The surface transformation and defect evolution of Cu-doped SrTiO₃ upon copper exsolution have been studied by exploiting a multi-technique approach which integrates, for the first time, common methods describing exsolution like XAS, XPS and STEM with unconventional strategies, namely electron paramagnetic resonance (EPR) and UV-Vis diffuse reflectance (UV-DRS). XAS and EPR indicated that copper is present in the matrix in a disordered coordination environment as amorphous Cu₂O and CuO located at the surface and as substitutional Cu²⁺ lattice species with a distorted octahedral structure. Interestingly, EPR unveiled that, during exsolution, Cu²⁺ surface sites with disordered coordination primarily migrate undergoing selective reduction, while a delay is observed for the lattice defects. UV-DRS resulted in a valid alternative to HRTEM to determine the size of exsolved nanoparticles by tracking the plasmon resonance effect. Moreover, when XANES showed the complete regain of the pristine state of Cu after reoxidation, both UV-DRS and EPR highlighted that the original features are not entirely restored. These outcomes suggest that the chemical environment of exsolvable species is much more heterogeneous and the exsolution process much less straightforward than expected. Thus, alternative and original characterization techniques should be exploited to provide a solid methodological benchmark for an effective evaluation of this phenomenon.

中文翻译：

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通过组合光谱方法对 Cu 掺杂 SrTiO3 中的溶出过程进行关键评估


通过利用一种多技术方法研究了铜掺杂 SrTiO₃ 在铜溶解时的表面转变和缺陷演变，该方法首次将描述 XAS、XPS 和 STEM 等常见方法与非常规策略相结合，即电子顺磁共振 （EPR） 和紫外-可见漫反射 （UV-DRS）。XAS 和 EPR 表明，铜在无序配位环境中以位于表面的非晶态 Cu₂O 和 CuO 以及具有扭曲八面体结构的取代 Cu²⁺ 晶格物种的形式存在于基体中。有趣的是，EPR 揭示了在溶解过程中，具有无序配位的 Cu²⁺ 表面位点主要通过选择性还原迁移，而观察到晶格缺陷的延迟。UV-DRS 产生了 HRTEM 的有效替代方案，通过跟踪等离激元共振效应来确定溶解的纳米颗粒的大小。此外，当 XANES 显示 Cu 在再氧化后完全恢复原始状态时，UV-DRS 和 EPR 都强调原始特征并未完全恢复。这些结果表明，可溶出物种的化学环境更加异质，溶出过程远不如预期那么简单。因此，应利用替代和原始的表征技术为有效评估这一现象提供可靠的方法基准。