T.W. Button

Hydrothermal and electrophoretic deposition of lead zirconate titanate (PZT) films

Abstract Hydrothermal synthesis in conjunction with colloidal processing has been used to make PZT films in an aqueous solution. Fine PZT powders with a particle size of 200 nm and a narrow particle size distribution were synthesised hydrothermally at 300°C. After washing, a dispersant (di-ammonium citrate) was added to the slurry to make a stable suspension. Electrophoretic deposition (EPD) was then employed to deposit PZT films directly from the hydrothermal PZT suspensions. The effects of the synthesis conditions on the particle size and size distribution of the PZT powders are briefly discussed. Various stabilisation mechanisms for the hydrothermal slurries have been investigated. The effects of the slurry properties and deposition parameters on the microstructure of deposited films are discussed. It is shown that PZT films with a thickness 1000°C) in comparison with powder compacts. In addition, interaction with the substrate was observed when PZT films were deposited and sintered on Pt-coated alumina substrates.

Routes to net shape electroceramic devices and thick films

Abstract The net shape fabrication of a range of electroceramic devices and thick films is described. The fabrication routes involve producing homogeneous and formable ceramic dough using a viscous polymer processing technique, with various subsequent shape-forming operations to produce devices with sizes ranging from tens of millimetres to tens of microns. The advantages of these processing routes are discussed and examples of large (>1 mm) planar and 3-D components (hemispheres, tubes and helices) and structures with small (

Dielectric and mechanical losses in (Ba,Sr) TiO3 systems

In the application of tuneable microwave devices of ferroelectric (BaSr)TiO3 systems the two critical parameters needed for optimal device performance are high tunability and low dielectric loss. The dielectric loss of the materials is strongly dependent on microstructure. This paper is concerned with an investigation of the variation in the dielectric and mechanical losses in BaxSr1 − xTiO3 systems (x = 0.5, 0.6, 0.7 and 1.0) with microstructure (grain sizes from 1 μm to 50 μm). The magnitude of the loss peak and sharpness of the anomaly in the dielectric constant/elastic modulus observed for the phase transitions in BaxSr1 − xTiO3, depend not only on the composition and but also on the grain size. A relaxation peak has been observed in large grain material, which is indication of interactions between different configurations of domain walls and the diffusion of oxygen vacancies in the domains.

Thick film YBCO receive coils for very low field MRI

Superconducting receive coils can be used to improve the signal to noise ratio of a MRI system. The greatest improvement is seen in cases where it is the coil noise dominates the noise. This is the case for low field MRI where surface coils are used. The properties of large area (100 mm square) YBCO thick film coils designed for a compact very low field MRI system are reported. The properties are compared with copper and silver mimics.

Properties and applications of thick film high temperature superconductors

Melt processed YBa/sub 2/Cu/sub 3/O/sub x/ thick films display low surface resistance, moderate performance in fields and can be applied to three-dimensional (3-D) substrates with ease. The processing and properties of such films are described. Possible applications are examined and prototype devices are described. These include high Q, low frequency resonators for cellular communications filters, low phase noise oscillators, magnetic resonance imaging receiver coils, low noise magnetic shields, coils, flux transformers, and antennas.

Processing and properties of silver/PZT composites

Abstract Commercial PZT powders were processed with various levels of silver (I) oxide powder and the effects on sintering behaviour, mechanical and electrical properties analysed. It was found that silver oxide additions significantly accelerate the sintering behaviour of soft doped PZT, but not hard doped PZT. The resulting metallic silver behaves as a heterovalent acceptor ion dopant, thereby depressing the soft piezoelectric properties such as coupling coefficients and dielectric constant in the poled direction. Above the saturation point of Ag in PZT, however, other effects begin to occur, resulting in a partial recovery of the dielectric constant. Silver additions were also found to increase the fracture strength of PZT, and values of over 170 MPa were measured. With sufficient additions the material formed after sintering was shown to be conductive.

HTS thick film components for fault current limiter applications

Fault current limiters are potentially one of the first applications of HTS materials in the power engineering field, and both inductive and resistive devices are being actively developed by many groups world-wide. A wide range of HTS materials is being considered for these devices including biaxially textured planar YBCO films, BSCCO silver clad wires, and textured bulk BSCCO and YBCO. Each type of device has its own particular requirements and restrictions with respect to acceptable component geometries, but the important physical property requirements of the materials appear to be similar in both cases. ALSTOM Research and Technology Centre is building a model current limiter based on an inductive design requiring superconducting components in the form of thick film materials on ceramic substrates. In this paper the design requirements for the current limiter are considered and the development and characterisation of the YBCO thick film materials for the device are reported. In particular, the property and performance issues concerning the scale-up of component sizes required for the demonstrator device are discussed. Preliminary results of the behaviour of the thick film components in an inductive FCL environment are also reported.

Novel piezoelectric structures for sensor and actuator applications

Abstract The piezoelectric behaviour of ferroelectric ceramics is commonly utilised for sensors and actuators. Simple shapes (bimorph beams, moonies and rainbows), thin films, composite and layered structures have been used thus far. Processing technologies developed at the University of Birmingham allow the production of novel complex shapes which, as well as improving the mechanical strength of the ceramic, may well allow the application of piezoelectric elements into areas previously unexplored. This paper concentrates on circular cross-sectional shapes in the form of helical springs, and describes the preliminary investigation carried out to characterise the response of springs to both dynamic and static impulses. The application of such geometries to sensor and actuator devices is discussed and possible areas of further work to realise the potential of the processing technology are also outlined.

YBCO thick films for high Q resonators

Three dimensional structures can have high geometric factors and have thus been favoured in applications requiring high Q resonant elements. In this paper the surface resistance of YBCO thick film materials measured in the frequency range 1-10 GHz in a variety of resonant structures is discussed. The power dependence of the materials in the 1 to 2 GHz region is also examined and at these frequencies it is possible to attain Qs of over 150000 using thick film materials.

Novel piezoelectric structures for sensor applications

Piezoelectric ceramic devices have been formed into the helical spring shapes from tubular extrudates. These structures are shown to possess low compliance and low natural resonant frequencies. Equations are presented allowing the prediction of the resonant frequencies of the devices; these are shown to be in good agreement with measured responses. Using the design criteria a device has been constructed to exhibit a low fundamental resonance and a clear spectrum up to 500 Hz. The frequency response is shown for this device and compared to a conventional electromagnetic geophone. The results show that the device acts as a displacement sensor providing an output charge of 0.427 mC/m with no observed spurious resonances.