Defect engineering in rare-earth-doped BaTiO3 ceramics: Route to high-temperature stability of colossal permittivity

High-performance colossal-permittivity (CP) materials have huge potential applications in the miniaturization of electronic components and high-energy storage applications. Here, we report CP behavior in rare-earth Ln-doped BaTiO3 (Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, and Er) ceramics. CP (>1 x 10(5)) and low loss (<5% at 1 kHz) were achieved. Additionally, all ceramic samples with excellent temperature stability over a wide temperature range (25-250 degrees C). X-ray photoelectron spectroscopy verified the existence of point defects (Ti3+ and VO center dot center dot$V_{\rm{O}}<^>{{\rm{ \bullet \bullet }}}$) in Ln-doped BaTiO3 ceramic samples annealed in an N-2 atmosphere. Electron paramagnetic resonance further demonstrated the existence of Ti3+. The coupling of point defects forms an electron-pinned defect-dipoles (EPDD) effect and induces strong hopping polarization. In addition, an internal barrier layer capacitance (IBLC) effect and a surface barrier layer capacitor (SBLC) effect are identified by impedance spectroscopy and DC bias voltage. The CP is attributed to the combined effect of EPDD, IBLC, and SBLC. Furthermore, the high-temperature stability of CP is related to the strong coupling of defect-dipole complexes.