Sympozjum Wydziału Fizyki 17 kwietnia 2008

Transport ładunku elektrycznego w amorficznych, nanokrystalicznych

i kompozytowych przewodnikach elektronowych i jonowych

Jerzy E.Garbarczyk, Wojciech Wróbel

Zakład Joniki Ciała Stałego

Wydział Fizyki PW

Motywacja

Cel poznawczyBadanie transportu ładunku elektrycznego w mało poznanych formach fazy skondensowanej

Cel aplikacyjnyZastosowania w urządzeniach do konwersji i magazynowania energii (baterie litowo-jonowe, ogniwa paliwowe, sensory gazowe, superkondensatory)

Sympozjum Wydziału Fizyki 17 kwietnia 2008

Prezentacje

Jerzy E.Garbarczyk

„Nowe nanomateriały i kompozyty oparte na szklistych przewodnikach elektronowych i jonowych”

Wojciech Wróbel

„Korelacja między elektrycznymi i mechanicznymi właściwościami cieczy szkłotwórczych”

Sympozjum Wydziału Fizyki 17 kwietnia 2008

Sympozjum Wydziału Fizyki 17 kwietnia 2008

Novel nanomaterials and composites based on electronic and ionic conductive glasses

Outline

• Advantages and disadvantages of ionic and electronic conductive

glasses

• Novel nanomaterials based on lithium-vanadate-phosphate (LVP)

glasses

• Novel nanomaterials based on lithium-iron-phosphate (LFP)

glasses

• Novel composites based on ionically conductive glasses

• Summary

Advantages and disadvantages of conductive glasses

Advantages simple processing possibility of forming various shapes isotropy and homogeneity absence of grain boundaries high ionic conductivity at room temperature

(up to 10-2 S/cm for AgI – based conducting glasses) high electronic conductivity at above 300ºC (up to 10-3 S/cm for vanadia – rich glasses)

inherent ability to nanocrystallization (this study) possibility of considerable modification of the composition and electrical properties

Example: vanadia-based glasses

V2O5 – main glass former, source of electronic conduction via V4+ → V5+ hopping of small polarons

P2O5 – supporting glass formerLi2O – glass modifier, source of mobile Li+ ionsAg2O – glass modifier, source of mobile Ag+ ionsAgI – dopant, main source of mobile Ag+ ions

Mixed ionic-electronic conductivity in systems: Li2O - V2O5 - P2O5 (Li+/e-)AgI - Ag2O - V2O5 - P2O5 (Ag+/e-)

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport

in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport

in Li2O-V2O5-P2O5 glasses

or

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

or

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

Model of the electrical charge transport in Li2O-V2O5-P2O5 glasses

or

Isotherms of the total electrical conductivity in Li2O-V2O5-P2O5 glasses

V2O5-rich glasses

ionic

electronic

mixed

P.Jozwiak, J.Garbarczyk, Solid State Ionics 176 (2005) 2163

H.Takahashi, T.Karasawa, T.Sakuma,J.E.Garbarczyk, ICPSSI-2, Yokohama, 2007

Total electrical conductivity at 100°C vs. composition in AgI-Ag2O-V2O5-P2O5 glasses

J.E.Garbarczyk, P.Machowski et al.Mol.Phys.Rep. 35 (2003) 139.

electronic

ionic

Total electrical conductivity at 100°C vs. composition in AgI-Ag2O-V2O5-P2O5 glasses

electronic

ionic

electronic

ionic

J.E.Garbarczyk, P.Machowski et al.Mol.Phys.Rep. 35 (2003) 139.

Advantages and disadvantages of conductive glasses (cont.)

Disadvantages

metastability composition and structure less known than those of the crystalline

materials low glass transition temperature of the best ion conductive glasses

(for AgI-doped glasses 60°C < Tg < 100°C) low fracture toughness moderate electronic conductivity at 20°C of glassy cathode materials

Aims of our studies

preparation of new nanomaterials derived from conductive glasses exhibiting better electrical properties and thermal stability than the initial glasses

preparation of new glassy-crystalline composites exhibiting improved mechanical properties compared to the glasses

Novel nanomaterials based on lithium-vanadate-phosphate (LVP) glasses

It is known that nanostructured materials exhibit attractive properties, often dramatically different than those of the crystalline or amorphous counterparts.

Effect of nanocrystallization on ionic conductivity St. Adams, K.Hariharan, J.Maier, Solid State Ionics 86-88 (1996) 503.

AgI-rich glasses of the system AgI-Ag2O-MxOy

Effect of nanocrystallization on electronic and mixed conductivity

J.E.Garbarczyk, P.Jozwiak et al. Solid State Ionics 175 (2004) 691.

V2O5-rich glasses of the system Li2O-V2O5-P2O5

a) 15Li2O·70V2O5· 15P2O5

b) 90V2O5· 10P2O5

DSC

Nanocrystallization of the90V2O5∙10P2O5 glass

SEM picture of a 90V2O5∙10P2O5 sample

after nanocrystallization at Tc ≈ 340°C

SEM picture of a 90V2O5∙10P2O5 sample

after nanocrystallization at Tc ≈ 340°C

20 nm

visible nanocrystallites of V2O5 covered by a glassy phase

SEM picture and XRD pattern of a 90V2O5∙10P2O5

sample after massive crystallization at 540°C

● - orthorhombic V2O5

SEM picture of a 90V2O5∙10P2O5 sample after massive crystallization at 540oC (another fragment)

orthorhombic V2O5 crystallites

Discussion of the results on vanadia-based nanomaterials

Mott theory of electron hoppingMott theory of electron hopping in disordered systems in disordered systems

0 expe ee

ET

T kT

R – average distance between hopping centers

C – fraction of hopping sites occupied by electrons

N – concentration of hopping centres – inverse localization length of the electron

wave function

rp – radius of a small polaron

2e mR

for T > / 2

– Debye temperature

2

0

1exp 2e e

e C CR

kR

1 3R N

4+

4+ 5+

V

V + VC

0 1

pe

rE W

R

Discussion of the results on vanadia-based nanomaterials

Samples after nanocrystallization

V2O5

20 nm

Discussion of the results on vanadia-based nanomaterials

Samples after nanocrystallization

V2O5

20 nm

higher concentration of

V4+ -V+5 pairs

Discussion of the results on vanadia-based nanomaterials

Samples after nanocrystallization

„Easy conduction paths” – interface regions between nanocrystallites and glassy phase.Higher concentration of V4+-V5+ pairs in these regions than inside grains.

V2O5

20 nm

high concentration of

V4+ -V+5 pairs

easy conduction path

–

+

Discussion of the results (cont.) Sample after massive crystallization

There is no intermediate glassy phase. The electrical transport between grains is partly blocked by the presence of grain boundaries.

Novel nanomaterials based on lithium-iron-phosphate (LFP) glasses

Crystalline lithium-iron-phosphates (olivines)

Nanocrystallization of glassy samples - SEM

Cooperation with Prof. Christian Julien, Univ. P.et M.Curie, Paris, France(local structure)

A.Ait Salah, P.Jozwiak, J.Garbarczyk, Ch.Julien et al.Journal of Power Sources 140 (2005) 370.

Związki interkalowane - przykłady

Oliwiny i związki pokrewne

Crystalline lithium-iron-phosphates

Crystalline olivine-type phases - LiFePO4 and FePO4 as well as LixFePO4 solid solutions - are under intensive studies worldwide as the most competitive cathode materials for Li-ion rechargeable batteries.

These cathode materials are: • highly stable (thermally and electrochemically),• inexpensive,• environment – friendly.

Furthermore they exhibit:• high specific capacity (170 mAh/g),• high discharge voltage (3.5 V vs. Li).

Crystalline lithium-iron-phosphates

Crystalline olivine-type phases - LiFePO4 and FePO4 as well as LixFePO4 solid solutions - are under intensive studies worldwide as the most competitive cathode materials for Li-ion rechargeable batteries.

These cathode materials are: • highly stable (thermally and electrochemically),• inexpensive,• environment – friendly.

Furthermore they exhibit:• high specific capacity (170 mAh/g),• high discharge voltage (3.5 V vs. Li).

Unfortunately they have one serious deficiency – very low electrical conductivity - ca. 10-10 S·cm‑1 at 25°C.

Crystalline olivines (cont.)

Many efforts have been undertaken to improve their electrical properties by:

• introduction of carbon additives, • doping with supervalent cations,• various synthesis routes.

Our alternative approach – nanocrystallization of glassy analogs of olivines:

• step 1: preparation of vitreous analogs of these materials,• step 2: turning these glasses into nanomaterials by an

appropriate thermal treatment.

Electrical properties after partial nanocrystallization (sample of x = 0)

SEM picture after partial nanocrystallization for sample of x = 0

Electrical properties after partial nanocrystallization (sample of x = 0.4)

σt(530°C)=1.1∙10-2 S/cm

σt(50°C)= 1.8∙10-8 S/cm

σt(50°C)=7.6∙10-8 S/cm

≈ 4 times

SEM micrograph after crystallization for sample of x = 0.4

SEM micrograph after crystallization for sample of x = 0.4

Novel composites based on ionically conductive glasses

Motivation

Ag+ - ion conductive glasses exhibit high electrical conductivity (up to 10-2 S·cm-1 at 25°C), but some of their mechanical properties may cause problems with samples machining (e.g. cutting and polishing) and limit eventual prospective applications.

In order to minimize this drawback we propose new composites based on silver-ion conductive glasses.

Novel composites based on ionically conductive glasses (cont.)

Glassy components:

AgI-Ag2O-B2O3

AgI-Ag2O-P2O5

AgI-Ag2O-V2O5

Ceramic powder components: Diamond (1-2 µm)

-Al2O3 (2 µm)

ZrO2 (1 and/or 10 µm)

Composites prepared in 50 - 50 % vol fractions

B2O3, P2O5, V2O5 – glass formersAg2O – glass modifierAgI – dopant

High-pressure route of preparation of the composites

Facility at the Institute of High Pressure Physics, Polish Academy of Sciences, Warsaw

com pactedglass pow dercom pactedceram ic pow der

graphiteheater

High-pressure route of preparation of the composites (cont.)

100-200°C

com pactedglass pow dercom pactedceram ic pow der

graphiteheater

Pressure

Pressure

Temperature

100-250°C

3-8 GPa

SEM and XRD studies

Obrazek SEM(fosforanowe z diamentem, boranowe z alumina)

Glass: 40AgI·30Ag2O·30P2O5

Diamond powder (1-2 m)Synthesis: p = 3 GPa, T = 250°C

as-prepared after annealing at 200°C

M.Zgirski, J.Garbarczyk et al., Solid State Ionics, 176 (2005) 2141

SEM studies (cont.)

50AgI·33Ag2O·17B2O3 : -Al2O3 (2 m) - a phase view

Al2O3

Al2O3

Glass

SEM studies (cont.)

55AgI·30Ag2O·15B2O3 : ZrO2 (1 m) - a phase view

ZrO2

Electrical properties of compositesabove room temperature

40AgI·30Ag2O·30P2O5 : diamond

200=1.6·10-2 S·cm-1

27=1·10-4 S·cm-1

E=0.34 eV

E=0.54 eV

Tg

glass

4 6 8 10 12-15

-10

-5

0

Glass50AgI·33Ag

2O·17B

2O

3

glass

E = 0.30 eV

E = 0.30 eV

Composite 50AgI·33Ag

2O·17B

2O

3 + Al

2O

3 (2 m)

Synthesis: T = 100°C, p = 7.7 GPa

log(T

/ S

·cm

-1K

)

1000 K / T

composite

40 0 -40 -80 -120 -160

t / °C

Electrical conductivity of compositesat low temperatures

M.Foltyn, M.Wasiucionek, J.E.Garbarczyk et al.., Solid State Ionics, 179 (2008) 38

Mechanical properties - Vickers microhardness

40 45 50 55 60

100

150

200

250

mic

roha

rdne

ss [k

G·m

m-2]

x [%mol]

xAgI·(100-x)(0.67Ag2O·0.33B2O3)

composites (with -Al2O3)

glasses

Electrical properties of composites (cont.)

Lower specific conductivity of the composites can be compensated by a possibility of preparing thinner samples.

Mechanically sound membranes of ca 100 m thickness can be fabricated.

sheet of paper - edge

composite 1. (ca 100 m)

composite 2. (ca 300 m)

Summary

Conductive glasses can be promising starting materials to prepare attractive composites and nanostructured materials.

The annealing of the V2O5 – rich glasses (LVP) to Tc leads to their nanocrystallization.

The resulting nanomaterials exhibit much higher electronic conductivity (10-1 S/cm at 300ºC), lower activation energy and better thermal stability than the initial glasses.

Summary (cont.)

Electrical properties of lithium-iron-phosphate (LFP) glasses are similar to crystalline olivines.

It was found that thermal nanocrystallization of LFP glasses leads to the conductivity enhancement,

Summary (cont.)

Electrical properties of lithium-iron-phosphate (LFP) glasses are similar to crystalline olivines.

It was found that thermal nanocrystallization of LFP glasses leads to the conductivity enhancement,

...therefore it seems to be a promising way for electrical conductivity improvement of amorphous lithium-iron-phosphates.

A prospective high-pressure method was used to produce silver ion conductive composites based on AgI – doped glasses with good electrical and mechanical properties.

Zespół badawczy

Marek Wasiucionek

Paweł Jóźwiak

Jan L.Nowiński

Marek Foltyn

Irena Gorzkowska – Wydział Chemiczny PW

Bogdan Pałosz – Unipress (IWC PAN)

Stanisław Gierlotka – Unipress (IWC PAN)

R. Bacewicz, M. Wasiucionek, A. Twaróg, J. Filipowicz, P. Jóźwiak, J.E. Garbarczyk, J. Mat. Sci. 40 (2005) 4267-4270.

Electrical properties of composites above room temperature

40AgI·40Ag2O·20B2O3 : -Al2O3

M.Foltyn, M.Wasiucionek, J.Garbarczyk et al.J.Power Sources 173 (2007) 795

=1.6·10-2

=2.5·10-3