Colossal permittivity of (Gd + Nb) co-doped TiO2 ceramics induced by interface effects and defect cluster

High dielectric performance and multifarious polarizations in (Lu + Ta) co-doped TiO2ceramics

“…Meanwhile, the impurity phase of Lu 3 TaO 7 (PDF card: 24-0696) was found in Lu+Ta codoped TiO 2 ceramics at the doping quantity of 0.04. Compared with other co-doped TiO 2 ceramics, Lu+Ta co-doped TiO 2 ceramics has a higher solid solution limit, as shown in Table 1 [18,19,21,[30][31][32][33]. As shown in Figure 1(b), the diffraction peak shifts to a low angle with the increase of x, indicating the lattice expansion.…”

“…This phenomenon is well explained by the increase in electrical conductivity [26]. The change of temperature coefficient of ε (1 kHz) relative to RT should be less than ±15% for X-R type capacitors [30]. The details of the temperature coefficients of the (Lu + Ta) co-doped TiO 2 ceramics were displayed in Figure 3 Complex impedance analysis is an effective method for exploring the electrical conduction information at the grain, grain boundary and electrode interfaces [30].…”

“…The change of temperature coefficient of ε (1 kHz) relative to RT should be less than ±15% for X-R type capacitors [30]. The details of the temperature coefficients of the (Lu + Ta) co-doped TiO 2 ceramics were displayed in Figure 3 Complex impedance analysis is an effective method for exploring the electrical conduction information at the grain, grain boundary and electrode interfaces [30]. The impedance spectra of (Lu 0.5 Ta 0.5 ) x Ti 1-x O 2 ceramics (x = 0.01-0.04) at RT are shown in Figure 4(a).…”

“…The ionic radius of Ti 4+ , Lu 3+ and Ta 5+ are around 0.605 Å, 0.861 Å, and 0.64 Å, respectively. According to the Hume-Rothery rule, a substitution solid solution is more likely to be formed if the mismatch of ionic radii is less than 15% [30]. The mismatch of Lu and Ti ionic radii (|(0.861-0.605)/ 0.605| = 42.0%) is much higher than the infinite solid solution's upper limit while that of Ta and Ti ionic radii (|(0.640-0.605)/ 0.605| = 5.7%) is far lower than the in finite solid solution's limit.…”

“…The low resistance of the grains is associated with the electron hopping between Ti 3+ and Ti 4+ [26]. In addition, the high resistivity of the grain boundary may be caused by the amorphous structure or relatively complete oxidation of grain boundary compared to the grain [30]. In general, the grain boundary resistance R gb and grain resistance R g can be determined by a large semicircular arc at low frequencies and a nonzero intercept on the Z′ axis at high frequencies from the Z* plane plots, respectively [30].…”