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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.
Dispersions of very small non-magnetic metal particles or inclusions in a non-magnetic semiconductor matrix are well known to produce unusually large and linear magnetoresistance effects. So far these materials were limited to the binary silver-rich chalcogenides Ag2Se and Ag2Te. In this contribution Ag3AuTe2 was selected as a first candidate for a ternary matrix material, thus offering enhanced capabilities for the generation of heterogeneous microstructure and spatially varying composition on the nanoscale. In gold-rich Ag3Au1.1Te2 two kinds of inhomogeneities are present, namely Au deposits with a size on the micron scale and an inhomogeneous distribution of Au and Ag within the matrix. The matrix consists of micron-sized grains with the structure type of Ag3AuTe2 as studied by electron microscopy. Like the binary silver chalcogenide phases, the material also shows a large and linear magnetoresistance effect. The transversal magnetoresistance effect was measured between 20 K and 270 K in magnetic fields up to B = 5 T. The results are discussed on the basis of existing models for a large and linear positive MR effect.