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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - Nano-PieZoelecTrics (Novel Nanoporous PZT Materials for Efficient Utrasonic Biomedical Sensors)

Teaser

Summary

State of the art and impact on society. Piezoelectric materials have become a key technology for a wide range of industrial and consumer products. Piezoceramics is the largest material group for piezoelectric devices, and, currently, the strongest demand comes from ultrasonic transducer for medical diagnostics and therapy (with â‚¬ 1.8 billion, represents the third largest market in the world), which are gaining ever-increasing importance among piezo-device suppliers. In this field, particular attention has been received by 3D and new generation 4D ultrasonic transducers (commonly known as medical probes) widely used to visualize the internal condition of the human body without damaging them in various medical inspections including prenatal examinations to which radiography cannot be applied. The most-commonly piezoceramics materials used, the highly-dense PZT ceramics with general formula Pb(ZrxTi1-x)O3, are characterized by high values of density and relative permittivity, which negatively influence the performance and limit their application in the ultrasonic devices. Furthermore, the presence of a lead-based material can be considered a critical issue for device working in contact with biological tissues. Objectives. Among the lead-free candidates, KxNa1-xNbO3 (KNN) has become one of the most investigated lead-free piezoelectric system. Despite the enormous efforts promoted by the scientific community to achieve KNN systems with similar properties of PZT in acoustic devices, the targets achieved are still far and not suitable for a rapid penetration into the market. For these reason, among the most important objectives fixed of this project, there was the synthesis of high performing KNN-based materials by using a novel fabrication approach and dopants. Main results. Along this horizon the research project Nanopiezoelectrics has been properly conducted exploiting advanced synthetic routes and achieving several results in terms of performance of the specimens fabricated. The research activity was addressed to accomplish several goals using different approaches through solid state reaction and sol gel routes, in order to fabricate the active and matching layers with high piezoelectric properties. As main results, KNN ceramics (as active layer) was opportunely doped with MgNb2O6 (MN) compound and Li ions. The both systems present significant improvement in terms of piezoelectric and electromechanical properties. For the first doped system, MgNb2O6, it was for the first time used in the current literature representing one of the novelty of this project. The experiments revealed the several benefits of this novel dopant which can be used for industrial application in transducer devices.

Work performed

At the beginning of the project, as planned in the working program of the proposal, the research activity has been focused on the study of the commercial PZT systems and their potential applications. To this regard a manuscript has been published concerning the application of a lead-based piezoceramic for detecting the sequence of hits in a mechanochemical reactor. The as mentioned manuscript has been published as gold open access. At the same time, the attention has been moved to lead-free piezoceramics systems for transducers in medical imaging. This was motivated to the fact that, lead oxide, the main reagent of PZT, is toxic and its use is restricted in many countries of UE. Following the methodologies mentioned in the proposal, two main approaches have been used to prepare the lead-free system based on Potassium Sodium Niobate (KNN): i) the classical solid state route using the combination of mechanical treatment and thermal annealing and ii) the wet chemistry method exploring new and sustainable way. Furthermore, an efficient dopant was finally selected to be used as agent for improving the electromechanical properties of the KNN samples. Firstly, the attention was focused on the preparation of porous undoped KNN. This was demonstrated feasible for the first time in the current literature and its final characterization is still under progress. The summary of this period have been presented, as poster contributions, to the MSCA alumni conferences placed at Salamanca (2017) and Leuven (2018). Secondly, a new and facile synthesis of KNN by a modified Pechini method has been developed. By this approach it was possible to tune the stoichiometry of the final system, using water as green solvent and obtaining a very high piezoresponse. The latter compared with the data reported in the current literature, represents one of the most promising for undoped KNN densified by hydraulic press. This work was published and presented by an oral contribution in an international conference, EMRS 2018. The end of the project was focused on the fabrication of KNN-doped sensors synthesized by a solid state route. The systems have been characterized in collaboration with the prestigious center of materials of CSIC in Madrid. The class of materials tested in this period have been doped with MgNb2O6 (MN) and Li-based additives. If for the latter similar properties have been achieved with respect the data reported in the specific literature, for the first system named KNN-MN, very promising results are emerged. In particular a detailed study on the properties of KNN doped with different amount of MN revealed that the composite KNN-0.1MN possesses the best electromechanical properties. The system has been also object of investigation for its up-scaling fabrication. In the next future, this system will be teste under real condition. These results have been presented, as oral contribution, in the conference on piezoceramics Spain-Portugal (2018) and it will be published by February 2019.

Final results

Nanopiezoelectrics deals with the synthesis and characterization of piezoceramics to be applied in ultrasonic transducers. Respect to the specific state of the art, a new synthetic route has been achieved and published for the preparation of potassium sodium niobate (KNN) with interesting piezo ceramics properties. A facile route which consists of exploiting water as green solvent, allows to control the stoichiometry of the system prepared and achieve a significant crystallization of the compacted powders. The piezoceramics properties resulted are amongst the best reported in the current literature for undoped KNN systems densified by a hydraulic press. Furthermore, the methodology stated in Nanopiezoelectrics has been published as Review format, where a new point of view and progress clearly emerged for the lead-free piezoceramics synthesis routes for application in ultrasound transducer. Finally, the MgNb2O6 reported in the proposal as one of the promising dopant, has been tested and relevant benefits in terms of electromechanical properties has been achieved. Up-scaling production of this system are realized and in the future the research will be moved to test it under real conditions. From a point of view of the socio-economic impact, the facile synthesis, can be exploited from two point of view i) the lead oxide is avoided, and this is a great benefit because its high toxicity, ii) low cost of the starting reagents used in the protocol and the use of water instead of toxic and environmental counterpart solvents typically used in this preparation route. Very important the system KNN-MN could be a potential candidate to replace commercial PZT in ultrasonic transducers.