Demonstration of enhanced functionalities in engineered thin films and single crystals
The top quality materials were made (epitaxial thin films by pulsed laser deposition method in École polytechnique fédérale de Lausanne) or purchased (highest quality single crystals from different vendors) and functional properties were engineered and later characterised by structural/local characterization techniques (HR XRD, PFM, TEM/SEM in Switzerland) and functional characterization techniques (dielectric spectroscopy, piezoelectric and pyroelectric measurements in Lithuania).
Epitaxial Ba0.7Sr0.3TiO3 (001) thin films (PLD). BST[70/30]/LSMO//STO heterostructure. XRD asymmetric RSM around STO 103 (BST 103), ~1.3 % in plane epitaxial strain. PFM topography after writing artificial domains, PFM phase after poling.
PMN-PT single crystals. Optical in situ monitoring of the poling process.
Complex impedance spectroscopy was performed varying an applied external electric field to investigate the tunability of dielectric properties in BST70/30 thin film with the bottom LSMO layer.
The dielectric strength can be reduced more than 50%, when external electric field is equal approximately to 1MV/cm. In comparison with the scientific literature, our experiment shows higher permittivity values at the room temperatures and enhanced tunability effect at 100 nm thickness.
Summarizing, BST thin films can be used in devices where variable capacitance is required e.g. varactors, phase shifters and many more.
Demonstration of effective air-coupled ultrasonic transducer
Very high piezoelectric properties of the lead magnesium niobate – lead titanate (PMN -32%PT crystals) allow development of a new type of air – coupled ultrasonic transducers. The high electromechanical factor of the transverse extension mode helps to achieve a good performance of air – coupled transducers. The developed and investigated ultrasonic transducer possesses in a transmission mode 10 times better efficiency than a PZT composite ultrasonic transducer.
Formation of charged ferroelectric domain walls with controlled periodicity
Charged domain walls in ferroelectrics were shown recently to possess metallic-like conductivity. Unlike conventional heterointerfaces, these walls can be displaced inside a dielectric by electric field, which is of interest for future electronic circuitry. We experimentally demonstrate, in BaTiO3 single crystals the controlled build-up of high density charged domain wall patterns, down to a spacing of 7 µm, hinting to a possible exploitation of charged domain walls in agile electronics and sensing devices.
BFO thin films with controlled charged domain walls
The stabilization of charged domain walls (CDW) requires the control of the polarization states in two adjacent domains, i.e. forcing two domain states into head-to-head (H-H) or tail-to-tail (T-T) configuration at their boundary and, simultaneously, delivery of free carriers on the charging interface to avoid the presence of a giant depolarizing field. We developed a new technique based on conductive-tip AFM that allows their controlled formation at predetermined positions in thin films at the micrometer and nanometer scales. The technique is based on a trailing in-plane field created by the tip motion on the surface during the poling procedure.
We demonstrated this technique on BFO/SRO//DSO heterostructures by creating straight H-H CDW.
Controlled creation of micro scale and nanoscale charged domain walls at predetermined positions.