Field enhanced bulk conductivity of acceptor-doped BaTi1−xCaxO3−x ceramics

Abstract

The electrical properties of Ca-doped BaTiO3 are very different when Ca substitutes onto Ba or Ti sites. The p-type semiconductivity of Ti-substituted ceramics increases reversibly by one to two orders of magnitude under a dc-bias voltage of ≤100 V cm−1, whereas Ba-substituted ceramics show little sensitivity to a dc bias. This increase in BaTi1−xCaxO3−x, studied over the temperature range 150–600 °C, is independent of electrode material and atmosphere and is attributed to ionization of underbonded O2− ions adjacent to acceptor-doped Ca2+ ions.

Semiconductor‐Insulator Transition in Undoped Rutile, TiO2, Ceramics

“…Thus, during slow cool, oxygen molecules absorb on the sample surface and ionize, with or without associated dissociation, by withdrawing electrons from the Ti 3d conduction band and create a depletion layer that extends into the sample interior. We do not know whether the oxygen molecules dissociate and ionize completely to give O 2− ions, or whether they remain on the sample surface as, for example, superoxide ions O 2 − …”

Non‐ohmic phenomena in Mn‐doped BaTiO3

“…Nonlinear low‐field behaviour has been observed recently 1–3 in p ‐type, acceptor‐doped BaTiO 3 ceramics in which the resistance decreased by 1–2 orders of magnitude on application of a small bias voltage, typically in the range 1–10 V, across pellets of thickness 1–2 mm; the resistance decrease was fully reversible on removal of the dc bias and was not associated with interfacial effects such as Schottky barriers. The rate of change of resistance with time was very temperature‐dependent.…”

Preparation and characterization of barium titanate stannate solid solutions

“…[35] and it was explained in terms of a non-Debye polar polydispersive relaxation; (iii) Anomalies of the imaginary part of permittivity above 10 4 Hz for all the compositions (Fig. 6b), which seems to be related to a Debye-type relaxation process with characteristic frequencies in the range of 10 6 -10 7 Hz, whose distribution of relaxation times strongly increases with Sn addition and tends to a glassy state for x ≥ 0.20, due to the freezing of the nanopolar regions [37]; (iv) At high frequencies (not shown in the Figure) The dielectric relaxations of the present ceramics are rather complex phenomena, due to the overlapped multiple contributions from: (a) the ferroelectric-relaxor crossover and its associated dipolar relaxation mechanisms which are expected to modify when increasing Sn addition (b) the charged defect-related relaxations caused by the oxygen vacancies present in the perovskite solid solutions which might be different in various ceramic samples [36] (c) grain core-grain boundary inhomogeneities of the electrical properties (grain boundary phenomena) [37,38] and other possible effects, imposing a more detailed study which is beyond of the purpose of the present work.…”