Phase-Change Materials Exhibiting Tristability: Interconverting Forms of Crystalline α-, β-, and Glassy K2ZnSn3S8

We show that K(2)ZnSn(3)S(8) is a phase-change system that exhibits tristability. Kinetic and thermodynamic forms of different compounds in the K/Zn/Sn/S system have been synthesized and thoroughly characterized. We report an example where slow and rapid cooling of a melt of K(2)CO(3)/S/Sn/Zn leads to different kinetically stable products (crystalline layered α-K(2)ZnSn(3)S(8), 1, and glassy K(2)ZnSn(3)S(8), A, respectively). These forms convert to a thermodynamically stable compound (crystalline cubic β-K(2)ZnSn(3)S(8), 2) upon annealing below their melting points. The band gaps of compounds 1, A, and 2 are 2.30, 2.15, and 2.55 eV, respectively.