Abstract
Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.
Highlights
Temperature monitoring is necessary in a wide range of applications, such as the biomedical, domestic and industrial sectors
Activated polaron hopping between Mn3+ and Mn4+ cations at octahedral sites is responsible for conduction in NiMn2 O4 [5], though recent research has shown that the thermal properties of nickel manganite can be modified by tuning cations on the tetrahedral sites [2]
The elemental composition and chemical state of elements in the synthesized nickel manganite powder were determined by recording X-ray photoelectron spectra (XPS) on a PHI-TFA
Summary
Temperature monitoring is necessary in a wide range of applications, such as the biomedical, domestic and industrial sectors. NiMn2 O4 is one the most studied materials for NTC thermistor applications and still remains the focus of current research [2,3,4] It has a mixed cubic spinel structure where A (Ni2+ ) and B (Mn3+ , Mn4+ ) cations can occupy both tetrahedral and octahedral sites. NTC thermistors with high stability and low room temperature resistivity have been achieved, and shown to depend on the synthesis and processing methods [6,7,8] and composition (improved with cation substitution) [8,9,10].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
