Defect chemistry and colossal dielectric behavior of Nd-modified SrTiO3 lead-free ceramic materials

Colossal permittivity (CP) ceramics have a great potential in the development of miniaturization, integration and lightweight of electronic components. In this work, NdxSr1-xTiO3 (0.000 ≤ x ≤ 0.014) (NST) ceramics are successfully prepared via sintering in N2. Simultaneously microstructure and dielectric properties of NST ceramics are characterized. It can be found that 0.010 ≤ x ≤ 0.014 ceramics show CP (>20000, 20–1 × 106 Hz) and low dielectric loss (<0.04, 20–1 × 106 Hz). In particular, x = 0.010 ceramics exhibit CP (33475, 1 kHz), high insulation resistivity (5.37×108 Ω cm, DC 100 V), low dielectric loss (0.01, 1 kHz) and excellent frequency (20–1 × 106 Hz) and temperature (25–420 °C) stability. In addition, the origin of CP behavior is discussed in NST ceramics based on the characterizations of EPR, XPS, XRD, SEM and complex impedance. The main reason is that the coupling of point defects (TiTi', NdSr⋅, VO⋅⋅) forms the defect dipoles (TiTi'−NdSr⋅, TiTi'−VO⋅⋅−TiTi') and the defect clusters (VO⋅⋅−3TiTi'−NdSr⋅), which produces the electron pinning effect and restricts the long-range movement of the carriers. Additionally, the grain boundary with high insulation resistivity plays a major role in the resistance of ceramics, and it also acts as a high barrier layer to limit the movement of several delocalized carriers.