The highest performing piezoelectric materials include lead as a major constituent.
Worldwide, increased restrictions on the use of lead have resulted in a search for
candidates to replace these lead-based piezoelectric materials. One promising material is
the solid solution of (Bi0.5Na0.5)TiO3 – (Bi0.5K0.5)TiO3 (BNT-BKT). Although promising
behavior has been observed in bulk materials, similar results have been elusive for BNTBKT
thin films. In this work, 0.8 BNT – 0.2 BKT thin films (near morphotropic phase
boundary composition) were synthesized on platinized silicon substrates via chemical
solution deposition. Well-crystallized BNT – BKT thin films were grown at varying
processing conditions. Phase purity was confirmed by X-ray diffraction. As Bi, Na, and
K are volatile elements, overdoping of these cations (addition of excess cation
precursors) was introduced to compensate for volatilization during synthesis.
Quantitative compositional analysis of films was performed with electron probe
microanalysis and compositional depth profiling to confirm atomic ratios via X-ray
photoelectron spectroscopy. The composition data from both measurements were
consistent and indicated stoichiometric films were achieved. Dependent on the
overdoping and annealing conditions, dense, smooth, crack-free films were achieved
with relative dielectric constants from 390 to 730 and low dielectric loss of 2 - 5% at 1
kHz. Additionally, maximum and remanent polarizations of 45 and 16 μC/cm2,
respectively, were recorded at 200 Hz. The addition of Bi(Mg0.5Ti0.5)O3 (BMgT) was
also explored, as promising piezoelectric response in bulk compositions has been
observed. BNT-BKT-BMgT thin films were prepared, showing very promising
piezoelectric response with d33,f up to 90 pm/V and strain values of 0.35%.
