  In this work we aim to study the effect of temperature on the mechanical
properties of a solid. For this, we have introduced a new first-principles
based methodology to obtain the thermal variation of the elastic constants of
NiTiSn, a multifunctional Heusler compound. In parallel using X-ray
diffraction, we have measured the isothermal bulk modulus at 300~K. The
agreement between the calculations and the experiments is within the
experimental error bars showing the accuracy of the calculations. Using two
other numerical methods, which give all coherent results, we have shown that
NiTiSn conserves its very good mechanical properties up to 1500~K. In
particular at 700~K (the best working temperature for thermoelectric
applications), NiTiSn remains a ductile and robust material making it a
compound of choice for applications in which large temperature fluctuations are
present.
