Negative thermal expansion and local lattice distortion in the (Sc1-xTix)F3 and related solid solutions

TL;DR

This study demonstrates how chemical modifications in cubic ScF3-based materials can tune negative thermal expansion properties by analyzing local lattice distortions and their impact on thermal behavior.

Contribution

It introduces a method to engineer and control NTE in cubic solids through chemical substitution and local lattice distortion analysis.

Findings

Achieved a broad range of negative thermal expansion coefficients.

Found a correlation between local lattice distortion and NTE weakness.

Proposed a coupled rotation model explaining the damping of F atom vibrations.

Abstract

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.