Enhanced colossal permittivity in mono-doped BaTiO3via particle hydroxylation-induced defect dipoles

Abstract

Hydroxyl defects in oxide particles are often avoided in the development of high-capacity energy storage devices, as they produce structural defects such as intragranular pores and delamination. However, the discovery of electron-pinning defect dipoles has highlighted the significance of a tailored defect distribution in the oxide lattice, wherein oxygen vacancies and Ti³⁺ polarons bind free electrons to defect dipoles and lead to quasi-intrinsic colossal permittivity and low dielectric loss. Inspired by this observation, herein, excess hydroxyl defects are intentionally introduced into BaTiO₃ nanoparticles to induce the formation of electron-pinning sites within the polycrystalline grains. A substantial number of oxygen vacancies are formed during the early stage of sintering. The addition of La³⁺ increases the permittivity by two orders of magnitude (ε_r ≈ 3.5 × 10⁵ at 1 kHz) with moderate dielectric loss (tan δ ≈ 0.06). The high defect concentration inhibits long-range hopping, thereby paving the way for the potential commercialization of ultrafine particles with defects. The present work emphasizes that the proper adjustment of defects, rather than complete elimination, in nanocrystal synthesis is a key approach for manipulating defect dipoles in ferroelectric oxides for high-performance ceramic capacitors and energy storage applications.