Modeling of transport properties of interfacially controlled electroceramics: Application to n-conducting barium titanate

Abstract

Grain boundary regions in n-conducting barium titanate (BaTiO 3 ) are re-oxidized during the cooling process after sintering the ceramics in air. The kinetics of this reoxidation process is determined by rapid transport of oxygen along the grain boundaries and slow (rate-determining) diffusion of cation vacancies from the grain boundaries into the grains until the diffusion process is frozen-in. Based on numerical calculations of frozen-in diffusion profiles of cation vacancies at grain boundary regions for various cooling rates, a modified Schottkybarrier model is introduced in order to calculate the grain boundary resistivity as a function of temperature from the Curie-point up to 900°C. A change of the activation energy at approximately 500°C is predicted owing to an enrichment of holes in the space charge layers at elevated temperatures. The modeling results are compared with experimental data for BaTiO 3 -based positive temperature coefficient resistors (PTCRs).

Defect chemistry and relaxation processes: effect of an amphoteric substituent in lead-free BCZT ceramics

“…Many authors have reported that GB resistivity is affected by the presence of surface acceptor states that originate from frozenin cation vacancies and act as conduction electron traps in the immediate vicinity of the grain boundary. 1,47,[54][55][56][57][58][59] Due to the repulsive Coulomb force, electrons are depleted in the near interface region giving rise to a positive space charge layer on either side of the GB core. The space charge layer is comprised of defects with positive effective charge whereas it is depleted of mobile negatively charged carriers.…”

Electrical properties and structure of grain boundaries in n-conducting BaTiO3 ceramics

“…This behaviour could be interpreted previously by means of an extended Schottky-barrier model. 23 Between 250 and 600 • C the activation energy corresponds to the Schottky-barrier height. In accordance with the Heywang model the PTC effect is accompanied by a rapid increase of the Schottky-barrier height at temperatures higher than the Curie-point.…”

Electrothermal Instabilities in Barium Titanate Based Ceramics

“…The validity of Eq. ( 14) well within the NTC regime and up to 900°C has been experimentally verified [31].…”