3. 3/48Hadermann
Overview
• Introduction:
- What are tunnel manganites?
- The possible frameworks (hosts) in a logical
order...
- The guests
• Generalization of the description and new
examples of tunnel manganites
- SrMn3O6
- CaMn3O6
- Todorokite with rock salt type tunnel contents
17. 17/48Hadermann
The guest cations
AxMnO2
•Size of guests determines size and shape of tunnels
•The charges on the tunnel cations are balanced by
the substitution of some Mn+3 by Mn+4
Mn+3 - Mn+4 charge order in hollandite,
romanechite and todorokite
•Different repeat periods guest and framework
often incommensurately modulated
18. 18/48Hadermann
Overview
• Introduction:
- What are tunnel manganites?
- The possible frameworks (hosts) in a logical
order...
- The guests
• Generalization of the description and new
examples of tunnel manganites
- SrMn3O6
- CaMn3O6
- Todorokite with rock salt type tunnel contents
36. 36/48Hadermann
Framework
MnO2
Guest cations
Ax
Subsystem I
c-parameter = c1
Subsystem II
c-parameter = c2
q=c2*= γ c1*
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
The composite structure approach
37. 37/48Hadermann
Example 1: Ba6Mn24O48
c1=2.8 Å and c2=4.6 Å so γ=0.609
p = 24
r = 10
So x= 0.609. 10 / 24 = 0.253
gives Ba0.253MnO2
is equal to Ba6.072Mn24O48
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
The composite structure approach
1
2
3
4
5 6
78
γ
38. 38/48Hadermann
Example 2: CaMn4O8
literature c=5.6474 Å
so c1=2.823 and c2= 5.6474 Å= 2 c1
so γ=0.5
p = 16
r = 8
So x= 0.5 . 8 / 16 = 0.25
gives Ca0.25MnO2
is equal to CaMn4O8
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
The composite structure approach
39. 39/48Hadermann
Framework
MnO2
Guest cations
A1-x
Subsystem I
c-parameter = c1
Subsystem II
c-parameter = c2
q=c2*= γ c1*
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
Simplification for square tunnels?
(Hollandite, todorokite,…)
Square tunnels: x= γ m / 2 n
m = number of cation columns in the tunnel
n= number of chains in the bricks
The composite structure approach
44. 44/48Hadermann
The composite structure approach
Framework
MnO2
Guest cations
A1-x
Subsystem I
c-parameter = c1
Subsystem II
c-parameter = c2
q=c2*= γ c1*
Square tunnels: x= γ m / 2n
m = number of cation columns in the tunnel
n= number of chains in the bricks
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
J. Mat. Chem. 19 (18) 2660
45. 45/48Hadermann
q=c2*= γ c1*
Square tunnels: x= γ m / 2n
n=number of chains in the brick
m = number of cation columns in the tunnel
Todorokite: q1=c2*=0.63181(3)c1*= γc1*
so γ = 0.63181
n = 3
m = 4
So x= 0.63181 . 4 / 2 .3 =0.421
gives [SrX]0.421MnO2
is equal to [SrX]2.53Mn6O12
The composite structure approach:
square tunnel simplification
J. Mat. Chem. 19 (18) 2660
46. 46/48Hadermann
q1=c2*=0.63181(3)c1*= γc1*
so γ = 0.63181
p = 6
r = 4
So x= 0.63181 . 4 / 6 = 0.421
gives [SrX]0.421MnO2
is equal to [SrX]2.53Mn6O12
p = number of octahedra in the average unit cell
r = number of A-cation columns in the average unit cell
General case: x= γ r / p
The composite structure approach:
q=c2*= γ c1*
Todorokite:
general formula
J. Mat. Chem. 19 (18) 2660
47. 47/48Hadermann
Conclusions
• The first manganite analogue of NaFeTiO4 is
synthesized: SrMn3O6
• The compound CaMn3O6 is synthesized and
turns out to have a CaMn2O4 framework
• The ordering of Ca with vacancies in the
tunnels is derived from the modulation vector
• A general formula is proposed to calculate the
composition of the different phases directly
from the modulation vector
A(1- γ)/2MnO2
- fits CaxMnO2 and SrxMnO2 compounds
48. 48/48Hadermann
Conclusions
• A new todorokite type phase is presented,
containing 4 cation columns instead of the
traditional 1: rock salt type ordered guest
• The general formula for determining the
composition directly from the ratio of the two c-
parameters in a composite structure is
AxMnO2 with x= γ r / p
r= # A-cations, p = # octahedra
• A simplified form for square tunnels:
AxMnO2 with x= γ m / 2n
m= # A-cations, n = # chains in brick