Title : Nano size effects on the tuning of thermal expansion
Thermal expansion, the tendency of materials to change in shape and volume in response to a change in temperature, is a significant problem for many materials and engineering applications, because when two coupled-materials expand differently when heated, this can lead to thermal shock breakage and failures of the system. As a consequence, the control of thermal expansion represents a challenge for materials design. In the last two decades, after the discovery of materials with large negative thermal expansion (NTE) over a wide temperature range, the goal of controlling thermal expansion has become feasible and the number of studies on this topic has grown rapidly. In this work, we show that nano size effects can be exploited to tune the thermal expansion of materials. Specifically, we present the case of scandium fluoride, ScF3, one of the most popular NTE materials, whose NTE is progressively inhibited by reducing the size of the crystal particles up to the nano-scale . Intriguingly, an isotropic zero thermal expansion is concurrently engineered by localized symmetry breaking: a localized rhombohedral distortion evidenced by combined x-ray analysis. These experimental findings are corroborated by first-principles calculations, which demonstrate that the length of the chemical bonds, shortened in the nano-scale regime, plays a key role in the tuning of thermal expansion.
Audience take away:
• The problem of the thermal expansion on materials design is pointed out.
• The research topic on the control of thermal expansion is presented, showing the current achievements and the state-of-the-art in the field.
• Nano size effects are shown to be a promising method for controlling the thermal expansion of materials.