Donor-Doped BaTiO

The results of a recent study [30] showed that, compared to the usual relaxation behavior of the undoped counterpart (see Figure 10.12), the relaxation behavior of donor-doped BaTiOs appeared somewhat unusual, and depended on the oxygen activity. 

In order to establish the model of intergranular impedance for doped barium titanate, it is important to notice that miorostructure properties of BaTiOj based materials, expressed in their grain boundary contacts, are of basic importance for electric properties of these materials. The barrier character of the grain boundaries is especially pronounced for doped BaTiOs materials which are used as PTC resistors. Basically two types of dopants can be introduced into BaTiOs large ions of valence 3+ and higher, can be incorporated into Ba positions, while the small ions of valence 5+ and higher, can be incorporated into the Ti sublattice [9-11], Usually, the extent of the solid solution of a dopant ion in a host structure depends on the site where the dopant ion is incorporated into the host structure, the compensation mechanism and the solid solubility limit [12], For the rare-earth-ion incorporation into the BaTiOs lattice, the BaTiOs defect chemistry mainly depends on the lattice site where the ion is incorporated [13], It has been shown that the three-valent ions incorporated at the Ba -sites act as donors, which extra donor charge is compensated by ionized Ti vacancies (V -), the three-valent ions... 

Figure 10.6 Equilibrium total electrical conductivity (a) versus logao of BaTiOs. (a) Undoped, polyc7Stalline BaTi03 [10] (b) Acceptor (1.8mol% AI)-doped single c stalline BaTi03 [28] (c) Donor (1.0 mol% La)-doped polyc stalline BaTlOs [11].

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