Relation between nonlinearity and semiconducting characteristics of SrCoO₃ additive in ZnO varistors sintered in a reducing atmosphere

Abstract

Air-sintered SrCoO 3 is strongly reduced at 1020°C in P O2 = 1.6 © 10 ¹9 MPa and then post-annealed at various temperatures in air. The conductive and structural characteristics are examined, comparing them with those of air-sintered. Although annealing in a reducing atmosphere breaks down SrCoO 3 to several compounds, SrCoO 3 is re-synthesized by post-annealing above 800°C. When post-annealed at 1000°C, the oxidation state of SrCoO 3 is believed to be the same higher level as that of sintered in air. The result shows that, enhancement of p-type carriers in SrCoO 3 at grain boundaries leads to nonlinearity improvement of SrCoO 3 -doped ZnO varistors sintered in reducing atmospheres.

Barrier formation of single junctions with oxidation in SrCoO₃-doped ZnO varistors sintered in a reducing atmosphere

“…7) Conductive characteritics of SrCoO 3 post-annealed at various temperatures were quoted from our previous study. 12) 3. Results and discussion 3.1 V-I characteristics for single junctions sintered in a reducing atmosphere Shown in Fig.…”

“…From the results of SrCoO 3 -doped ZnO varistors by reduced sintering, we discuss variations of the electrical barrier state and bulk properties with oxidation at grain boundaries. Journal of the Ceramic Society of Japan 127 [12] 912-917 2019 V 1mA ·mm ¹1 , V gb and ¡ 10¯A of bulks are listed on Table 1 for comparison with those values obtained with microprober measurements. V 1mA ·mm ¹1 is calculated from V 1mA normalized by unit thickness of bulk-bodies.…”

“…Thus, we have investigated the relation between nonlinear characteristics (¡ max and V ¡max ) of single junctions and conductivity of SrCoO 3 with various post-annealing temperatures. 12) The results are shown in Fig. 7.…”

“…As reported in the previous study, p-type carrier concentration in SrCoO 3 at grain boundaries is enhanced by the post-annealing effect after decreased with reduction sintering, providing nonlinear properties. 12) This suggests that the formation of potential barriers originates from an increase of p-type carriers of SrCoO 3 at grain boundaries. Thus, we have investigated the relation between nonlinear characteristics (¡ max and V ¡max ) of single junctions and conductivity of SrCoO 3 with various post-annealing temperatures.…”

“…10) Nonlinearity in varistors sintered in a reducing atmosphere is provided with increasing p-type carriers in SrCoO 3 at grain boundaries, due to postannealing effect. 11), 12) However, behaviors of individual single grain boundaries have yet to be revealed in the microstructure. Thus, we evaluated the variation in nonlinearity of many single grain boundaries in SrCoO 3 -doped ZnO varistors by the direct measurement using a nano-prober system as reported in our previous study.…”