PhD Thesis Arne Lüker final version V4 - Cranfield University

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Lead Strontium Titanate (PST)
moreover, the processing temperature is lower in lead-based materials compared to BST,
which offers an additional advantage. This signaled the beginning of extensive research
and the number of papers about PST are rocketing since Cross’s suggestion. Maybe an
other case like roman cement (see section 1.2).
In the following chapters the synthesis, characterisation, some realised applications and
benefits of PST 50/50 and 40/60, doped and undoped, are described and investigated.
5.1 Synthesis and Crystallisation of PST
The multicomponent PST precursor solution was prepared using high purity lead
acetate, Pb(CH3CO2)2, strontium acetate, Sr(CH3CO2)2 and titanium butoxide,
Ti(OC4H9)4. First lead acetate and strontium acetate were mixed in a stoichiometric ratio
in 8 ml acetic acid and 5 ml 1.3 propanediol. Heating was needed to help the dissolution
of the precursors. After a while titanium butoxide, diluted in 15 ml acetic acid to
minimise reaction with humidity, was added under constant stirring. The so-called parent
solution was then stirred over night at room temperature. Finally, 2-methoxyethanol was
added up to ~ 46 ml (0.4 M) to stabilise the solution.
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 different hot plates.
In the first heating step the gel was dried at a temperature of 350ºC for 30 seconds and
subsequently pyrolysed at 600ºC for 5 minutes on a second hot plate. These steps were
repeated several times to optain the necessary thickness. Finally a third hot plate was
used to crystallise the film at different temperatures for 15 minutes to investigate the
crystallisation pathway.
Fig. 5.3 shows that the dry gel begins to crystallise into the perovskite PST (110)-phase
in the pyrolysing step at 500°C. The (100)-, (200)-, and (211)-phases start to appear at
550°C and are increasing in intensity until 650°C. After 650°C the film is fully
crystallised. The peak, which appears after a relatively low annealing temperature of
400°C around 33° is often related to the (200) Si-“ghost peak”. A peak which arises
sometimes by destructive interference in case of Si (100) standard substrates at
approximately 32.9°. However, the behavior of this peak is strange in this case.