Séminaire du vendredi 24 juin 2011 à 10h30

Elastic Phase Transitions in Alkali Modified Oxide Glasses

P.Boolchand  (University of Cincinnati)

IMPMC, Université P. et M. Curie, 4, Place Jussieu, 75005 Paris  
Salle de Conférence - 401
4ème étage
Tour 23
Couloir 22-23

Résumé
 Chemical bonds in networks act as atomic constraints (both bond-bending and bond stretching kind) in assembling disordered solids. The count of constraints/atom has proved to be the single most significant parameter to understanding the physics of glasses including the elusive glass transition. These ideas have led to the recognition of two distinct elastic phase transitions- a rigidity and a stress transition as the count of constraints/atom is steadily increased either by chemical alloying or applying hydrostatic pressure. Experiments designed as test of these basic ideas show existence three elastic phases- flexible, intermediate and stressed rigid in semiconducting glasses with characteristic thermal, optical and mechanical signature. In alkali-modified-silicates,-germanates and -borates, these ideas show that packing considerations determined by alkali-ion size apparently control elastic phase diagrams in connectivity space. We provide examples.

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