Strong Negative Thermal Expansion along the O−Cu−O Linkage in CuScO₂

The structure of 2H CuScO 2 has been refined from single-crystal X-ray diffraction data obtained at room temperature and from neutron powder diffraction data obtained from 11 to 1206 K. Strong negative thermal expansion (−4.0 × 10 - 6 /K) has been found for the apparent Cu−O bond length below 300 K. This is the first example of strong negative thermal expansion in a metal oxide based on an O−M−O linkage instead of a M−O−M linkage. It is now the transverse thermal motion of Cu, instead of the transverse thermal motion of oxygen, that causes the negative thermal expansion. As expected for this mechanism for negative thermal expansion, the thermal displacement parameter for Cu is very pronounced perpendicular to the linear O−Cu−O linkage.