Transverse vibration driven large uniaxial negative and zero thermal expansion in boron bridged REPt3B framework materials

Abstract

In this work anomalous uniaxial thermal expansion behaviour at low temperatures along the c-direction of the tetragonal phase of different members of the antiperovskite REPt₃B (RE = Sm, Gd–Tm) compounds is reported. Negative or zero thermal expansion (NTE/ZTE) behaviour in these compounds arises due to the transverse vibration of boron atoms in the linear Pt–B–Pt linkage. The coefficient of thermal expansion along the c-axis tends to become more negative in annealed compounds in comparison to those estimated for as-cast samples. While the as-cast TmPt₃B and HoPt₃B exhibit essentially ZTE behaviour, the NTE coefficient of annealed GdPt₃B (∼−28 ppm K⁻¹) is found to be even larger than that of the well known framework material ZrW₂O₈ (∼−9 ppm K⁻¹) reported in the literature.