X-ray and neutron diffraction study of Co$_{\mathrm{2-x}}$TiSn (x \textless 0.5) solid solution

Heusler compounds are a large class of intermetallic materials with a wide range of applicable properties, spintronics and thermoelectrics just to mention a few. This class of materials can be divided into two main groups, materials with 2:1:1 composition called Heuslers and materials with 1:1:1 composition, also called Half-Heuslers. In some ternary systems with existence of Heusler structures there is a solid solution between Heusler and Half-heusler phases. In this work the Co-Ti-Sn ternary system was studied. Batches with different starting compositions ranging from CoTiSn to Co$_{\mathrm{2}}$TiSn were arc melted. The buttons resulting from the arc melting were crushed, annealed and studied by in-lab X-ray, synchrotron and neutron diffraction, and by scanning (SEM) and transmission (TEM) electron microscopy. Phase equilibria is discussed with focus on structural composition and disorder in solid solution Co$_{\mathrm{2-x}}$TiSn. In the literature there has been some discussion as to whether the Half-Heusler CoTiSn exists or not. Our observation supports the paper by T. Nobata et al. (2002) where Co$_{\mathrm{2-x}}$TiSn is reported for x ranging between 0.08 and 0.50.