Casañ-Pastor Nieves, Rius Jordi, Vallcorba Oriol, Peral Inma, Oró-Solé Judith, Cook Daniel S, Walton Richard I, García Alberto, Muñoz-Rojas David
Institut de Ciencia de Materials de Barcelona, CSIC, Campus UAB, Bellaterra 08193, Spain.
Alba synchrotron, 08290 Cerdanyola del Valles, Barcelona, Spain.
Dalton Trans. 2017 Jan 24;46(4):1093-1104. doi: 10.1039/c6dt03986c.
AgCuCrO(OH), a new Ag-Cu-Cr-O layered mixed oxide, prepared by soft hydrothermal heterogeneous reactions, is reported. The new phase is an oxyhydroxide and presents a structure with alternating brucite-like Cu-O and Ag-O layers connected by individual chromate groups. The crystallographic structure has been solved and refined from high resolution powder X-ray diffraction data and is supported by density functional theory calculations, yielding a triclinic, space group P1[combining macron], a = 5.3329(1) Å, b = 5.3871(1) Å, c = 10.0735(1) Å, α = 80.476(1)°, β = 87.020(1)°, γ = 62.383(1)°. Bond valence sums suggest the formulation of AgCuCrO(OH), an electronic state fully supported by X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near edge structure (XANES) measurements. AgCuCrO(OH) exhibits bidimensional Cu-O-Cu ferromagnetic correlations that are apparent at much higher temperatures than in other similar Cu-O layered structures, without coupling between Cu-O layers, which represents a unique case in the recent family of silver copper oxides. The role of Ag inducing bidimensionality in copper oxides is therefore expanded further with the presence of chromate anions. Ab initio calculations using density functional theory show that the electronic states involved originate mainly from Cu and OH orbitals, with minor contributions from Cr and the O atoms linking the Cr tetrahedra to the brucitic Cu-O layer, and almost no contribution from Ag. Further modeling of the in-plane magnetic interactions between Cu atoms suggests that the coupled magnetized stripes are responsible for the observed behavior. The results are discussed in relation with previous Ag-Cu mixed oxide phases where metallic behavior or ferro-antiferro transitions had been observed. The structure of this new Ag-Cu-O phase as compared with previous silver copper oxides supports the conclusion that the Ag-Cu layered ordering is favored under oxidizing conditions.
据报道，通过软水热非均相反应制备了一种新型的Ag-Cu-Cr-O层状混合氧化物AgCuCrO(OH)。该新相是一种羟基氧化物，具有由单个铬酸根基团连接的交替的类水镁石型Cu-O和Ag-O层结构。晶体结构已通过高分辨率粉末X射线衍射数据解析和精修，并得到密度泛函理论计算的支持，得到三斜晶系，空间群P1[上加一横]，a = 5.3329(1) Å，b = 5.3871(1) Å，c = 10.0735(1) Å，α = 80.476(1)°，β = 87.020(1)°，γ = 62.383(1)°。键价和表明其化学式为AgCuCrO(OH)，X射线光电子能谱(XPS)和Cr K边X射线吸收近边结构(XANES)测量充分支持了这一电子态。AgCuCrO(OH)表现出二维Cu-O-Cu铁磁相关性，这种相关性在比其他类似的Cu-O层状结构高得多的温度下就很明显，且Cu-O层之间没有耦合，这在最近的银铜氧化物家族中是一个独特的例子。因此，随着铬酸根阴离子的存在，Ag在氧化铜中诱导二维性的作用进一步扩大。使用密度泛函理论的从头算计算表明，所涉及的电子态主要来自Cu和OH轨道，Cr以及将Cr四面体与类水镁石型Cu-O层连接的O原子贡献较小，而Ag几乎没有贡献。对Cu原子之间面内磁相互作用的进一步建模表明，耦合的磁化条纹是观察到的行为的原因。结合先前观察到金属行为或铁-反铁磁转变的Ag-Cu混合氧化物相讨论了这些结果。与先前的银铜氧化物相比，这种新的Ag-Cu-O相的结构支持了在氧化条件下有利于Ag-Cu层状有序排列的结论。
