Enhancement and suppression of negative thermal expansion in YbNiAl4 compounds

Thermal expansion represents a problem when dimensional stability of structures or devices is desired in applications that undergo a temperature fluctuation. Therefore the control of thermal expansion represents a challenge for materials design and the negative thermal expansion (NTE) materials are essential to achieve this goal. Recently, we have found out a novel YbNiAl4 family which exhibits NTE in a wide temperature range. Moreover, the NTE can be suppressed or, more interestingly, enhanced, by replacing some chemical elements (Figure 1), thus allowing the control of thermal expansion. Because there is no idea about the origin of this intriguing thermal expansion behaviour, we aim to investigate the local structure, valance state and local dynamics of these YbNiAl4 compounds by means of temperature-dependent XAFS spectroscopy. This would help to shed light on this interesting phenomenon, providing an important step towards the design of controlled thermal expansion materials.