Phase change media utilize a remarkable property portfolio including the ability to rapidly switch between the amorphous and the crystalline state, which differ significantly in their properties. This property combination makes them very attractive for photonic applications ranging from data storage to fast optical switches, employing the pronounced difference of optical properties between the amorphous and crystalline state. This talk will discuss the origin of the unique material properties, which characterize phase change materials. In particular, it will be shown that only a rather small group of materials utilizes ‘metavalent bonding’, a novel, yet fundamental bonding mechanism, which can explain many of the characteristic features of phase change materials. This insight is employed to predict systematic property trends and to explore the limits in stoichiometry for photonic applications of this material class. It will be demonstrated how this concept can be used to tailor fast optical switches. Yet, the discoveries presented here also force us to revisit the concept of chemical bonding and bring back a history of vivid scientific disputes about ‘the nature of the chemical bond’.
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