TY - JOUR
T1 - Glass Transitions, Semiconductor-Metal Transitions, and Fragilities in Ge-V-Te (V=As, Sb) Liquid Alloys
T2 - The Difference One Element Can Make
AU - Wei, Shuai
AU - Coleman, Garrett J.
AU - Lucas, Pierre
AU - Angell, Charles
N1 - Publisher Copyright:
© 2017 American Physical Society.
PY - 2017/3/31
Y1 - 2017/3/31
N2 - Glass-transition temperatures (Tg) and liquid fragilities are measured along a line of constant Ge content in the system Ge-As-Te, and contrasted with the lack of glass-forming ability in the twin system Ge-Sb-Te at the same Ge content. The one composition established as free of crystal contamination in the latter system shows a behavior opposite to that of a more covalent system. The comparison of Tg vs bond density in the three systems Ge-As-chalcogen differing in chalcogen, i.e., S, Se, or Te, shows that as the chalcogen becomes more metallic, i.e., in the order S<Se<Te, the bond-density effect on Tg becomes systematically weaker, with a crossover at r =2.3. When the more metallic Sb replaces As at r greater than 2.3, incipient metallicity rather than directional bond covalency apparently gains control of the physics. This observation leads us to an examination of the electronic conductivity and then semiconductor-to-metal (SC-M) transitions, with their associated thermodynamic manifestations in relevant liquid alloys. The thermodynamic components, as seen previously, control liquid fragility and cause fragile-to-strong transitions during cooling. We tentatively conclude that liquid-state behavior in phase-change materials is controlled by liquid-liquid (LL) and SC-M transitions that have become submerged below the liquidus surface. In the case of the Ge-Te binary, a crude extrapolation to GeTe stoichiometry indicates that the SC-M transition lies about 20% below the melting point, suggesting a parallel with the intensely researched "hidden liquid-liquid transition" in supercooled water. In the water case, superfast crystallization initiates in the high-fragility domain some 4% above the LL transition temperature (TLL) which is located at approximately 15% below the (ambient pressure) melting point.
AB - Glass-transition temperatures (Tg) and liquid fragilities are measured along a line of constant Ge content in the system Ge-As-Te, and contrasted with the lack of glass-forming ability in the twin system Ge-Sb-Te at the same Ge content. The one composition established as free of crystal contamination in the latter system shows a behavior opposite to that of a more covalent system. The comparison of Tg vs bond density in the three systems Ge-As-chalcogen differing in chalcogen, i.e., S, Se, or Te, shows that as the chalcogen becomes more metallic, i.e., in the order S<Se<Te, the bond-density effect on Tg becomes systematically weaker, with a crossover at r =2.3. When the more metallic Sb replaces As at r greater than 2.3, incipient metallicity rather than directional bond covalency apparently gains control of the physics. This observation leads us to an examination of the electronic conductivity and then semiconductor-to-metal (SC-M) transitions, with their associated thermodynamic manifestations in relevant liquid alloys. The thermodynamic components, as seen previously, control liquid fragility and cause fragile-to-strong transitions during cooling. We tentatively conclude that liquid-state behavior in phase-change materials is controlled by liquid-liquid (LL) and SC-M transitions that have become submerged below the liquidus surface. In the case of the Ge-Te binary, a crude extrapolation to GeTe stoichiometry indicates that the SC-M transition lies about 20% below the melting point, suggesting a parallel with the intensely researched "hidden liquid-liquid transition" in supercooled water. In the water case, superfast crystallization initiates in the high-fragility domain some 4% above the LL transition temperature (TLL) which is located at approximately 15% below the (ambient pressure) melting point.
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U2 - 10.1103/PhysRevApplied.7.034035
DO - 10.1103/PhysRevApplied.7.034035
M3 - Article
AN - SCOPUS:85017035009
SN - 2331-7019
VL - 7
JO - Physical Review Applied
JF - Physical Review Applied
IS - 3
M1 - 034035
ER -