Formation Mechanism of Nonohmic Zinc Oxide Ceramics

概要

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For the formation of nonohmic ZnO ceramics based on the system ZnO-Bi_2O_3-Sb_2O_3, the reactions on heating (→) and on slow cooling (←), 2PY+17ZnO [numerical formula] 3X_<zso>+3Bi_2O_3 [L] (1), and X_<zso> [numerical formula] SP (2), play important roles, where PY is Zn_2Bi_3Sb_3O_<14> pyrochlore, X_<zso> a polymorph of Zn_7Sb_2O_<12> [SP] and L is a liquid. Oxide additives markedly influence these reactions and consequently the phases and microstructure of the ceramics, dissolving into the above phases and relating to composition and sintering conditions. In the case of Co, Mn and Cr oxides, the degree of influence is as follows : Co<Mu≲Co+Mu≲Cr<Co+Mn+Cr (3). On heating, those reactions occur at lower temperatures in this order, and finally for Cr oxide the X_<zso> is not formed. On slow cooling after the SP is formed, the reaction (2) and then (1) partially occur only for Co oxide ; for the others, the reaction, 3SP+3Bi_2O_3 [L]→2PY+17ZnO, occurs only partially and the degree of this reaction becomes smaller in that order (3) ; the nonreacting liquid crystallizes into Bi_2O_3-rich phases. On quenching, only the crystallization of the liquid occurs. The formation of various Bi_2O_3-rich phases is related to composition change of the liquid and cooling manner.
社団法人応用物理学会の論文
1980-03-05