„Schmelzen”︁ im festen Zustand

Samwer, K.; Ettl, C.

doi:10.1002/phbl.19940500511

Cited by 2 publications

(1 citation statement)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…nderstanding the formation of glasses by viscous slowdown with decreasing temperature is currently seen as a major intellectual challenge in condensed-matter physics (1)(2)(3)(4). Although substantial progress has been made in deciphering the short-and intermediate-range structure of metallic glasses (5-7), the atomic-scale dynamics of their strongly temperaturedependent properties are far less well understood.…”

mentioning

confidence: 99%

Reversible atomic processes as basic mechanisms of the glass transition

Sprengel

Wunderlich

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Reversible formation and disappearance of vacant spaces (vacancytype defects) in bulk Zr57Cu15.4Ni12.6Nb5Al10 glass are directly evidenced by high-resolution, time-differential dilatometry studies. The vacancy kinetics are strongly temperature-dependent, with an effective migration enthalpy of H V M ‫؍‬ 3.34 eV. This may explain the strong temperature dependence of glass properties such as viscosity. The results presented here are of general importance for understanding amorphous condensed matter and biomaterials and for the technical development of amorphous steels.bulk metallic glass ͉ dilatometry ͉ positron annihilation U nderstanding the formation of glasses by viscous slowdown with decreasing temperature is currently seen as a major intellectual challenge in condensed-matter physics (1-4). Although substantial progress has been made in deciphering the short-and intermediate-range structure of metallic glasses (5-7), the atomic-scale dynamics of their strongly temperaturedependent properties are far less well understood. Thus, specific studies of atomic processes in bulk metallic glasses (BMGs) (8-10) are of particular interest. A pivotal question has been whether the properties of these glasses differ at temperatures above or below the so-called ''glass transition temperature,'' T g , which is usually deduced from the endothermic overshooting peak in the specific heat, ⌬c p (11-13). In BMGs (8-10), the viscosity, (see ref. 9) and atomic diffusivity, D, after long-term annealing at lower temperatures (11, 14) vary continuously at T g , so that no change of mechanism at T g can be detected. Yet, and D change strongly (9, 11), by 2 to 3 orders of magnitude, in the narrow temperature window of T g Ϯ 20 K. This raises a question regarding the origin of the strong temperature dependence that gives rise to the observation that glasses basically do not flow below T g . Specific studies of atomic processes in BMGs, using time-differential dilatometry as reported here, may help to answer this question.Atomic processes in crystals in which atoms jump between neighboring lattice sites are mainly controlled by the formation and migration of thermal vacancies. Thermal formation of vacancies in crystals can be specifically identified by studying the three characteristic signatures:1. Upon vacancy formation, the specimen volume expands because of the vacancy formation volume V V F , whereas the volume reversibly shrinks when the vacancy disappears. 2. The vacancy formation process is time-dependent because of the diffusion-controlled filling of the specimen volume, after a fast temperature change, by vacancies formed at vacancy sources. 3. Vacancies in crystals show the size, ⍀, of one missing atom. In some cases, the size may be smaller (⍀/2) or larger (e.g., 2⍀ for divacancies).Time-dependent volume expansion due to thermal vacancy formation has been demonstrated, together with positron lifetime studies for the local investigation of vacancies, in the case of crystalline intermetallic alloys (15, 16). The kinetics of vac...

show abstract

mentioning

confidence: 99%