Thermochromic Doped Vanadium Dioxide Coatings

for Smart WindowsGhouwaa Philander

iThemba LABSSupervisor: Prof. M.

Maaza

Energy Postgraduate Conference 2013

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows

• Breaking it down– Vanadium Dioxide– Thermochromism and Doping

• Bringing it together– Smart Windows– Need

• Material Synthesized

• Conclusions and Future Work

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Contents

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

Vanadium Dioxide (VO2)

• VO2 undergoes a transition at 68°C from the semi-conducting monoclinic phase to the metallic rutile phase, the latter which is IR opaque.

• VO2 exists in a number of morphologies with varying properties, dependant largely on method synthesis and growth.Whittaker et al. J. Phys. Chem. Lett. 2011, 2, 745–758

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows

• A compound that displays a reversible change in colour as a result of a change in temperature is ‘thermochromic’.– change in geometry– variation in coordination number– change in lattice formation

• Doping is the process of introducing a ‘metal’, as an impurity, into the crystal structure which introduces additional energy levels.

• Doping of VO2 compounds with tungsten reduces the naturally occurring transition temperature to even closer to room temperature.

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Thermochromism and Doping

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

Smart Windows

Parkin and Manning. J. Chem. Ed. 2006, 83, 393-400

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows

• Heating, ventilation and air-conditioning, contribute an estimated 15% to South Africa’s current peak demand consumption.

• 33% saving in energy consumption will be realised if inside and outside temperature difference is maintained. (Eskom Communication Fact Sheet, January 2013)

• Objective: To develop a cost effective chemical method to produce efficient and viable VO2

coatings with enhanced properties, for use in smart window applications.

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Need

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

Material Synthesized

20 30 40 50 60

5k

6k

7k

8k

9k

10k

(220)

(200)

(011)

(100)

Intensit

y (

cps)

2 (deg)

• A chemical method was used to synthesize a range of W-doped VO2 films from 0.5-2.5 wt%.

• Polymer assisted deposition with annealing in an oxygen deficient environment.

• Crystalline particle sizes ranged from 30-62 nm along the (011) plane. Variability in the dhkl showed evidence of W integration into the crystal lattice structure.

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

Material Synthesized cont.

200 400 600 800 1000

0

10

20

30

40

50

60

Tra

nsm

itta

nce

(%

)

Wavelength (nm)

0.5% W

1% W

1.5% W

2% W

2.5% W

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows Energy Postgraduate Conference 2013

Material Synthesized cont.

20 30 40 50 60 70 80

0

10M

20M

30M

40M

50M

60M

Resis

tance (

ohm

s)

Temperature (oC)

• The phase transition is represented with a steep slope and takes place at approximately 33°C during the heating and cooling cycle.

• Hysteresis gap of 8.8°C at 27 MΩ .

Thermochromic Doped Vanadium Dioxide Coatings for Smart Windows

• The method has achieved its primary objective of producing thermochromic VO2 films with enhanced properties.

• The reduced transition temperature achieved renders this material suitable for smart window applications.

• Future work will include further optimization of this method, including IR modulation studies.

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Conclusions and Future Work

THANK YOU