Noise Studies of Disordered Condensed MatterM. B. Weissman, UIUC, DMR-0240644

Relaxor ferroelectrics are materials which freeze into a state with large electric polarization in small regions (“nanodomains”) but no long-range ordered polarization pattern. This combination allows them to have unusually huge piezoelectricity, i.e. coupling between electric fields and mechanical strain. They are already used for electro-mechanical transducers, but more applications are expected if the nature of the random-lookingfreezing can be better understood.One key question is whether some second type of order competes with ferroelectricity, as indicated by our previous experiments on noise and aging effects.. We find the field-induced conversion of the disordered to the ordered state proceeds via two very distinct steps, strongly supporting the idea that there is a well-defined glassy order competing with the ferroelectric order.

The change in polarization (i.e. the current) and the change in dielectric constant after applying anelectric field are shown for PbMg1/3Nb2/3O3, a standard relaxor. The two-step conversionprocess is evident.

T= 175 K

Zero-field cooled

E= 272 V/cm

Relaxor ferroelectrics have enormous responses to electrical fields and mechanical strains because they form ferroelectric regions (regions where the charges displace together to make big net charge displacements) yet these regions quit growing before they become so large that they lock into fixed orientations. Developing better relaxor ferroelectrics would be easier if we understood why those ferroelectric regions quit growing. The simplest models propose that these regions just get stuck, pinned on little irregularities or perhaps jammed in to neighboring regions. However, other models propose that the charge displacements may also try to line up in much more complicated, ‘glassy’ ways. If so, there should be another type of order present, but not one which directly shows up in standard measurements. We have used a variety of non-standard methods to show that such order is probably present. The latest measurements, showing a clear two-step conversion to the simpler order, indicate that melting of a non-ferroelectric order is involved.

Education:This grant supports work by four graduate students (Andrea Mills, Lambert Chao, Aki Palanisami, and David Layton) as well as a Visiting Research Professor (Eugene Colla). Colla and Chao work on this sub-project.Recent graduates from this group have gone on to work for several hard-drive developers, as well as for other hardware developers, national labs, and universities.

Outreach:The PI has prepared and edited many dozens of answers for a question-and-answer Web site run by the Physics Department http://van.hep.uiuc.edu/van/qa/qaform.htm

This site draws questions on all sorts of science topics from students of all ages from around the world. Here’s the PI’s favorite: http://van.hep.uiuc.edu/van/qa/section/stuff_about_space/the_earth_and_the_moon/

20020821210810.htm. Here’s another, with more serious substance: http://van.hep.uiuc.edu/van/qa/section/states_of_matter_and_energy/boiling_evaporating_and_condensing/20030626151340.htm.

Noise Studies of Disordered Condensed MatterM. B. Weissman, UIUC, DMR-0240644