Neutron powder diffraction study of the thermal expansion of cuprite

Abstract

Cuprite, Cu2O, crystallizes in a rare cubic structure (SG Pn $\bar\Box3\Box$ m; O $\bar\Box4\Box$ 3m; Cu $\bar\Box3\Box$ m) forming a framework of corner-sharing OCu4 tetrahedra and linear O-Cu-O arrangements along . According to Rietveld analyses of almost 100 neutron-diffraction patterns collected in steps of about 5 K between 15 K and 537 K the unit-cell volume is nearly constant (a0=4.2745±0.0003 A) between about 200 K and room temperature, but increases towards both lower and higher temperatures. Thermal displacement parameters of Cu and O have been analysed. The negative thermal expansion of cuprite at low temperatures is explained by transverse ‘guitar-string’ vibrations of Cu and rotations of the OCu4 tetrahedra decreasing the O-O distance.