cation ordering in tunnel compounds determined by tem

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Cation ordering in tunnel manganites solved by TEM

Joke Hadermann

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Acknowledgements

Moscow State University: A.M. Abakumov, M. Kovba, E.V. Antipov

CRISMAT, Ensicaen: L. Gillie, C. Martin, M. Hervieu, O. Pérez, E. Suard

EMAT: G. Van Tendeloo

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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

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MnO6

octahedra

connect octahedra into infinite chains by edge sharing

What are tunnel manganites?

connect chains by

edge- and/or corner sharing in a circular manner

chains of MnO6

octahedra

tunnel framework

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MnO6

Pyrolusite

Rutile-type tunnelsIndicated as "R“1 x 1

Ref.: A.S. John, Phys.Rev.21(1923)389

a=b= 4.40 Å

c= 2.87 Å

Pyrolusite or β-MnO2: 1 x 1

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Ref.: Bystroem, A.M., Acta Chemica Scandinavica (1949), 3, 163-173

Ramsdellite: 2 x 1

a= 4.46 Åb= 9.32 Åc= 2.85 Å

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alpha-MnO2

Ref.: Kondrashev, Yu.D.;Zaslavskii, A.I., Izvestiya Akademii Nauk SSSR, Seriya Fizicheskaya (1951), 15, 179-186

Ramsdellite

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Hollandite

Ref.: Bystroem, A.;Bystroem, A.M., Acta Crystallographica (1950), 3, 146-154

BaMn8O16

a= 4.46 Åb= 9.32 Åc= 2.85 Å

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And in the same manner...

Pyrolusite Ramsdellite

Hollandite Romanechite

Todorokite

1 x 1 2 x 1

2 x 2 3 x 2

3 x 3

Woodruffite

4 x 3

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Pyrolusite Ramsdellite Hollandite

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Pyrolusite Ramsdellite Hollandite

approx.2.85 Å

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Marokite: hexagonal tunnels

Ref.: Lepicard, G.;Protas, J., Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences (1964), 258, 1847-1849

CaMn2O4

a= 9.71 Åb= 10.03 Åc= 3.162 Å

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More complex forms

Ref.:N.Floros,C.Michel,M.Hervieu,B.Raveau,JSSC(2001), 162, 34-41

Na1.1Ca1.8Mn9O18Ba6Mn24O48

Ref.: P.Boullay,M.Hervieu,B.Raveau,JSSC (1997), 132, 239-248

CaMn4O8

Ref.: N.Barrier,C.Michel,A.Maignan,M.Hervieu,B.Raveau,J. Mat. Chem.(2005), 15, 386-393

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NaScTiO4: 8-shaped tunnels

A.F.Reid, A.D.Wadsley, M.J.Sienko, Inorganic Chemistry (1968), 7, 112-118

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More complex forms


Na1.1Ca1.8Mn9O18Ba6Mn24O48


CaMn4O8


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More complex forms

Ba6Mn24O48



Na1.1Ca1.8Mn9O18CaMn4O8


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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

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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

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SrMn3O6: 8-shaped tunnels

Gillie et al., JSSC 177 (2004) 3383-3391

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JSSC, 177 (2004) 3383

[001]

SrMn3O6

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q= 0.52a* + 0.28c*

JSSC, 177 (2004) 3383

2000

0010

00010002

00032011

-2011

2012-

2013-

2010

SrMn3O6

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q= 0.52a* + 0.28c* q= 0.54a* + 0.29c*

q= 0.66a* + 0.33c*q= 0.52a* + 0.31c*

SrMn3O6

JSSC, 177 (2004) 3383

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CaMn2O4

N.Barrier,C.Michel,A.Maignan,M.Hervieu,B.Raveau,J. Mat. Chem.(2005), 15, 386-393

Lepicard, G.;Protas, J., Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences (1964), 258, 1847-1849

m=2CaMn2O4

literatureCaMnmO2m

m=3CaMn3O6

this work

m=4CaMn4O8

literature

CaMn4O8

CaMn3O6

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CaMn2O4

CaMn3O6

Hadermann et al., Chem. Mater, 18 (2006) 5530

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CaMn3O6

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Sub a*

Sub c*

CaMn3O6= Ca0.66Mn2O4

CaMn3O6

2/3 of Ca-positions occupied


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q= 2/3a* + 1/3 c*


Subcell:a=9.07Åb=11.3 Åc=2.83 Å

CaMn3O6

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CaMn3O6:q= 2/3a* + 1/3 c* γ= 0.33

Ca(1-0.33)/2MnO2= Ca0.33MnO2= Ca1Mn3O6

CaMn2O4:c=3.162 Åq= 0 c* γ= 0

Ca(1-0)/2MnO2= Ca0.5MnO2 = Ca1Mn2O4

The compositionally modulated structure approach

CaMn4O8:c=5.6474 Åq= 1/2 c* γ= 0.5

Ca(1-0.5)/2Mn2O4= Ca0.25MnO2=CaMn4O8

CaxMnO2

x= (1- γ )/2 Ca(1- γ)/2MnO2J. Mat. Chem. 19 (18)2660

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Orange=Mn+4-δO6 octahedraYellow=Mn+3+δO6 octahedra

Charge ordering stabilizes the structure

CaMn3O6


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CaMn3O6

CaMn2O4

The compositionally modulated structure approach

CaMn4O8

x= (1- γ )/2 Ca(1- γ)/2MnO2

Fits forUse same formula Sr(1- γ)/2MnO2

for Sr1±δMn3O6

J. Mat. Chem. 19 (18), 2660

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q= 0.52a* + 0.28c* q= 0.54a* + 0.29c*

q= 0.66a* + 0.33c*q= 0.52a* + 0.31c*

SrMn3O6

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q= 0.66a* + 0.33c*

CaMn3O6:SrMn3O6:

q= 0.66a* + 0.33c*

SrMn3O6 versus CaMn3O6

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q= 0.52a* + 0.28c* q= 0.54a* + 0.29c*

q= 0.66a* + 0.33c*q= 0.52a* + 0.31c*

Sr0.72Mn2O4 Sr0.71Mn2O4

Sr0.69Mn2O4 Sr0.66Mn2O4

=Sr1.08Mn3O6 =Sr1.07Mn3O6

=Sr1.04Mn3O6 =Sr1Mn3O6

SrMn3O6

x= (1- γ )/2Sr(1- γ)/2MnO2

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The composite structure approach

Two subsystems:

FrameworkMnO2

Guest cations A1-x

Subsystem Ic-parameter = c1

Subsystem IIc-parameter = c2

g=ha*+kb*+lc1*+mc2*q=c2*= γ c1*

Ratio cell volumes= VI/VII = γ

c1*

c2*

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Composite structure Ba6Mn24O48

Tetragonal, a=18.2 Å,c1=2.8 Å and c2=4.6 Å

(a,c1) framework (a,c2) barium ions


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FrameworkMnO2

Guest cations Ax



q=c2*= γ c1*

p = number of octahedra in the average unit cellr = number of A-cation columns in the average unit cell

General case: x= γ r / p


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Example 1: Ba6Mn24O48

c1=2.8 Å and c2=4.6 Å so γ=0.609 p = 24r = 10

So x= 0.609. 10 / 24 = 0.253gives Ba0.253MnO2is equal to Ba6.072Mn24O48




123

456

78

γ

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Example 2: CaMn4O8literature c=5.6474 Å so c1=2.823 and c2= 5.6474 Å= 2 c1

so γ=0.5 p = 16r = 8

So x= 0.5 . 8 / 16 = 0.25gives Ca0.25MnO2is equal to CaMn4O8




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FrameworkMnO2

Guest cations A1-x



q=c2*= γ c1*



Simplification for square tunnels?(Hollandite, todorokite,…)

Square tunnels: x= γ m / 2 n

m = number of cation columns in the tunneln= number of chains in the bricks


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[SrF0.82(OH)0.18]2.5[Mn6O12]

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[SrF0.82(OH)0.18]2.5[Mn6O12]

a=9.7846(3) Åc1=2.8406(1) Å c2=4.49 Åq1=c2*=0.63181(3)c1*= γc1*

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[SrF0.82(OH)0.18]2.5[Mn6O12]

Electron diffraction:a=9.7846(3) Åc1=2.8406(1) Åc2=4.49 Åq1=c2*=0.63181(3)c1*= γc1*P42/m(00γ)s0

X-ray refinement:guests in rock salt type (NaCl) arrangement c

a

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Average interplanar spacing 89 Å

a’=2a

q2=0.0176(1)a*+0.07497b*

b

a

Submitted to Chemistry of Materials

[SrF0.82(OH)0.18]2.5[Mn6O12]

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The composite structure approachFramework

MnO2

Guest cations A1-x



q=c2*= γ c1*

Square tunnels: x= γ m / 2n

m = number of cation columns in the tunneln= number of chains in the bricks



J. Mat. Chem. 19 (18) 2660

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q=c2*= γ c1*

Square tunnels: x= γ m / 2n

n=number of chains in the brickm = number of cation columns in the tunnel

Todorokite: q1=c2*=0.63181(3)c1*= γc1*so γ = 0.63181n = 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

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q1=c2*=0.63181(3)c1*= γc1*so γ = 0.63181p = 6r = 4

So x= 0.63181 . 4 / 6 = 0.421gives [SrX]0.421MnO2is 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


The composite structure approach:

q=c2*= γ c1*

Todorokite:

general formula

J. Mat. Chem. 19 (18) 2660

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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

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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

cation ordering in tunnel compounds determined by tem

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