Electron Microscopic Investigations on the Mineral Lorándite from Allchar in Macedonia

Project Leaders

  • Tobias Necke, Maximilian Trapp, Stefan Lauterbach, Georg Amthauer and Hans-Joachim Kleebe

Description

Single crystals of the rare natural mineral lorándite, TlAsS2, were investigated via electron microscopy (SEM and TEM). The main focus of this study was to address the question as to whether those lorándite crystals are chemically and structurally homogeneous, to be utilized as an effective neutrino detector within the lorándite experiment (LOREX) project.

Apart from few secondary minerals, being present only at the surface of the lorándite samples, scanning electron microscopy (SEM) indicated homogeneous crystals. Similarly, transmission electron microscopy (TEM) imaging revealed a homogenous and undisturbed crystal structure, with the only exception of rarely observed local coffee-bean contrasts.

EDS in conjunction with EELS analysis did not show any significant chemical difference, when analysing regions on or off those coffee-bean features, indicating a chemically homogenous mineral. Since the presence of lattice disturbing secondary phase precipitates could be excluded as well as crystal defects such as dislocations and stacking faults; therefore, minor fluid inclusions that were incorporated during crystal growth, are discussed as the probable origin of this local elastic strain.

The experimental results confirm that the studied lorándite single crystals fulfill all structural and chemical requirements to be employed as the natural mineral that allows to determine solar neutrino fluxes.

Fig. 1: (a) STEM-BF image revealing coffee-bean contrast. These kinds of coffee-bean contrasts are a typical indicator for local strain within the crystal lattice. (b) Selected area electron diffraction (SAED) pattern of the [101] zone axis, depicting the orientation of coffee beans parallel to the [010] direction. The red circles mark systematic extinctions due to lorándites’ space group P21/a with reflection conditions k = 2n for (0k0).
Fig. 1: (a) STEM-BF image revealing coffee-bean contrast. These kinds of coffee-bean contrasts are a typical indicator for local strain within the crystal lattice. (b) Selected area electron diffraction (SAED) pattern of the [101] zone axis, depicting the orientation of coffee beans parallel to the [010] direction. The red circles mark systematic extinctions due to lorándites’ space group P21/a with reflection conditions k = 2n for (0k0).
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