Two-temperature synthesis of non-linear optical compound CdGeAs₂

In this work, we report on a new approach to synthesize large-scale nonlinear optical chalcopyrite compound CdGeAs₂ (cadmium germanium arsenide), in which the arsenic (As) precursor and the mixture of the cadmium (Cd) and the germanium (Ge) were separated in two distinct temperature-defined zones of a furnace. Through probing the intermediate product prepared at pre-set temperature points of hot-zone area, it was revealed that the ternary compound CdGeAs₂ was formed through chemical reactions among Cd₃As₂, CdAs₂, GeAs, GeAs₂ and Ge. A new intermediate crystalline compound, with determined crystal parameter c=0.9139 nm and unknown a parameter, was identified when the temperature of the mixture of Cd and Ge was set to 680 °C, which, however, disappeared when the temperature was set to 770 °C, yielding pure CdGeAs₂ product. Most likely, the identified new intermediate compound has layered graphite-like structure. Moreover, we show that the described two-temperature synthesis method allows us to produce near 250 g CdGeAs₂ product during one run in a horizontal furnace and 500 g in a tilted horizontal furnace with rotated reactor.