Novel KNN Fibres based on ferroelectric nanopowder

• Research unit: COST
• Project number: C11.0142

Key words (English)

Piezoelectreic fibres; lead free; KNN; Nanopowder

Research programs (English)

COST-Action MP0904 - Single- and multiphase ferroics and multiferroics with restricted geometries (SIMUFER)

Short description (English)

The aim of the project is to develop novel lead free piezoelectric fibres by using KNN nanopowder. This is due to three reasons. (1) Nowadays, the use of hazardous materials, i.e. lead, has been reduced or even eliminate. To replace lead zirconate titanate (PZT) in the field of piezoelectric ceramics, sodium potassium niobate (KNN) is a promising candidate in some area. (2) Nanopowders are very attractive for ceramic processing to increase the sinter activity. This higher sinter activity will help to decrease the sintering temperature, which is for KNN materials a very important issue to reduce the evaporation of the alkaline metal elements. (3) Recently, the use of fibres in piezoelectric application has increased and it will be necessary to investigate the use of lead-free fibrous materials. Based on the increase of fibre composite applications, the current need of lead-free materials and on a higher sinter activity of nanopowders this project will focus on the fabrication of KNN fibres by extrusion of nanopowder of the same material in a polymeric matrix. The piezoelectric properties of single fibres will be characterised by using a novel test device. With this new device, it will be possible to measure the single fibre properties with small voltage (± 10V) and large voltage (± 3 kV) configuration.

Further information (English)

Full name of research-institution/enterprise: EMPA - Eidg. Materialprüfungs- und Forschungsanstalt Laboratorium für Hochleistungskeramik

Partners and International Organizations (English)

AT; BE; BG; HR; CZ; FI; FR; DE; EL; IE; IT; LT; NL; PL; PT; RO; RS; SK; SI; ES; TR; UK; UA; JP; AU

Abstract (English)

Potassium sodium niobate (KNN) is an environmentally-friendly alternative to lead-based piezoelectric ceramics and could eventually play a comparable role to PZT in certain electronic applications in the future, with the added advantage of being bio-compatible. The advantages of KNN over other Pb-free ceramic powders include low toxicity, low cost and the relative ease of processing with respect to other bio-compatible Pb-free powders. Composites of piezoelectric ceramics and polymers are produced by combining the high dielectric constant and piezoelectricity of ceramics with the low density and flexibility of polymers. Applications of these hybrid smart ceramic-polymer composites include rod composites and active fibre composites (AFCs). Rod composites can be used for sonar, hydrophones, energy harvesting systems or medical diagnostic applications while AFC structures are used for sensor and actuator applications such as structural health monitoring, structural actuation and energy harvesting systems. The thermoplastic extrusion process involves the simultaneous extrusion of multiple materials, such as ceramic-thermoplastic feedstocks that can be used to manufacture fine-scaled piezo-composites. The limitation faced with the process is the minimum amount of material required to produce the feedstock. Depending on the density and desired volume of the materials used, the typical amount of ceramic powder required is a minimum of ~100g. Therefore the process is useful for the production of a large number of samples, but not for the development of novel ferroelectric powders (e.g. nano powder and available in tiny quantities), especially for fibre applications where prototyping of small numbers of low volume experimental powder samples is required. With the added advantage of utilising a special device that enables single fibre piezo- and ferroelectric measurements (FerroFib), working with low powder quantities (i.e. few grams) would be an appropriate application of a new low volume ceramic-thermoplastic feedstock preparation process. The FerroFib equipment allowed the determination of small and large signal electromechanical properties, such as piezoelectric charge coefficient, polarisation evolution loop, strain evolution loop and blocking force on single fibres. A new processing method in combination with the FerroFib analytic device helped to optimize ferroelectric materials especially for future fibrous applications. Using the new small volume compounding route it was possible to produce fibrous ferroelectric materials made of different kind of lead free ferroelectric powder (e.g. KNN and KNNT) and nano-powders (e.g. KNL-NTS and KNT-BKT) successfully. Sintered fibers have been characterized by microstructure analysis, XRD and electromechanical measurements.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C11.0142