Synthesis and electrical behavior study of Mn^sub 3^O^sub 4^ nanoceramic powder for low temperature NTC thermistor

Monodispersed Mn^sub 3^O^sub 4^ nanoparticles (NPs) were synthesized by reducing KMnO^sub 4^ at room temperature in the presence of cetyltetrabutylammonium bromide surfactant and short chain tetra-n-butylammonium bromide co-surfactant. Structural characterization done through XRD, TEM and FT-IR analysis techniques showed mono dispersity (5-8 nm) and capping of the NPs with surfactants. The temperature dependent behavior of dc resistivity of the nanopowder pellets showed reproducible NTC characteristics over a range of 40-200 °C with two thermistor constants (β1 = 10,897 K for 40 °C < T < 107 °C and β^sub 2^ = 1,529 K for 107 °C < T < 190 °C) and a negative temperature co-efficient of resistance (α = -0.111 K^sup -1^ at 40 °C). The thermistor constant (β^sub 1^) and NTC values are found to be higher than that of bulk Mn^sub 3^O^sub 4^ in range of 40 °C < T < 107 °C. This observed behavior implies an enhanced sensitivity in nano-powder based thermistors. Temperature and frequency dependent impedance behavior of the as-synthesized samples evaluated over a temperature range of 40-140 °C and a frequency range of 1 kHz to 1 MHz delineates the role of electron hopping between Mn^sup 2+^ and Mn^sup 3+^ in the conduction process. These studies present monodispersed Mn^sub 3^O^sub 4^ NPs as promising material for NTC thermistor in the low temperature range 40 °C < T < 107 °C.[PUBLICATION ABSTRACT]