Pressure induced silver ion displacement in La3Ag0.82SnS7

The compounds with the general formula Ln3MTX7 (space group P63) (Ln – rare-earth element, M – monovalent element (Cu, Ag), T – Si, Ge, Sn and X – S, Se) are interesting owing to the possible application in the field of ionic conductivity. In the crystal structure the face-sharing [Ag(S)6] triangular antiprisms form the channels where the Ag+ ion can migrate along the crystallographic c axis. High-pressure X-ray diffraction shows that Ag+ ion moves towards the central-point of [Ag(S)6] when pressure is risen. As a consequence, the coordination number of Ag+ changes from CN = 3 to CN = 6 at ∼3 GPa. The La3Ag0.82SnS7 has stiff structure; zero-pressure bulk modulus is B0 = 61.74 GPa and the pressure derivative is B ′ 0 = 4.02 .