Phase-Change Materials
Exhibiting Tristability: Interconverting
Forms of Crystalline α-, β-, and Glassy K<sub>2</sub>ZnSn<sub>3</sub>S<sub>8</sub>
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Abstract
We show that K<sub>2</sub>ZnSn<sub>3</sub>S<sub>8</sub> 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<sub>2</sub>CO<sub>3</sub>/S/Sn/Zn leads
to different kinetically stable products (crystalline layered α-K<sub>2</sub>ZnSn<sub>3</sub>S<sub>8</sub>, <b>1</b>, and glassy
K<sub>2</sub>ZnSn<sub>3</sub>S<sub>8</sub>, <b>A</b>, respectively).
These forms convert to a thermodynamically stable compound (crystalline
cubic β-K<sub>2</sub>ZnSn<sub>3</sub>S<sub>8</sub>, <b>2</b>) upon annealing below their melting points. The band gaps of compounds <b>1</b>, <b>A</b>, and <b>2</b> are 2.30, 2.15, and
2.55 eV, respectively
