Controlling graded microstructures in BaTiO3 with applied electric fields: Reversing grain-size gradients

Graded microstructures form in BaTiO₃ under applied electric fields, with the polarity of the gradient reversing as the voltage increases. At 5 V, grain growth is enhanced on the anode side, whereas at 15 V it shifts to the cathode side. Advanced electron microscopy was employed to characterize grain boundaries (GBs) and clarify the underlying mechanisms. At 5 V, anode-side enhancement is attributed to elevated concentrations of cation vacancies, nonstoichiometric GBs, and/or reduced GB space charges. At 15 V, cathode-side reduction, facilitated by SiO 2 segregation and an increased specimen temperature from Joule heating at this higher applied voltage, induces a GB disordering transition, forming glass-like intergranular films that enhance GB mobility and reverse the polarity of the graded microstructure. These findings reveal new mechanisms of electric-field–induced GB transitions, demonstrate how electric fields can be exploited to tailor microstructures, and advance the fundamental interfacial science of GB phase-like (complexion) transitions. • Grain-size gradients can be created and reversed in BaTiO 3 by electric fields. • Applying a lower voltage of 5 V, grain growth is enhanced at the anode side. • Applying a higher voltage of 15 V, grain growth is enhanced at the cathode side. • Ti cations at grain boundaries (GBs) are reduced at the cathode side under 15 V. • Reduction and SiO 2 segregation promote disordered GBs to enhance grain growth.