Microwave frequency behavior of the EPR copper(II) ion pairs spectrum formed in CuCe oxide
Microwave frequency behavior of the EPR copper(II) ion pairs spectrum formed in CuCe oxide
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DOI：
10.1021/cm00023a008
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发表时间：
1992-09
影响因子：
8.6
通讯作者：
A. Aboukaïs;A. Bennani;C. Aissi;M. Guelton;J. Védrine
中科院分区：
文献类型：
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作者：
A. Aboukaïs;A. Bennani;C. Aissi;M. Guelton;J. Védrine
两个信号 A1 和 A2 对应于 CeO2 中孤立的单体 Cu2+ 离子。第一个与具有四方扭曲的八面体位点中的铜 (II) 物质相关。从 EPR 参数可以看出，这些 Cu2+ 单体离子（AJ 是二氧化铈中铜 (II) 离子对的前体。另一个信号（A2 信号）归因于位于具有方锥体对称性的表面取代位点的 Cu2+ 离子。我们之前还注意到 A2 信号在 X 和 Q 频段频率均获得，而 仅在 X 波段光谱中观察到半场信号（图 1）。如前所述，当制备原子比 Cu/Ce= 2 的 CuCe 氧化物样品并在 1173 K 下煅烧时，X 波段 EPR 光谱主要由 K 和 A2 信号形成，显然没有观察到 Al 信号的痕迹（图 2a）。与 CuCe 氧化物中观察到的相反 (Cu/Ce= 0.01) X波段谱图，A2信号的相对强度弱于K二聚体信号。当记录该固体的 Q 带光谱时（图 2b），A2 信号的强度变得大于 K，并且观察到 Aj 信号的强度较弱。
Two signals, A1 and A2, correspond to isolated monom-eric Cu2+ ions in Ce02. The first one has been correlated with copper (II) species in octahedral sites with a tetragonal distorsión. From EPR parameters, it has been shown that these Cu2+ monomeric ions (AJ are the precursors of the copper (II) ion pairs in ceria. The other one (A2 signal) has been attributed to Cu2+ ions localized in surface substi-tutional sites with a square-pyramidal symmetry. We have also noticed previously2 that the A2 signal has been obtained at both X-and Q-band frequencies, whereas the half-field signal has been observed only in the X-band spectrum (Figure 1).When a CuCe oxide sample with an atomic ratio Cu/Ce= 2 was prepared and calcined at 1173 K as indicated previously, the X-band EPR spectrum is mainly formed of the K and A2 signals, and apparently no trace of the Al signal is observed (Figure 2a). Contrary to that observed in CuCe oxide (Cu/Ce= 0.01) X-band spectrum, the relative intensityof the A2 signal is weaker than K dimer signal. When the Q-band spectrum of this solid is recorded (Figure 2b), the intensityof the A2 signal becomes larger than K and the Aj signal is observed with a weak intensity.