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Stabilizing several anions (F, O, OH, S) in the vicinity of transition metals or rare earths

Stabilizing several anions (F, O, OH, S) in the vicinity of transition metals or rare earths to tune the electronic properties of new materials. Alain Demourgues. CNRS, Université de Bordeaux, ICMCB, UPR9048, F-33600 Pessac, France. GDR MEETICC.

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Stabilizing several anions (F, O, OH, S) in the vicinity of transition metals or rare earths

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  1. Stabilizing several anions (F, O, OH, S) in the vicinity of transition metals or rare earths to tune the electronic properties of new materials Alain Demourgues CNRS, Université de Bordeaux, ICMCB, UPR9048, F-33600 Pessac, France GDR MEETICC Matériaux, Etats ElecTronIques et Couplages non-Conventionnels 28-31 Mars 2017, AEROCAMPUS, Latresne(33)

  2. E (q) =  q +  q2 Mulliken-Jaffé (1935 – 1963) • (q) = E(q)/q =  + 2 q : Electronegativity • = 2E(q)/2q = 2 : Hardness= 1/Polarizability (Pearson) The anions Xp- + electronegative (q) S2- Cl- O2- F- N3- H- OH- * (Green apatites) H- + O2- 2e- + OH- Ca5(PO4)3(F, OH, H)  N3- S2- Cl- O2- F- + hard + polarizable * K. Hayashi and H. Hosono, J. Phys. Chem. Chem. Phys, 2016, 18, 323, 8186-8195

  3. Hard-Soft Acid-Base (HSAB) theory Ralph Pearson (1960) Energy H+(1s0), Ti4+(3d0), K+, Ba2+, La3+ Hard acid : Soft acid : Fe2+(3d6), Cu+(3d10) H-(1s2), S2-, I-, SO42-, CO32- Soft base : Hard base : F-, O2-, OH-, Cl-, NH3 Hard-Hard or Soft-Soft ABreactfasterleading to stronger bonds !

  4. Fluorine, a super-halogen ! The anomolous properties of Fluorine Bond-Dissociation Energy (kJ.mol-1) HX CH3X F F X2 Cl Cl Br Br 300 F- Cl I I Only for X2 240 Br F I 160 4 6 Fluorine is small in size and its supported charge is too high !

  5. The M-X chemical bonding and the effect of mixed anions Mq+ : Partial density of charges and oxydation states Point group ( Mq+ / Xp- ), anisotropy and networks Crystal field, Polarization, Covalency SO42- / PO43- / CO32-…? N3- S2- F- Mq+ H+/H- O2- A way to tune the ionicity-covalency of the chemical bonding and consequently the electronic properties !

  6. Outline Rare-Earth (Ce) oxy-fluoro-sulfides and Transition Metal (Ti) oxy-hydroxy-fluorides Composition, Structural features and Energy Gap From 2D layers to 3D tunnel networks OH- F- O2- S2- Ti4+(J=0)/Ti3+(J=3/2) Ti Ce 22 58 Pauling : 1.4 Pauling : 1.1 The key role of Electronegativity (), Charge (q+), Ionic radius (rion) of Mq+ to define local electrical field = (q)/ rion [Ar] 4s23d2 [Xe] 6s24f2 Ce4+(J=0)/Ce3+(J=5/2) Point group symmetry (M vs X), Mixing empty d orbitals with filled ligand p orbitals, Looking for non-bonding character Lowering the band gap Second order Jahn-Teller distortion

  7. LaF3 La2O3 -La2S3 abs 230 nm 440 nm 175 nm 2.1 2.7 1.8 n(400 nm) The mixed anions systems : absorption k() and refractive index n() - Electronegativity  (Polarizability ) : F- > O2- > S2- - Modulation of the chemical bond : Ln-S/O/F : Variation of the absorption wavelength and refractive index - Competitive bonds around metals : anisotropy, modification of the chemical bonds and electronic properties

  8. A new class of compounds : rare earth oxyfluorosulfides LaSF : abs = 440 nm (Eg = 2.8 eV) High absorption efficiency and refractive index UV Absorbers : abs = 400 nm (Eg = 3.1 eV) ?? Modification of rare earth environment Intergrowth of How to change the ionicity of blocks ? Size + Charge Ionic blocks [Ln2F2]4+ Covalent blocks [S2]4-

  9. A new class of compounds : rare earth oxyfluorosulfides Modification of the size (ionicity) of ‘[Ln-O,F]’ blocks : double sulphur sheets Powder and Single crystal X-Ray and Electron Diffraction analysis [Ln3OF4]4+ [Ln2AF4]4+ [S2]4- [S2]4- 2 LnSF + AF2 Ln2AF4S2 (A= Ca, Sr) 2 LnSF + LnOF Ln3OF3S2 Tetragonal I4/mmm a  4 Å, c  19 Å Orthorhombic Pnnm a  5.6 Å, c  19 Å A. Demourgues et al. , J. Alloys Comp, 2001, 323, 223-230 D. Pauwels, A. Demourgues et al .Solid State Sciences, 2002, 4,. 1471-1479.

  10. A new class of compounds : rare earth oxyfluorosulfides Modification of the charge (ionicity) of ‘[Ln-O,F]’ blocks : single sulphur sheet Powder X-ray and Neutron Diffraction analysis [Ln2O1.5F]2+ [S]2- c a Ln2O1.5FS Hexagonal P-3m1 a  4.1 Å, c  6.9 Å D. Pauwels, A. Demourgues et al .Solid State Sciences, 2002, 4,. 1471-1479.

  11. 100 90 80 70 60 LaSF 50 La2CaF4S2 % Reflexion 40 La3OF3S2 La2SrF4S2 30 La2O1,5FS 20 La2O2S 10 0 300 400 500 600 700 800 Wavelength (nm) A, Ln Rare earth oxyfluorosulfides and optical absorption properties d(La-O)  2.45 Å  4 d(La-S)  3 Å  3 La2O2S =La2O1.5FS d(La-O)  2.5 Å  4 d(La-S)  3 Å  5 LaSF La3OF3S2 La2AF4S2 Relaxation of Sulphur sheets S-S distances  Optical band gap  4f,5d(La) Number of S atoms  Optical band gap  3p(S) [La(A)-F,O] blocks A/Ln-F/O bond distances 

  12. The Ce valence states in fluorides, oxides and sulfides J = 5/2 Low crystal field J = 0 High crystal field CeIII(4f1) CeIV (4f0) F2 H2 CeF3 Ce2S3 CeO2 Ce4O4S3 CeSF CeOF Ce4+/Ce3+ F- : (Pauling) = 4 Hard base O2- : (Pauling) = 3.5 Hard base Ce4O2F2S3 - Ce4O3FS3 S2- : (Pauling) = 2.6 Soft base High crystal field High Madelung Potential VO2- Low crystal field Low Madelung Potential VF-, VS2- Distorted Polyhedron [9] Ce-F = 2.40-2.53 A Cubic site [8] Ce-O = 2.34 A Twotetrahedra surrounding Ce [8] Ce-S = 2.80-3.00 A

  13. Ce(5d) Ce(5d) Ce(5d) 3 eV 5 eV 4f0 Ce4+ 4f1 Ce3+ S(3p) O(2p) F(2p) F(2p) Ce2S3/CeSF CeF3 CeO2 From the composition and structural features of Ce compounds to theoptical absorption properties 2 eV 4f1 Ce3+ 5 eV 7 eV 3 eV CTB Which strategy to keep the Ce4+ valence state in oxyfluoride ?

  14. The solid solution CeO2 (a = 5.41Å ) - CaF2 (a = 5.46 Å) - CaO Chemical analysis Ce1-xCaxO2-x-y/2Fy 0  x  0,29 (1) 0  y  0,24 (3) Ca2+ content F- rate 5,4097 (1)  a (Å) 5,4217 (4) Ce0,92Ca0,05Na0,03O1,91 Ce0,71Ca0,29O1,59F0.24 Diffuse reflectance % Wavelength (nm) % F, Ca  Ionic character of Ce4+-O2- chemical bonding  F- [4] : FCa2Ce2 and FCa3Ce major sites (19F MAS-NMR) 2p(O)  4f (Ce) Charge Transfer Band energy  L. Sronek, A.. Demourgues et al. Chem. Mater. , 2007, 19, 5110-5121 L. Sronek, A.. Demourgues et al. J. Phys. Chem. C, 2008, 112, 860-866

  15. Structural relationships with RE TM PN O1-xFx oxypnictides Takahashi, H. et al. Superconductivity at 43K in iron-based layered compound .LaO1-xFxFeAs. Nature, 2008, 453, 376-378 (LaO)+ layer (LaF)2+ layer (S)2- layer (FeAs)- layer • LaFS = PbFCl = BiOCl • Charge density into Layers ( LaO)+ -Fluorite- and ( FeAs)- -Anti Fluorite-  e- Transfer : LaO1-xFxFeAs • LaO « réservoir » layer FeAs conducting layer : B.I. Zimmer , W. Jeitschko et al. J. Alloys and Comp, 1995, 229, 238

  16. Structural parameters which influence superconducting properties of REO1-xFxFeAs compounds Reduction of cell parameters 17 • Parameters which influence Tc : • Doping with F- • Increasing of electron density into FeAs layers • Application of High Pressure • 2D Structure and critical temperature Tc : • Converging to Tetrahedron FeAs4 [Td]Symmetry • Inter layers Fe2As2 distance increasing

  17. From rare earth to transition metal : the Fe2+ (3d6) case stabilized in mixed anions environment Sr2F2Fe2+2OS2 Sr2Fe2+CuO3Se (Oh) FeO2S4 [Perovskitelayers] [5] FeO5 + [AntiFluoritesheets] [4] CuSe4 [Fluorite blocks] [Sr2F2]2+ + [ Anti CuO2 layers] [Fe2O (S2) ]2- P4/nmm p-type (Cu+)-SC + AFM (TN>300K) H. Kabbour, L. Cario et al. J.A.C.S, 2008, 130, 8261 D. Berthebaud et al. Sol. Stat. Sci. 2014, 36, 94-100 I4/mmm SC + 2D Ising AFM (TN<110K) S=2 AFM checkerboard spin lattice CaOFe2+S [Rocksalt blocks] [6] CaO3S3 + [Wutzitesheets] [4] FeOS3 (Td) FeOS3 Polar structure (P63mc), Magnetodielectric TN=35K C. Dellacotte et al. Inorg. Chem. 2015, 54, 6560-6565

  18. x (q) S2- O2- F- OH- Polarizability Transition Metal (Ti)

  19. Ti-based hydroxy-fluorides with ReO3-derived network and band gap • Ti vacancies distorted Oh site Stabilization of CB Ti(3d)  electronegativity [F-] >  [O2-] > [OH-] (ReO3) Ti0.750.25OH1.5F1.5 TiO2 BaTiO3 CB Ti(3d) CB Ti(3d) CB Ti(3d) CTB O [3] Ti-O = 1.93 1.98 Å O [2] Ti-OH-F = 1.95- 1.90 Å O [2] Ti-O = 2.00 Å CTB CTB 3.1-3.2 eV 3.2 eV 3.4 eV VB OH(2p) F(2p) VB O(2p) VB O(2p) A. Demourgues et al. Chem. Mater. 21, 2009, 1275-1283

  20. Ti-based hydroxy-fluoride with ReO3-derived network c* Electron (SG : Pn-3m) X Ray, Neutron (Atomic positions) diffraction investigations 002 Ordered ReO3 supercell (SG : Pn-3m , a = 7.6177 A) Ti vacancies ! 020 b* [100] 1.90 A 1.95 A 1.90 A 1.95 A 1.90 A [ Ti2/31/3 (OH/F)2F/OH ]6 [Ti (F/OH)3]2 exp = 2.63 g.cm-3 (theo = 2.70 g.cm-3) A. Demourgues et al. Chem. Mater. 21, 2009, 1275-1283

  21. Structural features of Ti1-(O,OH,F)3 HTB Ti0.93O0.7OH0.9F1.4, 0.27 H2O (TGA/density) Pnma, a=7.5581(1) Å, b= 7.322(1) Å, c= 12.7893(2) Å Powder XRD Rietveld Refinement (Cu Kα = 1.5406 Å) Powder Neutron Rietveld Refinement (= 1.496 Å, SINQ-SWI) 3 TiO2(OH,F)4 distorded octahedra (Neutrons) : Ti1 - 1.88-1.93 Å F1/F2/O2 Ti2 - 1.90-1.96 Å F1/O3/F3 Ti3 - 1.70- 2.11 Å O1/F2/F3- Ti vacancies

  22. Energy gap and band diagram of Ti oxy-hydroxy-fluorides (HTB) Solvothermal route : HTB- Ti0.930.07O0.7OH0.9F1.4 (Eg=3.42 eV) S. F. Matar (DFT calculation) Aqueous route : HTB-Ti0.80.2O0.2OH1.6F1.2 (Eg=3.35 eV) ReO3- Ti0.750.25OH1.5F1.5 (Eg=3.22 eV) CB Ti(3d) OH(F)/Ti  (O2-  )  (Ti)  Oh distortion O2-   Disorder   main species OH-/F- CTB 3.2-3.4 eV VB OH(2p)/O(2p) F(2p)  Eg  , E/k  (direct transition)

  23. V/Mo/W substitution into Ti1-(O,OH,F)3 HTB to tune the O content and enhance the TM site distortion Hydrothermal route (TiOCl2 , NH4VO3/(NH4)2MoO4/(NH4)6W12O39, aqueous HF(40%), R= HF/Ti= 1.7, water as solvent, T=90°C) x (0-5%)  (a,c,V)  and b  :  Ti and Oh distortion (SOJT) 

  24. V/Mo/W substitution into Ti1-(O,OH,F)3 HTB Structure refinement (Pnma hypothesis) Enhancement of TM (Ti4+/V5+) site distortion with shorter bond distances 0% 10% V 10% Mo 10% W

  25. Mo substitution into Ti1-(O,OH,F)3 HTB Clear evidence of Mo5+ by ESR : 3 various sites (Pnma hypothesis) 10%Mo 10% Mo 5% Mo The Mo5+ sites distribution in 3 various sites varies with the Mo rate (low Mo content : stabilization in the most distorted octahedra)

  26. From Ti-based oxy-hydroxy-fluorides with HTB-derived network to blue conductive Anatase TiO2:F The key role of structural/electronic defects: ReO3 - Ti0.75(OH)1.5F1.5 TiO2 white (500°C-600°C) HTB - Ti0.93O0.7OH0.9F1.4  TiO2: F blue (500°C-600°C) TGA under Ar + Anatase

  27. Blue conductive Anatase TiO2:F Strong UV and NIR absorption, conduction e- and Ti3+. ESR analysis XPS analysis

  28. Blue conductive Anatase TiO2:F, V/Nb doped Strong UV and NIR absorption, %V  (e-) %Nb  (e-)(2%) then 

  29. Blue conductive Anatase TiO2:F, V/Nb doped conduction e- (VO)2+ species (V4+, 3d1, I=7/2) V-doped TiO2:F XPS analysis conduction e- F1s ~685 eV 0.7% F and 2% Nb (Ti3+, 3d1) Nb-doped TiO2:F

  30. Anatase-TiO2 and orbital molecular diagram : Generation of defects induced by mixed anions compounds * anti-bonding Ti4+ (eg) dxz dyz * anti-bonding Ti4+ (t2g) Non-bonding character of dxy orbitals, 4 interactions Ti4+ - Ti4+ at 3.04 Å dxy dxy non-bonding dxy (Ti) and p (O) levels with non-bonding character O(p) p non-bonding Dense pellet obtained by SPS (82%) (T=600°C, P=100 MPa) TiO2: Nb (2%) / F (1%) O(p)  bonding Conductivity (RT) = 0.2 -1cm-1 Seebeck coefficient (RT) = -77V/K  bonding

  31. Conclusions and future works • How to build mixed anions 2D network ? • The simple key role of electronegativity and polarisability 1/ of elements • Hard-Hard and Soft-Soft Acid-Base rules • CN(X withhigher ) = CN(M withlower ) • The main networks : • Ionic blocks (F/O) vs covalent sheets (S/Se) • Fluorite, Perovskite, Rocksaltvs anti-Fluorite, anti-CuO2, Würtzite . The key role of F-: the highest  and itsanomalousproperties ! Designing new compounds (tuning Mn+oxidation states) 2D/3D Ribbons (S2-, O2-, F- ) vs 3D (OH-, O2-, F- ) tunnel networks Tuning the band gap and opto-electronicproperties by playingwithcompetitive bonds around Mn+ Precursors to generatedefectsintooxides

  32. Acknowledgments Mathieu Duttine, ICMCB Laetitia Sronek, PhD, ICMCB(2007) Nicolas Penin, ICMCB Damien Dambournet, PhD ICMCB(2008) PHENIX, Paris Madhu Chennabassapa, Post-doc (2014) ICMCB Belto Dieudonné, Post-doc (2016) ICMCB Damien Pauwels, PhD, ICMCB (2003), St Gobain Etienne Durand, ICMCB Alain Tressaud, ICMCB

  33. Structural features of Ti1-(O,OH,F)3 HTB-Pnma Atomic positions and bond distances

  34. Structural features of (Ti0.9M0.1)1-(O,OH,F)3 HTB-Pnma (M=V, Mo, W) atomic positions and bond distances

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