Domain Wall-Defect Interactions in Ferroelectric Films

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering


Ferroelectric materials are in widespread commercial use as capacitors, precision positioning devices, fuel injectors, non-volatile memory elements, and as medical ultrasound transducers, among other applications. The measured properties of ferroelectric materials are a function of both the intrinsic response of the crystal to applied fields and the extrinsic response due to motion of domain walls under applied electric fields and stresses. The role of domain wall motion in optimising the extrinsic properties of bulk piezoelectrics has been extensively investigated but in thin films there have been few coherent studies that have attempted to understand how domain walls interact with defects.

For piezoelectric thin film based micro electromechanical systems (i.e. nano-motors and actuators) to gain widespread usage, their properties need to be optimised and their reliability improved. One aspect of reliability is the ability to maintain the same piezoelectric response over the lifetime of the device. This is currently limited by progressive pinning of domain walls during cycling by defects such as grain boundaries, point and planar defects within the film. This proposal aims to establish a fundamental understanding of the role of defects in pinning domain walls by applying a combination of advanced transmission electron microscopy, piezo-force microscopy and classic FEstack measurements to the study of a bespoke series of ferroelectric films in which specific types of defects have been engineered. The UK effort concentrates exclusively on TEM and links directly to an already funded programme between Pennsylvania State University (Trolier-McKinstry, film deposition and FEStack) and Oak Ridge National Laboratory (Kalinin, piezo-force microscopy).

Planned Impact

Piezoelectric based micro electromechanical systems (MEMS) have the potential to gain widespread usage in the fabrication of nano-motors, nano-sensors, nano-pumps and nano-actuators. They offer the possibility of larger displacements and greater voltage outputs than many competitor systems. However, they are currently limited in exploitation by their ability to perform at optimum displacement/voltage over the lifetime of the device. This problem relates to a progressive pinning of domain walls under cyclic field which ultimately suppresses the extrinsic contribution to the piezoelectric response. The project is fundamental in nature and is designed to understand the complex interactions of domain walls with pinning centres in thin films Currently, there is no coherent overview of how domain walls interact on an atomic scale with grain boundaries, dislocations and point defects. For the first time, a combination of transmission electron microscopy, piezo-force microscopy and conventional FEstack measurement will be applied to a bespoke set of films in which various types of defect have been engineered. The programme is in collaboration with the Materials Research Institute at Pennslylvania State University (Trolier-McKinstry) and the Centre for Nanophasic Material Sciences (Kalinin) at Oak Ridge National Laboratories. The goal is to combine the expertise of these two world renowned institutes with the exceptional knowledge of electroceramics, crystal chemistry, and electron microscopy at Sheffield (Reaney, Rainforth). The high profile of the subject matter and the reputation of the assembled team ensures, in the short term, potent academic impact with the possibility, in the long term, of improving the performance of ferroelectric thin films in MEMS based applications.


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Description Grant is still active but to dat we have determined:

i) a new model for the behaviour of domains in the vicinity of the grain boundary in PZT
ii) A new perovskite structured Fe2O3 rich phase in BiFeO3 thin film
Exploitation Route The work on PZT explains the role of grain boundaries in piezoelectric applications and will act as a bench mark for future studies in this area.

The discovery of a new Fe2O3 rich perovskite phase explains many unresolved reports of unusual ferromagnetic behaviour in BiFeO3
Sectors Aerospace, Defence and Marine,Electronics

Description Centre for Dielectrics and Piezoelectrics (CDP 
Organisation Center for Dielectrics & Piezoelectrics
PI Contribution Centre for Dielectrics and Piezoelectrics (CDP). Sheffield has now been voted in as an Affiliate Partner in the NSF funded CDP alongside North Carolina State University (NCSU) and Pennsylvania State University (PSU. The CDP has ~25 members which include Samsung, Apple, Murata and 3M. The joint grant with PSU was instrumental in cement our relationship with the centre based on a number of high profile publications with the CDP co-director Susan Mckinstry (international CoI on grant)
Collaborator Contribution Susan McKinstry and Ian M. Reaney are now co-directors of the CDP. The publications helped demontrate to the Industrial Members the strength of the partnership between the CDP and Sheffield
Impact Multidisciplinary. Ceramic Engineering, Life Cycle Assessment, Materials Modelling. Has led to joint projects, research, secondments and industrial funding
Start Year 2017
Description International Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The research formed party of several invited talks by myself and my collaborators, including part of the IEEE 2014 distinguished lecture series given by Susan McKinstry (collaborator and now president of the Materials Research Society)
Year(s) Of Engagement Activity 2013,2014,2015