Ink-jet printed new core@shell ceramic for high stability NTC thermistors

Mn1.95Co0.21Ni0.84O4‒core@LaMnO3‒shell microbeads were in‒situ processed by an ink‒jet printing method. The composition of the LaMnO3 on the electrical properties compared with the only core Mn1.95Co0.21Ni0.84O4 (MCN) ceramic were studied. X‒ray diffraction analysis showed that the ceramics were composed mainly of cubic spinel NiMn2O4 with rhombohedral perovskite LaMnO3 phase. The X-ray photoelectron spectroscopy (XPS) results explained the ion migration occurred in the composite materials. These ceramics had negative temperature coefficients and B25/50 and Ea values of 1456–5972 K and 0.0814–0.5148 eV, respectively. Moreover, the aging coefficients (△R/R) of the bilayer core@shell structure ceramics were <0.51%, which is much lower than that of uncoated Mn1.95Co0.21Ni0.84O4 microbeads (4.1%). The grain boundaries were verified to dominate important role in the electrical property of the Mn1.95Co0.21Ni0.84O4–core@LaMnO3‒shell ceramics.