Layer Structures of Cu_xAg_1−xI Crystals

Abstract

X-ray diffraction studies were made on layer structures in the quasi-binary system CuI–AgI and their structural changes were investigated by standing them at room temperature and by heating. The proportion of Cu to Ag in a crystal was determined by the atomic absorption method. The following facts were revealed. The Cu_xAg_1−xI crystals have faulted 2H structures, which often coexist with long-period polytypes, in the composition range 0<x<0.025, the 4H structure in 0.025≤x≤0.034, the 4H structure immediately after growth in 0.061≤x≤0.092 and the 3R structure (the zincblende-type structure) in 0.148≤x≤0.277. The 4H structure in the range 0.061≤x≤0.092 changes to twins of the 3R at room temperature and this structural change occurs earlier with increasing x value. The 3R structure is stable at high temperatures below 146°C over the range x≥0.025. Reduced lattice parameters of the layer structures decrease with the increase of Cu concentration and the Cu ion is substituted for the Ag ion.