Core–shell NTC materials with low thermal constant and high resistivity for wide‐temperature thermistor ceramics

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 coreshell 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 widetemperature NTC thermistor ceramics. K E Y W O R D S ceramic matrix composites, core-shell structures, electrical properties, NTC thermistors 4394 | LIU et aL.

Enhanced aging and thermal shock performance of Mn1.95-xCo0.21Ni0.84SrxO4 NTC ceramics

“…8b). One should note that the MCNS spinel phase contains Mn element with different valence states, which facilitates electron (5) where Noct refers to the concentration of octahedral sites per cubic centimeter, d represents the jumping distance for charge carriers, υ0 denotes the lattice vibrational frequency, which is associated with conduction, k refers the Boltzmann constant, e represents the electronic charge, N denotes the concentration of per formula unit of sites, which are available for the charge carriers, NC (1-C) is related to the number of Mn 3+ and Mn 4+ cations at octahedral sites and Ea refers to the hopping energy. Furthermore, XPS analysis was carried out to quantify the Mn 3+ /Mn 4+ couple and clarify the mechanism of resistivity variation.…”

“…Negative temperature coefficient (NTC) ceramic thermistors based on mixed-valence transition manganites are being widely employed in temperature sensors, temperature controllers, time delay, voltage regulators and infrared detectors [1][2][3][4][5].…”

“…The electrical properties of spinel Mn3O4, doped with different transition metals (Co, Ni, Zn, Fe, Cu) cations, are mainly influenced by the Mn 3+ /Mn 4+ couple at B-sites and changed with dopant content [2,[4][5][6]8]. Moreover, a ternary spinel compound, i.e., (Mn3-x-yCoxNiy)O4(MCN), renders promising electrical properties due to simple fabrication and outstanding thermistors properties [9].…”

Enhanced aging and thermal shock performance of Mn1.95-xCo0.21Ni0.84SrxO4 NTC ceramics

“…Negative temperature coefficient (NTC) ceramic thermistors based on mixed-valence transition manganites are being widely employed in temperature sensors, controllers, infrared detectors, time delay and voltage regulators [1][2][3][4][5][6][7][8].…”

“…The electrical properties of spinel Mn 3 O 4 , doped with different transition metals (Co, Ni, Zn, Fe, Cu) cations, are mainly influenced by the Mn 3+ /Mn 4+ couple at B-sites and changed with dopant content [2,[4][5][6]8]. Moreover, a ternary spinel compound, i.e., (Mn 3-x-y Co x Ni y )O 4 (MCN), renders promising electrical properties due to easy fabrication and outstanding thermistors properties [9].…”