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Limei Xu WPI-AIMR, Tohoku University, Japan Unusual phase behaviour in one-component systems with isotropic interactions In collaboration with: C. A. Angell Arizona State University S. V. Buldyrev Yeshiva University N. Giovambattista New York Brookline college H. E. Stanley Boston University M. Tokuyama Tohoku university
Motivation Similar phase behaviors shared by very different materials • Liquid-liquid phase transition: • Tetrahedral structured systems: water, Si, Ge, SiO2, BeF2 • Metallic system, such as Y3Al5O12 • Polyamorphism (amorphous-amorphous transition under pressure) • Tetrahedral structured systems: water, Ge • Metallic system: Ce55Al45 Both liquid transitions and polyamorphism, although caused in different materials by different chemical properties, have similar physics: involving two local structures, with one having large open spaces between particles that collapse under pressure.
Questions we ask • Universal model that determine whether these features and • phenomena are related or exist independently • How we can guide experimentalists to search for new • materials with better performance?
MD simulation Number of particles:N=1728 E. A. Jagla, J. Chem. Phys. 111, 8980 (1999) L. Xu et.al. Phys. Rev. E (2006) Two-scale isotropic interaction potentials Effective potential of water at T=280K T. Head-Gordon and F. H. Stilinger. J. Chem. Phys. 98, 3313 (1993) U( r ) ~ ln g ( r )
Phase Diagram Widom line • Stable liquid-liquid critical point (LLCP) • Negative sloped melting line • LDA and HDA L. Xu, S. V. Buldyrev, C. A. Angell, H. E. Stanley, Phys. Rev. E (2006) L. Xu, P. Kumar, S. V. Buldyrev, P. H. Poole, F. Sciortino, S.-H Chen, H. E. Stanley, PNAS (2005)
Pc=0.24 compressibility TW(P) Changes in thermodynamics upon crossing widom line • P<Pc :No anomalous behaviour! (Metastability) • P>Pc :Response functions show peaks. The location of the peaks decreases approaching to the critical pressure
Changes in structures upon crossing Widom line Orientational order parameter: Perfect Crystal: Q6=0.57; Random configuration: Q6=0.28
Two glass states upon cooling: HDA and LDA Two glass states obtained upon cooling LDL LDA HDL HDA
Polyamorphism System with LLCP: approach of new high density glasses by compression and decompression along constant pressure L. Xu, S. V. Buldyrev, H. E. Stanley, M. Tokuyama (in preparition)
HDL-LDA glass transition and liquid-liquid phase transition Detection of glass transition: thermal expansion L. Xu, S. V. Buldyrev, N. Giovambattista, C. A. Angell H. E. Stanley, JCP (2009)
HDL-HDA glass transition and liquid-liquid phase transition H=U+PV Detection of glass transition: thermal expansion or Cp The second approach is more pronounced, indicating that: Glass transition is the onset of the kinetics, while liquid-liquid Phase transition is the onset of the volume/density change L. Xu, S. V. Buldyrev, N. Giovambattista, C. A. Angell H. E. Stanley, JCP (2009)
Anomaly in melting curve as a function of pressure water, Si, Ge, Cs, Ba, Eu
Conclusions • Simple two-scale potential shows rich phase behavior: LLPT and polyamorphism • Near the critical point, response functions (thermodynamic and structural) show maxima upon crossing the Widom line, thus provide a way for experiments to locate the possible liquid-liquid critical point • The model tells us how to distinguish glass transition from the Widom line associated with the liquid-liquid phase transition. • Our study indicates an alternative way to make glasses via polyamorphism.
Possibility of synthesizing superstable metallic glasses • Mechanism of forming superstable metallic glasses
Pc=0.24 TW Changes in dynamics upon crossing Widom line P>Pc: Upon crossover the Widom line, a kink in D occurs near TW P<Pc: Upon crossing coexistence line, No kink in D
HDL-like TWidom LDL-like Translational order parameter: Random configuration: t=0