Preliminary study of KNN thin films doped by rare-earths for sensor applications

Among ferroelectrics systems, potassium sodium niobate KNN) has drawn much attention due to a clear-cut advantage of high piezoelectric and ferroelectric performances. The volatility of alkaline element (K,Na) is detrimental to the stoichiometry of KNN, contributing to the formation of intrinsic defects. Thus, the primary goal of this study is to design a solution to overcome the volatility issue of KNN. Introduction of rare-earth cations in the host KNN could reduce the vacancies in KNN. Currently, three arrays of dopants were integrated into KNN. In this preliminary work, a sol-gel technique was employed to produce a thin film that can be utilized later in the sensor applications. The structural and electrical properties were characterized using Raman spectroscopy and 2-point probe equipment, respectively. The typical Raman spectra of KNN thin films were shifted towards lower or higher wavenumbers depending on the cations deficiencies or redundancies. The conductivity of thin films was found to be increased as the dopant concentration was increased

Potassium sodium niobate (KNN) lead-free piezoceramics: A review of phase boundary engineering based on KNN materials

Lead zirconia titanate (PZT) is the most often used piezoelectric material in various electronic applications like energy harvesters, ultrasonic capacitors and motors. It is true that PZT has a lot of significant drawbacks due to its 60% lead content, despite its outstanding ferroelectric, dielectric and piezoelectric properties which influenced by PZT's morphotropic phase boundary. The recently found potassium sodium niobate (KNN) is one of the most promising candidates for a new lead-free piezoelectric material. For the purpose of providing a resource and shedding light on the future, this paper provides a summary of the historical development of different phase boundaries in KNN materials and provides some guidance on how to achieve piezoelectric activity on par with PZT through a thorough examination and critical analysis of relevant articles by providing insight and perspective of KNN, which consists of detailed evaluation of the design, construction of phase boundaries and engineering for applications

Vibrational piezoelectric energy harvester’s performance using lead zirconate titanate versus lead-free potassium sodium niobate

Piezoelectric energy harvester (PEH) is considered as a robust power source, which can power electronic devices by scavenging small magnitudes of energy from ambient vibration. The fundamental advantage of PEH lies in the inherent ability of the piezoelectric material to generate electricity depending on the amount of vibration applied to the material. Although lead zirconate titanate (PZT) is the most common type of piezoelectric material used, the toxicity of PZT damages the environment and causes health issues, thus necessitates the need for the discovery of lead-free piezoelectric material. Hence, potassium sodium niobate (KNN) was chosen to eradicate the toxicity of the PZT material. In this paper, the performance of KNN energy harvester was compared with a commercial lead-based material using finite element modelling. Both harvesters showed a comparable output power of 0.104 mW for KNN and 0.115 mW for PZT, respectively. The recorded maximum output voltage of KNN was 0.952 V when resonated at 2097.7 Hz. KNN also rank among the best piezoelectric energy harvester compared to the commonly reported electromechanical coupling coefficient and figure of merit. The proposed KNN energy harvester provides a very promising solution to substitute lead-based energy harvester in the future

Structural evolution and dopant occupancy preference of yttrium-doped potassium sodium niobate thin films

Sodium potassium niobate (KNN) is the most promising candidate for lead-free piezoelectric material, owing to its high Curie temperature and piezoelectric coefficients among the non-lead piezoelectric. Numerous studies have been carried out to enhance piezoelectric properties of KNN through composition design. This research studied the effects of yttrium concentrations and lattice site occupancy preference in KNN films. For this research, the yttrium-doped KNN thin films (mol% = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) were fabricated using the sol-gel spin coating technique and had revealed the orthorhombic perovskite structures. Based on the replacement of Y3+ ions for K+/ Na+ ions, it was found that the films doped with 0.1 to 0.5 mol% of yttrium had less lattice strain, while films with more than 0.5 mol% of Y3+ ions had increased strain due to the tendency of Y3+ to occupy the B-site in the perovskite lattice. Furthermore, by analysing the vibrational attributes of octahedron bonding, the dopant occupancy at A-site and B-site lattices could be identified. O-Nb-O bonding was asymmetric and became distorted due to the B-site occupancy of yttrium dopants at high dopant concentrations of >0.5 mol%. Extra conduction electrons had resulted in better resistivity of 2.153× 106 Ω at 0.5 mol%, while higher resistivity was recorded for films prepared with higher concentration of more than 0.5 mol%. The introduction of Y3+ improved the grain distribution of KNN structure. Further investigations indicated that yttrium enhances the surface smoothness of the films. However, at high concentrations (0.9 mol%), the yttrium increases the roughness of the surface. Within the studied range of Y3+ , the film with 0.5 mol% Y3+ represented a relatively desirable improvement in dielectric loss, tan δ and quality factor, Qm

Microbial chitosan for the fabrication of piezoelectric thin film

Chitin has proven to have a good mechanical and electrical properties to be used in making piezoelectric thin films. However, due to the restriction in solubilizing chitosan in many solvents, there is increasing interest in exploring the used of chitosan in producing thin films. Chitosan, compared to chitin, can be easily solubilized in certain dilute acids. Chitosan that has been extracted from fungal biomass can be used for the fabrication of biomaterial thin films. There are different ways that can be used to fabricate a thin film such as electrospinning, spin-coating, solvent casting and also the hot press technique

The Effects Of Different Annealing Temperature And Number Of Deposition Layers On The Crystallographic Properties Sodium Niobate (KNN) Thin Films Synthesized By Sol-Gel Spin Coating Technique

In this paper, the effects of different annealing temperature and number of deposition layers on the crystallographic properties of potassium sodium niobate (KNN) thin films were investigated. X-ray diffraction (XRD) analysis was carried out to determine the crystallographic orientation and phase formation of thin films deposited at different annealing temperatures (600°C, 650°C and 700°C) and various number of deposition layers (1, 2, 3, 4 and 4 layers). The XRD patterns and texture coefficient of the synthesized films confirmed that a highly oriented orthorhombic perovskite structure was obtained at 650°C, while at higher temperature a spurious phase of K4Nb6O17 was evolved. The effective number of deposition layers was found to be five due to the formation of interconnected cracks at sixth deposited layers. The XPPA analysis showed that the unit cell volume of the films was increased gradually from 110.83 cm3 at one layer to 124.31 cm3 at fifth deposited layers. Nevertheless, the lattice strain effect was small and negligible at high layer deposition due to the increased distance of the lattice with the film/substrate interface

Influence of ZnO dopant on piezoelectric properties of potassium sodium niobate thin films

Lead zirconia titanate (PZT) is widely used due to its ferroelectric and piezoelectric properties. However, toxic lead in PZT is extensively linked to the greenhouse effect. For this constraint, extensive research is being done to find new piezoelectric materials such as potassium sodium niobate (K0.5Na0.5NbO3 or KNN). Due to processing difficulties, KNN has been disregarded for a long time. Volatilization of alkaline elements causes compositional inhomogeneity and lowers piezoelectric activity of ceramics. This research examines how ZnO-doping affects the structural and electrical changes and characteristics of potassium sodium niobate (KNN) ceramics. Potassium Sodium Niobate (KNN) thin films were grown on ITO substrate by using sol-gel spin coating method. The as-deposited thin films were heated 250 ℃ pyrolysis for 5 min and then was annealed at the temperature 650 ℃. Following this, KNN thin films were characterized using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM). The electrical properties of KNN thin films were analysed using Atomic Force Microscopy (AFM) and Piezoresponse Force Microscopy (PFM). Based on the findings, it can be inferred that a doping concentration of 0.9 mol ZnO is considered the most appropriate for the production of a homogeneous and cohesive KNN thin film. This film demonstrates favourable electrical properties, making it well-suited for implementation in piezoelectric applications

The effects of different pyrolysis and annealing temperature on structural and resistivity of K0.5Na0.5NbO3 thin film

Potassium sodium niobate (KNN) thin film is a very promising candidate for piezoelectric applications such as for the usage in wireless sensor, actuator, and transducer. In this paper, a low-cost sol-gel spin coating technique was employed to fabricate KNN thin films on silicon (Si) substrate. The effect of pyrolysis and annealing temperature on the material properties of KNN thin films were investigated. X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) were used to examine the structural properties of the KNN thin films. The electrical properties of KNN thin films were characterized using resistivity testing. The experimental results reveal that high pyrolysis and annealing temperature greatly enhanced the structural and electrical properties of KNN thin films

Characterization of ZnO–TiO2-coated tapered fibres synthesized by a low-temperature hydrothermal method

We characterize ZnO-nanorod fibres doped with different concentrations of TiO2 powder which is introduced on the final stage of synthesis of ZnO nanorods, using a low-temperature hydrothermal method. Their surface morphology, size of particles, behaviour of crystallites and optical properties are investigated using techniques of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and an optical spectrometer. A presence of ZnO nanorods and a globular structure of TiO2 are confirmed by the SEM analysis. The EDS spectra and chemical-element mapping reveals a presence of Ti incorporated into a globular surface, along with Zn. The XRD analysis testifies that ZnO doped with TiO2 has a primary crystallite phase of ZnO. ZnO doped with 10 and 15 mM of TiO2 shows a stronger and more expressed peak corresponding to (002) and (011) planes, which implies improved crystallinity of ZnO–TiO2 system. Optical properties of ZnO–TiO2 are studied by measuring the intensity of halogen-source light transmitted through the fibres. The ZnO & 15 mM TiO2 fibre sample shows the lowest intensity of the transmitted light due to higher refractive index of a cladding layer coated under condition of high TiO2 concentration. The increased light leakage in such a fibre can improve sensitivity of a relevant sensor, especially a gas one