Effect of manganese dopant on the structural, morphological and piezoelectric properties of potassium sodium niobate thin films

Azman, Muhd. Afiq Hafizuddin (2025) Effect of manganese dopant on the structural, morphological and piezoelectric properties of potassium sodium niobate thin films. Masters thesis, Universiti Teknikal Malaysia Melaka.

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Abstract

The urgent need to replace toxic lead-based piezoelectric, particularly Pb(Zr,Ti)O₃ (PZT), has intensified research into lead-free alternatives such as potassium sodium niobate (KNN), though practical applications remain limited by poor densification, volatilization of light cations, porosity, and reduced domain mobility compared to Pb-based systems. Manganese (Mn) doping has been proposed to address these challenges by refining grains, suppressing oxygen vacancies, stabilizing ferroelectric domains, and enhancing polarization, though its effects are strongly concentration dependent. The main aim of this research was to enhance the structural, morphological and piezoelectric properties of KNN thin films by incorporating Mn dopants of varying concentrations (0.1 mol, 0.3 mol, 0.5 mol, 0.7 mol, and 0.9 mol) through the sol–gel method. Specifically, the objectives were: (a) to fabricate and validate KNN thin films with different MnO concentrations using the sol–gel method, (b) to analyze and evaluate the structural, morphological, and electrical properties of Mn-doped KNN thin films, and (c) to determine and justify the optimal Mn doping concentration that maximizes piezoelectric performance. KNN thin films with Mn concentrations ranging from 0.1-0.9 mol were synthesized and systematically characterized to achieve these objectives. X-ray diffraction (XRD) confirmed that all films crystallized into a stable orthorhombic perovskite phase without secondary phases, while high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) revealed clear lattice fringes and sharp diffraction rings, confirming high crystallinity. Field-emission scanning electron microscopy (FESEM) demonstrated that pure KNN films exhibited irregular and porous grains, whereas 0.3-0.5 mol Mn-doped films displayed dense, uniform grains with reduced porosity, consistent with atomic force microscopy (AFM) roughness measurements that showed stabilization at 0.5 mol. Electrical resistivity analysis revealed a non-linear correlation with Mn doping, reaching an optimal minimum of 0.05 MΩ at 0.3 mol before increasing at higher concentrations due to defect accumulation and porosity effects. Piezoelectric force microscopy (PFM) measurements demonstrated substantial improvements over pure KNN, with stable coefficients between 0.3-0.7 mol and a maximum at 0.9 mol, though the latter was accompanied by increased roughness, resistivity, and structural degradation. By integrating these findings, 0.3 mol Mn doping was identified as the optimal concentration, providing the best balance of densification, resistivity reduction, roughness stabilization, and consistent piezoelectric response, while 0.5 mol also exhibited promising results. Overall, this study demonstrates that Mn doping in the range of 0.3-0.5 mol optimally enhances the piezoelectric performance of KNN thin films, offering a viable lead-free alternative to toxic PZT systems and providing insights into the growth mechanism by which Mn influences grain structure, defect chemistry, and polarization dynamics for improved electromechanical properties.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Piezoelectric devices -- Materials, Thin films
Divisions:	Library > Tesis > FTKIP
Depositing User:	Norhairol Khalid
Date Deposited:	18 Aug 2026 08:27
Last Modified:	18 Aug 2026 08:27
URI:	http://eprints.utem.edu.my/id/eprint/30367
Statistic Details:	View Download Statistic

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