In-plane impedance spectroscopy in aerosol deposited NiMn_(2)O_(4) negative temperature coefficient thermistor films

Temperature dependent in-plane impedance spectroscopy measurements were carried out in order to analyze the charge transport properties of functional oxide NiMn_(2)O_(4) negative temperature coefficient thermistor films deposited via aerosol deposition techniques onto glass and Al_(2)O_(3) substrates. The in-plane resistivity (ρ) versus temperature (T) curves of all films were uniform over a large temperature range (180 K to 500 K) and showed the typical exponential power-law behavior associated with variable-range hopping. The ρ-T dependences of annealed and as-deposited films exhibited power-law exponents ρ of about 0.6 and thermistor constants B in the range of 3500 K to 5000 K. As-deposited films showed higher ρ values as compared to annealed films. As-deposited films exhibited also increased B values, leading to increased sensitivity of the resistance to temperature changes, whereas annealed films deposited on Al_(2)O_(3) showed the lowest scatter in differentiated ρ-T data and might display superior reliability for temperature sensing applications