1. Impedance Spectroscopy on Aerosol Deposited NiMn2O4 NTC Thermistor Films
Rainer Schmidt 1 Jungho Ryu 2 Dong-Soo Park 2
1 Universidad Complutense de Madrid, Dpto. Física Aplicada III, GFMC, Madrid, Spain
2 Korea Institute of Materials Science (KIMS), Functional Ceramics Group, Changwon, Gyeongnam , South Korea
P.20
Introduction
  Complex manganese oxides have recently evoked strong interest in various structures with different Mn valence states and Mn coordinations for example in perovskites, spinels, or pyrochlores. The manganites display a vast range of fascinating electrical and magnetic properties (colossal magnetoresistance, ferromagnetism, charge ordering and many more), which often come about due to the mixed valence states of manganese. Nickel manganite NiMn2O4 exhibits a partially inverse cubic spinel structure, which is well known since many years.1,2 NiMn2O4 is widely used in industry as the basis for the production of ceramic temperature sensors due to its electrical properties of a negative temperature coefficient (NTC) of the semi-conducting electrical resistance (R) where charge transport is by Mn3+/Mn4+ hopping.3,4
1. J.A. Becker, C.B. Green, G.L. Pearson, Properties and Uses of Thermistors-Thermally Sensitive Resistors, Bell Syst.Tech.J. 26 (1947) p.170.
2. A. Feltz, J. Töpfer, Bildung von Defektspinellen und Phasenbeziehungen im System NixMn3-xO4, Z.Anorg.Allg.Chem. 576 (1989) p.71.
3. A. Feteira, Negative Temperature Coefficient Resistance (NTCR) Ceramic Thermistors: An Industrial Perspective, J.Am.Ceram.Soc. 92 (2009) p.967.
4. R. Schmidt, A. Basu, A.W. Brinkman, Small polaron hopping in spinel manganates, Phys.Rev.B 72 (2005) p
Aerosol Deposition of NiMn2O4 Thick Films
Dried Air Carrier Gas Flow
Rate: 5 l / min
Deposition of Aerosolized
Floating NiMn2O4 Particles Onto
Glass and Al2O3 Substrates at
1 Torr Chamber Pressure
Post Deposition Annealing at
600°C (Glass) or 850°C (Al2O3)
for 1 Hour
Ti Electrode Deposition by
Thermal Evaporation
NiMn2O4
R-T dependence of
various thermistor
materials
Reproduced from Ref. [1]
See also: Ryu et al. J.Am.Ceram.Soc. 92 (2009) p.3084
ZnFe2O4
Ni1-x-yCoz+yMn2-yO4
Cross Sectional SEM of Thick Film NiMn2O4
Commercial NTC Thermistor Bead
In-plane Impedance Spectroscopy
The films show good adhesion to the substrate and high density with no micro-cracks or pores. The colour-coded elemental analysis (left figure inset) shows clear separation between Ti electrodes, NiMn2O4 films and Si-glass substrates. Inter-diffusion appears to be minimal. Phase purity of the source powders and the films was confirmed by X-ray diffraction (XRD).
Rdc
CPE0
Complex Impedance Data of Thick Film NiMn2O4
Frequency Range: 0.5 Hz – 1 MHz ; Voltage Signal Amplitude: 100 mV
Constant-Phase-
Element (CPE)
Impedance:
Conversion for the R-CPE Circuit Used:
wmax = Frequency at Semicircle Maximum, i.e. Dielectric Relaxation Peak Maximum in -Z’’; n ≤1 Describes the “Non-ideality” of a Capacitor (Ideal Case: n =1). C.H. Hsu, F. Mansfeld, Corrosion, 57(2001) p.747
R – T Dependence of Thick Film NiMn2O4
Symbols Represent the Resistivity Rdc Obtained From Equivalent Circuit Fits
Solid Lines Represent Fits to a Variable- Range-Hopping (VRH) Power Law: p
T0 in K
C in Wcm/K2p
Rdc
CPE0
Discussion and Conclusions
Thick films of NiMn2O4 NTC thermistor material were successfully produced by aerosol deposition and may be applicable in temperature sensing applications. The dc film in-plane R -T dependence was determined by impedance spectroscopy. The R-T curves for all films showed the typical NTC thermistor behaviour over a large temperature range (180 K – 500 K) and followed a VRH law.
This work is dedicated to the memory of
Prof. Andy W. Brinkman
† 7th July 2011