Session Chair: John Wang, National University of Singapore
1:30pm - 2:00pm Invited
The Low Temperature Dielectric Relaxation in Lead Titanate-Relaxor Single Crystals
Andrew John BELL
University of Leeds, United Kingdom
The mechanism of the low temperature dielectric relaxation and accompanying reduction in piezoelectric charge coefficient is crucial to understanding the mechanism for the large piezoelectric coupling in Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals and related materials at room temperature. Over the last 2 decades the room temperature mechanism has generally been understood in terms of polarization rotation between rhombohedral and tetragonal variants through a shallow free-energy landscape, which does not directly involve a temperature activated mechanism that would lead to a relaxation response. Li et al have proposed a mechanism involving the freezing of polar nanoregions, in which the frozen regions exhibit a polar axis rotated from that of the matrix.
This paper considers the microscopic mechanism of polarization rotation using the Landau-Ginzburg-Devonshire approach. Whilst the magnitude of the room temperature effect is consistent with the predictions of a simple rotation model, for polarization coherence length of < 10 nm heterophase fluctuations become relevant, providing an additional contribution to the electromechanical response between ambient and cryogenic temperatures. The freezing of these fluctuations is consistent with the low temperature relaxation seen experimentally.
There are many kinds of the electronic components with piezoelectric ceramics such as acceleration sensors, small size actuators, ultrasonic sensors, gyro sensors, speakers, buzzers, resonators and filters, in advanced electronics application fields. For these applications, lead zirconate titanate (PZT) is widely used as a piezoelectric material. Because its piezoelectric and mechanical properties can be easily controlled by composition modifications. However, many kinds of PZT based compositions have been researched for decades, therefore the piezoelectric performances have almost saturated.
The first example of new piezoelectric technologies we show here is based on ceramic material designs. A candidate for future small size actuators is (K,Na)NbO3 (KNN) multilayer ceramics with Ni inner electrodes. In the PZT multilayer ceramics, the inner electrodes of Ag or Ag-Pd are commonly used. Then, they show low reliability because the Ag migration causes electrical short. However, KNN multilayer ceramics shows high reliability against to the electrical short because the Ni of the inner electrodes migration can't occur. Furthermore, the strain of KNN multilayer ceramics may exceed those of PZT.
The other example of new technology that we consider is a grain orientation method. The drastically improved piezoelectric properties were obtained by the grain alignment. We controlled the grain alignment of SrBi2Nb2O9 (SBN) by a templated grain growth method, and fabricated the ceramics with c-axis alignment. The thickness shear mode vibration of the grain oriented SBN shows a smaller tolerance of resonant frequency compared to that of a quartz in a wide temperature range. Furthermore, we also obtained the grain oriented PZT ceramics by a slip casting method under a high magnetic field. Its electromechanical coupling coefficient k31 was 1.5 times larger than that of the non-oriented PZT.
These new ceramic technologies as mentioned above will lead higer performances of electronic devices in the future.
2:30pm - 3:00pm Invited
Integrated Piezoelectrics for Smart Microsystems
Fraunhofer Institute for Ceramic Technologies and Systems IKTS, Germany
The trend towards highly miniaturized and complex microsystems demands for new solutions of integrated sensor and actuator functions. Microelectronic substrates like silicon, alumina, zirconia and LTCC (Low Temperature Cofired Ceramics) allow for 3D packaging (electrical connection, channels, cavities and membranes), high robustness and reliability as well as for integration and application of electronic components, whereas piezoceramic materials enable sensor and actuator operations. To combine the advantages of both, integrated solutions are of great interest.
Piezoceramic thick films with typical thickness of 30-150 µm fulfill microsystems requirements for low profile and compact devices. They are of great importance for applications, where construction height is limited, outgassing has to be prevented, and complex structures are needed. Using screen-printing technology, net-shaped structures can be easily applied and combined with isolation and electrode layers. The functionality of the smart microsystem not only depends on design and construction but also on material interactions. A thorough choise of substrate and piezoceramic material as well as the understanding and prevention of chemical reactions are necessary to build effective systems.
The presentation will give an overview covering design aspects, technology and applications of integrated piezoceramic thick films in multilayer material systems. Detailed information on application for active optics, adaptive structures, force sensors and ultrasonic transducers will be shown.
3:00pm - 3:15pm Oral
Multifunctional Piezoelectric Composites for Ultrasound Imaging and Therapy Applications
University of Glasgow Singapore, Singapore
The electromechanical properties and performances of 1-3 piezoelectric composites can be tailored for specific applications. In addition, these composites have the flexibilty to conform to curved surfaces. Due to these advantages, there are many practical applications on the use of 1-3 piezoelectric composites in the area of biomedical engineering, such as ultrasound imaging, ultrasound therapy and bone tissue engineering. The addition of soft polymer inclusions can further improve the performances of the composites. In this paper, the performances of a 1-3 piezoelectric composite with soft polymer inclusions for ultrasound imaging and therapy will be presented. A multi-step micromechanics-based analytical model is developed to evaluate the performances of the composite where the fibre is piezoelectric and the matrix can be piezoelectric or non-piezoelectric. Results of the studies show that the piezoelectric composite performances are largely dependent on the fibre volume fraction and that the presence of soft polymer inclusions further improved the performances of the composites. Various non-lead piezoelectric materials are also considered in the study.
3:15pm - 3:30pm Oral
Preparation, Characterization and Sensing Performance Study on PVDF-Trfe/Zno Nanocomposites
Rashmi PN, Gayathri A, Anjana J
National Aerospace Laboratories, Bangalore, India
The objective of this study is to develop, characterize piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensitivity study. It will be shown that these films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to commercial PVDF. The incorporation of piezoelectric ZnO nanoparticles to Copolymer (PVDF-TrFE) thin films improves the sensitivity of PVDF by approximately 2times. For the purpose of future SHM applications, the present studies as well as the results obtained from it are essential. The piezoelectric nanocomposite fabrication began with the solvent casting dispersed ZnO-based solutions followed by ultrasonication process. The concentration of ZnO nanoparticles was varied from 10 & 60 wt. % to determine their influence on bulk film piezoelectricity. Prepared film studied for its phase confirmation using X-ray diffraction, morpohological study has been done using Scanning Electron Microscopy, and dielectric study has been done to compare the dielectric constant of PVDF and PVDF nanocomposite. The poled film has been checked for Piezoelectric properties such as Piezoelectric charge & voltage coefficient. Later the film was silver electroded to make film conductive. These films are bonded on aluminium cantilever along with commercial PVDF sensor for the comparison of sensitivity. Sensitivity has been checked using Pitch catch measurement technique using PZT as an actuator. Voltage response from nanocomposite sensor and PVDF was compared by keeping the excited voltage constant for PZT at 10Vpp. Another experiment with Voltage response from nanocomposite sensor and PVDF was compared by keeping the frequency constant at 100 and 500 Hz with varied amplitude. Further studies are under progress for calibrating the sensor for measuring the structural parameters like strain and later studies are also planned to use the superior properties of the nanocomposites for the detection of damages in composite aircraft structures.