Incommensurate structure of GdBaCo2O5+δ (δ∼0.38)
Incommensurate structure of GdBaCo2O5+δ (δ∼0.38)
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DOI：
10.1016/j.jssc.2012.11.004
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发表时间：
2013-02-01
影响因子：
3.3
通讯作者：
Arima, T.
中科院分区：
文献类型：
--
作者：
Ishizawa, N.;Asaka, T.;Arima, T.
用X射线单晶衍射研究了GdBaCo_2O_5 + δ（δ = 0.38）顺磁相的无公度结构。该化合物的基本结构为双层钙钛矿，沿c轴具有[GdO δ]-[CoO 2]-[BaO]-[CoO 2]沿着交替的层序列。该晶体属于五维超空间群P4/mmm（alpha 00）0000（0 alpha 0）0000，alpha=0.3368（1），具有1 x 1 x 2型四元晶胞，alpha=3.8934（1）埃，c=7.5267（1）埃。对于所有观测到的2216个I > 3 sigma（I）的反射，结构被细化到R=0.028，包括331个主反射（R=0.017），1039个观测到的一级卫星（R=0.033）和846个观测到的二级卫星（R=0.045）。该晶体具有仅发生在[GdO δ]层中的氧缺乏;然而，它导致整个晶体中的组成原子的许多位置调制与Co在二价和三价状态之间的价态波动相关联。由于α的值非常接近1/3，因此还使用双调制方法和传统的三维方法研究了该结构，假设P4/mmm对称的3 x 3 x 2超晶胞。这些方法成功地再现了一个总理结构的化合物，由交叉CoO 5金字塔阵列平行于α或B轴。根据键价和和电中性原理，二价和三价钴离子呈有序分布。的不相称的方法也表明可能存在的局部障碍具有结构相似性的高温修改。(c)2012 Elsevier Inc. All rights reserved.
The incommensurate structure of the GdBaCo2O5+delta (delta similar to 0.38) paramagnetic phase was studied using the single-crystal X-ray diffraction. The basic structure of the compound is a double-layered perovskite with an alternating layer sequence of [GdO delta]-[CoO2]-[BaO]-[CoO2] along the c axis. The crystal belongs to the five-dimensional superspace group P4/mmm(alpha 00)0000(0 alpha 0)0000, alpha=0.3368(1), with a 1 x 1 x 2-type tetragonal fundamental unit cell of alpha=3.8934(1) angstrom and c=7.5267(1)angstrom. The structure was refined to R=0.028 for all the observed 2216 reflections with I > 3 sigma(I), including 331 main reflections (R=0.017), 1039 observed first-order satellites (R=0.033), and 846 observed second-order satellites (R=0.045). The crystal has oxygen deficiency that occurs only in the [GdO delta] layer; however, it causes many positional modulations of the constituent atoms throughout the crystal in association with a valence fluctuation of Co between the divalent and trivalent states. Because the value of alpha was very close to 1/3, the structure was also investigated using both the commensurately modulated approach and the conventional three-dimensional approach assuming a 3 x 3 x 2 supercell of P4/mmm symmetry. These approaches successfully reproduced a prime structure of the compound that consists of intersecting CoO5 pyramidal arrays parallel to alpha or b axes. The bond valence sum and the charge neutrality principle suggested that the divalent and trivalent cobalt cations are distributed in an ordered way. The incommensurate approach also indicated the possible presence of a local disorder having a structural similarity with that of a high-temperature modification. (c) 2012 Elsevier Inc. All rights reserved.