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Cordes, Niklas; Niklaus, Robin; Schnick, Wolfgang (2019): Ammonothermal Crystal Growth of ATaN(2) with A = Na, K, Rb, and Cs and Their Optical and Electronic Properties. In: Crystal Growth & Design, Vol. 19, No. 6: pp. 3484-3490
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Abstract

Crystals of alkali nitridotantalates, ATaN(2)(A = Na, K, Rb, Cs), with well developed shape were grown from corresponding alkali amides or azides and elementary Ta in supercritical ammonia. The aforementioned alkali mineralizers provide an ammonobasic environment for crystal growth. Temperatures of up to 1070 K resulted in an internal pressure of up to 170 MPa in high-pressure custom-built autoclaves. For successful crystal growth, a custom-built Ta liner was used as substrate. The obtained ATaN(2) crystals vary in size depending on the used alkali metal (Na, 50 mu m;K, 40 mu m;Rb, 200 mu m;Cs, 50 mu m). In addition, a second temperature step at the decomposition temperature of the respective mineralizer is required for the successful synthesis of crystals, due to formation of intermediates at lower temperatures. The obtained products were examined by PXRD, SEM, and UV-vis spectroscopy. The electronic properties were investigated by DFT calculations.