| Green energies, which comprise kinds of new candidates, have excited worldwide interest due to the threatening of global environmental pollution and energy crises. Piezoelectric materials can generate an output signal with a strain. Potassium sodium niobate(KNN) based materials are widely focused due to their lead free nature, high Curie temperature and relatively high piezoresponse compared to PZT system. However, the synthesis and characterization of single crystalline KNN nanomaterials are still in the initial phase because of lacking of appropriate fabrication method and characterization approach. It should be noted that the single crystal nature and nanoscale of KNN nanorods(NRs) make them crucial in sensors, actuators and so on. This study focused on the controllable synthesis of KNN NRs via molten salt method, modification of composition and piezoresponse via advanced facilities, thus the preparation of nanosized generator.Firstly, the morphology and composition of resultant KNN NRs was modified by adjusting reaction parameters, such as molten salts/reactants concentration, process details and impurity during synthesis. As a result, the KNN NRs with length of 10-20μm and width(diameter) of 400-500 nm were achieved. The NRs were uniform throughout the length, and the K/Na ratios of which range from 43/57 to 77/23. In addition, the evolution of products between the intermediate product and KNN NRs was investigated.Secondly, Raman spectrum, inductively coupled plasma spectroscopya, transmission electron microscopy, ect. Instruments were introduced to the composition and microstructure charactrization of KNN NRs. The growth mechanism was confirmed by the observation of nanosteps with the heights of 5-10 nm at the end of NR. More importantly, the correspondence between the characteristic frequencies and the compositions of KNN single crystals was implied by Raman spectra, which enables a facile and non-destructive method to determine the composition, especially the K/Na ratios of KNN materials, and certainly paves the way for further investigations concerning fabrication of KNN NRs, even other materials at nano/submicro- scale.Furthermore, the morphology mapping and the piezoelectric effect of KNN NRs were presented by AFM, SS-PFM in SPM system, respectively. It could be known that the piezoresponse along the NR was consistent, indicating the composition-uniformity of NRs. Therefore, the composition-dependent piezoelectric displacement was investigatred, and the correspondence of the piezoelectric amplitudes, coercive voltage(Vc), together with the specific nanodomain structures were observed in KNN NRs with K/Na of 45/55, indicates the existence of phase boundary in KNN NRs. Therefore, the OI-OII induced MPB does exist in KNN single crystals.Finally, the generator which consists of the KNN NRs with relatively high piezoperformance and PDMS(polydimethylsiloxane) were fabricated via flow casting method. The average output voltage of the generator could reach at 0.38 V with a certain strain, and the singal stability was further confirmed after repeated tests. Additionally, the output singals could increase from ~35mV to ~0.5V with the enhancement of applied strain to the generator composite. This kind of composite is expected to be applied in energy harvesting systems due to its independent and sustainable operations properties. |
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