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Core–shell NTC materials with low thermal constant and high resistivity for wide‐temperature thermistor ceramics
Author(s) -
Liu Ting,
Zhang Huimin,
Ma Panfei,
Chang Aimin,
Jiang Hui
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16418
Subject(s) - thermistor , ceramic , materials science , temperature coefficient , electrical resistivity and conductivity , sintering , shell (structure) , thermal stability , analytical chemistry (journal) , composite material , mineralogy , metallurgy , chemical engineering , chemistry , electrical engineering , engineering , chromatography
Abstract Core–shell structures have been proposed to improve the electrical properties of negative‐temperature coefficient (NTC) thermistor ceramics. In this work, Al 2 O 3 ‐modified Co 1.5 Mn 1.2 Ni 0.3 O 4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate‐chelation followed by conventional sintering. Co 1.5 Mn 1.2 Ni 0.3 O 4 powder was coated with a thin Al 2 O 3 shell layer to form a core–shell structure. Resistivity ( ρ ) increased rapidly with increasing thickness of the Al 2 O 3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 ceramic with 0.08 wt% Al 2 O 3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as‐prepared Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 NTC ceramics with a core–shell structure may be promising candidates for application as wide‐temperature NTC thermistor ceramics.