The group concentrates on investigation of lattice dynamics and critical phenomena in polar materials, like ferroelectrics and relaxor ferroelectrics. These materials are known for their extraordinary dielectric and electromechanical properties, widely used in industrial applications ranging from micro-capacitors and ferroelectric memories to transducers and actuators.
Search for new materials, such as lead-free piezoelectrics, which should replace toxic lead-based compounds in the near future, typically requires a detailed insight in the nature of their material–property relationships. Spectral studies of polar fluctuations in these substances, and in particular, of those revealing the dynamical origin of the ferroelectric phase transitions (so-called soft modes) are often the most fundamental starting points for quantitative modelling or in the search of reasonable material design rules.
The main in-house technique used in our group is Raman spectroscopy, which is a unique method to study inelastic scattering of light. It offers information about various excitations in solids, liquids and gases. In solids, these excitations are mainly lattice vibrations (phonons) or, as the case may be, magnetic excitations (magnons), etc. Analyzing the frequency, intensity, lineshape and polarization of the inelastically scattered light, often as a function of temperature (structural phase transitions) or electric field. Thanks small laser spot (a few micrometers) one can perform Raman mapping of the sample surface, with very good spatial resolution. Using a helium cryostat or high temperature cells, makes possible to measure the spectra in a broad temperature range: from -270 to 1200 °C. Computer programs have been developed to analyze the spectra, enabling us to determine the parameters of the measured excitations (e.g. by studying the dependence of polarized spectra on rotation about the axis of the incident laser beam)
To obtain comprehensive information about the lattice and relaxation dynamics of investigated materials, we frequently collaborate with other groups of the Department of Dielectrics, like Dielectric and IR spectroscopy or THz science and technology. Moreover, to overcome selection rules of Raman and IR spectroscopic techniques, we perform Hyper-Raman scattering experiments in collaboration with
Brillouin scattering experiments at
inelastic neutron scattering experiments at
- Institut Laue-Langevin (ILL), Grenoble, France,
- Laboratoire Léon Brillouin (LLB), Saclay, France,
- Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany,
and x-ray scattering studies at