Influence of the temperature and composition on the crystal structure of the AgBiSe2-AgBiS2 system

We report on the synthesis and structural study of the system AgBiSe2-AgBiS2. Single phase samples have been synthesized for every compositions of the solid solution, we have studied the temperature dependence of the crystal structure using high-temperature X-ray diffraction coupled to DSC, and established the structural phase diagram of the system. From this diagram, sulfur-rich samples exhibit one structural phase transition from a low temperature hexagonal phase to a high temperature cubic one, whereas selenium-rich samples also exhibit an intermediate rhombohedral phase, with a limit between the 2-phases and 3-phases region at Se = 0.8. Besides, significant changes of the volume of the unit cell have been observed at the phase transitions, coupled to crystal structure dependent coefficients of thermal expansion.