Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO₃ ceramics prepared by the reduction‐reoxidation method

Abstract

Ba-excess La-doped BaTiO 3 ceramics have been successfully applied to prepare laminated chip thermistor. Ceramics were firstly fired in a high-purity N 2 flow and then reoxidized in air to obtain positive temperature coefficient of resistivity effect. However, an abnormal reduction trend of room-temperature (RT) resistivity was found to be always beginning at~800°C during reoxidation. This anomaly was found closely correlated with the insulating second phase (Ba 2 TiO 4 ) at grain boundary, which destroyed conducting pathways between semiconducting BaTiO 3 grains. When reoxidation temperature was up to~800°C, the insulating Ba 2 TiO 4 could be gradually consumed and then conducting pathways reestablished leading to RT resistivity reduction. To further prove the proposed explanation, the reoxidation effects of TiO 2 -added ceramics were also studied, in which no Ba 2 TiO 4 existed and certainly the abnormal RT resistivity reduction disappeared. K E Y W O R D S electrical properties, grain boundaries, oxidation resistance, positive temperature coefficient of resistivity

(Ba0.55Sr0.45)1−xLaxTi1.01O3-Bi0.5Na0.5TiO3 Positive Temperature Coefficient Resistivity Ceramics with Low Curie Temperature (~−15 °C)

“…As a result, La 3+ ions are more likely to substitute the A sites in ABO 3 -type structures. Once La substitutes Ba or Sr, defective reactions that may occur, as shown in Equations ( 3)-( 5) [22,23]:…”

“…Based on the research that La-doped BaTiO 3 ceramics show a pronounced PTCR effect [22][23][24], and that a low content of Bi 0.5 Na 0.5 TiO 3 (BNT) could enhance the PTCR effect by increasing the acceptor density states [25][26][27][28][29][30], in this work, (Ba 0.55 Sr 0.45 ) 1−x La x Ti 1.01 O 3 -yBNT PTCR ceramics were designed and fabricated. The aim of this work was to achieve low-Curie-temperature (around −15 • C) PTCR ceramics which possess a large resistance jump, as well as a narrow resistance jump temperature span.…”

Effects of Manganese on Highly Donor-Doped Barium Titanate Ceramics with Resistivity of Positive Temperature Coefficient

“…In recent decades, the technique of reducing sintering was introduced to protect the electrodes of laminated ceramics [36]. In the reducing atmosphere, the ceramic characteristics revealed great differences from the ones sintered in air [37,38]. Also, the donor dopant density was much higher than before [39].…”