Structural Phase Transitions in SrRh2As2

TL;DR

This paper investigates the structural phase transitions of SrRh2As2, revealing three polymorphs with distinct structures and clarifying that the distortions are due to Rh-Rh bonding rather than magnetism, contrasting with related compounds.

Contribution

It provides detailed structural characterization of SrRh2As2 polymorphs and clarifies the origin of distortions through electronic structure calculations, expanding understanding of phase transitions in this material.

Findings

SrRh2As2 has three polymorphs with distinct structures.

The alpha phase is monoclinic with a pseudo merohedral twin structure.

Structural distortions are caused by Rh-Rh bonding, not magnetic interactions.

Abstract

SrRh2As2 exhibits structural phase transitions reminiscent to those of BaFe2As2, but crystallizes with three polymorphs derived from the tetragonal ThCr2Si2-type structure. The structure of \alpha-SrRh2As2 is monoclinic with a = 421.2(1) pm, b = 1105.6(2) pm, c = 843.0(1) pm and \beta = 95{\deg} and was refined as a partially pseudo meroedric twin in the space group P21/c with R1 = 0.0928. \beta-SrRh2As2 crystallizes with a modulated structure in the (3+1) dimensional superspace group Fmmm(10\gamma)\sigma 00 with the unit cell parameters a = 1114.4(3) pm, b = 574.4(2) pm and c = 611.5(2) pm and an incommensurable modulation vector q = (1, 0, 0.3311(4)). High temperature single crystal diffraction experiments confirm the tetragonal ThCr2Si2-type structure for \gamma-SrRh2As2 above 350{\deg}C. Electronic band structure calculations indicate that the structural distortion in alpha-SrRh2As2 is caused by strong Rh-Rh bonding interactions and has no magnetic origin as suggested for isotypic BaFe2As2.