Vibration-energy-harvesting properties of hydrothermally synthesized (K,Na)NbO3films deposited on flexible metal foil substrates

Kim

ACS Appl. Mater. Interfaces

2019

The successful utilization of Pb-free piezoelectric materials is considered as critical since the piezoelectric material-based thin-film cantilever is still the preferred choice for commercial vibrational energy harvesters. Herein, we introduce a highly efficient piezoelectric energy harvester based on a Pb-free representative compound, Bi0.5Na0.5TiO3, which has not been explored so far. Applying a strong electric field for poling purposes brought unexpectedly huge changes in the dielectric constant and piezoelectric coefficient, which were responsible for the promising power density of 21.2 μW/cm2/g2/Hz with 537.7 mV output voltage and 2.22 μW output power for a 2 μm thick 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 thin-film cantilever. The power density value is the best so far compared with any reported values for thin-film-based harvesters. As the origin of the effects of poling, the surface potentials across the grain structure are discussed in conjunction with the defect-dipole alignment, as evidenced by the increased oxygen vacancies on the film surface under an external bias field.

Section: Resultsmentioning

confidence: 99%

Electric-Field-Dependent Surface Potentials and Vibrational Energy-Harvesting Characteristics of Bi(Na_0.5Ti_0.5)O₃-Based Pb-Free Piezoelectric Thin Films

Kim

ACS Appl. Mater. Interfaces

2019

“…In our previous studies, it was found that K-rich (K,Na)-NbO 3 films (sodium content: between 1020 %) deposited by the hydrothermal method exhibited dielectric and piezoelectric properties suitable for applications to sensors and energy harvesters. 25) It was also shown that the piezoelectric property can be improved by Ta substitution. 26) Therefore, it is expected that the morphological control of the hydrothermally-synthesized (K,Na)(Nb,Ta)O 3 powders with K-rich composition lead to achieve the highperformance devices.…”

Section: Introductionmentioning

confidence: 99%

Effect of Ta substitution on the synthesis of (K,Na)(Nb,Ta)O3 powders by hydrothermal reaction: Insight into the combination of alkaline solution and raw powder

Sano¹,

Shiraishi

Kiguchi

et al. 2021

J. Ceram. Soc. Japan

Self Cite

Ta substituted (K,Na)NbO 3 powders with K-rich composition across polymorphic phase boundary were synthesized at 200°C by hydrothermal method. The amount of Ta content in the powders was controlled by changing the nominal composition of raw powders,). Elemental mappings using a transmission electron microscope showed all the elements (K, Na, Nb, and Ta) were contained in the powders. X-ray diffraction measurement showed that (K,Na)(Nb,Ta)O 3 solid solution powders can be obtained for all nominal compositions (C = 01), and that the orthorhombic-tetragonal phase transition can be induced by controlling C value, yet the diffraction peaks arising from a secondary phase were also detected in the range of C = 0.51. Scanning electron microscopy (SEM) observation revealed that the morphology of powder changed from polymorphic to square, and the size of the square-shaped (K,Na)(Nb,Ta)O 3 powder decreased, with increasing the nominal composition. Temporal evolution of the emerged phases revealed that the range of intermediate phase became shorter with increasing the nominal composition, allowing the perovskite phase to form from early stages. In addition, the cause of the secondary phase was unreacted raw powder. Observations on the powder synthesis with end-member composition (KOHNb 2 O 5 , NaOHNb 2 O 5 , KOHTa 2 O 5 , and NaOH Ta 2 O 5 ) has shown that perovskite single-phase was formed in KOH-Nb 2 O 5 , NaOH-Nb 2 O 5 , and KOH-Ta 2 O 5 , while that unreacted raw powder was detected in the combination of NaOH and Ta 2 O 5 . These results demonstrated that Ta substitution is an effective way to control the morphology of powder and that the synthesis behavior of (K,Na)(Nb,Ta)O 3 is strongly dependent on the combination of alkaline solution and raw powder.

“…Their power density was relatively high value in an ambient frequency among lead-free piezoelectric films. 23) To increase power generation i.e. act as energy harvesters, the thicker films are required because the generated power is proportional to the film thickness.…”

Section: Introductionmentioning

confidence: 99%

High yield preparation of (100)c-oriented (K,Na)NbO3 thick films by hydrothermal method using amorphous niobium source

Ito

Tateyama

Nakamura

et al. 2020

J. Ceram. Soc. Japan

Self Cite

NbO 3 thick films were prepared at 240°C on (100) c SrRuO 3 //(100)SrTiO 3 substrates by hydrothermal method. Film thickness increased using an amorphous niobium source instead of conventionally used crystalline one and have the maximum thickness at 0.5 mmol of input mass of niobium source within the range of 0.02 7.5 mmol in case of the 20 h deposition. The yield of (K,Na)NbO 3 films from 0.5 mmol amorphous niobium source becomes 20 times higher than that from conventionally used a 2 mmol crystalline niobium source. In addition, crystal structure, surface morphology, dielectric constant, and ferroelectric and piezoelectric properties of these films were almost independent of the kinds of niobium sources and their input mass within the limitation of the present results.