A new polymorphic material? Structural degeneracy of ZrMn_2

TL;DR

This study uses density functional calculations to predict that ZrMn_2 exhibits structural degeneracy among different phases at low temperatures, with a temperature-induced transition to the experimentally observed structure at higher temperatures.

Contribution

It introduces the concept of structural degeneracy in ZrMn_2 and predicts a temperature-driven phase transition based on energetic calculations.

Findings

Cubic C15, hexagonal C14 and C36 structures are nearly equally stable at low temperatures.

A transition from C15 to C14 structure occurs around 160K.

The predicted transition aligns with experimental observations at elevated temperatures.

Abstract

Based on density functional calculations, we propose that ZrMn_2 is a polymorphic material. We predict that at low temperatures the cubic C15, and the hexagonal C14 and C36 structures of the Laves phase compound ZrMn_2 are nearly equally stable within 0.3 kJmol^{-1} or 30 K. This degeneracy occurs when the Mn atoms magnetize spontaneously in a ferromagnetic arrangement forming the states of lowest energy. From the temperature dependent free energies at T approx 160K we predict a transition from the most stable C15 to the C14 structure, which is the experimentally observed structure at elevated temperatures.