Polyamorphism denotes a structural transition between different amorphous states, similar to the well-known polymorphism in crystalline materials. Pressure-induced polyamorphism in traditional network-forming glassy state materials, such as ice, silica and silicon, has been reported. Generally, this polyamorphism involves in an open packed structure transforming to a more densely packed one, namely, with increase in atomic coordination under pressure. Metallic glasses, as a new member of the glass family, are distinct from the traditional network-forming glasses, since they have non-directional metallic bonds in nature. Metallic glasses also exhibit pressure-induced polyamorphism, although they are spatially densely packed and have a maximum coordination number already.
The pressure-induced polyamorphic transformation from the low-density to the high-density state was found in lanthanide-based metallic glasses. These polyamorphic transformations demonstrate the electronic structure inheritance of lanthanide atoms in metallic glasses. So far, polyamorphic phase transitions in lanthanide-containing metallic glasses have been observed only in lanthanide-solvent metallic glasses. A question arises whether polyamorphism is also possible in lanthanide-solute metallic glasses.
In their recent paper in pss RRL the collaborative team from Harbin Institute of Technology, HPSTAR, and Argonne National Laboratory investigated this puzzle using an advanced synchrotron X-ray technique. A pressure-induced transition between two distinct amorphous states was observed in La43.4Pr18.6Al14Cu24 metallic glass with low lanthanide content. The transformation also manifested itself as a change in short- and medium-range orders. Thus, it was proposed that the lanthanide-solute metallic glasses also inherit 4f electronic transition from pure lanthanide element upon compression. This discovery provides a new perspective on the polyamorphic transformation in metallic glasses.
The text is kindly provided by Liangliang Li. Image credit: Phillip Minnis/Shutterstock