Rigidity and intermediate phases in glasses driven by speciation

Rigidity transitions that separate elastic phases in glasses are studied in the case where the local structure is not fully determined from the macroscopic concentration. It is shown that the location of the rigidity transitions, and the intermediate phase that separates flexible from stressed rigid glasses, depend crucially on the way local structures are selected, a selection usually termed speciation. Broadening of the intermediate phase is obtained for networks combining a large amount of flexible local structural units and extensive medium range order. This applies to systems of the form (1-x)SiX₂-xM₂X ( X=O,S,Se , M=Li,Na,K ) and opens additional perspectives for the observation of self-organized fast ionic conductors or geomaterials.