The phase diagram and tetragonal superstructures of the rare earth cobaltate phases Ln1-xSrxCoO3-δ (Ln = La3+, Pr3+, Nd3+, Sm3+, Gd3+, Y3+, Ho3+, Dy3+, Er3+, Tm3+ and Yb3+)

被引:89
作者
James, M
Cassidy, D
Goossens, DJ
Withers, RL
机构
[1] Australian Nucl Sci & Technol Org, Bragg Inst, Neutron Scattering Grp, Menai, NSW 2234, Australia
[2] Australian Nucl Sci & Technol Org, Mat & Engn Sci, Menai, NSW 2234, Australia
[3] Australian Natl Univ, Res Sch Chem, Canberra, ACT 0200, Australia
基金
澳大利亚研究理事会;
关键词
strontium doped cobaltate; electron diffraction; perovskite superstructure; phase diagram;
D O I
10.1016/j.jssc.2004.01.012
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Single phase perovskite-based rare earth cobaltates (Ln(1-x)Sr(x)CoO(3-sigma)) (Ln = La3+, Pr3+, Nd3+, Sm3+, Gd3+, Dy3+, Y3+, Ho3+, Er3+, Tm3+ and Yb3+; 0.67 less than or equal to x less than or equal to 0.9) have been synthesized at 1100degreesC under 1 atmosphere of oxygen. X-ray diffraction of phases containing the larger rare earth ions La3+, Pr3+ and Nd3+ reveals simple cubic structures; however electron diffraction shows orientational twinning of a local, tetragonal (I4/mmm; a(p) x a(p) x 2a(p)) superstructure phase. Orientational twinning is also present for Ln(1-x)Sr(x)CoO(3-delta) compounds containing rare earth ions smaller than Nd\(3+). These compounds show a modulated intermediate parent with a tetragonal superstructure (14/mmm; 2a(p) x 2a(p) x 4a(p)). Thermogravimetric measurements have determined the overall oxygen content, and these phases show mixed valence (3(+)/4(+)) cobalt oxidation states with up to 50% Co(IV). X-ray diffraction data and Rietveld techniques have been used to refine the structures of each of these tetragonal superstructure phases (Ln=Sm3+-Yb3+). Coupled Ln/Sr and oxygen/vacancy ordering and associated structural relaxation are shown to be responsible for the observed superstructure. (C) 2004 Published by Elsevier Inc.
引用
收藏
页码:1886 / 1895
页数:10
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