Abstract
The Mn1.95−xCo0.21Ni0.84SrxO4 (MCNS) (0 ≼ x ≼ 0.15) based negative temperature coefficient (NTC) materials are prepared by co-precipitation method. The replacement of Mn by Sr plays a critical role in controlling the lattice parameter, relative density, microstructure, and electrical properties. The lattice parameter and relative density increase with the increase of Sr content. A small amount of Sr restrains the grain growth and increases the bulk density. Moreover, the room resistivity ρ25, material constant B25/50, activation energy Ea, and temperature coefficient α values of MCNS ceramics are influenced by the Sr content and ranged in 1535.0–2053.6 Ω·cm, 3654–3709 K, 0.3149–0.3197 eV, and (−4.173%)–(−4.111%), respectively. The X-ray photoelectron spectroscopy (XPS) results explain the transformation of MCNS ceramics from n- to p-type semiconductors. The conduction could arise from the hopping polaron between Mn3+/Mn4+ and Co2+/Co3+ in the octahedral sites. The impedance data analysis also discusses the conduction mechanism of the MCNS ceramic, whereas grain resistance dominates the whole resistance of the samples. Furthermore, the aging coefficient (ΔR/R) of MCNS ceramics is found to be < 0.2%, which indicates the stable distribution of cations in the spinel. Finally, the MCNS ceramics demonstrate excellent thermal durability with < 1.3% of resistance shift after100 thermal shock cycles.
Highlights
IntroductionThe electrical properties of spinel Mn3O4, doped with different transition metal (Co, Ni, Zn, Fe, Cu) cations, are mainly influenced by the Mn3+/Mn4+ couple at B-sites www.springer.com/journal/40145
Negative temperature coefficient (NTC) ceramic therm-The electrical properties of spinel Mn3O4, doped with different transition metal (Co, Ni, Zn, Fe, Cu) cations, are mainly influenced by the Mn3+/Mn4+ couple at B-sites www.springer.com/journal/40145J Adv Ceram 2021, 10(2): 258–270 and changed with dopant content [2,4,5,6,8]
The DTA curve exhibits an endothermic peak at 125 °C, and an initial weight loss of 5.07% in the temperature range from room temperature (RT) to 200 °C, which can be ascribed to the removal of water adsorbed by hydroxide and crystal lattice
Summary
The electrical properties of spinel Mn3O4, doped with different transition metal (Co, Ni, Zn, Fe, Cu) cations, are mainly influenced by the Mn3+/Mn4+ couple at B-sites www.springer.com/journal/40145. The electrical properties of MCN can be tuned by doping small-sized transition metals at B-sites, such as Fe, Zn, and Cu [2,8,11,12]. Mohapatra et al [13] have synthesized Sr-substituted polycrystalline LiFe5O8 spinel by solid-state method, resulting in improved dielectric and magnetic properties. Liao et al [19] have synthesized multi-walled carbon nanotubes (MWCNTs)-enhanced Si2BC3N ceramics by spark plasma sintering (SPS) and demonstrated improved thermal stress resistance due to the presence of MWCNTs. It can be concluded that the formation of microcracks or pores under thermal shock greatly influences the electrical properties of NTC ceramic thermistors. The thermal shock testing is used to characterize the thermal stability of ceramic materials
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