Abnormal thermal expansion in anti-perovskite manganese nitride

The thermal expansion properties of anti-perovskite Mn₃XN (X=Ga, Zn, Sn, Cu) compounds were investigated by X-ray diffraction at different temperatures, and a large negative thermal expansion effect in the compounds was observed. Near magnetic transition, abrupt lattice contraction such as Mn₃ZnN, Mn₃CuN, Mn₃SnN does not always happen. The peculiar thermal expansion behavior of the compounds and its relationship with the different valence electrons at the X site were discussed. The results show that the abnormal thermal expansion behavior is related to the number of valence electrons at the X site and 3 valence electrons is beneficial to obtain a compound with negative thermal expansion. The negative thermal expansion coefficient value and the temperature range of the compound could be adjusted by doping at the X site in Mn₃XN. For example, the negative thermal expansion temperature range of Mn₃Zn_0.5Ge_0.5N can reach 100 K, with a thermal expansion coefficient of -7.15 × 10^-6/K. For Mn₃GaN and Mn₃Zn_0.7Sn_0.3N, their lattice constants almost remain constant with the increase of temperature at around room temperature, implying the occurrence of near zero thermal expansion.