experimentally andV0= 115.8(3) Å3,B0= 92(4) GPa,B0′= 4(fixed) theoretically. The transition mechanism from brownmillerite to Ba2In2O5-type phase is the displacement of four-coordinated Fe3+ions to higher coordinated positions upon compression. In addition, a semiconductor-to-metal crossover is predicted from brownmillerite to Ba2In2O5-type or Sr2Mn2O5-type phase.