The surface transformation and defect evolution of Cu-doped SrTiO_(3)upon copper exsolution have been studied by exploiting a multi-technique approach which integrates,for the first time,common methods describing exso...The surface transformation and defect evolution of Cu-doped SrTiO_(3)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 Cu_(2)O and CuO located at the surface and as substitutional Cu^(2+)lattice species with a distorted octahedral structure.Interestingly,EPR unveiled that,during exsolution,Cu^(2+)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.展开更多
基金funded by the European Union-NextGenerationEU,Italian National Recovery and Resilience Plan,Mission 4,Component 2,Investment 1.5“Innovation Ecosystems”,project MUSA(grant No.ECS 000037)funding support from BMBF(SITCOM project,grant No.05K22GU3)the DFG(grant No.MA-7146-7-1).
文摘The surface transformation and defect evolution of Cu-doped SrTiO_(3)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 Cu_(2)O and CuO located at the surface and as substitutional Cu^(2+)lattice species with a distorted octahedral structure.Interestingly,EPR unveiled that,during exsolution,Cu^(2+)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.
