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In the present work, modulated four- and five-layered orthorhombic, seven-layered monoclinic (4O, 10M and 14M) and unmodulated double tetragonal (L1₀) martensites are characterized in Heusler Ni–Mn–Sn alloys using X-ray diffraction, high-resolution transmission electron microscopy, electron diffraction techniques and thermal analysis. All modulated layered martensites exhibit twins and stacking faults, while the L1₀ martensite shows fewer structural defects. The substitution of Sn with Mn in Ni₅₀Mn_37+xSn_13−x (x = 0, 2, 4) enhances the martensitic transition temperatures, while the transition temperatures decrease with increasing Mn content for constant Sn levels in Ni_50−yMn_37+ySn₁₃ (y = 0, 2, 4). The compositional dependence of the martensitic transition temperatures is mainly attributed to the valence electron concentration (e/a) and the unit-cell volume of the high-temperature phase. With increasing transition temperatures (or e/a), the resultant martensitic crystal structure evolves in a sequence of 4O → 10M → 14M → L1₀ in bulk Ni–Mn–Sn alloys.