University
of Toronto
Physics Department
Quantum Optics and Condensed Matter
MONDAY SEMINAR
University
of Toronto
| Speaker : | PROF. ALLAN JACOBS
Department of Physics University of Toronto |
| Topic : | DOMAIN PATTERNS IN FERROELASTICS |
| Time : | Monday, September 25, 2000 at 12:10 p.m. |
| Place : | Room MP408, Burton Tower 60 St. George Street / 255 Huron Street |
Abstract
Ferroelastics are solids with shape-changing phase transitions; ideally,
the low-temperature state is one of several ``variants''
with identical energies but differing orientations. An example:
in YBa2Cu3O7 , the
O chains can form in either the x or the y
direction, giving 2 variants. The microscope shows, however,
multiple variants which form patterns quite unlike those in other
materials. The analogy with ferromagnets and ferroelectrics is superficial,
and entirely different theories are required. Using
a simple elastic theory in the strains only, adapted for the symmetry
of the high-T phase, we have obtained the essential elements
observed in both tetragonal-orthorhombic and hexagonal-orthorhombic
materials. The latter are a rare physical realization of
disclinations in crystals. Interesting features of the dynamics are
that time-dependent Ginzburg-Landau theory is wrong for proper
ferroelastics, and that the relaxation is nonlocal.
Research performed in collaboration with Dr. S. H. Curnoe.
Local Host: Prof.
Allan Griffin 
(416-978-5199)