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X-ray Structural Study of Charge and Anion Orderings of TMTTF Salts.

X-ray Structural Study of Charge and Anion Orderings of TMTTF Salts. Charge Ordering Phase Diagram of (TMTTF) 2 X. Dimerization. Dimerization of Dimer by AO. Dimer Mott state. Cooling. 2k F CO. Cooling. X : ClO 4. X : ReO 4 FSO 3. 4k F CO. X : SCN PF 6, AsF 6, SbF 6.

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X-ray Structural Study of Charge and Anion Orderings of TMTTF Salts.

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  1. X-ray Structural Study of Charge and Anion Orderings of TMTTF Salts.

  2. Charge Ordering Phase Diagram of (TMTTF)2X Dimerization Dimerization of Dimer by AO Dimer Mott state Cooling 2kF CO Cooling X: ClO4 X: ReO4 FSO3 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization • From low temperature structure analyses and electronic structure calculation

  3. Structure of (TMTTF)2X • 2 molecules 1 monovalent anion in unit cell(1/4 filling) • 1D zigzag stack • Dimeric structure along the 1D stack • Anion orientational degrees of freedom (order, disorder) • Dimerization and Anion controls physical properties!

  4. Charge Ordering in (TMTTF)2X & (TMTSF)2X Possible 4kF charge order (TMTTF)2X X= PF6, AsF6, SbF6 Charge disproportionation observed by NMR* and Ac dielectric** permittivity has been of particular interest. SDW *Chow et al.，PRL 85(2000)1698 **Monceau et al.,PRL 86(2001)4080 X= ReO4 Charge ordering has been proposed from X-ray analysis***. ***Y. Nogami et al.,J. Phys. IV 12, Pr-9-145(2002).

  5. Our focus point of structure analysis in (TMTTF)2X • Observation of charge ordering(CO) pattern by X-ray measurement. • Calculation of transfer integrals to evaluate the magnitude of dimerization. • Studying anion ordering(AO) influence on the electronic state.

  6. 2kF and 4kF Charge Ordering(CDW) in 1/4 filled Q1D system. Possible state • 2kF charge disproportionation. • 4kF charge disproportionation. • localization at dimer X-ray analysis can estimate the degrees of Charge and Dimerization.

  7. c a b d Ionic molecule higher HOMO energy Estimation of charge and dimerization using atomic coordinates by X-ray. • Dimerization : t2 t1 t2 t1 t1 • Transfer integral calc. • Extended Huckel Theory Dt / <t> = 2(t1-t2) / (t1+t2) • Charge : A B Shape of Molecules HOMO energy r = 6.347-7.463(b+c-a-d) P.Guionneau et al., Synth. Met, 86, 1973 (1997)

  8. Structure analysis at LT was limited in 2000. Only 4 study on electronic structure. Twinning, Iradiation Damage

  9. High S/N IP X-ray camera Okayama University He gas cryostat (20K) No window scattering SPring-8 Liq He Cryostat(10K) Vacuum camera No window and air scattering High resolution R= 2〜4%

  10. Competition between dimerization & 4kF CO again. (TMTTF)2SCN Above 160K of TAO Dimerization T(K) Dt / <t> = - 0 . 25 0 . 26 4kF CO Below 160K of TAO AO reduces dimerization and induces 4kF CO. Dt / <t> AO Good accordance in charge estimations between by HOMO and by bond lengths.

  11. Competition between dimerization and 4kF CO. At HT, enhanced dimerization When crosses 0.25, 4kF CO has been observed. Dt / <t> 4kF Charge Ordering At LT, 4kF CO

  12. (TMTTF)2ReO4 t2’ t2” • Anion shift induces tetramerization • Tetramerization causes 2kF CO. 2kF CO ReO4 at 100K t2”/t2’ 1.51 Dr=(rA- rB)/2 0.25 TAO Good accordance in charge estimations between by HOMO and by bond lengths.

  13. Comparison of ReO4 and ClO4 X: ClO4 X: ReO4 t2’ t2” • Little anion shift andtetramerization • Reversal 2kF CO. • Anion shift induces tetramerization • Tetramerization causes 2kF CO. ReO4 at 100K t2”/t2’ 1.51 Dr=(rA- rB)/2 0.25 ClO4 at 40K t2”/t2’ 1.04 Dr=(rA- rB)/2 -0.06 Similar electronic structure above Tc. ReO4 ts1=0.119 ts2=0.087 eV ClO4 ts1=0.121 ts2=0.089 eV at 160K CO occurs by dimerization of dimer.

  14. (TMTTF)2FSO3 Dimerization of dimer. Enhanced tetramerization in FSO3 Tetramer 3.92A 3.66A Dimer 3.9A 3.73A 3.62A 3.55A 3.7A 3.89A 3.73A 3.75A 3.62A 3.92A 3.7A 3.66A 3.9A Col.1 Col.2 FSO3 ReO4

  15. Role of Anion In (TMTTF)2X, the anionic sublattice controls their electronic properties. Shape of anion Dimerization Electronic state Octahedral Linear Tetrahedral Weak Weak Strong 4kF 4kF 2kF

  16. Charge Ordering Phase Diagram of (TMTTF)2X Dimerization Dimerization of Dimer by AO Dimer Mott state Cooling 2kF CO Cooling X: ClO4 X: ReO4 FSO3 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  17. Dimerization Dimer Mott state Cooling 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization Summary Charge Disproportionation(4kFCO) is triggered by the decrease in the dimerization with cooling. HT dimerization LT 4kF CO

  18. Summary In (TMTTF)2ReO4, 2kF CO is triggered by the molecular tetramerization induced by displacement of ReO4. X=ReO4 X=SCN Dimerization Dimerization of Dimer by AO 2kF CO Dimer Mott state Cooling X: ReO4 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  19. Summary But not in smaller ClO4. X=ReO4 X=ClO4 Dimerization Dimerization of Dimer by AO 2kF CO Dimer Mott state Cooling X: ClO4 X: ReO4 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  20. Summary In (TMTTF)2FSO3, 2kF CO is triggered by the ENHANCED molecular tetramerization. X=ReO4 X=FSO3 Dimerization Dimerization of Dimer by AO 2kF CO Dimer Mott state Cooling X: ReO4 FSO3 X: ClO4 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  21. Charge Ordering Phase Diagram of (TMTTF)2X Dimerization Dimerization of Dimer by AO Dimer Mott state Cooling 2kF CO Cooling X: ClO4 X: ReO4 FSO3 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  22. Dimerization Dimerization of Dimer by AO Dimer Mott state Cooling Cooling 2kF CO X: ReO4 FSO3 X: ClO4 4kF CO X: SCN PF6, AsF6, SbF6 Tetramerization

  23. Summary of 2kF ordering • (TMTTF)2ReO4, 2kF CO is triggered by the molecular tetramerization induced by displacement of ReO4. • But not in smaller ClO4. • In (TMTTF)2FSO3, 2kF CO is triggered by the ENHANCED molecular tetramerization. The CO is can also be induced by 2kF anionic potential of anion.

  24. Summary Charge Disproportionation(4kFCO) is triggered by the decrease in the dimerization with cooling. In (TMTTF)2ReO4, 2kF CO is triggered by the molecular tetramerization induced by displacement of ReO4. But not inClO4. HT dimerization LT 4kF CO Competition between dimerization and 4kF CO

  25. ORSAY Superstructure observation Structure analysis at LT was limited in 2000. Only 4 study on electronic structure. Twinning, Iradiation Damage S1 S2 Today’s our interest.

  26. Charge Ordering in (TMTTF)2X & (TMTSF)2X Possible 4kF charge order SDW

  27. Role of Anion In (TMTTF)2X, the anionic sublattice controls their electronic properties. • Size and shape of anion modifies the degrees of the dimerization and thereby charge disproportionation. • Anion ordering modifies the anionic potential on 1D electron, and changes dimerization and tetramerization. X=SCN X=ReO4 X=FSO3

  28. Structure of (TMTTF)2X & (TMTSF)2X • 2 molecules 1 monovalent anion in unit cell(1/4 filling) • 1D zig-zag stack • Dimeric structure along the 1D stack • Anion orientational degrees of freedom (order, disorder) • Dimerization and Anion controls physical properties!

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