Piezoelectric materials are critical for applications in sensors and actuators that enable medical ultrasound, therapies that promote bone healing, highly efficient portable power transformers, high performance diesel engines and many other applications involving conversion between electrical and mechanical energy. The goal of this research team is to improve our understanding of piezoelectrics by fully optimizing existing materials and enabling enhanced potential for industrial development of environmentally friendly, lead free piezoelectrics. The research project will also be directed towards developing educational materials on the science and engineering of piezoelectrics for students from middle school to beginning college. The educational materials will be used to enhance skill development in math and science and to foster interest in science and engineering.
TECHNICAL DETAILS: Exploration of crystallographic texture with domain orientation and anisotropy in poled, lead free piezoelectrics enables understanding of the interrelationships between texture and microstructure that can lead to replacement of lead-containing piezoelectrics. This project will couple domain textures and crystallographic textures in bulk materials to understand the development of piezoelectric and other anisotropic properties. Effects of poling field, poling temperature, conductivity and intrinsic materials properties such as electrical and thermal conductivity, elasticity and thermal expansion are critical aspects for developing this understanding. The project consists of development of processing approaches to produce bulk materials that can be used to fully describe the interplay between texture and anisotropy in the rapidly evolving classes of lead free piezoelectric materials. Project investigators are considering nanoscale and microscale interactions between ferroelastic and ferroelectric domains across grain boundaries as a function of stress state, temperature and processing history via scanned surface probe techniques. The experimental aspects are pivotal to describing the relationship of texture and microstructure to properties for comparison to incisive microstructure-based numerical simulations that capture the thermodynamics and physics occurring on the scale of the domains and grains. Both the experimental and computational aspects of this project will be carried out in collaboration with colleagues in the automobile and diesel engine industries and at the Technical University of Darmstadt. This project is producing a better understanding of poling processes, the limitations imposed on poling by the underlying ferroelastic and ferroelectric domains and their interactions with grain boundaries and microstructure. Undergraduate and graduate student researchers are learning advanced techniques for numerical simulation of nanoscale and microscale effects on properties, sample preparation techniques for surface probe analysis and electron microscopy, surface probe techniques, electron microscopy and x-ray and neutron diffraction techniques.
Piezoelectric materials are used in a variety of commercially important applications as sensors, actuators, motors, power transformers and transducers. Piezoelectric materials enable the conversion of mechanical signals into electrical signals and vice versa. Specific applications include transducers for ultrasound imaging, sensors for detecting motion and high performance actuators for diesel fuel injectors. The market of piezoelectric components exceeds $10 billion per year and is likely to grow considerably in the next decade. Lead-containing materials are expected to dominate applications despite environmental and workplace safety considerations. To replace lead-containing materials with equivalently well performing lead-free piezoelectric ceramics many different material systems have been investigated. This research project investigated ceramic materials based on sodium bismuth titanium oxides (BNT) and barium zirconium calcium titanium oxides (BZT-BCT). Considerable research into developing high performance materials from these two systems has taken place throughout the world. In our investigations we produced a wide range of these materials through processing of powders into bulk and thin film samples. Some of these materials were processed using techniques that are expected to cause preferred orientations of crystals within the final samples. Following processing and preparation into samples conducting electrodes were applied that enable the application of electric fields and the measurement of the electrical state within the samples. This research demonstrated that introducing preferred orientations of the crystals produced changes in the properties of the materials that would enable improved performance for samples aligned along particular directions. Electric poling, which is the application of an electric field over an extended amount of time, can further increase the piezoelectric properties significantly. The researchers explored the effects of chemistry as well as the effects of electrical and mechanical loading on the performance of these materials in order to identify potential reasons for enhanced performance and to aide in further improvements of these materials so that they may have a chance to replace lead-containing materials in at least some applications. Rearrangements and redistributions of sub-micron portions of crystals called domains were evaluated using x-ray diffraction and surface probe techniques. In addition to the experimental work, numerical simulations were also done to help in explaining the properties of these materials. What is evident from this research and the research of collaborators on this project is that a better understanding of crystal size, crystal orientation and the long term performance of these materials is required if lead free materials are going to make significant inroads into the market for piezoelectric materials.
