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A study was conducted to understand the strong negative thermal expansion (NTE) exhibited by scandium trifluoride at low temperature, which maintains a cubic Re[O.sub.3] type structure down to at least 10K. Sc[F.sub.3] is found to be the first material with structure similar to Re[O.sub.3] which provide a clear experimental explanation for the observed NTE mechanism.

Scandium trifluoride maintains a cubic ReO3 type structure down to at least 10 K, although the pressure at which its cubic to rhombohedral phase transition occurs drops from >0.5 GPa at ∼300 K to 0.1-0.2 GPa at 50 K. At low temperatures it shows strong negative thermal expansion (NTE) (60-110 K, α, ≈ -14 ppm K-1). On heating, its coefficient of thermal expansion (CTE) smoothly increases, leading to a room temperature CTE that is similar to that of ZrW2O8 and positive thermal expansion above ∼1100 K. While the cubic ReO3 structure type is often used as a simple illustration of how negative thermal expansion can arise from the thermally induced rocking of rigid structural units, ScF3 is the first material with this structure to provide a clear experimental illustration of this mechanism for NTE. [ABSTRACT FROM AUTHOR]