The results from the field of twinning in spinel were presented by dr. Nina Daneu at the 3rd International Conference on Crystallogenesis and Mineralogy from September 27th to October 1st 2013 in Novosibirsk, Russia. The conference is specialized in the field of crystal growth in minerals, therefore it was extremely important to present the results of our investigations to this public. Our findings on twinning in spinel, the formation of taaffeite phases in BeO-doped MgAl2O4 spinel and the role of chemically induced twins on crystal growth were presented in the lecture. One of the most important results of my active presence at the conference is the application for a Slovenian-Russian bilateral project (call in October 2013) with dr. Victor Gaberielevich Thomas from the Sobolev Institute of Geology and Mineralogy, Siberian Branch of RAS entitled 'Characterisation of growth features and planar defects in crystals grown under hydrothermal conditions' (BI-RU/14-15-025) approved by the Slovenian Research Agency in March. The Russian partners on this project are exterst for crystal growth under hydrothermal conditions, therefore we will study hydrothermal crystal growth of spinel and taaffeite among others in the frame of this project.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 27581479In the frame of the spinel-chrysoberyl work package we investigate twinning in both end-members of this system. Besides twinning in spinel, we performed also atomic-scale analyses of {130} contact twins in chrysoberyl (BeAl2O4). HRTEM analyses of natural samples from Pratinhas in Brazil have revealed that these crystals contal a high concentration of nanosized rutile precipitates, which are epitaxially related to the matrix chrysoberyl phase. The rutile precipitates are arranged in two distinct crystallographic directions and are the most probable cause of asterism in chrysoberyl. Based on detailed HRTEM analyses of twins and rutile precipitates we set atomic models of the {130} twin boundary and the rutile-chrysoberyl contact. The theoretical models and their structural details were validated by comparison of simulated and experimental images. The results of this study were presented at the conference for electron microscopy in Regensburg. Sandra Drev, our PhD student and the presenting author of this work received the best poster award for her presentation in the Ceramics, oxides and geomaterials section.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 27020839An important result of our research in the frame of the rock salt - nickeline work package is the doctoral dissertation by Janez Zavašnik. The candidate focused on the synthesis of different types of Fe-sulphides with a special emphasis on the influence of Cu-doping on the subsequent phase transformations. Using different methods of electron microscopy, the structural defects and epitaxial relationships between the phases in this wide group of (Fe,Cu)- mono- and di-sulphides were characterized. The group of compounds is interesting because of their excellent physical properties and wide application possibilities in modern technologies (batteries, solar cells, for ecological applications). Many questions regarding nucleation, phase transformations and structural variations were open despite many previous studies in this field. The candidate used two different methods for the synthesis: chemical vapour transport (CVT) method and combined sonoclemical/solvothermal method. CVT method was used to synthesize FeS2 (pyrite, markasite), FeS (pyrothite, troilite and other monosulphides) and yet unknown and undescribed sphalerite-wurtzite type compound (Fe,Cu)S in the temperature range 700-450°C. For the low-temperature synthesis of Fe- sulphides, iron and copper chlorides were mixed in different ratios with sulphur and the organic precursor diethanolamine (DEA), and sonicated to achieve efficient mixing. Using this method, abundant formation of /Fe, Cu)S was achieved. The result this study is the description between the pyrite morphology and crystallization temperature, the influence of copper addition to the stability of the initial FeS precipitates and on the formation of cubic (Fe, Cu)S. It was shown that already sonication at room temperature causes precipitation of metastable FeS that transforms to mackinawite-type FeS and further to pyrite without intermediate greigite phase as reported previously. Greigite forms only in the precence of copper and at higher concentrations of Cu, chalcopyrite and bornite form instead of the cubic sphalerite-type (Fe, Cuz)S. The research within this PhD thesis offer answers to many questions related to the initial phase transformations in Fe-sulphides.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 27575079