Do butterflies make you relax?

These materials have mechanical and electrical properties that are useful in applications such as sonar and ultrasound. The more scientists understand about the nanoscale short-ranged “local structures” that exist inside relaxor ferroelectrics, the better materials we can develop for these and other applications.¹

Researchers have long understood that the important technological applications of these materials are related to local structures. They have also known that a characteristic pattern of diffuse scattering from these local structures can be observed using x-rays and neutrons, which is often described as the “butterfly” due to the characteristic shape (Fig 1a,d). However, a detailed understanding of these structures is lacking, despite much effort. Now, by performing unprecedentedly detailed and comprehensive neutron and x-ray measurements (at the Spallation Neutron Source and CHESS, respectively), and pioneering new techniques to analyze these large datasets, researchers have uncovered evidence of 4 different types of local structures in the prototype relaxor material PMN-xPT. Each of these structures is shown to have a different, unique effect on the material performance.

What did the Scientists Discover?

The team, lead by scientists in the Materials Science Division of Argonne National Lab, discovered that relaxor behaviour does not correlate simply with ferroic diffuse scattering (i.e. the “butterfly” patterns) at all; instead, it results from a competition between local antiferroelectric correlations, seeded by chemical short-range order, and local ferroic order. The ferroic (butterfly) diffuse scattering is strongest where piezoelectricity is maximal and displays previously unrecognized modulations caused by anion displacements. The ability to correlate diffuse scattering features with materials function across a range of materials with different chemical doping is a striking new advance, that will unlock many problems in disordered functional materials. This breakthrough is driven by great leaps in technology for performing diffuse scattering measurements with x-rays and neutrons, as well as software to handle the large datasets.

The accomplishments here suggest that more complex alloys can be attacked with similar tools, yielding additional insights. The present study paves the way for future materials design and discovery, guiding understanding of changes in properties as additional chemical components are considered, including lead-free relaxors.

The research, lead by graduate student first author Matt Krogstad and corresponding author Daniel Phelan, appears in as a full-length article in the August 2018 issue of Nature Materials: “The relation of local order to material properties in relaxor ferroelectrics.” The article is accompanied in the same issue by a “News & Views” summary entitled “Seeing the forest and the trees”.²

Impact:

Krogstad et al. shed light on one of the most interesting problems in relaxor studies, namely the relationship between relaxational behaviour and piezoelectric performance, as well as what local structres are related to each. These results provide a new benchmark for theoretical and computational studies of relaxors and enable further elucidation of relationships between composition, structure and properties in these materials. More fundamentally, this research is a landmark example of how the study of complex nanoscale order/disorder systems requires and benefits from techniques that consider the full complexity of the system, with this success opening the door for the application of this powerful diffuse scattering method to a wide variety of other glassy materials with multiple length scales.² These techniques are proposed to be a core thrust of the new <QM>² beamline after CHESS-U.

Collaborators:

Daniel Phelan, Argonne National Lab; corresponding author email:  dphelan@anl.gov
M.J. Krogstad, Argonne National Lab and Northern Illinois University
P. Gehring, NIST, Ctr Neutron Res
S. Rosenkranz, Argonne National Lab
R. Osborn, Argonne National Lab
F. Ye, Oak Ridge National Lab
Y. Liu, Oak Ridge National Lab
J.P.C. Ruff, Cornell High Energy Synchrotron Source
W. Chen, Simon Fraser University
J.M. Wozniak, Argonne National Lab, University of Chicago
H. Luo, Chinese Academy of Science
O. Chmaissem, Argonne National Lab and Northern Illinois University
Z.G. Ye, Simon Fraser University

Publication citation:

Krogstad, MJ, Gehring, PM, Rosenkranz, S., Osborn, R., Ye, F., Liu, Y., Ruff, JPC, Chen, W., Wozniak, JM, Luo, H., Chmaissem, O., Ye, ZG, Phelan, D., The relation of local order to material properties in relaxor ferroelectrics, Nature Materials, 2018, 17(8), 718, DOI: 10.1038/s41563-018-0112-7

Funding:

References:

[1] Mitchem, S., Relax, just break it, Argonne National Lab Press Release, 7/19/2018

[2] Takenaka, H., Grinberg, I., Rappe, AM., Seeing the forest and the trees, Nature Materials, 17(8), 657-658 (2018).