Nature of the Electronic Charge Carriers Involved in Triboluminescence

Freund, Friedemann

doi:10.1007/978-3-319-38842-7_2

Cited by 2 publications

(1 citation statement)

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“…Friction between metal oxide interfaces can have important implications for surface chemistry and occurs naturally in the course of handling and compaction of nanoparticle powders. While there are a large number of triboinduced phenomena reported for metal oxides, such as tribocharging, triboelectricity, or triboluminescence, − there exists almost no mechanistic and chemical understanding of these processes at the atomistic scale . A major challenge in characterizing contact phenomena in powders is the difficulty in precisely determining the contact area between the particles .…”

Section: Introductionmentioning

confidence: 99%

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

et al. 2021

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Powder compaction-induced surface chemistry in metal oxide nanocrystal ensembles is important for very diverse fields such as triboelectrics, tribocatalysts, surface abrasion, and cold sintering of ceramics. Using a range of spectroscopic techniques, we show that MgO nanocube powder compaction with uniaxial pressures that can be achieved by gentle manual rubbing or pressing ( p ≥ 5 MPa) excites energetic electron–hole pairs and generates oxygen radicals at interfacial defect structures. While the identification of paramagnetic O – radicals and their adsorption complexes with O 2 point to the emergence of hole centers, triboemitted electrons become scavenged by molecular oxygen to convert into adsorbed superoxide anions O 2 – as measured by electron paramagnetic resonance (EPR). By means of complementary UV-photoexcitation experiments, we found that photon energies in the range between 3 and 6 eV produce essentially the same EPR spectroscopic fingerprints and optical absorption features. To provide insights into this effect, we performed density functional theory calculations to explore the energetics of charge separation involving the ionization of low-coordinated anions and surface-adsorbed O 2 – radicals at points of contact. For all selected configurations, charge transfer is not spontaneous but requires an additional driving force. We propose that a plausible mechanism for oxygen radical formation is the generation of significant surface potential differences at points of contact under loading as a result of the highly inhomogeneous elastic deformations coupled with the flexoelectric effect.

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Section: Introductionmentioning

confidence: 99%

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

et al. 2021

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BaTiO₃ Nanoparticle Interfaces in Contact: Ferroelectricity Drives Tribochemically Induced Oxygen Radical Formation

Aicher,

Berger,

Diwald

2024

Langmuir

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Chemical transformations at metal oxide interfaces that are triggered by mechanical energy set the basis for applications in the fields of tribo-and mechanochemistry, ceramic and composite processing, and piezoelectric devices. We investigated the early stages of tribochemically initiated radical chemistry of structurally well-defined TiO 2 and BaTiO 3 nanoparticles in argon or in oxygen atmosphere. Electron paramagnetic resonance spectroscopy enabled the determination of the chemical nature and concentration of paramagnetic surface species which form upon uniaxial powder compaction at room temperature. Trapped hole centers (O − ) as well as trapped or scavenged electrons (Ti 3+ or O 2 − , respectively) were analyzed as products of mechanical surface activation. For ferroelectric BaTiO 3 nanoparticles, we found that the spontaneous polarization effects of the oxide lattice increase the yield of paramagnetic surface species by a factor >20 as compared to paraelectric TiO 2 nanoparticles. Comparison with UV excitation experiments, where the energy required to drive the corresponding charge separation phenomena is hν ≥ 3.2 eV, indicates that the paramagnetic species that originate from uniaxial powder compaction in the dark result from mechanically induced surface redox processes that are supported by local flexoelectric potential differences.

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Nature of the Electronic Charge Carriers Involved in Triboluminescence

Cited by 2 publications

References 31 publications

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

BaTiO₃ Nanoparticle Interfaces in Contact: Ferroelectricity Drives Tribochemically Induced Oxygen Radical Formation

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Nature of the Electronic Charge Carriers Involved in Triboluminescence

Cited by 2 publications

References 31 publications

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

Rubbing Powders: Direct Spectroscopic Observation of Triboinduced Oxygen Radical Formation in MgO Nanocube Ensembles

BaTiO3 Nanoparticle Interfaces in Contact: Ferroelectricity Drives Tribochemically Induced Oxygen Radical Formation

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BaTiO₃ Nanoparticle Interfaces in Contact: Ferroelectricity Drives Tribochemically Induced Oxygen Radical Formation