Transient Mesoscopic Immiscibility, Viscosity Anomaly, and High Internal Pressure at the Semiconductor–Metal Transition in Liquid Ga₂Te₃

Abstract

Gallium tellurides appear to be promising phase-change materials (PCMs) of the next generation for brain-inspired computing and reconfigurable optical metasurfaces. They are different from the benchmark PCMs because of sp3 gallium hybridization in both cubic Ga2Te3 and amorphous pulsed laser deposition (PLD) films. Liquid Ga2Te3 also shows a viscosity η(T) anomaly just above melting when η(T) first increases and only then starts decreasing. We used high-energy X-ray diffraction to observe a transient mesoscopic immiscibility that suggested dense metallic liquid droplets in a semiconducting melt. The η(T) shape was consistent with this finding. A vanishing first sharp diffraction peak that also shifts to a higher Q indicates a high internal pressure in the metallic melt, which produces a remarkable asymmetry of the Ga–Te nearest neighbor distances and is reminiscent of high-pressure rhombohedral Ga2Te3. The observed phenomena provide a realistic scenario for a fast, multilevel SET–RESET response, which also unravels similar trends in the purported density-driven liquid polyamorphism of water, phosphorus, sulfur, and other materials.

Glassy and liquid Sb2S3: insight into the structure and dynamics of a promising functional material

“…We do not expect for Sb 2 S 3 either a fragile-to-strong transition [112][113][114][115] or mesoscopic immiscibility accompanied by a viscosity anomaly 116,127 since both the experimental conductivity (Fig. 2) and FPMD simulations (Fig.…”

Decoding the Atomic Structure of Ga2Te5 Pulsed Laser Deposition Films for Memory Applications Using Diffraction and First-Principles Simulations

“…The viscosity anomaly for several Ga-Te melts in the vicinity of a sesquitelluride composition [ 18 , 19 ] appears to be more significant than the observed “double kink” in liquid germanium tellurides and other PCM alloys [ 20 , 21 , 22 , 23 ], allowing us to distinguish between two contrasting models: (1) fragile-to-strong transition [ 20 , 21 , 22 ] and (2) incipient liquid–liquid immiscibility [ 23 ]. Recent high-energy X-ray [ 24 ] and neutron diffraction measurements have shown enhanced small-angle scattering below the scattering vector ≲ 0.4 Å −1 ; this is related to the dense metallic liquid droplets in the semiconducting Ga 2 Te 3 melt and correlates with non-monotonic viscosity behavior, which can be quantitatively described by the Taylor model [ 25 ] for two-phase emulsions. The incipient transient immiscibility within a semiconductor–metal transition in liquid telluride PCMs is an interesting topic for further studies.…”