Effect of Reoxidation on the Grain‐Boundary Acceptor‐State Density of Reduced BaTiO₃ Ceramics

Abstract

KaohsiungTo investigate the effect of reoxidation on the grainboundary acceptor-state density of reduced barium titanate, n-doped BaTiOa ceramics are sintered in a reducing atmosphere (2% H2 + 98% N2) and then annealed in oxygen.After annealing at 1150°C for different times, the experimental results show a relationship between temperatureaveraged acceptor-state density and annealing time as N, = N,,Bt'/" with n between 2 and 3. An inherent acceptorstate density N,, = 4.25 X 10" cm-' is obtained with an increase rate B = 4.8 X 10" cm-2-min-1/3, when n reaches 3. The inherent grain-boundary acceptor states in the reduced n-doped BaTi03 ceramics are believed not due to adsorbed oxygen ions. [

Response characteristics to reducing gases in BaTiO3-based thick films

“…This figure shows that the PTCR effect of samples B and C is higher than that of sample A primarily because of the oxidation at grain boundaries owing to the chemisorbed oxygen during sintering [27][28][29][30]. This observation strongly supports the validity of the Heywang model as an explanation of the PTCR effect in BaTiO 3 ceramics [13][14][15]. Fig.…”

“…This behavior, known as the positive temperature coefficient of resistivity (PTCR) effect, has been substantially investigated owing to the applications of thermistor devices such as TV screens, computer monitors, self-regulated heaters, and current suppressors [11][12][13][14][15]. Theoretical models of the PTCR effect have been proposed by both Heywang [13][14][15] and Jonker [16]. Both theories and experiments reported that the effect is a grain-boundary related phenomenon [13][14][15][16].…”

“…Theoretical models of the PTCR effect have been proposed by both Heywang [13][14][15] and Jonker [16]. Both theories and experiments reported that the effect is a grain-boundary related phenomenon [13][14][15][16]. Since then, the defects of BaTiO 3 and the effects of sintering conditions, porosity, and additives on the PTCR effect have been extensively studied in order to understand the phenomena [17][18][19][20][21].…”

“…The donordoped BaTiO 3 ceramics sintered in air or oxidizing atmosphere exhibit an anomalous increase in electrical resistivity near the ferroelectric Curie temperature (∼120 • C) [7][8][9][10]. This behavior, known as the positive temperature coefficient of resistivity (PTCR) effect, has been substantially investigated owing to the applications of thermistor devices such as TV screens, computer monitors, self-regulated heaters, and current suppressors [11][12][13][14][15]. Theoretical models of the PTCR effect have been proposed by both Heywang [13][14][15] and Jonker [16].…”

Preparation and electrical properties of Ni/(Ba,Sr)TiO3 PTC composite with low resistivity

“…However, such a reducing atmosphere resulted in a poor PTC effect or no PTC effect due to desorption of grain boundary oxygen [12]. In the present work, a mildly reducing atmosphere has been employed.…”