Formation of Collapsed Tetragonal Phase in EuCo2As2 under High Pressure

TL;DR

This study investigates how EuCo2As2's crystal structure changes under high pressure, revealing a phase transition to a collapsed tetragonal state at 4.7 GPa with implications for related superconductors.

Contribution

It provides the first detailed high-pressure structural analysis of EuCo2As2, identifying the phase transition and its correlation with superconducting properties.

Findings

EuCo2As2 undergoes a second-order phase transition at 4.7 GPa.

The transition involves a collapse of the tetragonal structure with increased bulk modulus.

A correlation exists between ambient volume and transition pressure in related superconductors.

Abstract

The structural properties of EuCo2As2 have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo2As2 (I4/mmm) has a tetragonal lattice structure with a bulk modulus of 48 +/-4 GPa. With the application of pressure, the a-axis exhibits negative compressibility with a concurrent sharp decrease in c-axis length. The anomalous compressibility of the a-axis continues until 4.7 GPa, at which point the structure undergoes a second-order phase transition to a collapsed tetragonal (CT) state with a bulk modulus of 111 +/- 2 GPa. We found a strong correlation between the ambient pressure volume of 122 parents of superconductors and the corresponding tetragonal to collapsed tetragonal phase transition pressures