1. Impedance spectroscopy of nickel manganite NiMn2O4
Universidad Complutense de Madrid Rainer Schmidt
Impedance spectroscopy of nickel manganite NiMn2O4
obtained from different synthesis routes
Universidad Complutense de Madrid
Madrid, Spain
Rainer Schmidt
Carlos Leon
Departamento Física Aplicada III, GFMC
Emilio Moran
Departamento de Química Inorgánica
Emilio Matesanz
Centro de Difracción de Rayos X
Universidad Nacional del Sur
Bahía Blanca, Argentina
Alejandra Diez
Aurora E. Sagua
Departamento de Química
Laboratorio de Fisicoquímica
Marisa A. Frechero
CONICET’Fisicoquímica
Abstract 340

2. Impedance spectroscopy of nickel manganite NiMn2O4 obtained
Contents Rainer Schmidt
Impedance spectroscopy of
nickel manganite NiMn2O4 obtained
from nickel permanganate precursor
Part One: Principals of Impedance Spectroscopy
Part Two: Impedance Spectroscopy Data
from NiMn2O4 polycrystalline NTC Thermistors

3. Separation of Contributions from
Principals of Impedance Spectroscopy Rainer Schmidt
Impedance Analyzer (Hewlett Packard 4192A)
Separation of
Contributions from
Electrode - Sample
Interface Layer
Grain Boundary Areas
Grain Interior
Bulk Material
Heating/
Cooling
Magnetic
Field

4. Impedance Spectroscopy
Principals of Impedance Spectroscopy Rainer Schmidt
Impedance Spectroscopy
Application of an Alternating Voltage Signal to a Sample:
Measurement of the Alternating Current Response:
Time Dependent Definition of the Impedance:
U(w,t )=U0 cos(w t )
U, I
I(w,t ) = I0 cos(w t +d )
U(w,t ) U0 cos(w t )
I(w,t ) I0 cos(w t + d )
Z(w,t )

5. U, I Time Dependent Notation Phasor Diagram C
Principals of Impedance Spectroscopy Rainer Schmidt
Time Dependent Notation
Phasor Diagram
U, I
U=U0 cos(w t)
IC=I0 cos(w t-p/2) C R
IRC=I0 cos(w t –d ) d C
IR=I0 cos(w t)
ZR=R
ZC=1/iwC
Time Independent Complex Impedance

6. Complex Relationships
Principals of Impedance Spectroscopy Rainer Schmidt
Complex Relationships
Dielectric Constant – Capacitance Relationship
Contact Area A
Capacitance of the Measuring Cell in Vacuum d
Contact Distance

7. Z '' Z ' Z '' M '' Frequency Frequency Brick Work Layer Model
Principals of Impedance Spectroscopy Rainer Schmidt
Brick Work Layer Model
Narrow, Homogeneous
Distribution of Grain Sizes
Uniform Grain Boundary,
Electrode and Bulk
Properties
- Bulk, GB and Electrode
Areas Behave Differently
Dielectric Bulk
Cb ~ 1 x F
Grain Boundary
Cgb ~ 1 x 10-9 F
Electrodes
Cel ~ 1 x 10-6 F
Z ''
Z '
Rb+Rgb Rb
frequency
Rb+Rgb+Rel
Z ''
R/2
Frequency
M ''
Frequency
C0/2C
Equivalent Circuit
Modulus vs Frequency Plot
Imaginary Part of Modulus –M '' vs Frequency
Impedance vs Frequency Plot
Imaginary Part of Impedance –Z '' vs Frequency
Complex Impedance Plot
Imaginary Part of Impedance –Z '' vs Real Part of Impedance Z '

8. NiMn2O4 Partially Inverse Spinel NTC Thermistor Materials
NiMn2O Rainer Schmidt
NiMn2O4 Partially Inverse Spinel NTC Thermistor Materials
[Octahedral Interstice]
Tetrahedral Interstice
Resistance vs Temperature Characteristics
Ni1-x-zCoz+yMn2-yO4
NiMn2O4
107
106
105
104
103
102
101
100
10-1
10-2
Specific Resistance in Ohm cm
x10-3
1/Temperature in 1/Celcius
Becker et al. Bell Syst. Tech. J. 26 (1947) p.170
Kingery, et al., Introduction to Ceramics, New York:1960,
John Wiley & Sons

9. Calcination of permanganate
NiMn2O Rainer Schmidt
NiMn2O4 Powder Synthesis and Pellet Sintering
Powder Synthesis
Pellet Sintering
Phase Composition
Calcination of permanganate
precursor Ni(MnO4)2 ·6H2O
at 900°C + slow cooling
Combustion synthesis of nitrate precursor using saccharose fuel at 900°C
Combustion synthesis at
850°C
Microwave irradiation of nitrate precursor at 850°C
Conventional precursor oxide route at 850°C
900°C + slow cooling
900°C + annealing at 800°C + quench cooling
850°C + quench cooling
850°C + slow cooling
850°C + slow cooling
NiO impurity
Phase pure

10. Z ' ' Z ' ' Frequency Z ' □ Permanganates ■ Combustion 900°C
Impedance Spectroscopy of NiMn2O Rainer Schmidt
Impedance vs Frequency Plot
Complex Impedance Plot
Z ' '
Frequency
Z '
Z ' '
□ Permanganates
■ Combustion 900°C
○ Oxides 850°C
▼ Combustion 850C°
● Microwave

11. Impedance Spectroscopy of NiMn2O4 Rainer Schmidt
Circuit Fit

12. M ' ' Frequency □ Permanganates ■ Combustion 900°C ○ Oxides 850°C
Impedance Spectroscopy of NiMn2O Rainer Schmidt
Modulus vs Frequency Plot
Frequency
M ' '
□ Permanganates
■ Combustion 900°C
○ Oxides 850°C
▼ Combustion 850C°
● Microwave

13. M ' ' Frequency Modulus vs Frequency Plot □ Permanganates
2. Powder synthesis Rainer Schmidt
Modulus vs Frequency Plot
M ' '
Frequency
□ Permanganates
■ Combustion 900°C
○ Combustion 850°C
● Microwave
High Frequency Extra relaxation: High Capacitance & Low Resistance

14. Conclusions 1.) NiMn2O4 shows two conventional GB and
Conclusions Rainer Schmidt
Conclusions
1.) NiMn2O4 shows two conventional GB and
bulk relaxation processes
2.) Indications for a third conductive relaxation
were found
3.) The third relaxation seems to be intrinsic
and may not be a NiO secondary phase
4.) More work is necessary to identify the
origin of the third conducting relaxation

15. i = 0.93 – 0.74 at room temperature
1. Introduction: Crystal structure Rainer Schmidt
Spinel Structure
General formula A2+ B3+2 O2-4 (regular spinel)
Closed packed oxygen anions, cations on tetrahedral and octahedral lattice interstices
Regular spinel: all A2+ cations are on tetrahedral and B3+ on octahedral Sites
In manganate spinels some divalent cations can move to [octahedral sites] T t
Tetrahedral Interstice
Octahedral Interstice B A
i = 0.93 – 0.74 at room temperature
Kingery, et al., Introduction to Ceramics,
New York:1960, John Wiley & Sons
Boucher et al. Acta Cryst., B25 (1969) p.2326
Boucher et al. J.Phys.Chem.Solids, 31 (1970) p.363

16. Phase Diagram for NiO-Mn2O3
2. Phase diagram Rainer Schmidt
Phase Diagram for
NiO-Mn2O3
NiMn2O4 h
a: NiO, Ni6MnO8
b: Cubic Spinel, NiO
c: Rock Salt (NiO)
d: Ni6MnO8, NiMnO3
e: Cubic Spinel, Rock Salt
f: NiMnO3, Mn2O3
g: Mn2O3
h:Cubic Spinel (NiMn2O4)
i: Cubic+Tetragonal Spinel
j: Tetrag. Spinel (Mn3O4)
k: Cubic Spinel, NiMnO3
l: Cubic Spinel, Mn2O3
m: Cubic Spinel
n: Cubic Spinel, Mn5O8
x (Ni content)
Wickham, J.Inorg.Nucl.Chem. 26 (1964) p.1369 / Tang et al. J.Less-Comm.Met. 156 (1989) p.357

17. 2. Powder synthesis Rainer Schmidt