Objectif
Through the compositional study performed it has been identified that bulk ceramic materials produced with sodium modified lithium compositions gave the best overall properties. From the parallel investigations that were conducted in an effort to enhance material properties the use of chemical additives with the pure and sodium modified lithium niobate invariably produced materials that although they produced an increase in one particular property this was at the expense of the other properties.
Powders prepared from the traditional mixed oxide route showed promising properties, however, reproducibility of the properties in the sintered ceramics has yet to be proved. Although the typical values for density of the sintered ceramic are not as high as those produced by the sol-gel route the general properties of the ceramic exhibited superior electromechanical properties: again there is difficulty achieving reproducible results. This process, in addition to being the most cost effective of the routes, can be used as one of the easiest ways to study compositional modification.
From a processing stand point, the sol-gel route is highly versatile and flexible powder synthesis route. A high purity reactive powder can be produced with relative ease and with good reproducibility, with quality powder produced within a broad processing window. It is considered that scaling up to yield industrial quantities of this process is feasible.
Choice of electrode material is crucial to the behaviour of a piezoelectric material, particularly at elevated temperatures. Efforts have been focused on the development of a high temperature electrode material with good compatibility with the ceramic material under actual working conditions. High quality co-fired electrodes have been developed that show good adherence, conductivity and integrity before and after ageing studies.
The resistivity, dielectric and piezoelectric properties of the ceramics produced were determined from room temperature to 1000 C. Finally, the oxygen loss behaviour as a function of temperature and time have been established. The results obtained were used to improve composition and fabrication.
The most promising materials were selected for each of the particular devices. Prototype accelerometer and ultrasonic probe devices were designed and constructed to investigate the material properties under actual working conditions. These tests, as well as giving valuable information as to the behaviour of different materials, have enabled device design to be improved. Therefore results have been used to further adjust ceramic composition and processing and to modify device design
Despite the need for high temperature piezoelectric materials in, for example, ultrasonic probes and accelerometers, the choice of materials available is very limited. At present, only single crystals of tourmaline, which has poor piezoelectric sensitivity, can be operated above 650 C. The aim of this project to develop a piezoceramic with improved properties, which can be operated up to 800 C. Two materials with Curie temperatures above 1000 C have been selected, namely LiNbO3 and Sr2Nb2O7. Preparation of dense ceramics with the required properties will be achieved by carrying out composition and processing studies, material characterisation and finally, testing of materials in two high temperature devices. At the same time a new high temperature electrode material will be developed for use with the piezoceramics. After 18 months the most promising composition(s) and processing routes will be chosen for further development. At the end of the project it is envisaged that the ceramics produced will not only be suitable for high temperature applications, but also for SAW substrates and electro-optic and pyroelectric applications.
Champ scientifique (EuroSciVoc)
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CORDIS classe les projets avec EuroSciVoc, une taxonomie multilingue des domaines scientifiques, grâce à un processus semi-automatique basé sur des techniques TLN. Voir: Le vocabulaire scientifique européen.
- sciences naturelles sciences chimiques chimie inorganique métal alcalin
- ingénierie et technologie ingénierie des materiaux céramique
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Coordinateur
3490 KVITSGARD
Danemark
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