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