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

Area of Science:

• Surface science
• Materials chemistry
• Nanotechnology

Background:

• Mechanical energy can induce chemical transformations at metal oxide interfaces.
• These transformations are relevant to tribochemistry, mechanochemistry, and piezoelectric devices.
• Understanding radical chemistry at nanoparticle surfaces is crucial for these applications.

Purpose of the Study:

• To investigate the early stages of tribochemically initiated radical chemistry in TiO2 and BaTiO3 nanoparticles.
• To analyze the nature and concentration of paramagnetic surface species formed by mechanical activation.
• To compare the mechanochemical response of ferroelectric BaTiO3 with paraelectric TiO2.

Main Methods:

• Uniaxial powder compaction of TiO2 and BaTiO3 nanoparticles at room temperature.
• Analysis of paramagnetic surface species using electron paramagnetic resonance (EPR) spectroscopy.
• Comparison with UV excitation experiments to understand energy transfer mechanisms.

Main Results:

• Mechanical surface activation produced trapped hole centers (O-) and trapped/scavenged electrons (Ti3+, O2-).
• Ferroelectric BaTiO3 nanoparticles exhibited over a 20-fold increase in paramagnetic species yield compared to TiO2.
• Mechanically induced redox processes, supported by flexoelectric effects, were identified as the source of these species.

Conclusions:

• Spontaneous polarization in ferroelectric BaTiO3 significantly enhances mechanochemically induced radical formation.
• Mechanical surface activation in the dark leads to redox processes, similar to UV excitation, but driven by mechanical force.
• Flexoelectric potential differences play a role in supporting mechanically induced charge separation at oxide nanoparticle surfaces.