Lead-free piezoelectric energy harvester based on optimised potassium sodium niobate thin film

• Main Author: Mat Harttar @ Mohd Hatta, Maziati Akmal
• Format: Thesis
• Language: English; English
• Published: 2017
• Subjects: T Technology (General); TK Electrical engineering. Electronics Nuclear engineering
• Online Access: http://eprints.utem.edu.my/id/eprint/20632/; https://plh.utem.edu.my/cgi-bin/koha/opac-detail.pl?biblionumber=107021

Piezoelectric energy harvester (PEH) is considered as a robust power source, which can power the electronic devices by scavenging small magnitudes of energy from ambient vibration. The fundamental advantage of PEH lies on the inherent ability of the piezoelectric material to generate electricity depending on the amount of vibration applied on the material. Although lead zirconate titanate (PZT) is the most common type of piezoelectric material used, the toxicity of PZT content has damaged the environment and health, in which it necessitates the discovery of lead-free piezoelectric material. Hence, potassium sodium niobate (KNN) is chosen as the potential candidate since good piezoelectric properties can be achieved by compositionally-engineered the perovskite structure. However, the thermal treatment of KNN at high temperature is challenging due to alkali metal cations volatility. In order to address this issue, a series of systematic reviews and a consecutive study on KNN energy harvester was conducted. In the present study, KNN thin films were fabricated via chemical solution deposition method. The effects of the annealing temperature and various number of coating layers on both the structural and electrical properties were looked into in order to find the optimum annealing temperature and coating layers to fabricate KNN thin films. The present study has shown that KNN thin film annealed at 650 °C presented a well-crystallised orthorhombic perovskite structure without the presence of secondary phase which confirmed by X-ray powder diffraction analysis. Crystallinity, molecular vibration, surface morphology, and resistivity were found to depend on the coating layers. Particularly, the optimum properties were found for KNN thin films with five coating layers. In addition, the structural and electrical properties were strongly affected by yttrium doping. All the thin films had a preferred (0 0 1) orientation with formation of pure orthorhombic perovskite structure. Small shift on Raman active mode, together with dense and homogenous surface morphology were obtained for 0.5 mol% yttrium-doped KNN. Besides, 0.5 mol% yttrium-doped KNN had intermediate electrical resistivity (2.153 × 106 Ω.cm), low dielectric loss (0.018 %), high dielectric permittivity (508), and high quality factor (25.730). Next, finite element modelling was performed to determine the resonance frequency of the as-fabricated KNN thin film to generate the optimum voltage and power output. The performance of KNN energy harvester was compared with a commercial lead based material, namely PZT-5H. Both harvesters showed a comparable output power of 0.104 mW and 0.115 mW for KNN and PZT-5H, respectively. Further, energy harvester performance analysis involving finite element modelling and experimental testing recorded a maximum voltage of 0.968 V and a power output of 0.1067 mW, when 0.5 mol% yttrium-doped KNN was resonated at 2098.7 Hz. To compare with pure KNN, 0.5 mol% yttrium-doped KNN exhibited a relatively desirable electromechanical coupling factor about 0.49, which has the potential as an energy harvester to substitute PZT in the future.