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Igor Djerdj and Markus Niederberger

CHARACTERIZATION AND PROPERTIES OF NOVEL OXYGEN CONTAINED HOLLANDITE VO 1.52 (OH) 0.77 NANORODS SYNTHESIZED BY NONAQUEOUS SOL-GEL ROUTE. Igor Djerdj and Markus Niederberger ETH Zürich, Department of Materials, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland www.multimat.mat.ethz.ch

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Igor Djerdj and Markus Niederberger

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  1. CHARACTERIZATION AND PROPERTIES OF NOVEL OXYGEN CONTAINED HOLLANDITE VO1.52(OH)0.77 NANORODS SYNTHESIZED BY NONAQUEOUS SOL-GEL ROUTE Igor Djerdj and Markus Niederberger ETH Zürich, Department of Materials, Wolfgang-Pauli-Strasse 10,8093 Zürich, Switzerland www.multimat.mat.ethz.ch igor.djerdj@mat.ethz.ch

  2. OUTLINE • SYNTHESIS OF A NEW MATERIAL (NONAQUEOUS SOL-GEL CHEMISTRY) • MOTIVATION • STRUCTURAL CHARACTERIZATION • DC CONDUCTIVITY • DFT CALCULATION • DC MAGNETIC SUSCEPTIBILITY • CONCLUSION AND OUTLOOK

  3. Molecular Precursor+ Organic Solvent Metal Oxide Network Metal Halides Metal Alkoxides Metal Acetylacetonates NONAQUEOUS SOL-GEL CHEMISTRY No water! The oxygen is provided by the precursor or by the solvent. • Advantages: • Better control of particle formation due to slower reaction rates • High crystallinity at moderate temperatures • No surfactants – high purity • Homogeneous particles within one system (uniform size and shape, narrow size distribution)

  4. Selected Reaction Systems La(OiPr)3 + benzyl alcohol + (2-butanone) Mn(acac)2 + benzyl alcohol MnO La(OH)3 Djerdj et al., J. Phys. Chem. C111 (2007) , 9; 3614-3623. Djerdj et al., J. Solid State Chem. 180 (2007) , 7; 2154-2165.

  5. SYNTHESIS • Materials: Vanadium(V) oxychloride (0.5 ml) and benzyl alcohol (20 ml); • The vial was stirred at RT; The solution gradually turns from a red to a green-blue color; • The reaction took place in autoclave at 150 °C for 24h • The resulting black suspension was centrifuged, the precipitate washed with ethanol (3×) and dried at 60°C in air. • BLACK POWDER

  6. MOTIVATION • Variety of oxidation states of V (+2, +3,+4,+5)→28 V-O compounds (ICSD) • Wealth of physical (outstanding structural flexibility, metal-insulator transition, different magnetic ground state) and chemical (oxidative catalysis, cathode materials for lithium batteries, electrochemical application) properties • 3d electrons →non-diamagnetic ground state

  7. STRUCTURAL CHARACTERIZATION 1. Laboratory XRD XRD pattern matched with ICDD-PDF No. 00-500-1797 →V8.18O16·1.46H2O (s.g. I4/m)-Hollandite type of structure

  8. 2. Complementarity of neutron and synchrotron X-ray powder diffraction Scattering amplitudes Hydrogen is virtually invisible for X-rays, Vanadium is almost invisible for neutrons: X-rays Neutrons Need to exploit both techniques for the complete crystal structure analysis: Solution and refinement

  9. STRUCTURAL SOLUTION High-resolution X-ray data used toestablish the main structural motif: Neutron dataset used to find out where hydrogens are:

  10. Highly distortedVO6 octahedra arranged in double chains along edge-shared lines results in 2 × 2 tunnel structure along c-axis with diameter (opposite O-O distance) of 5.5 Å O2 O1 5.5 Å H V O3 d(V-O1)=1.868 Å and 1.985 Å (2×); d(V-O2)=2.106 Å and 2.055 Å (2×); d(O2-H)= 0.949 Å, typical O-H bond

  11. MICROSTRUCTURAL CHARACTERIZATION Morphology-ellipsoidal nanorods (nanorice, nanocorn): 140-500 nm long,Av. length= 330nm), 50-105 nm wide (Av. width =78 nm) Crystallinity: anisotropic single-crystalline nanorods-growth direction [002]; Average crystallite size (nm): 49.1 Standard deviation-measure of anisotropy (nm): 3.9 Average crystallite size in [002] direction (nm): 65.4

  12. EDX MICROANALYSIS Deduced composition: V 32.3 at.% O 62.4 at.% Cl 5.3 at.% Cl instead of O3? Density measurement: 3.593(4) g/cm3 -assuming the proposed formula, 3.822(4) g/cm3 -assuming chlorine in the channels, 3.535(5) g/cm3 -three independent measurements. Chlorine is attached to the surface of nanorods

  13. TRANSPORT PROPERTIES:DC CONDUCTIVITY Semiconducting-like behavior, Arrhenius law for thermally activated conduction: σ = σ0exp(-Eσ/kT) Eg = 2Eσ-band gap Eg=0.64 eV in a cooling modeEg=0.76 eV in a heating mode The electrical resistivity of the VO1.52(OH)0.77 at room temperature (32 °C): 1.2×106 Ω cm

  14. ELECTRONIC STRUCTURE-DFT CALCULATION LSDA+ U(SIC) method; U-Coulomb correlation energy (Wien2k package) spin ↑ spin ↓

  15. U= 4.0 eV

  16. DC MAGNETIC SUSCEPTIBILITY short range order effects 20 K 80 K =dia+vv+ C/(T-θ) Fitting in the range 150-300 K: θ=-157(2) K, C=0.457(2) emu/mol peff=1.91μB , pcalc=1.94μB (V3.81+) p(V4+)=1.73 μB, p(V3+)=2.83 μB diamagnetic -20.6·10-6 emu/mol Van-Vleck 2·10-4 emu/mol Curie-Weiss

  17. -t2g degeneracy can be lifted by a strong exchange interaction via the overlap of neighboring vanadium orbitals (Pen et al., Phys. Rev. Lett.78 1323 (1997) T graph indicates possible orbital ordering probably induced by the charge ordering below 80 K, hopping between neighbouring V sites may be frozen Low-temperature range Magnetization curve lin=11.8·10-3 emu/molOe J=8.5-formation of magnetic clusters

  18. MAGNETIC ORDERING MODEL V4+/V3+=4:1 (V4+V4+)(V4+V4+)V3+ -charge ordering At very low temperature, within the correlation length ξ, V3+ moments localy polarize neighbourhood leading to a local staggered magnetization

  19. CONCLUSIONS • The nonaqueous sol-gel reaction between VOCl3 and benzyl alcohol yielded the formation of non-stoichiometric vanadium oxyhydroxide VO1.52(OH)0.77nanorods (nanorice, nanocorn); • The data show that the structure can be described as hollandite-type structure containing only oxygen in the 2×2 channels along c-axis, with hydrogen attached to the one octahedral-coordinating oxygen, forming thus OH− group. The Cl− is attached onto the surface of nanorods; • The nanorods are single-crystalline up to 500 nm long and 105 nm in diameter with growth direction along [002] axis; • The formal valence of vanadium, 3.81+ (V4+/V3+=4:1) is corroborated by neutron diffraction, synchrotron XRD as well as magnetization measurement; • DC conductivity evidenced the semiconducting ground state with Eg=0.64 eV formed by splitting of t2g orbitals hybridized with O 2p; • DC magnetization points to the possible orbital ordering (below 80 K) and charge ordering [(V4+V4+)(V4+V4+)V3+] below 20 K.

  20. OUTLOOK • T-dependent XRD; • AC susceptibility; • 51V NMR; • EPR; • Li-ion intercalation - from the application point of view (Li-ion batteries) and from the electronic point of view (metallic states, doping,...).

  21. ACKNOWLEDGEMENT ETHZFHI Berlin Prof. Dr. Reinhard NesperProf. Dr. Robert Schlögl Christian MensingDr. Dang Sheng Su Dr. Noemi CsabaDr. Marc Willinger IJS Ljubljana PSI Villigen, CH Dr. Denis Arčon Dr. Denis Sheptyakov Dr. Fabia Gozzo Thank you!

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