Tunable negative thermal expansion and structural evolution in antiperovskite Mn₃Ga_1−xGe_xN (0 ≤ x ≤ 1.0)

The negative thermal expansion (NTE) and structural evolution of antiperovskite compounds Mn₃Ga_1−xGe_xN (0 ≤ x ≤ 1.0) were systematically investigated. Our results indicate the crystal structure of Mn₃Ga_1−xGe_xN changes from cubic (C) to tetragonal (T₄) with increasing Ge content by X-ray diffraction (XRD).The negative thermal expansion from x = 0 (operation-temperature range ▵T = 20 K) to x = 0.4 (▵T = 60 K) becomes broad and shifts to higher temperature, and then it became positive from x = 0.5 in Mn₃Ga_1−xGe_xN. Typically, Mn₃Ga_0.5Ge_0.5N shows low thermal expansion behavior between 300 and 450 K (∆T = 150 K), and thermal expansion coefficient α is estimated to be 2 × 10⁻⁶ K⁻¹. Furthermore, variable temperature XRD was measured to reveal the origin of NTE. The cubic I - cubic II phases coexistence (x = 0.2) and cubic I - tetragonal coexistence (x = 0.5, 0.6) was observed at low temperature. The tunable NTE is highly valuable for practical applications in precision devices.