One-dimensional chain "melting" in incommensurate potassium

TL;DR

This study investigates the order-disorder transition of guest chains in incommensurate potassium under high pressure and temperature, revealing a chain 'melting' transition over a broad pressure range with complex phase boundary behavior.

Contribution

It provides detailed synchrotron X-ray diffraction data on the chain 'melting' transition in incommensurate potassium up to 47 GPa and 750 K, highlighting the influence of intraphase transitions.

Findings

Chain 'melting' occurs over a 22 GPa range.

Significant changes in phase boundary slope are observed.

Order-disorder transition is linked to intraphase structural changes.

Abstract

Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest chains. Here, we report single crystal, quasi-single crystal, and powder synchrotron X-ray diffraction measurements of this order-disorder phenomenon in incommensurate potassium to 47 GPa and 750 K. The so-called chain "melting" transition is clearly visible over a 22 GPa pressure range, and there are significant changes in the slope of the phase boundary which divides the ordered and disordered phases, one of which results from the intraphase transitions in the guest structure.