Лекция на проф. Линдзи Гриър
Департамент по Материалознание и Металургия
в Университета в Кеймбридж, Великобритания
на тема „ Extending the applicability of the glassy state„
20 юли, 2018 г. в 11:00 ч., заседателна зала на Факултета по химия и фармация на Софийския университет
„The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition“ [1]. We cover some recent research on metallic and on chalcogenide glasses.
Reasons for interest in metallic glasses include their excellent, even record-breaking, mechanical properties. Mechanical working can be used to change the structure and properties of these materials [2], something hardly explored for conventional glasses. While plastic deformation can be expected to have structural effects, it is surprising that there can be significant effects even well within the (nominally) elastic regime [3,4]. The focus of interest is the diversity that can be achieved in the metallic glassy state, from very-high-energy (‘rejuvenated’) to very-low-energy (‘relaxed’ and even ‘ultrastable’) states.
Reasons for interest in chalcogenide glasses include their application in non-volatile computer memory, dependent on fast switching from the glassy to crystalline state. Ultra-fast differential scanning calorimetry can characterize crystal growth rates up to their maxima at intermediate supercooling [5]. This permits studies of the liquid fragility, revealing a fragile-to-strong crossover in some systems [6]. Studies of fast crystallization are directly relevant for phase-change memory, and may point to the application of metals for fast switching [7].
[1] P.W. Anderson, Through the glass lightly, Science 267 (1995) 1615–1616.
[2] Y.H. Sun, A. Concustell, A.L. Greer, Thermomechanical processing of metallic glasses: extending the range of the glassy state. Nature Rev. Mater. 1 (2016) 16039.
[3] S.V. Ketov, Y.H. Sun, S. Nachum, Z. Lu, A. Checchi, A.R. Beraldin, H.Y. Bai, W.H. Wang, D.V. Louzguine-Luzgin, M.A. Carpenter, A.L. Greer, Rejuvenation of metallic glasses by non-affine thermal strain, Nature 524 (2015) 200–203.
[4] A.L. Greer, Y.H. Sun, Stored energy in metallic glasses due to strains within the elastic limit, Philos. Mag. 96 (2016) 1643–1663.
[5] J. Orava, A.L. Greer, B. Gholipour, D.W. Hewak, C.E. Smith, Characterization of supercooled liquid Ge2Sb2Te5 and its crystallization by ultra-fast-heating calorimetry, Nature Mater. 11 (2012) 279‒283.
[6] J. Orava, D.W. Hewak, A.L. Greer, Fragile-to-strong crossover in supercooled liquid Ag-In-Sb-Te studied by ultrafast calorimetry, Adv. Funct. Mater. 25 (2015) 4851–4858.
[7] A.L. Greer, New horizons for glass formation and stability, Nature Mater. 14 (2015) 542–546.