X-ray diffraction and infrared spectra studies of FexMn2.34?xNi0.66O4 (0 < x < 1) NTC ceramics

Series of Fe_xMn_2.34?xNi_0.66O₄ (0 < x < 1) NTC ceramics were prepared by the Pechini method. Resistivity, thermal constant (B) and aging values were measured. It was found that the resistivity increased with increasing iron content x. The B value however first decreased with increasing x in the range of x < 0.6 and then increased with further increase in x. Aging reached a maximum in the middle range (x = 0.4–0.6) of iron content. X-ray diffraction (XRD) and infrared analysis were used to determine the distribution of Fe³⁺ ions. The Fe³⁺ ions were found to occupy both A- and B-site when x < 0.6 and then go to B-site when x > 0.6. An redistribution of the Fe³⁺ ions between A- and B-site was related to the aging of the NTC thermistor.