  Negative thermal expansion (NTE) is unusual but important property for
control of thermal expansion. In the present study, the chemical modification
is utilized to engineer controllable thermal expansion in cubic NTE ScF3. A
broad window of the coefficient of thermal expansion (CTE = -1.51 ~ -3.4*10^-6
K-1, 300-800 K) has been achieved in Sc1-xMxF3 (M = Ti, Al and Ga). The
long-range crystallographic structure of (Sc1-xTix)F3 adheres to the cubic
Pm-3m symmetry according to the analysis of high-energy synchrotron X-ray
powder diffraction. Pair distribution function (PDF) analysis of synchrotron
X-ray total scattering was performed to investigate the local lattice
distortion. It was found that the weakness of NTE has a close correlation with
the local lattice distortion. Based on the coupled rotation model, it is
presumably that this local distortion might dampen the transverse vibration of
F atoms and thus reduce NTE. The present work provides a possible reference for
the design of controllable NTE in open framework solids.
