Fig. 4.

Atomic displacement parameters and potential energy curves. a Calculated (Rietveld method) and observed synchrotron PXRD patterns of Mg₃Sb₂ at 770 K upon cooling. Red open circles and black line are observed and calculated data, respectively. The blue line represents the difference between the observed and calculated patterns. The green and orange vertical bars correspond to the Bragg positions of the main phase Mg₃Sb₂ and the secondary phase Sb, respectively. b Temperature dependence of the experimental isotropic atomic displacement parameters of Mg₃Sb₂. c, d Temperature dependence of the theoretical atomic displacement parameters along different axial directions of (c) Mg₃Sb₂ and (d) SnS₂. e, f The potential energy curves for the nonequivalent atoms of (e) Mg₃Sb₂ and (f) SnS₂ as a function of the displacements from the equilibrium positions