PhD Thesis Arne Lüker final version V4 - Cranfield University

86
Barium Strontium Titanate (BST)
The solution was then spin coated on Pt/Ti/SiO2/Si at 3000 rpm for 30 sec. The as
deposited wet films were heated in a three-step heating process using two different hot
plates and a furnace. In the first heating step at low temperature of 300ºC for 40 seconds
the gel was dried and subsequently pyrolysed at 550ºC for 2 minutes on a second hot
plate. These steps were repeated several times to optain the necessary thickness. At the
end the film was inserted into a furnace for annealing and crystallisation. The annealing
Intensity (arb. Units)
(100)
(e) ■
(d) ■
(c)
(b)
(a)
■
20 30 40 50 60
Fig. 4.1: X-ray diffractograms of BST (a) pyrolised at 550°C; annealed at (b) 600°C, (c) 700°C,
(d) 800°C, and (e) 900°C for 30 minutes.
time was 30 minutes at different temperatures from 600ºC up to 900ºC to get information
about the lowest crystallisation temperature.
Fig. 4.1 shows that the dry gel first begins to crystallise into barium carbonate, BaCO3, in
the pyrolysing step at 550°C [8]. During the annealing bake at 600°C the peroskite BST
(110) phase begins to crystallise while the BaCO3-phase is still present. Finally, after
700°C the BST is fully crystallised. The (100), (110), (200), and (211) phases are present
and the BaCO3-phase has vanished. A further increase in the annealing temperature has
no visible effect in the X-ray diffractograms.
*
*
(110)
■
■
■
■
Pt (111)
2-Theta [º]
* BaCO3
■ perovskite BST
(200) (211)
■
■
■
■
■
■