Manganese double substituted pyrochlore type semiconducting oxides for high temperature NTC thermistor applications

The effect of simultaneous substitution of Mn in both A and B sites of the pyrochlore type semiconducting oxides: (CaCe_1?2x Mn_2x )(Sn_1?x Mn _x Nb)O_7?δ (x = 0, 0.1, 0.2, 0.3 and 0.4) was studied by employing powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and electrical conductivity measurements. Besides the structural confirmation, Raman spectroscopy studies revealed the increased local disordering in the structure with progressive Mn substitution which is not observable in X-ray diffraction studies. The conductivity measurements confirm the negative temperature coefficient (NTC) behavior of the samples. Grain boundary dominant electrical characteristics have been observed in compounds with higher Mn concentration. Thermistor constant of the system lies in the range 6,700–8,500 K and the sensitivity values are in the range ?1 to ?2 %. The double substitution of Mn in this system offers to tune the NTC thermistor properties with increased localization of electrons in the lattice.