Uncovering β-relaxations in amorphous phase-change materials

Abstract

Relaxation processes are decisive for many physical properties of amorphous materials. For amorphous phasechange materials (PCMs) used in nonvolatile memories, relaxation processes are, however, difficult to characterize because of the lack of bulk samples. Here, instead of bulk samples, we use powder mechanical spectroscopy for powder samples to detect the prominent excess wings-a characteristic feature of -relaxations-in a series of amorphous PCMs at temperatures below glass transitions. By contrast, -relaxations are vanishingly small in amorphous chalcogenides of similar composition, which lack the characteristic features of PCMs. This conclusion is corroborated upon crossing the border from PCMs to non-PCMs, where -relaxations drop substantially. Such a distinction implies that amorphous PCMs belong to a special kind of covalent glasses whose locally fast atomic motions are preserved even below the glass transitions. These findings suggest a correlation between -relaxation and crystallization kinetics of PCMs, which have technological implications for phase-change memory functionalities.

Mechanism of amorphous phase stabilization in ultrathin films of monoatomic phase change material

“…Actually, the processes responsible for the β relaxation have been proposed to accelerate the crystallization kinetics in metallic glasses 53 and more recently in phase change chalcogenide alloys as well. 54 The presence of a β relaxation process in phase change materials has been recently identified from the so called β-wing in the temperature dependence of the loss modulus measured by dynamical mechanical spectroscopy (DMS). 54 On these premises on the crystallization process in the bulk, we moved to study the crystallization in ultrathin films.…”

“…54 The presence of a β relaxation process in phase change materials has been recently identified from the so called β-wing in the temperature dependence of the loss modulus measured by dynamical mechanical spectroscopy (DMS). 54 On these premises on the crystallization process in the bulk, we moved to study the crystallization in ultrathin films. We considered the thinnest film of 3 nm studied experimentally in ref.…”

Vitrification of octonary perylene mixtures with ultralow fragility

“…Fragility plots that feature a change in slope have been observed in the case of other materials such as water ( 35 ), SiO 2 ( 36 ), BeF 2 ( 37 ), ZnCl 2 ( 38 ), and different metallic glass-forming liquids ( 39 – 41 ). This type of behavior, which is often referred to as a fragile-to-strong transition, has been suggested to arise because the liquid adopts a new local structure and density, affecting the relaxation kinetics ( 42 – 45 ).…”

Physical Aging Behavior of a Glassy Polyether

“…This result suggests that the origin of complex aging behavior must be based on a framework disregarding the chemical details of the glass. Indeed, the presence of a fast mechanism of equilibrium recovery has been encountered on the base of a variety of observations in a wide range of system, including bulk metallic glasses [ 21 , 22 , 29 , 32 , 65 , 66 , 67 ], phase change materials [ 68 ], a plastic crystal [ 28 ], chalcogenide glasses [ 19 ], and a low molecular weight glass former [ 20 ]. Although glass-former specific approaches are of interests [ 25 ], these results calls for a universal description.…”