1. Mixed-valence vanadates at high-pressures Andrzej Grzechnik Institute of Crystallography, RWTH Aachen University

2. P.Y. Zavalij and M.S. Whittingham, Acta Cryst. B55, 627 (1999) Vanadium coordination polyhedra in vanadates in relation to the oxidation states of vanadium at atmospheric pressure

3. Vanadium coordination polyhedra in vanadates in relation to the oxidation states of vanadium at atmospheric pressure Electrochemistry ► Electrochemistry Catalysis ► Catalysis Correlated electron systems ► Correlated electron systems Spin-Peierls transitions Spin gap formation Charge, spin & orbital ordering Metal-insulator transitions Magnetism ► Magnetism P.Y. Zavalij and M.S. Whittingham, Acta Cryst. B55, 627 (1999)

4. Wadsley phases: V n O 2n+1 (n = 3, 4, 6) the VO 2 – V 2 O 5 system VO 2 (P4 2 /mnm) V 2 O 5 (Pmmn) Binary vanadium oxides Rutile type

5. Wadsley phases: V n O 2n+1 (n = 3, 4, 6) the VO 2 – V 2 O 5 system VO 2 (P4 2 /mnm) V 2 O 5 (Pmmn) V 3 O 7 (C2/c) n = 3 Binary vanadium oxides Rutile type An insulator and a uniaxial ferromagnet: H. Nishihara, Y. Ueda, K. Kosuge, H. Yasuoka, S. Kachi, J. Phys. Soc. Jpn. 47, 790 (1979).

6. Wadsley phases: V n O 2n+1 (n = 3, 4, 6) the VO 2 – V 2 O 5 system VO 2 (P4 2 /mnm) V 2 O 5 (Pmmn) V 4 O 9 (Pnma) n = 4 Binary vanadium oxides Rutile type An antiferromagnet: S. Yamazaki, C. Li, K. Ohoyama, M. Nishi, M. Ichihara, H. Ueda, Y. Ueda, J. Solid State Chem. 183, 1496 (2010).

7. Wadsley phases: V n O 2n+1 (n = 3, 4, 6) the VO 2 – V 2 O 5 system VO 2 (P4 2 /mnm) V 2 O 5 (Pmmn) V 6 O 13 (Pnma) n = 6 Binary vanadium oxides Rutile type A metal-insulator phase transition followed by an antiferromagnetic transition: Y. Ueda, K. Kosuge, S. Kachi, Mater. Res. Bull. 11, 293 (1976).

8. Magnéli phases: V n O 2n-1 (n = 3÷9) the V 2 O 3 – VO 2 system V 2 O 3 (R-3c) VO 2 (P4 2 /mnm) V 8 O 15 (P-1) V 3 O 5 (Cc) Binary vanadium oxides Rutile type Corundum type

9. Vanadium coordination polyhedra in vanadates in relation to the oxidation states of vanadium at high pressures?

10. Vanadium coordination polyhedra in vanadates in relation to the oxidation states of vanadium at high pressures P An interplay of the effects of a chemical composition and of high pressure on the structural stability and physical properties of mixed valence vanadates

11. Ca 3 V 2 O 8 at high pressures palmierite type R3c

12. palmierite type R3c Ca 3 V 2 O 8 at high pressures A. Grzechnik, Chem. Mater. 10, 1034 (1998) A. Grzechnik, J. Solid State Chem. 139, 161 (1998) Onset of amorphization at about 10 GPa

13. HP-HT synthesis of a powder material 11 GPa, 1373 K C2/m A. Grzechnik, Solid State Sciences 4, 523 (2002) Ca 3 V 2 O 8 at high pressures palmierite type R3c

14. V 2 O 5 and A x V 2 O 5 (A = Li, Na, Cs, Ag, Mg, Ca, …; x ≤ 1) V 2 O 5 (Pmmn)NaV 2 O 5 (Pmmn)

15.  -Na 0.33 V 2 O 5 (C2/m) Wadsley-type bronze NaV 2 O 5 (Pmmn) V 2 O 5 and A x V 2 O 5 (A = Li, Na, Cs, Ag, Mg, Ca, …; x ≤ 1)

16. T. Yamauchi, Y. Ueda, N. Môri, Phys. Rev. Lett. 89, 057002 (2002) Pressure-induced superconductivity in  -Na 0.33 V 2 O 5 : T SC = 8 K, P = 8 GPa Phase transition from the charge ordered to the superconducting phase at 8 K and 8 GPa?

17. Local structures in high-pressure phases of V 2 O 5 A. Grzechnik, Chem. Mater. 10, 2507 (1998) I. Loa, A. Grzechnik, U. Schwarz, K. Syassen, M. Hanfland, R.K. Kremer, J. Alloys Comp. 317–318, 103 (2001)

18. High-pressure phases of V 2 O 5 and NaV 2 O 5 from powder diffraction? A. Grzechnik, Chem. Mater. 10, 2507 (1998) I. Loa, A. Grzechnik, U. Schwarz, K. Syassen, M. Hanfland, R.K. Kremer, J. Alloys Comp. 317–318, 103 (2001)

19. High-pressure phases of  -Na 0.33 V 2 O 5 from powder diffraction? High-pressure synchrotron powder diffraction at room temperature K. Rabia, A. Pashkin, S. Frank, G. Obermeier, S. Horn, M. Hanfland, C.A. Kuntscher, High Press. Res. 29, 504 (2009)

20. (NH 4 ) 2 V 3 O 8 fresnoite V 4+ V 5+ Ambient pressure 6.90 GPa P4bm Synchrotron single-crystal diffraction (D3/Hasylab) A. Grzechnik, T.Z. Ren, J.M. Posse, K. Friese, Dalton Trans. 40, 4572 (2011)

21. (NH 4 ) 2 V 3 O 8 fresnoite Ambient Ambient pressure 6.90 GPa V 4+ V 5+ No charge transfer P4bmP4/mbm Synchrotron single-crystal diffraction (D3/Hasylab) A. Grzechnik, T.Z. Ren, J.M. Posse, K. Friese, Dalton Trans. 40, 4572 (2011)

22. MV 6 O 11 compounds (M = Na, K, Sr, Ba, Pb) P6 3 /mmc M + V 3 3+ V 3 4+ O 11 or M 2+ V 4 3+ V 2 4+ O 11 Structures related to magnetoplumbite Pb(Fe 3+,Mn 3+ ) 12 O 19 V(1)O 6 V(2)O 6 V(3)O 5 regular Kagomé lattice V(1)O 6 M NaV 6 O 11 : A. Grzechnik, Y. Kanke, K. Friese, J. Phys.: Condens. Matter 20, 285208 (2008) BaV 6 O 11 : K. Friese, Y. Kanke, A. Grzechnik, Acta Cryst. B65, 326 (2009)

23. Phase transitions in NaV 6 O 11 : low T V 3+ (1)O 6 V 4+ (2)O 6 V 4+ (3)O 5 Spontaneous magnetization with the easy axis II to [001] ► A Curie-Weiss paramagnetic metal at ambient conditions ► Spontaneous magnetization is suppressed at high pressures (T c ↓ P↑) while the T H temperature increases on compression (*) and is expected to be at 1.15 GPa and room T (*) T. Naka, T. Matsumoto, Y. Kanke, K. Murata, Physica B 206/207, 853 (1995) 64.2 K 80 K T H = 243 K Na +  ║║

24. Phase transitions in BaV 6 O 11 : low T Single-crystal growth at 6 GPa and 1473-2323 K Yasushi Kanke (NIMS, Tsukuba) V(1)O 6 V(2)O 6 Ba 2+ V(3)O 5

25. V(1)O 6 V(2)O 6 Ba 2+ P6 3 mc ↔ P6 3 /mmc 250 K 115 K 75 K Specific heat V(3)O 5 Phase transitions in BaV 6 O 11 : low T Single-crystal growth at 6 GPa and 1473-2323 K Yasushi Kanke (NIMS, Tsukuba)

26. P6 3 mc ↔ P6 3 /mmc 250 K 115 K 75 K No structural phase transitions (no Cmc2 1 phase) Specific heat V(1)O 6 V(2)O 6 Ba 2+ V(3)O 5 Phase transitions in BaV 6 O 11 : low T Single-crystal growth at 6 GPa and 1473-2323 K Yasushi Kanke (NIMS, Tsukuba)

27. P6 3 mc ↔ P6 3 /mmc 250 K 75 K Specific heat 115 K 75 K Magnetic susceptibility Phase transitions in BaV 6 O 11 : low T Single-crystal growth at 6 GPa and 1473-2323 K Yasushi Kanke (NIMS, Tsukuba) No structural phase transitions (no Cmc2 1 phase)

28. Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice

29. NaV 6 O 11

30. 290 K V(1) V(2) 2.86 Å Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice NaV 6 O 11

31. 290 K V(1) V(2) 85.5 K 2.72 Å2.99 Å 2.86 Å Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice NaV 6 O 11

32. 290 K V(1) V(2) 85.5 K4.2 GPa 2.66 Å3.01 Å 2.86 Å 2.72 Å2.99 Å Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice NaV 6 O 11

33. Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice NaV 6 O 11 BaV 6 O 11

34. Phase transitions in NaV 6 O 11 and BaV 6 O 11 : breaking the Kagomé lattice V(1)O 6 V(2)O 6 V(3)O 5 M NaV 6 O 11 Hardly any bond valence changes at V sites BaV 6 O 11 Bond valence changes at all V sites Charge transfer

35. Mixed-valence vanadates MV 4 O 8 (M = Y, Yb, Lu) 3V 3+ + 1V 4+ K. Friese, Y. Kanke, A.N. Fitch, A. Grzechnik, Chem. Mater. 19, 4882 (2007) K. Friese, Y. Kanke, A.N. Fitch, W. Morgenroth, A. Grzechnik, Acta Cryst. B64, 652 (2008)

36. ↓a↓a →b→b ↓c↓c Calcium ferrite type structure (CaFe 2 O 4 ) Orthorhombic Pnam a= 9.230 Å b=10.705 Å c= 3.024 Å Fe(1)O 6 Fe(2)O 6 Ca Pnam (Z = 4) a = 9.230 Å b = 10.705 Å c = 3.024 Å →b→b

37. V(1)O 6 V(3)O 6 V(2)O 6 V(4)O 6 Yb ↓a↓a →b→b P 1 2 1 /n 1 (Z = 4) a = 9.0648(3) Å b = 10.6215(4) Å c = 5.7607(1) Å  = 90.184(3)°  -YbV 4 O 8 ↓c↓c →b→b

38. A 2 1 /d 1 1 (Z = 8) a = 9.030(5) Å b = 21.44(3) Å c = 5.752(2) Å  = 89.911(3)° β-YbV 4 O 8 ↓a↓a →b→b ↓c↓c V(1)O 6 V(3)O 6 V(2)O 6 V(4)O 6 Yb →b→b

39. Average structure P12 1 /n1 A2 1 /d11 Pnam α-phase β-phase Polytypism, twinning, and composite crystals in MV 4 O 8 (M = Y, Yb, Lu)

40. Phase transitions in MV 4 O 8 (M = Y, Yb, Lu) at low temperatures  -YV 4 O 8  -YV 4 O 8 ( ,  )-YV 4 O 8 Q Magnetic susceptibility Specific heat Domain size effects:  ≈ 40-50 Å,  ≈ 500 Å

41. A2 1 /d11 (Z = 4) β-Phase A2 1 /d11 (Z = 4) β’-Phase 180-185 K Guinier simulation of synchrotron powder diffraction data for  -YbV  O  ID31/ESRF

42. α-phase β-phase Isostructural phase transitions in  -YbV 4 O 8 and  -YbV 4 O 8 due to charge ordering at low temperatures (single-crystal data from ANKA & DESY) te Temperature [K]

43. High-pressure behaviour of  -YbV 4 O 8 and  -YbV 4 O 8 polytypes? P12 1 /n1, Z =4A2 1 /d11, Z =8

44. High-pressure behaviour of  -YbV 4 O 8 and  -YbV 4 O 8 polytypes?  -YbV 4 O 8 seems to be stable at least to 16 GPa  -YbV 4 O 8 seems to be stable at least to 10 GPa P12 1 /n1, Z =4A2 1 /d11, Z =8 (0.3 mm capillary) ID31/ESRF (0.3 mm capillary) ID31/ESRF (DAC) SNBL/ESRF, PETRA III (DAC) SNBL/ESRF, PETRA III

45. ► In situ high-pressure x-ray studies (diamond anvil cells and multi-anvils) Phase transitions P-T phase diagrams Chemical reactions ► High-pressure synthesis ► Physical properties under high pressures Magnetism Transport properties The future: an interplay of the effects of a chemical composition and of high pressure on the structural stability and physical properties and of high pressure on the structural stability and physical properties of mixed valence vanadates

46. Collaborators Karen Friese (JCNS, Jülich) Yasushi Kanke (NIMS, Tsukuba) Oleg Petracic (JCNS, Jülich) Georg Roth (RWTH Aachen University)