Effect of Internal Pressure and Temperature on Phase Transitions in Perovskite Oxides: The Case of the Solid Oxide Fuel Cell Cathode Materials of the La2-xSrxCoTiO6 Series.
Effect of Internal Pressure and Temperature on Phase Transitions in Perovskite Oxides: The Case of the Solid Oxide Fuel Cell Cathode Materials of the La2-xSrxCoTiO6 Series.
复制标题
内部压力和温度对钙钛矿氧化物相变的影响：以 La2-xSrxCoTiO6 系列固体氧化物燃料电池阴极材料为例。
DOI：
10.1021/acs.inorgchem.6b02066
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发表时间：
2016
影响因子：
4.6
通讯作者：
U. Amador
中科院分区：
文献类型：
--
作者：
Alejandro Gomez;M. Hoelzel;A. Muñoz;F. García;U. Amador
标题化合物La_（2-x）Sr_xCoTiO_（6-δ）的室温结构对称性随x的变化，从P_21/n（0 ≤ x ≤ 0.2）到Pnma（0.3 ≤ x ≤ 0.5）和R_3_（10）c（0.6 ≤ x ≤ 1）。对于x = 1的三个pseudocubic细胞参数变得非常接近，表明过渡到立方结构的Sr含量更高。类似的相变，预计会发生加热，平行的影响，由Sr 2+取代的La 3+引起的内部压力。然而，只有一些上述的转变已经热诱导。本文用自适应模方法对RT ~ 1273 K的中子衍射数据进行了结构修正和拟合。因此，当x = 1时，BO 6八面体的异相倾斜在加热时逐渐消失，并且在1073 K时发现具有Pm 3 m对称性的立方结构。对于较低的Sr含量，这种转变预计发生远高于常见的实验装置的温度限制。的钙钛矿容差因子，t-因子，与Sr含量和温度的演变的分析表明，温度具有有限的能力，以释放结构应力，从而使过渡到更对称的相。当与由Sr取代La引起的内部压力的影响相比时，这是特别真实的。通常暴露于加热-冷却循环的固体氧化物燃料电池的材料中的相变的存在可能具有不利的影响。本工作提出了通过内压化学诱导来稳定钙钛矿氧化物的高对称高温相的策略。
The symmetry of the room-temperature (RT) structure of title compounds La2-xSrxCoTiO6-δ changes with x, from P21/n (0 ≤ x ≤ 0.2) to Pnma (0.3 ≤ x ≤ 0.5) and to R3̅c (0.6 ≤ x ≤ 1). For x = 1 the three pseudocubic cell parameters become very close suggesting a transition to a cubic structure for higher Sr contents. Similar phase transitions were expected to occur on heating, paralleling the effect of internal pressure induced by substitution of La3+ by Sr2+. However, only some of these aforementioned transitions have been thermally induced. The symmetry-adapted modes formalism is used in the structural refinements and fitting of neutron diffraction data recorded from RT to 1273 K. Thus, for x = 1, the out-of-phase tilting of the BO6 octahedra vanishes progressively on heating, and a cubic structure with Pm3̅m symmetry is found at 1073 K. For lower Sr contents this transition is predicted to occur far above the temperature limit of common experimental setups. The analysis of the evolution of the perovskite tolerance factor, t-factor, with both Sr content and temperature indicates that temperature has a limited ability to release structural stress and thus to enable transitions to more symmetric phases. This is particularly true when compared to the effect of internal pressure induced by substitution of La by Sr. The existence of phase transitions in materials for solid oxide fuel cells that are usually exposed to heating-cooling cycles may have a detrimental effect. This work suggests strategies to stabilize the high-symmetry high-temperature phase of perovskite oxides through internal-pressure chemically induced.