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Projects / Programmes source: ARIS

Nanostructural investigations of special boundaries in minerals

Research activity

Code Science Field Subfield
1.06.00  Natural sciences and mathematics  Geology   

Code Science Field
P250  Natural sciences and mathematics  Condensed matter: structure, thermal and mechanical properties, crystallography, phase equilibria 
Keywords
minerals, special grain boundaries, twinning, atomic structure, transmission electron microscopy
Evaluation (rules)
source: COBISS
Researchers (2)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  19029  PhD Nina Daneu  Materials science and technology  Researcher  2004 - 2006  426 
2.  06264  PhD Tadej Dolenec  Geology  Head  2004 - 2006  483 
Organisations (2)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,415 
2.  1555  University of Ljubljana, Faculty of Natural Sciences and Engeneering  Ljubljana  1627074  19,865 
Abstract
Special grain boundaries, such as twin boundaries, inversion boundaries or antiphase boundaries form regularly in natural and synthetic minerals. Special boundaries consist of two-dimensional, usually single-atomic, layers over which the two adjacent crystal domains are in a special crystallographic relationship. These layers have a different atomic structure and chemical composition as the host crystal, which is, however, similar to that of the closest secondary phase existing between the matrix crystal and the dopant that triggered its formation. Our previous investigations, performed in various ceramic systems, have shown that special boundaries like inversion boundaries in zinc oxide, are growth defects. We demonstrated that in addition to their specific atomic structure they are also of interest because of their significant influence on crystal growth. In our future studies we will include local atomic structure studies of different special boundaries that are observed in natural minerals. In contrast to synthetic minerals, where the composition and the formation conditions can be controlled accurately, these conditions are incomparably more complex during the nucleation and growth of natural minerals. In natural crystals, special boundaries are very common. Twin boundaries are the most prominent type of special boundaries and they morphologically reflect in minerals as characteristic angles of incidence between the crystal domains. Other special boundaries alter macroscopic appearance of the crystals less significantly. Low-angle tilt boundaries, for example, result in twisting of single crystals (so-called gwindel crystals). Special boundaries may occur individually or in groups. Individual twin boundaries can be contact twins, (i.e. rutile) or penetration twins (i.e. fluorite), whereas multiple twinning results in polysynthetic twins (i.e. albite). The reasons for the formation of the growth twins in minerals are not understood in detail and are often described as accidental overgrowing of single crystals in certain orientations. The nanostructural investigations of special grain boundaries in natural minerals could give the reasons for special boundaries formation in them. In our atomic-scale investigations we will focus on different types of special boundaries, mostly contact and penetration twins in minerals like rutile, fluorite, pyrite, cerussite and staurolite among others.
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