Multistates and Polyamorphism in Phase-Change K₂Sb₈Se₁₃

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Phase-change (PC) materials are crucial for optical data storage, utilizing reversible crystal-amorphous transitions for binary states.
• Polyamorphism, an amorphous-to-amorphous transition, is exceptionally rare in solid-state inorganic materials.

Purpose of the Study:

• To report the discovery of K₂Sb₈Se₁₃ (KSS) as a material exhibiting both polyamorphic and crystalline phase transitions.
• To characterize the distinct properties of KSS in its multiple stable states.

Main Methods:

• Investigated phase transitions of K₂Sb₈Se₁₃ at accessible temperatures.
• Analyzed the optical bandgaps and electrical conductivity of the different KSS states.

Main Results:

• KSS exhibits both amorphous-to-amorphous polyamorphic and amorphous-to-crystal transitions at 227 °C and 263 °C, respectively.
• All three states (amorphous-I, amorphous-II, crystalline) are stable under ambient conditions.
• Distinct optical bandgaps (1.25, 1.0, 0.74 eV) and significant conductivity changes (>2 orders of magnitude) were observed across the states.

Conclusions:

• KSS represents a new class of materials with multiple stable states due to polyamorphism.
• These properties are promising for developing multistate logic circuits, reconfigurable devices, and advanced optical switches.