The structures and properties of silver selenide samples strongly depend on the method of preparation. Thin films prepared by pulsed laser deposition (PLD) contain lamellae of two low-temperature modifications of Ag2Se whose structures were analyzed in detail by electron microscopy techniques. Besides the stable and known Naumannite-type phase (LT1), a metastable phase was observed (LT2), and the phase transformation was examined in situ. Via cooling and annealing, LT2 becomes dominant in thin films, thus enabling solving the structure of LT2 by electron diffraction. These experiments and HRTEM point to an Acanthite-type (stable low-temperature modification of Ag2S) structure of LT2. Rapid-quenching procedures were applied for the first synthesis of LT2 as bulk sample. Depending on the conditions of melt spinning experiments, well-defined products were formed. In one series, we found a separation of LT1 and LT2 into distinct morphologies, i.e. microspheres and dendrites, respectively. The results on the magnetoresistance of the rapidly quenched materials support previous work.
During the processing of superconducting Nb3Sn wire, several intermediate intermetallic phases including a previously encountered Cu-Nb-Sn phase show up. The yet unknown crystal structure of this phase is now identified by a combination of different experimental techniques and database search to be of the hexagonal NiMg2 type with a proposed composition of about (Nb0.75Cu0.25)Sn2. The structure determination started from an evaluation of the lattice parameters from EBSD Kikuchi patterns from quenched material suggesting hexagonal or orthorhombic symmetry. A database search then led to the hexagonal NiMg2 type structure, the presence of which was confirmed by a Rietveld analysis on the basis of high energy synchrotron X-ray powder diffraction data. Assuming a partial substitution of Nb in orthorhombic NbSn2 by Cu, the change of the valence electron concentration provokes a structural transformation from the CuMg2 type for NbSn2 to the NiMg2 type for (Nb0.75Cu0.25)Sn2. In the previous literature the (Nb0.75Cu0.25)Sn2 phase described here has occasionally been referred to as Nausite.