CRYSTAL-STRUCTURE AND PHASE-RELATIONS FOR MN3SN2 AND NONSTOICHIOMETRIC MN2-XSN

Ordered Mn3Sn2 appears as a distinct low-temperature phase in the bina ry Mn-Sn system. On heating it decomposes peritectoidally around 813 K into the grossly non-stoichiometric Mn2-xSn phase and MnSn2 Phase rel ations are described for Mn3Sn2 and Mn2-xSn on the basis of samples wh ere great fare has been taken during synthesis to minimize inhomogenei ty owing to manganese evaporation and/or transportation. Mn2-xSn exist s between 753 and 1157 K. The non-stoichiometry of Mn2-xSn is strongly temperature dependent. At 1073 K, the homogeneity range is 0.18 less than or equal to x less than or equal to 0.23, whereas at 873 K 0.28 l ess than or equal to x less than or equal to 0.34. The crystal structu re of Mn2-xSn is of the partly filled-up NiAs-type. The crystal struct ure of the ordered Mn3Sn2 phase was solved on the basis of powder X-ra y and neutron diffraction data. Mn3Sn2 is isostructural to Co3Sn2 and Ni3Sn2. Phase transformation and structural relationships are discusse d. (C) 1997 Elsevier Science S.A.