Projects / Programmes
Engineering of structural and microstructural characteristics in contemporary dielectrics and ferroelectrics with perovskite and perovskite-like crystal structures
| Code |
Science |
Field |
Subfield |
| 2.04.00 |
Engineering sciences and technologies |
Materials science and technology |
|
| Code |
Science |
Field |
| T153 |
Technological sciences |
Ceramic materials and powders |
| Code |
Science |
Field |
| 2.05 |
Engineering and Technology |
Materials engineering |
perovskites, crystal structure, nanoparticles, thin films, heterostructures, functional properties
Researchers (12)
Organisations (2)
Abstract
The investigations of ferroelectrics and microwave dielectrics in the proposed project will follow the current trend of electronic component miniaturization, improved efficiency and multifunctionality. The research on ferroelectrics will be focused on the preparation of defined-shape particles and their ordered assembly in thin-film or hetero-multilayer structures by using chemical solution methods. The control of the BaxSr1-xTiO3 (0£x£1), Na0.5Bi0.5TiO3 and K0.5Bi0.5TiO3 particles’ morphology will be realized by approaches that are all based on an understanding of growth mechanisms. The crystal-growth control will include a knowledge of the Ti-precursor hydrolysis rate, the modifying of certain perovskite crystal plane energies by the adsorption of ligands through a coordination with cations, the directing of oriented attachment or inducing the topochemical transformation of a defined-shaped Ti-precursor into the perovskite with the same shape. In the continuation, well-defined nano-sized particles (cubes, belts, plates) will be arranged in an ordered manner in thin-film or in 3D bulk structure. These ordered structures will be prepared from one-type of perovskite or from mixtures of two different perovskite types (for example, BaTiO3/SrTiO3, Na0.5Bi0.5TiO3/ K0.5Bi0.5TiO3 BaTiO3/Na0.5Bi0.5TiO3, etc.). The latter will require the matching of both perovskites in the particle shape and size. The ferroelectric and piezoelectric behaviours of such structures will be studied in terms of lattice strains, which are induced at the hetero-interfaces due to the lattice mismatch between the two perovskites. The mixing and ordered assembly of the proposed defined-shape perovskites in an arbitrary ratio is expected to offer the possibility to introduce innumerable and various hetero-interfaces structures, which are expected to represent many possibilities for tailoring the dielectric, ferroelectric and piezoelectric properties.
We also intend to explore the possibilities of taking advantage of some of the perovskite morphologies for the preparation of lead-free ferroelectric and piezoelectric ceramics by using different sintering approaches. The ferroelectric and piezoelectric properties of the most promising systems will be studied in terms of grain size and domain structure.
Following the trend for miniaturization of electronic components we will investigate the complex perovskite systems with MW dielectric properties The research of the microwave dielectrics based on complex perovskites will be focused on the development of intergrowth structures between the cubic perovskite Ba(Co1/3Nb2/3)O3 and the shifted hexagonal perovskite Ba5Nb4O15, which form as a consequence of the B-site cation deficiency or as a transient phase during the synthesis of ordered Ba8CoNb6O24.
The research on microwave dielectrics, based on La2/3TiO3-LaAlO3 complex perovskites, will be focused on the preparation of fine-grained ceramics and thin films: i) For the ceramics the focus will be on the preparation of well-defined, nanosized starting particles by using selected wet methods and by the subsequent application of suitable sintering methods, to prepare dense, fine-grained ceramics. The final MW dielectric properties of the ceramics will be tuned by the starting composition, size and morphology of the starting particles and the micro/nanostructural properties of the prepared ceramics. The fabricated, pore-free ceramics with fine-grained microstructure and improved MW dielectric properties will be developed. ii) For the LaAlO3-La2/3TiO3 thin-film investigation we will prepare thin films with outstanding electrical properties by varying the LaAlO3/La2/3TiO3 ratio, the thickness, structural and nanostructural properties of the thin films. The prepared films will be used as a substrate for ordered assemblies of defined shape perovskite particles, prepared in the scope of this project.
Significance for science
Through the development of nanotechnology and miniaturization of electronic devices, the morphology control of nanocrystallites of functional materials (ferroelectrics, ferromagnets, magnetoelectrics, etc.) has become more and more important. The scientific interest for such nanocrystallites increased because physical and chemical properties depend on their shape and size and differ from their bulk counterparts. In addition, particles with a defined shape, such as (nano) cubes and (nano) plates, can be self-assembled forming two-dimensional or three-dimensional structures, which are the basis of so-called bottom up approach for fabrication of miniaturized electronic devices. From the standpoint of controlling the shape of particles and their aggregation, classical synthesis methods such as solid-state and sol-gel are not appropriate. Similarly, the conventional hydrothermal (solvotermal) conditions or molten salt synthesis often lead to aggregated particles with spherical or undefined shape. In the framework of this project, we showed that with the proper selection of a starting precursor and by controlling the reaction conditions, the synthesis can be directed to the formation of particles with well-defined shape, such as (nano)needles, (nano)plates or (nano)blocks. The understanding of the reaction mechanism is crucial for preparation of particles with predefined shape. We have shown that anisotropic MTiO3 perovskite particles (M=Ba, Sr, Ca), such as (nano)needles and (nano)plates , can be prepared by topochemical transformation of the corresponding titanate particles with defined shape (i.e., template precursors). This is a carefully planned synthesis, which started with the selection and synthesis of the template particles with predefined shape and structure and their transformation to target MTiO3 perovskite particles with the shape similar to that of template. The last conversion required the knowledge of the electrokinetic potential and solubility of the template particles in the reaction medium. Furthermore, the reaction conditions should ensure the epitaxial growth of the perovskite phase on the template particles and their complete transformation. With these approaches it is also possible to control the preferential orientation, which is important from the standpoint of the direction of electrical polarization and also for the catalytic properties, since the latter are highly dependent on the type of exposed crystallographic faces. Similarly, it is also true that due to the lattice strains induced at the hetero-interfaces the piezoelectric properties of composite perovskite particles are enhanced. These approaches are innovative since the mechanisms of topochemical transformations and epitaxial growth under molten salt, hydrothermal or solvotermal synthesis conditions, have not been well investigated and described in the literature. In the scope of this project we have systematically studied these mechanisms, which is extremely important for the synthesis of new materials (other shapes and size of particles, preferential orientation, new solid-solution compositions) and creation of new functional properties. It is known that perovskite particles with ferroelectric, piezoelectric and catalytic properties have great potential for use in advanced electronic devices and in the field of catalysis, respectively. It is therefore unambiguous that the results of the research obtained under this project provide a good starting point for further research and also for publishing results in scientific journals with even-higher impact factors.
Significance for the country
With the results obtained in the scope of this project we contributed to the general increase of the knowledge of oxide ceramic materials with perovskite structure, which are important due to their dielectric and ferroelectric properties. We also contributed to the development and training of new students, since the new knowledge was included in the content of learning subjects at Faculty of Chemistry and Chemical Technology, University of Ljubljana (FKKT-UL). In addition, in the framework of this project, one master's thesis was carried out at the 2nd Bologna level of Chemistry (FKKT-UL, University of Ljubljana). In the scope of one doctoral study at Jožef Stefan International Postgraduate School, the investigated perovskite materials and the inconsistencies in their synthesis will be further studied and explained. The results of the project were presented at numerous invited lectures in Europe and around the world (more than 20 invited lectures). There is a lot of interest in the topic, so it is not surprising that we managed to get partners and prepare a new international project, in the scope of which we are trying to use the developed new materials for the fabrication of a piezoelectric energy harvestesting device. In order to verify the catalytic properties of preferentially oriented perovskite particles with a defined shape (nanocubes, nanoplates), we have already established an informal collaboration with the National Institute of Chemistry. Researchers from the University of Science and Technology from Wroclaw, Poland, also expressed the interest for testing of our perovskite particles for non-linear optical applications. All these indicate a versatile and useful value of perovskite particles with a defined shape, crystal structure and preferential orientation. Unfortunately, at the moment we cannot talk about significant influence of our research results on the Slovenian industry, because there are no companies in Slovenia that could have an appropriate technology for production of these materials. Since we have not yet completely investigated all the functional properties of the developed materials, we do not yet know the total useful value of the developed materials. However, it is unambiguous that the mechanisms of topochemical transformations that we have studied are important for designing the shape and preferential orientation of particles of other materials, which will certainly accelerate the development of materials with new or improved functional properties.
Most important scientific results
Annual report
2014,
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2015,
final report
