Novel defect clusters from density functional theory calculations for colossal dielectric response in In3+ and F− co-doped TiO2 ceramics

In TiO 2 colossal dielectric ceramics co-doped with In 3+ and Nb 5+ , the electron-pinned defect-dipoles effect is strongly influenced by the adjacent and overlapping interaction between diamond ( Nb 2 5 + Ti 3 + A Ti ${\mathrm{Nb}}_{\mathrm{2}}^{{\mathrm{5 + }}}{\mathrm{Ti}}^{{\mathrm{3 + }}}{{\mathrm{A}}}_{{\mathrm{Ti}}}$ (A = Ti 4+ /In 3+ /Ti 3+ )) and triangle ( In 2 3 + V O · · Ti 3 + ${\mathrm{In}}_{\mathrm{2}}^{{\mathrm{3 + }}}V_{\mathrm{O}}^{ \cdot \cdot }{\mathrm{Ti}}^{{\mathrm{3 + }}}$ ) defect clusters. Although acceptor doping introduces oxygen vacancies ( V O · · $V_{\mathrm{O}}^{ \cdot \cdot }$ ) that facilitate the formation of triangular ( In 2 3 + V O · · Ti 3 + ${\mathrm{In}}_{\mathrm{2}}^{{\mathrm{3 + }}}V_{\mathrm{O}}^{ \cdot \cdot }{\mathrm{Ti}}^{{\mathrm{3 + }}}$ ) defect clusters, this doping inevitably results in the presence of additional diamond ( Nb 2 5 + Ti 3 + A Ti ${\mathrm{Nb}}_{\mathrm{2}}^{{\mathrm{5 + }}}{\mathrm{Ti}}^{{\mathrm{3 + }}}{{\mathrm{A}}}_{{\mathrm{Ti}}}$ (A = In 3+ )) defect clusters. Unfortunately, this structure complexity hinders a clear understanding of the intrinsic relationship between the colossal dielectric properties and low-temperature dielectric relaxation associated with individual defect clusters. Therefore, creating novel defect clusters to achieve high electron localization is crucial for the advanced TiO 2 -based ceramics. Herein, a colossal dielectric constant of up to 3.4 × 10 4 and a low dielectric loss of 0.044 are observed at 1 kHz and room temperature for the first time in cation–anion (In 3+ and F − ) co-doped TiO 2 ceramics. Meanwhile, the materials exhibit excellent frequency stability and meet the temperature requirements defined by the X9R standard. Dielectric relaxation associated with electrons in the low-temperature range of 2–30 K is attributed to the generation of novel diamond defect clusters ( In 3 + Ti 4 + F 2 − ${\mathrm{In}}^{3+}{\mathrm{Ti}}^{4+}{\mathrm{F}}_{2}^{-}$ ). Combined with density functional theory calculations, the notable electronegativity of F − promotes electron localization without relying on V O · · $V_{\mathrm{O}}^{ \cdot \cdot }$ -related defect clusters formations. Overall, the study presents a novel strategy for designing next-generation colossal dielectric ceramics.