Structural, thermodynamic, and transport properties of Laves-phase Zr Mn2 from x-ray and neutron diffraction and first principles

Recently, the prediction of structural degeneracy for the ground state of Zr Mn2 by ab initio methods has stimulated research on this system. We investigated the structural and thermodynamic properties by single crystal and powder x-ray diffraction (at zero and high pressure) as well as by neutron powder diffraction, demonstrating that the C14 Laves phase structure is stable down to a temperature of 4.2 K and up to applied pressure of 56 GPa. The bulk modulus and enthalpy of formation (measured by high-temperature drop calorimetric experiments) of Zr Mn2 are found to be 150 GPa and -66.6 kJ (mol of f.u.)-1, respectively, in nice agreement with the ab initio calculated results. The experimental bulk thermal-expansion data of Zr Mn2 resembles that of a typical metal. However, the temperature-dependent electrical resisitivity shows that there is a power law with n≈1.1 at low temperature quite different from simple metals which originates probably from scattering of the charge carriers on the frustrated Mn moments. The phonons have been investigated in detail by comparing results of ab initio calculations with neutron spectra and experimental specific-heat data.