Below you see an animation of the frequency
dependence of the real part of the dielectric constant displaying two types
of dispersions: resonant and relaxational. The relaxation time for the second
one changes as a function of temperature. It starts at 1 microsecond and ends
at 1/10 of a second. The animation is set to go back and forth for no
particular reason.
Below is a little animation. Two resonsnt
dispersion one of which decreases with temperature.
Here is a little movie showing a structure of KDP
crystal. Hydrogen atoms are not shown.
Ever since I became serious about doing Physics (in 1996) I was
investigating phase transitions in crystals. As a master student in
Poland at
Adam Mickiewicz University I became
fammiliar with such techniques as: thermal condactivity
measurements, dielectric spectroscopy, polarizing microscopy,
Differential Thermal Analysis (DTA), Differential Scanning
Calorymetry (DSC), Differential Thermo-Gravimetry (DTG) and the
very basics of Brillouin Light Scattering (BLS). At that time I was
investigating a crystal which belongs to a family of crystals with a
general chemical formula ABSO4. But more about this some other time.
I am currently studing elastic properties of some new ferroelectric
crystals as a function of temperature. The technique of my choice is
Brillouin Light Scattering (BLS). With a sample properly oriented and
using appropriate experimental geometry it is possible to measure
frequencies of acoustic phonons propagating in a crystal. The bigest
advanteage of this technique over the ultrasonic pulse-echo (UPE)
method is a possibility of registering two transverse and one
longitudinal acoustic modes in one spectrum. In a case of
UPE experiment it requires either a different piezoelectric
transducer or its rotation with respect to sample face. Low
temperature studies are also easier to conduct in the case of BLS,
because of problems with maintaining a contact between transducer
and sample. I am not trying to say here that BLS is the better
technique. Both are very helpfull in studing phase
transitions in various materials.
But to get to the point. I am interested in symmetry changes in
crystals undergoing a structural phase transition. My long term goal
would be to understand applications of group
theory in phase transition modeling (Landau type modeling). However as
an experimentalist I would like to know as much as
possible about solid state spectroscopy. The techniques of interest to
me include and are not limited to:
