Projects / Programmes
Atomic-scale studies of initial stages of phase transformations in minerals
| Code |
Science |
Field |
Subfield |
| 1.06.00 |
Natural sciences and mathematics |
Geology |
|
| Code |
Science |
Field |
| P420 |
Natural sciences and mathematics |
Petrology, mineralogy, geochemistry |
| Code |
Science |
Field |
| 1.05 |
Natural Sciences |
Earth and related Environmental sciences |
growth twins, chemical twinning, transformational faults, polytypism, polysomatism, phase transformations, epitaxies, atomic strucutre, minerals, magmatic and metamorphic rocks
Researchers (12)
Organisations (4)
Abstract
In nature we find many examples of transformation faults, polytypic structures and epitaxial overgrowths of minerals and the reasons for their formation are poorly studied at the atomic scale and are generally not well understood. The main reasons are the dynamics and the complexity of growth conditions. Namely, during their growth, natural minerals are exposed to far more unpredictable thermodynamic conditions and diverse geochemical environments than the minerals synthesized in the laboratory. The formation of minerals often involves a sequence of temperature dependent phase transformations, which are reflected in local structure and chemistry of the samples. To reconstruct a sequence of these unknown transient processes, a detailed structural and chemical characterization of the samples is of great help. Based on nanostructural investigations of planar defects, precipitates and other topotaxial reactions we can not only reconstruct the dynamics of past geochemical processes, but also get a better insight into regional rock-forming and tectonic processes that were active during crystal growth. Phase transformations in minerals are essential indicators of geochemical and thermodynamic changes during crystal growth. The initial stages of phase transformations can be recognized by the formation of thermodynamically or chemically induced planar defects, such as twin, antiphase, or inversion boundaries in the affected crystals. Based on the principles of crystal chemistry, it has been suggested that the atomic structure of a twin boundary must somehow be related to an existing polymorphic modification of the source phase. The confirmation of this hypothesis was not possible until the development of advanced electron microscopy techniques, which enable a direct insight into the local atomic structure and chemistry of the transformation faults. Investigations of the initial stages of phase transformations will therefore be one of the central scientific objectives of this project that offers possibilities for in-depth understanding the basic building principles of solids and fundamentals of transformations in minerals. After identifying structural and chemical elements that lead to a particular transformation, our understanding will be challenged by reproducing the conditions of their formation in a controlled laboratory environment, as successfully demonstrated on some case studies in the past (zincite, spinel).
The concept of chemically triggered phase transformations in minerals is an innovative approach towards understanding the atomistic principles of phase formation and related crystal growth, where our group is leading worldwide. The results of the proposed project will be a groundbreaking contribution to our basic knowledge on thermodynamics and kinetics of processes during crystal nucleation and growth at the atomic scale, which have far-reaching implications not only for understanding geochemical processes, but offer unforeseen technological implications in development of novel materials with targeted physical properties. Observing and learning from nature has always been the best way to generate new technological breakthroughs, therefore the systems studied within the scope of the project are selected with an outlook that the results can potentially be implemented for development of novel technologically interesting materials: i.e. ilmenite-to-rutile transformation (production of inorganic fractal supports for separation technology and catalysis), growth defects and twins in perovskite (dielectric and thermoelectric applications), twinning in diamond (structural applications) among others. Our previous investigations of this inadequately studied phenomenon, the expertise of the research team and the accessibility of top research equipment through established international collaboration schemes are a solid foundation for the successful accomplishment of the ambitious goals within the proposed research project.
Significance for science
The results of our investigations in the field of chemically induced twinning and topotaxial phase transformations at the atomic scale are a contribution to deeper understanding of fundamental crystal chemistry thermodynamic principles related to solid state crystal growth. Growth-type twins and related oriented mineral intergrowths and the reasons for their formation are the main research topic of our group for many years and during this time we have contributed several important fundamental scientific findings to the fields of mineralogy, crystallography and also materials science. We have introduced the concept of chemically induced phase transformations in minerals and proved that the formation of growth-type twins is not a result of accidental attachment but is related to a combination of geochemical and geophysical conditions during the crystal nucleation stage. We have shown quantitatively that chemically induced twins have lower formation energy compared to chemically 'clean' twin boundaries and even compared to the formation of the host crystal, which is an important contribution in the field of solid state thermodynamics and investigations of twinned crystals (mineralogy, crystallography). Recently we have identified alternative twinning mechanism related to topotaxial (oriented) recrystallization of the precursor crystal and revealed that the orientation relationship between the products depends on the kinetics of recrystallization reaction. Since oriented mineral intergrowth occur frequently in magmatic and metamorphic rocks, understanding of their formation is especially important for correct interpretation of past petrogenetic processes. In this part, our results are a contribution to petrology. The main tool for atomic-scale analyses of oriented mineral intergrowths are methods of transmission electron microscopy (TEM). We use a specific approach where each planar defect or textured sample is analyzed along two perpendicular orientations enabling 3D reconstruction. For solving specific problems related to the atomic structure and chemical composition of interfaces we develop innovative approaches, contributing to the progress in the field of electron microscopy. All our findings are a result of comprehensive and thorough investigations of representative samples and contribute to better understanding of (re)crystallization processes in rocks. Reconstruction of the mechanisms leading to oriented intergrowths in nature can be transferred to the laboratory for controlled synthesis of functional materials. Learning form Nature has always been the best approach for creating technological breakthroughs and we have demonstrated this principle on different systems, for example by synthesis of multilevel branched rutile-based structures. In this field the results of our work contribute to the development in the field of materials science. The main advantage of our approach is involvement of experts from different scientific fields resulting in synergetic effects and faster progress in all scientific fields.
Significance for the country
The results of our research are a contribution to the basic knowledge in the field of mineralogy, petrology and synthesis of functional materials. Our nanostructural investigations of complex mineral and rock samples contribute fundamental insights to the petrology of magmatic and metamorphic rocks. The work of our group is increasingly recognized and appreciated due to our publications in high-impact scientific journals and presentations of our results at international conferences. This is reflected in the increasing number of international collaborations with different groups working in the fields of mineralogy, petrology and synthesis of functional materials for various applications from Russia, France, Austria, and many other countries. Researchers from these groups have recognized the potential of our specific approach to investigations of nanostructural phenomena in minerals and they initiate collaborations in the field of nanoscale characterization of their complex mineralogical and petrological samples by transmission electron microscopy (TEM) methods. The many benefits of international cooperation for Slovenia are gaining new knowledge in the field of mineralogy, petrology and functional materials, and development of skills related to the application of TEM methods for analyses of challenging rock and mineral samples. The quality of our work is also reflected in a large number of invitations to international scientific conferences (6 within this project) and foreign universities and institutes (11 related to this project). All newly established collaborations and invitation to present the results of our research work are a direct recognition of our scientific efforts and represent effective dissemination of the Slovenian knowledge. We are also aware that education of students in the field of geological sciences is extremely important for the future of Slovenia, therefore graduate geology students (in cooperation with FNT) and doctoral students are constantly involved in our research projects. Two young researchers have finished their doctoral studies on topics related to oriented mineral intergrowths related to this project and two candidates will finish in near future.
Most important scientific results
Annual report
2015,
final report
Most important socioeconomically and culturally relevant results
Annual report
2014,
2015,
final report
