PhD Thesis Arne Lüker final version V4 - Cranfield University

B Site Doping of PST 40/60
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B Site Doping of PST 40/60
In section 5.2 it was discovered that the Curie temperature of PST 50/50 is too close to
room temperature, resulting in increased losses due to domain switching. By decreasing
the Pb-content down to 40% the transition temperature is pushed to lower temperatures.
No other change in the preparation of the solution or deposition procedure is necessary,
one of the big advantages of the so-gel deposition method.
It has been shown for BST that some dopants including Mg 2+ , Ni 2+ , Fe 3+ , Mn 2+ , Mn 3+ ,
Co 2+ , Co 3+ , Al 3+ , Cr 3+ and Bi 3+ , which can occupy the B site of the ABO3 perovskite
structure and behave as electron acceptors, can lower the dielectric loss, enhance the
dielectric constant and thus the tunability and figure of merrit [1 – 10]. For PST, being a
relatively new system under increasing investigation for voltage tunable devices, only a
few paper on B site doping can be found [e.g. 11 – 13] and the shown results are not very
clear and satisfying. Manganese has been used in our lab to improve successfully the
ferroelectric and pyroelectric properties of sol-gel derived PZT thin films [14 – 16]. The
aim of the study in this chapter is to improve the material performance of PST further
more by doping of the B site with manganese (Mn 2+ ), which has an ionic radius of 0.67
Å, comparable to that of Ti 4+ (0.68 Å), and to gain a deeper understanding of the effect of
doping.
6.1 Synthesis and Characterisation of (Pb0.4,Sr0.6)(Ti1-x,Mnx)O3
To prepare a 40/60 composition of (Pb,Sr) TiO3 with, for example, 3 mol% of
manganese, 1.591 g of lead acetate and 1.177 g of strontium acetate were dissolved in a
mixture of 5 ml 1.3 propanediol and 8 ml acetic acid. Stirring and slightly heating helped
to get a clear solution. Meanwhile 3.245 g of titanium butoxide and 0.0495 g of
manganese acetate were mixed in a glove box and diluted with 15 ml acetic acid. Both
solutions were mixed and stirred at room temperature over night. The final solution was
diluted with 2-methoxyethanol up to a volume of 50 ml to adjust the concentration of the
solution to 0.4 M.