Le Nestour A, Gaudon M, Villeneuve G, Andriessen R, Demourgues A
Institut de Chimie de la Matière Condensée, UPR 9048 CNRS, Université de Bordeaux I, 87 avenue du Dr A. Schweitzer 33608 Pessac Cedex, France, and Agfa-Gevaert, Septestraat 27 - B-2640 Mortsel, Belgium.
Inorg Chem. 2007 Apr 2;46(7):2645-58. doi: 10.1021/ic062329c. Epub 2007 Feb 10.
Zn1-xCuxAl2O4 (0<or= x <or= 1) compositions have been synthesized by solid-state route, and a color scale going from white (x = 0) to brownish-red (x = 1) with intermediate colors as pale green for x = 0.10 and pale brown for x = 0.30 can be observed. XRD-data refinements on the whole solid solution have allowed defining two critical areas where structural features such as cell parameter and inversion rate as well as cation-oxygen bond distances in 8a and 16d sites of the spinel network exhibit clear unique variations. By observing the direct environment of tetrahedral and octahedral sites potentially occupied by Cu2+ Jahn-Teller cations, the two critical compositions have been estimated to x1 =1/6 and x2 = 4/7. Actually from the x1 and x2 copper contents, the probability of getting Cu2+-Cu2+ pairs involving tetrahedral-octahedral or two octahedral sites respectively is high. Then, the stabilization of Cu2+ JT ions in distorted octahedral site, identified by ESR, is in competition with the occurrence of Cu2+ in tetrahedral sites, and both electronic and steric effects of Cu2+ JT cations lead to the explanation of the evolution of the inversion rate in this series. The study of the optical absorption properties clearly shows that the position and the intensity of the various absorption bands are influenced by the distribution of Cu2+ ions in tetrahedral and octahedral sites, the creation of Cu2+-Cu2+ pairs around the x1 and x2 critical compositions, and the increasing of Cu-O bond covalency. Such an evolution of structural features correlated with electronic properties where various critical compositions have been identified can be generalized to other spinel oxides, considering local distortion around Jahn-Teller ions.
通过固态路线合成了Zn1-xCuxAl2O4（0≤x≤1）组合物，并且可以观察到一个颜色范围，从白色（x = 0）到棕红色（x = 1），中间颜色如x = 0.10时为浅绿色，x = 0.30时为浅棕色。对整个固溶体的XRD数据进行细化，确定了两个关键区域，在这些区域中，尖晶石网络8a和16d位点的结构特征（如晶胞参数、反转率以及阳离子-氧键距离）呈现出明显独特的变化。通过观察可能被Cu2+ Jahn-Teller阳离子占据的四面体和八面体位点的直接环境，估计两个关键组合物的x值分别为x1 = 1/6和x2 = 4/7。实际上，从x1和x2的铜含量来看，分别涉及四面体-八面体或两个八面体位点的Cu2+-Cu2+对出现的概率很高。然后，通过ESR鉴定出在扭曲八面体位点中Cu2+ JT离子的稳定化与四面体位点中Cu2+的出现相互竞争，并且Cu2+ JT阳离子的电子和空间效应共同解释了该系列中反转率的变化。光吸收性质的研究清楚地表明，各种吸收带的位置和强度受四面体和八面体位点中Cu2+离子的分布、x1和x2关键组合物周围Cu2+-Cu2+对的形成以及Cu-O键共价性增加的影响。考虑到Jahn-Teller离子周围的局部畸变，这种与电子性质相关的结构特征演变（其中已确定了各种关键组合物）可以推广到其他尖晶石氧化物。
