This is a joint project between Virginia Tech and Lehigh University (US team members) and international partners consisting of the University of Warwick (UK), the University of Oxford (UK), Novgorod State University (Russia), and the Shanghai Institute of Ceramics (China). The research addresses the mechanisms controlling the piezoelectric response in lead free systems by systematically studying the local domain and crystal structure and their effect on properties. (Na1/2Bi1/2)TiO3?BaTiO3 (NBT-BT) single crystals of compositions close to morphotrophic phase boundary (MPB) are used as the representative lead free system. The nanoscale domain structure and its ferroelectric response are studied as a function of electric field, pressure and temperature to identify the phase transformational sequences in the MPB region and to determine the presence of intermediate bridging phases. Another challenging issue confronted in this research is formulation of the mechanism of domain engineering in the lead free materials. Both the local nano-structure and the microstructure of the lead-free crystals is studied using diffraction and spectroscopic techniques to delineate the symmetry relations, nature of the dipole moment, long-range average crystal structure, order/disorder in the atom?s local environment, and orientation of polarization.
These studies enable the understanding of the structure-property relations on the nano- and macro- length scales and are used to identify similarities and differences between MPBs in lead-free and lead-based systems. Wide dissemination of the results obtained is done through joint publications in peer-reviewed journals, by developing a website on lead free materials, and by organizing the symposia on lead ? free piezoelectrics at future annual scientific meetings. A US ? UK, US ? Russia, and US-China student exchange program is implemented to expose the graduate students working on the project to an international research environment. A website will be launched in the second year of this effort posting all the developments, achievements, publications, and power point presentations. A pilot education program will be initiated with Montgomery County School (Blacksburg, VA), with focus on incorporating lead-free piezo-actuators and sensors into their robotics program.
This award is co-funded by the NSF Office of International Science and Engineering (OISE) and the MPS Office of Multidisciplinary Activities (OMA).
This project involved an international collaboration between Virginia Tech (US team members) and International partners consisting of the University of Warwick (UK), the University of Oxford (UK), Novgorod State University (Russia), and the Shanghai Institute of Ceramics (China). The research focused on the mechanisms controlling the piezoelectric response in lead free systems by studying the local structure of (Na1/2Bi1/2)TiO3-xat%BaTiO3 (NBT-BT) single crystals and grain oriented ceramics. With regards to the scientific activities, the program focus was on (i) identification of the mechanism underlying the relatively large piezoelectric response in the NBT-BT Pb-free piezoelectric systems, and how the contribution might be further enhanced; (ii) investigations of induced phase transformations in these systems and how they depend upon crystallographic orientation; and (iii) the synthesis and characterization of NBT-BT grain oriented ceramics and whiskers. The program resulted in over 20 peer-reviewed publications in academic journals, numerous presentations by students, several organized symposia at international conferences, and a US-China workshop sponsored by the National Science foundation (San Francisco, April 2011). For example, NBT-BT whiskers were synthesized by topo-chemical microcrystal conversion beginning with Na2Ti6O13 whiskers. Piezoelectricity of the NBT-BT whiskers was confirmed by PFM mapping (see Fig.1). Phase and amplitude contrast can be seen indicating the presence of ferroelectric domain structures. 180o phased angle variation was achieved with applied DC bias field, which demonstrate domain switching among the whisker (Fig.2). These whiskers were then used to synthesize ceramic ink, in order to print various 3D structures using aerosol jet deposition. With regards to education activities, the investigators were kept very busy continuing their world-wide activities in their duties in the educational portion of this Materials World Network program. We had continued exchange visits with our partners in the UK (3), Shanghai Institute of Ceramics (3), and Novogorod State University (1). These visits resulted in many joint publications. The team members organized several international workshops on Pb-free piezoelectric materials and applications, which were held in Shanghai-China. These workshops were a direct consequence of the teaming made possible by the MWN, and involved scientist from 12 countries. We have published a book on the topic lead-free piezoelectrics that consists of chapters from the leading scientists all around the world.
