Spark plasma sintering of MgAl2O4–LaCr0.5Mn0.5O3 composite thermistor ceramics and a comparison investigation with conventional sintering

• MgAl2O4–LaCr0.5Mn0.5O3 composite ceramics have been successfully fabricated by SPS.
• Comparison investigation has been performed on the SPS- and CS-sintered ceramics.
• The NTC electrical properties of these composite ceramics have been investigated.
• The aging mechanism of the thermistor ceramics has been investigated.

The microstructure and negative temperature coefficient (NTC) electrical properties of the MgAl2O4–LaCr0.5Mn0.5O3 composite ceramics prepared by spark plasma sintering (SPS) were investigated. The effects of SPS and conventional sintering (CS) on electrical properties and high temperature aging characteristics of 0.6MgAl2O4–0.4LaCr0.5Mn0.5O3 ceramics were comparatively studied. X-ray diffraction (XRD) results showed both SPS- and CS-sintered ceramics were indexed to be cubic spinel MgAl2O4 phase and orthorhombic perovskite LaCr0.5Mn0.5O3 phase isomorphic to LaCrO3. Microstructural study reveled that SPS-sintered specimens had a higher relative density more than 96%. The electrical properties of the SPS-sintered NTC thermistors could be adjusted by changing MgAl2O4 content and sintering temperature. The SPS-sintered samples possessed a higher resistivity than that from conventionally sintered ceramics. The reasons for the increase of resistivity in the SPS-sintered samples, and the aging mechanism of the thermistor ceramics were investigated through applying the defect chemistry theory.