TY - JOUR
T1 - A monatomic system with a liquid-liquid critical point and two distinct glassy states
AU - Xu, Limei
AU - Buldyrev, Sergey V.
AU - Giovambattista, Nicolas
AU - Angell, Charles
AU - Stanley, H. Eugene
N1 - Funding Information:
We thank F. Mallamace, S. Sastry, and F. W. Starr for helpful discussions, I. Ehrenberg for important contributions at the earlier stage of this work, and NSF Grant No. CHE 0404673 for support. C.A.A. acknowledges support from NSF-DMR Grant No. 0454672. XML acknowledges support from World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. We also thank the Boston University Computation Center for allocation of CPU time. S.V.B. thanks the Office of the Academic Affairs of Yeshiva University for funding the Yeshiva University high-performance computer cluster and acknowledges the partial support of this research through the Dr. Bernard W. Gamson Computational Science Center at Yeshiva College.
PY - 2009
Y1 - 2009
N2 - We study the glass transition (GT) in a model system that exhibits the presence of more than one liquid or glassy state ("polyamorphism") using molecular dynamics simulations. We study the Jagla model [E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)], a two-scale spherically symmetric ramp potential with both attractive and repulsive interactions. The Jagla model is particularly interesting since, depending on its parametrization, it predicts two phases ("polyamorphism") not only in the glassy state but also in equilibrium as a liquid-liquid phase transition (LLPT). The Jagla model may also be useful in understanding a recent observation of polyamorphism in metallic glasses containing cerium. We use a parametrization for which crystallization can be avoided and the GT and LLPT are clearly separated, providing a unique opportunity to study the effects of the LLPT on the GT. We follow the experimental protocol employed in the classical differential scanning calorimetry experiments used to characterize the GT, cooling and heating the system through the GT and calculating the constant-pressure specific heat CP and the thermal expansion coefficient αP. At pressures below and well above the LLPT, the same basic GT phenomenology of metallic glasses is observed, i.e., a single peak in CP (typical of ergodicity restoration) occurs upon heating across the GT. At pressures above the LLPT, a second peak in CP develops at higher temperature above the GT. This second peak in CP arises from the presence of a Widom line TW defined as the locus of maximum correlation length in the one-phase region above the liquid-liquid critical point (LLCP). The behavior of αP is different across the GT and Widom line. Near the GT temperature Tg, αP displays a small peak upon heating, which makes a negligible contribution to the CP peak. On the other hand, near TW, αP displays a much larger peak, which makes a substantial contribution to the CP peak at higher temperature. We find that Tg is almost independent of pressure for each of the two coexisting liquids, but shows an apparent discontinuity upon crossing the LLPT line, to a lower value for the higher-entropy phase. We compare the entropies of both phases, and the corresponding temperature dependencies, with those of the crystal phase. We also study the dependence of the GT on heating rate and find that for pressures below the LLCP, slow heating results in crystallization, as occurs in laboratory experiments. Regarding the thermal expansion properties of the Jagla model, we study the interplay of the density minimum recently observed in confined water and the GT.
AB - We study the glass transition (GT) in a model system that exhibits the presence of more than one liquid or glassy state ("polyamorphism") using molecular dynamics simulations. We study the Jagla model [E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)], a two-scale spherically symmetric ramp potential with both attractive and repulsive interactions. The Jagla model is particularly interesting since, depending on its parametrization, it predicts two phases ("polyamorphism") not only in the glassy state but also in equilibrium as a liquid-liquid phase transition (LLPT). The Jagla model may also be useful in understanding a recent observation of polyamorphism in metallic glasses containing cerium. We use a parametrization for which crystallization can be avoided and the GT and LLPT are clearly separated, providing a unique opportunity to study the effects of the LLPT on the GT. We follow the experimental protocol employed in the classical differential scanning calorimetry experiments used to characterize the GT, cooling and heating the system through the GT and calculating the constant-pressure specific heat CP and the thermal expansion coefficient αP. At pressures below and well above the LLPT, the same basic GT phenomenology of metallic glasses is observed, i.e., a single peak in CP (typical of ergodicity restoration) occurs upon heating across the GT. At pressures above the LLPT, a second peak in CP develops at higher temperature above the GT. This second peak in CP arises from the presence of a Widom line TW defined as the locus of maximum correlation length in the one-phase region above the liquid-liquid critical point (LLCP). The behavior of αP is different across the GT and Widom line. Near the GT temperature Tg, αP displays a small peak upon heating, which makes a negligible contribution to the CP peak. On the other hand, near TW, αP displays a much larger peak, which makes a substantial contribution to the CP peak at higher temperature. We find that Tg is almost independent of pressure for each of the two coexisting liquids, but shows an apparent discontinuity upon crossing the LLPT line, to a lower value for the higher-entropy phase. We compare the entropies of both phases, and the corresponding temperature dependencies, with those of the crystal phase. We also study the dependence of the GT on heating rate and find that for pressures below the LLCP, slow heating results in crystallization, as occurs in laboratory experiments. Regarding the thermal expansion properties of the Jagla model, we study the interplay of the density minimum recently observed in confined water and the GT.
UR - http://www.scopus.com/inward/record.url?scp=59949090369&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=59949090369&partnerID=8YFLogxK
U2 - 10.1063/1.3043665
DO - 10.1063/1.3043665
M3 - Article
C2 - 19206982
AN - SCOPUS:59949090369
SN - 0021-9606
VL - 130
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
IS - 5
M1 - 054505
ER -