Author(s) Tkach, A.; Santos, A.; Zlotnik, S.; Serrazina, R.; Okhay, O.; Bdikin, I.; Costa, M.Elisabete; Vilarinho, P.M.
Journal Nanomaterials (Basel)
Date Published 2019 Nov 11

If piezoelectric micro-devices based on KNaNbO (KNN) thin films are to achieve commercialization, it is critical to optimize the films' performance using low-cost scalable processing conditions. Here, sol-gel derived KNN thin films are deposited using 0.2 and 0.4 M precursor solutions with 5% solely potassium excess and 20% alkali (both potassium and sodium) excess on platinized sapphire substrates with reduced thermal expansion mismatch in relation to KNN. Being then rapid thermal annealed at 750 °C for 5 min, the films revealed an identical thickness of ~340 nm but different properties. An average grain size of ~100 nm and nearly stoichiometric KNN films are obtained when using 5% potassium excess solution, while 20% alkali excess solutions give the grain size of 500-600 nm and (Na + K)/Nb ratio of 1.07-1.08 in the prepared films. Moreover, the 5% potassium excess solution films have a perovskite structure without clear preferential orientation, whereas a (100) texture appears for 20% alkali excess solutions, being particularly strong for the 0.4 M solution concentration. As a result of the grain size and (100) texturing competition, the highest room-temperature dielectric permittivity and lowest dissipation factor measured in the parallel-plate-capacitor geometry were obtained for KNN films using 0.2 M precursor solutions with 20% alkali excess. These films were also shown to possess more quadratic-like and less coercive local piezoelectric loops, compared to those from 5% potassium excess solution. Furthermore, KNN films with large (100)-textured grains prepared from 0.4 M precursor solution with 20% alkali excess were found to possess superior local piezoresponse attributed to multiscale domain microstructures.

DOI 10.3390/nano9111600
ISSN 2079-4991
Citation Nanomaterials (Basel). 2019;9(11).

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