This project identified a new piezoceramic
material which can be used at temperatures as high as 800° C, and
developed reliable, cost-effective methods for producing this material
on a commercial scale.
Bringing together industrial and academic partners from five Member
States, the project also developed a high temperature thick film electrode
compatible with the new piezoceramic, and built prototype probes and
sensors incorporating them.
A new high-temperature probe has also been developed for the non-destructive
testing of very hot steel plates and pipes. A patent application has
been made, and the probe is being actively promoted on the German
Piezoelectric ceramic materials, or piezoceramics,
convert electrical energy into mechanical energy, and vice versa.
They are the key components of high-precision sensors and ultrasonic
probes which play an important role in the maintenance of many critical
Such devices are particularly valuable as a means of monitoring
equipment or operations which it would be impossible or dangerous
for a human operator to approach, and where non-destructive testing
(NDT) methods are required. For example, they provide a means of
assessing the integrity of pipe welds in chemical or power plants
without incurring the enormous expense of shutting down the entire
However, the industrial use of commercially available sensors is
constrained by the temperature range within which they are able
to operate. Currently this does not go beyond 600° C, too low for
optimal performance in many of the applications where they are most
needed. They must also be used at a distance, with inevitable loss
of measuring accuracy.
The partners set out to identify a new piezoceramic material which
could be used at temperatures as high as 800° C, and to develop
reliable and cost-effective methods for producing this material
on a commercial scale. It also sought to develop a high temperature
thick film electrode suitable for use in conjunction with the new
piezoceramic, and to design and build one or more prototype devices.
The work was oriented towards two specific high-temperature applications.
The first of these was a vibration control device for use in aircraft
engines. The second was a high resolution probe for monitoring wall
thickness and crack development in pipes carrying liquid metals
or super-heated gases.
Prior to the project, the only known piezoelectric materials which
could operate in the target temperature range were single crystal
ceramics such as tourmaline. However, these had low sensitivity
and varied in quality.
The partners took as their starting-point ceramics based on lithium
niobate (LiNbO3), whose Curie temperature - the point at which piezoelectric
properties are lost - was known to be high. Single crystal lithium
niobate has a Curie temperature of 1,100° C, but at 600° C it starts
to lose oxygen to the environment, which makes it impossible to
The partners' hypothesis was that the oxygen loss might be blocked
by replacing some of the lithium with another element. They chose
sodium, which offers better piezoelectric sensitivity than lithium,
and concentrated their efforts on an exhaustive examination of the
Li1-xNaxNbO3 family, with an atomic percentage of sodium between
0 and 25. Their problem was that the more lithium they replaced
with sodium, the lower the Curie temperature fell.
They also found that fabrication methods and conditions played an
important role in determining the characteristics of the final ceramic.
Sol-gel and co-precipitation techniques, as well as the traditional
mixed oxide route, were used to prepare precursor powders. Processing
studies also included sintering conditions and post-sintering hot
isostatic pressing (HIP).
This initial element of the workplan turned out to be considerably
more complex than the partners, led by Danish electronic component
manufacturer Ferroperm, had anticipated. The involvement of two
university materials schools was crucial to their efforts to characterise
the material structure and properties of each composition.
While conventional mixed oxide production was tested by Ferroperm
itself, the University of Limoges assessed the sol-gel technique,
while the University of Leeds focused on the co-precipitation method.
In each case, the sensitivity, oxygen loss and other properties
of each variant were measured across the relevant temperature range.
Zero oxygen loss
Eventually, the research programme led to the successful identification
of a polycrystalline material which can operate at 800° C without
oxygen loss, and can be produced economically.
The commercial pricing of the piezoceramic material was critical.
However, if the partners were to achieve their overall objective
of making piezoceramics accessible to a range of new industrial
applications, other sensor components would also have to be upgraded
to match the higher temperature performance.
In response, Cerdec, the French industrial partner, successfully
developed a platinum paste electrode material. In addition to its
compatibility with the new piezoceramic, the paste has excellent
adhesion and conductivity, and is one of the very few cadmium-free
electrode materials available. Offering environmental as well as
technical advantages, Cerdec's electrode has already been commercialised
with considerable success.
German partner BAM has also marketed a high-temperature probe which
incorporates the materials developed in the course of the research
programme. Designed for the non-destructive testing of very hot
steel plates and pipes, the probe emits a signal at a specified
frequency and identifies cracks as changes in the acoustic response.
The company has applied for a patent to protect its innovation.
Early industrial applications
The partners are confident that the project has produced some significant
results in the field of materials science. But they are under no
illusions about the speed with which this new scientific knowledge
is likely to be commercialised, even in the target applications.
BAM, of course, already has a marketable product, and is organising
a series of promotional short courses for German small and medium-sized
enterprises, as a way of educating potential users about the new
The development of a high-temperature accelerometer, undertaken
by an unfunded Swiss partner, Vibro-Meter, illustrates the difficulties
of feeding the new piezoceramic material through into industrial
A prototype accelerometer has been built and tested, using a housing
designed for use with existing devices. Before the prototype can
be put into production, a new housing is needed, optimised to match
the temperature performance of the device itself, and this development
will be a lengthy and expensive business.
Nevertheless, the new piezoceramic material is almost certain to
achieve widespread acceptance, even if industrial take-up is slow.
The range of potential applications is enormous, and there is simply
no other material available which is capable of operating for extended
periods in the 600° to 800° C range.
Ferroperm itself, though it has no plans to patent the new material,
is making every effort to promote its use, and hopes to interest
the oil-drilling industry in the new technology.