Aqueous Chemical Solution Deposition of Epitaxial Lead-Free Ferroelectric Sodium Potassium Niobate (KNN) thin films

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Potassium Sodium Niobate (KxNa1-xNbO3, KNN) thin films were fabricated on SrTiO3 (STO) substrates using an environmentally friendly aqueous Chemical Solution Deposition (CSD) approach, employing water-soluble Na, K, and Nb polyoxometalate precursors. This green route for KNN thin film fabrication offers reduced environmental impact and potential industrial scalability. The annealing recipe was optimized through a detailed investigation, finding that a one-minute annealing at 700°C after each deposition yielded the best structural properties. The impact of varying the K+/Na+ stoichiometry on the films' structural properties was systematically examined. The investigation demonstrated a trend between the K+/Na+ molar ratio in the precursor solution and the strain-state and lattice parameters of the resulting films, suggesting adding 50% excess potassium in the precursor solution is promising for optimal ferroelectric performance. Leveraging the versatility of the aqueous synthesis, lithium was incorporated as a dopant in the precursor solution. Different Li concentrations were investigated, and it was determined that a 6% Li concentration improved the films' structure compared to undoped samples. This demonstrates the potential of aqueous deposition for incorporating dopants to enhance material properties. The study further highlighted the potential for strain engineering and additional dopant incorporation using the aqueous CSD method, opening up avenues for further exploration and optimization of KNN thin films' properties.
Mohammed, A. Z. (2023). Aqueous chemical solution deposition of epitaxial lead-free ferroelectric sodium potassium niobate (KNN) thin films (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from