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

OUTLINE

SYNTHESIS OF A NEW MATERIAL (NONAQUEOUS SOL-GEL CHEMISTRY)

MOTIVATION STRUCTURAL CHARACTERIZATION DC CONDUCTIVITY DFT CALCULATION DC MAGNETIC SUSCEPTIBILITY CONCLUSION AND OUTLOOK

NONAQUEOUS SOL-GEL CHEMISTRYNONAQUEOUS SOL-GEL CHEMISTRY Molecular Precursor+ Organic Solvent Metal Oxide Network

Metal Halides

Metal Alkoxides

Metal Acetylacetonates

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)

La(OiPr)3

+ benzyl alcohol

+ (2-butanone)

Mn(acac)2

+benzyl alcohol

La(OH)3

MnO

Djerdj et al., J. Solid State Chem. 180 (2007) , 7; 2154-2165.

Djerdj et al., J. Phys. Chem. C 111 (2007) , 9; 3614-3623.

Selected Reaction Systems

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

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

STRUCTURAL CHARACTERIZATION

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

1. Laboratory XRD

2. Complementarity of neutron and synchrotron X-ray powder diffraction

Hydrogen

is virtually invisible for X-rays,

Vanadium

is almost invisible for neutrons:

X-rays NeutronsScatteringamplitudes

Need to exploit both techniques for the complete crystal structure analysis:

Solution and refinement

STRUCTURAL SOLUTION

High-resolution X-ray data used toestablish the main structural motif:

Neutron dataset used to find out where hydrogens are:

Highly distorted VO6 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

Compound name Vanadium Oxyhydroxide

Chemical formula V1O2.29H0.77 → VO1.52(OH)0.77 V-oxidation number +3.81

Space group I4/m (87)

Z 8

Crystal system tetragonal

Lattice parameters (Å) a = 10.4255(6), c = 3.0056(2)

Cell volume (Å3) 326.684(42)

Label Site x y z Bisotropic (Å2)

V 8h 0.1424(2) 0.6596(2) 0 1.18(8)

O1 8h 0.3375(8) 0.9632(6) 0 0.99(5)

O2 8h 0.3387(8) 0.7073(6) 0 0.99(5)

O3 4e 0 0 0.101(4) 0.99(5)

H 8h 0.3640(13) 0.4006(13) 0 0.99(5)

O1

O2

H

O3V

5.5 Å

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

MICROSTRUCTURAL CHARACTERIZATION

Morphology-ellipsoidal nanorods (nanorice, nanocorn): 140-500 nm long, Av. length= 330 nm),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): 3.9Average crystallite size in [002] direction (nm): 65.4

EDX MICROANALYSIS

1 2 3 4 5 6

V

V

Cl

CuO

Inte

nsity

(a.

u.)

Energy (keV)

C

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

TRANSPORT PROPERTIES:DC CONDUCTIVITY

300 320 340 360 380 400 420 4400.0

1.0x10-5

2.0x10-5

3.0x10-5

4.0x10-5

5.0x10-5

Cooling mode

T (K)

(

-1 c

m-1

)

Heating mode

Semiconducting-like behavior,Arrhenius law for thermally activated conduction: σ = σ0exp(-Eσ/kT)Eg = 2 Eσ-band gap Eg=0.64 eV in a cooling mode Eg=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

ELECTRONIC STRUCTURE-DFT CALCULATION

LSDA+ U(SIC) method; U-Coulomb correlation energy (Wien2k package)

spin ↑ spin ↓

U= 4.0 eV

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7-0.9

-0.6

-0.3

0.0

0.3

0.6

0.9

1.2

E-EF (eV)

DO

S (1

/eV

)

V 3dz2

V 3dx2-y2

V 3dxy

V 3dxz

V 3dyz

Majority

Minority

J1

J2

i

i+1i-1

i+2

DC MAGNETIC SUSCEPTIBILITY

0 50 100 150 200 250 3000.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0 50 100 150 200 250 3000

200

400

600

800

mol

-1 (c

m-3

mol

)

T (K)

mol (

cm3 m

ol-1

)

T (K)0 50 100 150 200 250 300

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

T (

em

u K

/mol

)

Temperature (K)

80 K20 K

=dia+vv+ C/(T-θ)

diamagnetic-20.6·10-6 emu/mol

Van-Vleck2·10-4 emu/mol

Curie-Weiss

Fitting in the range 150-300 K:θ=-157(2) K, C=0.457(2) emu/molpeff=1.91μB , pcalc=1.94 μB (V3.81+)p(V4+)=1.73 μB, p(V3+)=2.83 μB

short range order effects

-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

lin=11.8·10-3 emu/molOeJ=8.5-formation of magnetic clusters

Magnetization curve

-40 -20 0 20 40-800

-600

-400

-200

0

200

400

600

800

Data: VO13_A2Model: BrillouenWeighting: y No weighting Chi^2/DoF = 21.28978R^2 = 0.99969 g 2 ±0S 8.5763 ±0.17916Temp 4.2659 ±0n 1.86255 ±0.06774chiLin 11.80856 ±0.08539

-0.4 -0.2 0.0 0.2 0.4-16-12

-8-4048

1216

M (e

mu

mol

-1)

H (kOe)

M (

emu

mol

-1)

H (kOe)

4.2 K

Tk

JHgJBngHHM

B

BJBlin

)(

MAGNETIC ORDERING MODEL

J1

J2

i

i+1i-1

i+2

V4+/V3+=4:1

(V4+V4+)(V4+V4+)V3+ -charge orderingAt very low temperature, within the correlation length ξ,V3+ moments localy polarize neighbourhood leading to a local staggered magnetization

CONCLUSIONS

The nonaqueous sol-gel reaction between VOCl3 and benzyl alcohol yielded the formation of non-stoichiometric vanadium oxyhydroxide VO1.52(OH)0.77 nanorods (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.

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,...).

ACKNOWLEDGEMENT

ETHZ FHI Berlin

Prof. Dr. Reinhard Nesper Prof. Dr. Robert Schlögl

Christian Mensing Dr. Dang Sheng Su

Dr. Noemi Csaba Dr. Marc Willinger

IJS Ljubljana PSI Villigen, CH

Dr. Denis Arčon Dr. Denis Sheptyakov Dr. Fabia GozzoThank you!