Relaxation processes and the mixed alkali effect in alkali metasilicate glasses
- Tokyo Inst. of Tech., Yokohama, Kanagawa (Japan)
- Kanazawa Univ. (Japan)
A molecular dynamics simulation (MD) of lithium metasilicate (Li{sub 2}SiO{sub 3}) and related mixed alkali system (LiKSiO{sub 3}) has been performed. Changes in the mean squared displacement and the corresponding clear two-step ({beta} and {alpha}1) relaxations in a density correlation function have been observed at 700 K (self-part) for each ion in Li{sub 2}SiO{sub 3} following an exponential decay by vibrational motion in a simulation up to 300 ps (run 1). The mean squared displacement of the atoms shows the change in the slope at ca. 300 ps when the simulation is extended up to 1 ns (run 2). Here the authors call the slowest relaxation (ca. 300 ps{approximately}) the {alpha}2 region. Oscillation, which is clearer for O and Si than for Li, is found in the second ({beta}-relaxation) region of the function, which is attributed to the so called boson peak. Both the {beta}-relaxation and the boson peak are found to be due to the correlated motion. The slower relaxation ({alpha}1 relaxation) can be fitted to a stretched exponential form and the origin of this type of decay is confirmed to be waiting time distribution of jump motions. The back-correlated jumps also decrease the decay rate. Components A and B in {alpha}1 and {alpha}2 regions for Li ion are analyzed, where the Li ion of component A is located within the first neighboring sites and that of component B moves longer than the nearest neighbor distances by cooperative jump motion. The component B shows accelerated dynamics larger than t-linear ones ({approximately}t{sup 1.77}) in the region 50--300 ps, and the dynamics can be characterized as Levy flight. They have found that the contribution of the cooperative jumps decreases in the mixed alkali glass. This explains the maximum of the Haven ratio accompanied with the mixed alkali effect.
- Sponsoring Organization:
- New Energy and Industrial Technology Development Organization, Tokyo (Japan)
- OSTI ID:
- 580855
- Report Number(s):
- CONF-961202-; ISBN 1-55899-359-2; TRN: IM9807%%61
- Resource Relation:
- Conference: 1996 Fall meeting of the Materials Research Society (MRS), Boston, MA (United States), 2-6 Dec 1996; Other Information: PBD: 1997; Related Information: Is Part Of Structure and dynamics of glasses and glass formers; Angell, C.A. [ed.] [Arizona State Univ., Tempe, AZ (United States)]; Ngai, K.L. [ed.] [Naval Research Lab., Washington, DC (United States)]; Kieffer, J. [ed.] [Univ. of Illinois, Urbana, IL (United States)]; Egami, T. [ed.] [Univ. of Pennsylvania, Philadelphia, PA (United States)]; Nienhaus, G.U. [ed.] [Univ. of Ulm (Germany)]; PB: 530 p.; Materials Research Society symposium proceedings, Volume 455
- Country of Publication:
- United States
- Language:
- English
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