• [2013-06-17]

  Effect of Relaxor-Ferroelectric Transitions on Fatigue of BNT-Based Lead-Free Piezoceramics

Speaker： Prof. Mark Hoffman 
Time：15:00 pm
Date：June 18, 2013
Venue：Room 210, COE Building No.1
Host: Prof. Faxin Li 

Abstract:

Piezoceramics are currently lead-based, causing toxic by-products, especially during manufacture and waste incineration. Consequently, the search for non-toxic piezoceramics which can replace lead-based materials such as Pb(Zr,Ti)O3 (PZT) is one of the major challenges in science and engineering and BNT-based systems show considerable promise as an alternative. The fatigue behavior of a ferroelectric composition 94BNT-6BT under bipolar and unipolar electrical cycling was investigated as a function of temperature from 25 to >100°C. For both bipolar and unipolar cycling a decrease of polarization, mechanical strain, permittivityε33 and piezoelectric coefficient d33 are observed, with most of the degradation occurring within 104 cycles. In situ neutron diffraction in the unloaded state revealed a phase transformation and formation of ferroelectric order within 1000 cycles at room temperature but then a disappearance of the ferroelectric order with subsequent cycles, despite the retention of piezoelectric properties. However, as temperature increased observable ferroelectric order disappeared at all levels of cycling. The presentation will posit that fatigue behavior in these systems can be explained by an electric field-temperature (E-T) phase relationship with the loci of transitions between phases varying with composition.

Biography：

Professor Hoffman is Pro Vice-Chancellor Research of the University of New South Wales. From 2007-12 He was Head of the School of Materials Science & Engineering at UNSW. He holds a BE (1989) and PhD (1994) from the University of Sydney and Masters of Business and Technology from UNSW. His research expertise is in the area of structural integrity of materials, specifically the design of materials for high reliability in complex environments. In recent years he has focused on piezoelectric materials. Prof. Hoffman has obtained over $10m in research funding and has been co-investigator on grants from international agencies including the US NSF, the German DFG and the Hong Kong Sci. and Tech. Fund. He has published over 170 international journal papers and graduated 23 PhD and Masters students. In 2007 he received the UNSW Vice-Chancellors Award for Excellence in Postgraduate Supervision. Prof. Hoffman is currently a Director of the International Congress on Fracture, a Research Program Leader for the ARC Centre of Excellence in Design in Light Metals, Fellow of the Institute of Engineers Australia and an Associate Editor of the Journal of the American Ceramic Society.