Sintering-modified mixed Ni–Co–Cu oxymanganospinels for NTC electroceramics

▶ Cu 0.1Ni 0.8Co 0.2Mn 1.9O 4 ceramics can be modified by high-temperature sintering. ▶ NiO phase serves as effective barrier to inhibit degradation in the ceramics. ▶ Ceramics changes from fine-grained to monolithic with sintering. ▶ Experimental degradation kinetics attains stretched-exponential form. Mixed Ni–Co–Cu oxymanganospinels of Cu 0.1Ni 0.8Co 0.2Mn 1.9O 4 composition with improved functional reliability are first developed for possible application as high-precise NTC thermistors. It is established the amount of additional rock-salt NiO phase in these ceramics, which was not externally introduced at the initial stages of ceramics processing, but extracted during sintering route occurs a decisive role to inhibit the parasitic degradation caused by thermal storage at the elevated temperatures. This effect is well revealed only in ceramics having a character fine-grain microstructure obtained due to injection of small amount of thermally transferred energy, while structural monolithization caused by great value of thermally transferred energy into ceramics bulk reveals an opposite influence. The fact, the ceramics with fine-grain microstructure and large content of rock-salt NiO extractions demonstrate the best suitability for stretched-exponential relaxation kinetics (the most appropriate one for describing degradation kinetics in structurally dispersive solids like ceramics) serves as additional confirmation to the above conclusion.