SYNTHESIS OF BULK FULLY DENSE NANOCRYSTALLINEFUNCTIONAL OXIDES WITH GRAIN SIZE APPROACHING 10 nm

U. Anselmi‐Tamburini

Department of ChemistryUniversity of Pavia

Italy

GRAIN SIZE APPROACHING 10 nm. WHY?

Physical properties of materials change with grain size

•Trivial effectsDue only to increase of the density of interfaces and grain boundaries

A.V. Chadwick, S.L.P. Savin, Solid State Ionics 177 (2006) 3001–3008

R l ff t•Real effectsDue to a change in local properties

Example: confinement effect in semiconductors – quantum dots

GRAIN SIZE APPROACHING 10 nm. WHY?

Grain boundaries collect impurities and defects but have also an intrinsic effect

Space Charge effect

intrinsic effect

X.Guo, R.Waser, Progress in Materials Science 51 (2006) 151–210

GRAIN SIZE APPROACHING 10 nm. WHY?

Effect of nanostructure and space charge effect on the electrical properties of ionic materialsof ionic materials

TRIVIAL EFFECT REAL EFFECT

SYNTHESIS OF BULK OXIDES WITH GRAIN SIZESYNTHESIS OF BULK OXIDES WITH GRAIN SIZE APPROACHING 10 nm

It is one of the biggest challanges that materials scientists are facing

In principle there are two possible routes:

•Densification of nanopowders •General applicability•Grain growth difficult to control•Very sensitive to the characteristics of the nanopowders

•Controlled crystallization of amorphous precursors•Applicable only to few systemsSi l h l diffi lt t bt i•Single phase samples are difficult to obtain

HIGH-PRESSURE FIELD ASSISTED SINTERING (HP-FAST)

U. Anselmi-Tamburini , J.E. Garay, Z.A. Munir, Scripta Materialia 54 (2006) 823–828

HIGH-PRESSURE FIELD ASSISTED SINTERING (HP-FAST)

8%YSZ

>98% relative density

sintering time 5 min

U. Anselmi-Tamburini , J.E. Garay, Z.A. Munir, Scripta Materialia 54 (2006) 823–828

EXAMPLES OF THE PECULIAR PROPERTIES OBSERVED IN FUNCTIONAL NANOCRYSTALLINE OXIDES OBTAINED BY HP-FASTFUNCTIONAL NANOCRYSTALLINE OXIDES OBTAINED BY HP FAST

YSZ – high proton conductivity

CGO – disappearance of the grain boundary resistivity in fully ionic conduction regime ionic conduction regime

ZrO2 – bulk undoped tetragonal zirconia

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

Anselmi-Tamburini U., Maglia F., Chiodelli G., Tacca A., Spinolo G., Riello P., Bucella S., Munir Z.A., Adv. Funct. Mater., 16 (2006) 2363

F. Maglia, M. Dapiaggi, I.Tredici, B. Maroni, U.Anselmi-Tamburini, J.Am.Cerm.Soc. 93(7) (2010) 2092-2097.

EXAMPLE #1EXAMPLE #1

INFLUENCE OF GRAIN SIZE ON THE ELECTRICAL PROPERTIES OF (Ce Sm )OELECTRICAL PROPERTIES OF (Ce0.7Sm0.3)O2

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

INFLUENCE OF GRAIN SIZE ON (Ce0.7Sm0.3)O2

dr > 98%

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

INFLUENCE OF GRAIN SIZE ON (Ce0.7Sm0.3)O2

G i iGrain size 16.5 nm

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

University of Pavia, Italy Umberto Anselmi‐Tamburini

INFLUENCE OF GRAIN SIZE ON THE PROPERTIES OF (Ce0.7Sm0.3)O2

Sample. Ea(eV)

εr 35 nm16.5 nm

35 nm 0.98 58.8

16.5 nm 0.99 60.0

Microcryst 1.053 25.0.

Synthesis of fully dense functional oxides with grain size approaching 10 nm

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

INFLUENCE OF GRAIN SIZE ON (Ce0.7Sm0.3)O2

Possible interpretation:accumulation of free e- in the Space Charge regionaccumulation of free e- in the Space Charge regionIt is possible only if mixed conductor

S.Kim and J.Maier, J.Electrochem. Soc., 149, J73-J83 (2002)

INFLUENCE OF GRAIN SIZE ON (Ce0.7Sm0.3)O2

No dependence from p(O2)p p( 2)

Purely ionic

Cerium Oxide (Ce0.7Sm0.3O2)

Anselmi-Tamburini U., Maglia F., Chiodelli G., Riello P., Bucella S., Munir Z.A., Appl. Phys. Lett., 89 (2006) 163116

INFLUENCE OF GRAIN SIZE ON (Ce0.7Sm0.3)O2

Other Possible interpretations:

1) Overlap of space charge regions with desappareance of distinction

p

with desappareance of distinction between bulk and grain boundary

( )kTe

kTe

gb

bulk

/)0(4/)0(2exp

ϕϕ

σσ

ΔΔ

=2) Reduction of the potential at the core of the grain boundary gb

EXAMPLE #2EXAMPLE #2EXAMPLE #2EXAMPLE #2

PROTONIC CONDUCTIVITY IN NANOCRYSTALLINE YSZPROTONIC CONDUCTIVITY IN NANOCRYSTALLINE YSZ

Anselmi-Tamburini U., Maglia F., Chiodelli G., Tacca A., Spinolo G., Riello P., Bucella S., Munir Z.A., Adv. Funct. Mater., 16 (2006) 2363

INFLUENCE OF GRAIN SIZE ON YSZ

Very large apparent grain boundary resistance

Th diff b d d i h i iThe difference between σgb and σbulk reduces with grain size

Guo X, Zhang Z. Acta Mater 2003;51:2539

INFLUENCE OF GRAIN SIZE ON YSZ

200 nm T=200°C

Composition 8%mol Y2O3

Grain size 15.5 nm

dr > 98%

INTERACTION OF NANOCRYSTALLINE YSZ WITH WATER

•If exposed to air saturated with water200°C If exposed to air saturated with water the conductivity increases almost 2 orders of magnitude.

200 C

•The change involves both bulk and grain gboundaries

•It is totaly reversible

Dehydration at 200°C for (b) 10 min, (c) 20 min, (d) 30 min, (e) 40 min , (f) 80 min

•It is observed only in samples with grain size below 50 nm

Anselmi-Tamburini U., Maglia F., Chiodelli G., Tacca A., Spinolo G., Riello P., Bucella S., Munir Z.A., Adv. Funct. Mater., 16 (2006) 2363

INTERACTION OF NANOCRYSTALLINE YSZ WITH WATER

Anselmi-Tamburini U., Maglia F., Chiodelli G., Tacca A., Spinolo G., Riello P., Bucella S., Munir Z.A., Adv. Funct. Mater., 16 (2006) 2363

INTERACTION OF NANOCRYSTALLINE YSZ WITH WATER

(a) nanocristalline(a) nanocristalline

(b) microcristalline

•Results suggests protonic conductivity

•Protonic conductivity in YSZ has been ••• →++ X OHOVOH )(2proposed before but never observed

•Nanostructure can enhance the localization of protons at the grain boundary

→++ OOO OHOVOH )(22

Anselmi-Tamburini U., Maglia F., Chiodelli G., Tacca A., Spinolo G., Riello P., Bucella S., Munir Z.A., Adv. Funct. Mater., 16 (2006) 2363

EXAMPLE #3EXAMPLE #3EXAMPLE #3EXAMPLE #3

SYNTHESIS OF BULK, FULLY DENSE UNDOPED TETRAGONAL ZIRCONIA

F. Maglia, M. Dapiaggi, I.Tredici, B. Maroni, U.Anselmi-Tamburini, J.Am.Cerm.Soc. 93(7) (2010) 2092-2097.

ZIRCONIA PHASE STABILITY

Monoclinic Tetragonal Cubic

ZIRCONIA PHASE STABILITY

J.Chevalier, L.Gremillard, A.V. Virkar, D.R. Clarke, J. Am. Ceram. Soc., 92 (2009) 1901–1920

ZIRCONIA PHASE STABILITY

Effect of nanostructure

• In nanocrystals of undoped zirconia the tetragonal phase can be stabilized at room temperature

• It is generally recognized that there is a critical dimension <Dc>

Author <Dc> nmValmalette J.Ch. et al., Chem. Mater. 14 (2002) 5098–102 3

Morgan P.E.D. J.Am.Ceram.Soc. 67 (1984) C204–5 < 6Morgan P.E.D.  J.Am.Ceram.Soc.  67 (1984) C204 5 < 6

Garvie R.C. et al., Nature 258 (1975) 703–4 10

Clearfield A. Inorg. Chem . 3 (1964) 146–8. 12

Djurado E.  et al. J.Solid State Chem.  149 (2000) 399–407. 13

Chraska T. et al. Mater. Sci. Eng. A 286 (2000) 169–78. 18

Shukla S. et al. J.Phys.Chem. B 108 (2004) 3395–9. 20‐25

Mitsuhashi T . et al. J. Am. Ceram. Soc. 52 (1974) 97–101 > 30 agglomerated

Shukla S. et al. NanoLett.  2 (2002) 989–93 500‐600 agglomerated

ZIRCONIA PHASE STABILITY

Effect of nanostructure

The stabilization of the tetragonal structure in nanocrystals of pure zirconia is a complex phenomena that is influenced by several factors

• Surface energy• Interfacial energy• Strain energy• External pressure• Presence of water vapour• Presence of contaminant anionsO i i• Oxygen vacancies concentration

ZIRCONIA PHASE STABILITY

Effect of nanostructure

The stabilization of tetragonal structure in pure zirconia has been realized only in nanopowders and thin films. 

No attempt to produce bulk materials has ever been reported

Thi ill ll th i ti ti f b lk ti f d d t t l i iThis will allow the investigation of bulk properties of undoped tetragonal zirconia• Mechanical properties• Nature and concentration of point defects• Transport properties• Transport properties

SYNTHESIS OF UNDOPED ZIRCONIA NANOPOWDERS

We tested few synthesis routesy

Main objectives:

•Minimum amount of monoclinic phase

•small grain size (< 10 nm)  to enhance stabilization of monoclinic phase

•Minimum agglomeration to enhance densification

•Minimum amount of organic impurities to enhance densification

SYNTHESIS OF UNDOPED ZIRCONIA NANOPOWDERS

Synthesis methods investigated

Route Precursors Method SolventRoute Precursors Method Solvent Pechini ZrO(NO3)2

Ci i idpolymerization @ 80°C water

Citric acid Alkoxides hydrolysis Zr Isopropoxide acidic hydrolysis isopropanol Zr Propoxide acidic hydrolysis propanol Zr Propoxide acidic hydrolysis – inverted addition propanol Solvothermal treatment of gels precipitated at basic pH ZrO(NO3)2 treatment @ 130°C, 10-72 h water ZrOCl2 treatment @ 130°C, 10 h water

ZrO(NO3)2 treatment @ 160°C 20 h methanolZrO(NO3)2 treatment @ 160 C, 20 h methanol ZrO(NO3)2 treatment @ 160°C, 20 h isopropanol/methanol 90/10

PHASE STABILITY IN UNDOPED NANOPOWDERS

Annealing time 20 min

heating

Sintering temperature cannot exceed 850-900°C

M.Dapiaggi, F.Maglia, I.Tredici, B.Maroni, G.Borghini, U.Anselmi-Tamburini, J.Phys.Chem.Solid 71 (2010) 1038cooling

DENSIFICATION OF UNDOPED ZIRCONIA NANOPOWDERS

Typical sintering conditions

200°C/ i

900°C5 min

200°C/min

Sintering pressure 700-800 MPa

DENSIFICATION OF UNDOPED ZIRCONIA NANOPOWDERS

1800

Best result

1500

1800

densified

Relative density 95%

900

1200

d

Relative density 95%

300

600powder

020 25 30 35 40 45 50 55 60 65 70

2 theta