Washington, DC, 15 April 2010- Single-crystal relaxor ferroelectrics are useful and fascinating systems, but understanding the inner workings of these complex materials has been very challenging. They have spatial and temporal heterogeneities over a range of length and time scales.

Relaxors and relaxor-ferroelectrics such as Pb(Mg1/3 Nb2/3)O3 and Pb(Sc1/2 Nb1/2)O3 respectively have a temperature and frequency dependent dielectric maximum reaching colossal values. Relaxor-ferroelectrics show an additional ferroelectric phase at low temperatures, characterized by a spontaneous macroscopic electric polarization in the crystal, which is absent in pure relaxors. Observing them with x-rays and neutrons reveal interesting patterns in which are encoded the atomistic information responsible for the very origin of their relaxor behavior. This property coupled to a large piezoelectric response i.e. ability to convert mechanical energy to electrical energy and vice versa, make some of these materials such as Pb(Mg1/3 Nb2/3)O3 and Pb(Mg1/3 Nb2/3)O3-PbTiO3technologically useful.

The origin of the relaxor phenomenon and the observed x-ray and neutron diffuse scattering has been a topic of debate for over several decades. A team that includes Geophysical Laboratory's Panchapakesan Ganesh with collaborators from Carnegie, NIST, Argonne, and Simon Fraser University performed joint theory and experimental studies to explain the origin of the characteristic diffuse scattering and investigate their temperature and pressure dependence. They showed that correlations among chemically ordered regions, which act as polar nano-regions, are responsible for the relaxor behavior. Their findings further suggest a possible route to engineer superior dielectric/piezoelectric materials by nano-engineering different types of regions in a bulk or thin-film relaxor material. 

The article appears in: P.Ganesh et al., Phys. Rev. B.81,144102 (2010) (PDF).

Scientific Area: