Densification, grain growth and texturation in SPS nanoZnO ceramics - - PowerPoint PPT Presentation

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Densification, grain growth and texturation in SPS nanoZnO ceramics - - PowerPoint PPT Presentation

Aug 13, 2022 136 likes •301 views

Densification, grain growth and texturation in SPS nanoZnO ceramics Giovannelli F. a , Daz-Chao P. b Lebedev O. b , Chateigner D. b , Guilmeau E. b , Delorme F. a A Universit Franois Rabelais de Tours, CNRS, CEA, INSA CVL, GREMAN, IUT Blois,

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SLIDE 1

Giovannelli F.a, Díaz-Chao P.b Lebedev O.b, Chateigner D.b, Guilmeau E.b, Delorme F.a

A Université François Rabelais de Tours, CNRS, CEA, INSA CVL, GREMAN, IUT Blois, France. BCRISMAT, UCBN, ENSICAEN, Caen, France

Densification, grain growth and texturation in SPS nanoZnO ceramics

27th september 2016 Limoges

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SLIDE 2

Motivation

2

  • n-type TE oxide
  • Abundant elements
  • ZT ~ 0.6

Seebeck Electrical conductivity Thermal conductivity Temperature

ZnO as thermoelectric material

  • High densities at low temperatures
  • Small grain sizes Low thermal conductivity (κ)

Why SPS?

  • Transparent oxide (Gap ~ 3.3 eV)
  • Hexagonal structure
  • Stability at high temperatures
  • Biocompatible
  • Multiple applications: Photovoltaics, varistors, medicine…

ZnO:

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SLIDE 3

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125 ml 4 M NaOH 100 ml 1 M Zn(NO3)2·6H2O (+ 5 % AlCl3) Dropwise addition, stirring, 20°C Centrifugation (4000 rpm-5 min) Washing 4 times

Controlled precipitation in aqueous solution

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SLIDE 4

Starting material

  • Pure and Al doped (0.3%) ZnO powder

prepared by co-precipitation

  • No secondary phases
  • Non-isotropic morphologies

Al doped ZnO Pure ZnO

4

10 20 30 40 50 60 70 80 90 100

1 0 1 0 0 2 1 0 0

Starting powders Pure ZnO Al-doped ZnO

Intensity (arb. units) 2θ

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SLIDE 5

Starting Powder: No secondary phases (Al doped 0.3%) Non-isotropic morphologies:

  • Pure ZnO:
  • platelets, flower-like structures (c-axis in plane)
  • Al-doped ZnO:
  • platelets, isolated (c-axis in the plane)
  • spherical small particles
  • needle like (along the c-axis)

5

Al doped ZnO Pure ZnO

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SLIDE 6

200 400 600 800 1000 1200 30 40 50 60 70 80 90 100

a)

Relative Density (%) Temperature (°C)

Pure ZnO Doped ZnO (Al 0.3% at.)

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Pure ZnO T<800°C Low densities (<70%) T > 800°C High densities (>90%) Al-doped ZnO T > 500°C High densities (>90%) SPS sintering Conditions

  • P = 100 MPa
  • 500°C < T < 1100°C
  • 100°C/min, 5’
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SLIDE 7

Al doped ZnO

  • High texturation degree
  • Suppression of the 0 0 2 peak
  • c-axis perpendicular to pressure

Pure ZnO

  • Low texturation degree
  • Evolution of the 1 0 0 peak

7

XRD on the surface

28 30 32 34 36 38 40

Pure ZnO

600°C 800°C 1000°C 1100°C Intensity (arb. units) 2θ

28 30 32 34 36 38 40

800°C 1000°C 600°C 500°C

Al:ZnO (0.3%)

Intensity (arb. units) 2θ

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SLIDE 8

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φ γ φ γ Pure ZnO

  • Low texturation degree
  • Low T: (1 0 0)//pressure axis
  • High T: (0 0 2)//pressure axis

Al doped ZnO

  • High texturation degree
  • (1 0 0)//pressure
  • (0 0 2)⊥pressure

∀T 500°C 600°C 800°C 1000°C 600°C 800°C 1000°C 1100°C

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SLIDE 9

Cross Section Surface

Al-doped ZnO 500°C

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MORPHOLOGY: Isotropic grain

28 30 32 34 36 38 40

Intensity (arb. units) 2θ

28 30 32 34 36 38 40

Intensity (arb. units) 2θ

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SLIDE 10

Pure ZnO:

  • Isotrope grains at high temperatures
  • Grain growth from T > 800°C

Al doped ZnO:

  • Isotrope grains at all temperatures
  • Grain growth from T ~ 500°C

10

MORPHOLOGY: Evolution of the grain size Al doped ZnO Pure ZnO

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SLIDE 11

DENSIFICATION MECHANISM Al doped ZnO

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Pure ZnO

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SLIDE 12

Thermoelectric properties: influence of the texturation

100 200 300 400 500 600 700 0.03 0.04 0.05 0.06

a)

ρ (Ω·cm)

T (°C)

Perpendicular pressure direction Parallel pressure direction

100 200 300 400 500 600 700

  • 380
  • 360
  • 340
  • 320
  • 300
  • 280

b) S (µV/K) T (°C)

Perpendicular pressure direction Parallel pressure direction

100 200 300 400 500 600 700 5 10 15 20 25 30

c) Thermal conductivity (W/m·K) T(°C)

Perpendicular pressure direction Parallel pressure direction

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  • No influence of texturation on Seebeck and thermal conductivity
  • Low influence of texturation on electrical resistivity

1 0 0 direction more resistive at room temperature No influence at high temperatures (T > 300°C)

Perpendicular to pressure direction (c-axis randomly in plane) Parallel to pressure direction (1 0 0 direction)

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SLIDE 13

13

Al doped ZnO 60°C 80% 98% 86% Powder synthesis

  • Isotropic nanoparticles

(< 50 nm)

Sintering

100 nm

800°C , 5 min 850°C , 30 min 900°C , 5 min

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SLIDE 14

14

Effect of microstructure on thermal conductivity at 50°C

45 W/m K 35 W/m K 34 W/m K Interconnected platelets

Pure ZnO Al doped ZnO

Nanoparticles Platelets + nanoparticles Nanoparticles 12 W/m K 29 W/m K

800°C 500°C 850°C/30 min

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SLIDE 15

Conclusions

15

Starting powder:

  • Synthesis by co-precipitation of pure and 0.3% Al-doped ZnO
  • Non isotropic morphologies
  • Flower like structures in pure ZnO
  • Isolated platelets, nanoparticles and needles in doped ZnO
  • Isotropic nanoparticles in doped ZnO

SPS :

  • Dense ceramic at 500°C
  • Differences in shrinkage due to different starting morphologies

TE properties (doped samples):

  • No influence of texturation on Seebeck and thermal conductivity
  • Influence of texturation on the electrical resistivity:
  • Higher resistivity along the 100 direction at low T (T < 300°C)
  • No influence at high temperatures (T > 300°C)
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SLIDE 16

Thank you for your attention

16

Giovannelli F.a, Díaz-Chao P.b Lebedev O.b, Chateigner D.b, Guilmeau E.b, Delorme F.a

A Université François Rabelais de Tours, CNRS, CEA, INSA CVL, GREMAN, IUT Blois, France. BCRISMAT, UCBN, ENSICAEN, Caen, France

Densification, grain growth and texturation in SPS nanoZnO ceramics