Research On The Negative Thermal Expansion Behavior Of Ge,Sn And Si Doped Manganese Gallium Nitride

With the development of the material science,negative thermal expansion materials play more and more important roles in cryogenic engineering and aerospace field,while the negative thermal expansion temperature range of the anti perovskite manganese nitride negative thermal expansion material was mostly concentrated at room temperature and high temperature,and relatively few was reported about low temperature.They were obtained by elements doping method,and their expansion properties were also investigated.The negative thermal expansion mechanism of this material is discussed through the study of the magnetic energy and electron structure of the material.Based on the Mn₃GaN,a series of doped manganese nitride materials,including Mn₃Ga_1-xGe_xN,Mn₃Ga_1-xSn_xN and Mn₃Ga_1-xSi_xN were prepared.The phase structure of these samples were characterized using X-ray diffraction?XRD?,the thermal expansion of materials was analyzed by thermal expansion tester,meanwhile,the magnetic energy and electron structure of the materials were analyzed by means of integrated physical measurement system?PPMS?and VASP software.The experimental results show that the three group samples are anti-perovskite cubic structure,and the space group is Pm3m.The NTE operation-temperature of Mn₃Ga_1-xGe_xN and Mn₃Ga_1-xSn_xN move gradually to high temperature,and the negative thermal expansion rate decreases gradually with the increase of Ge and Sn doping content,but the NTE operation-temperature is basically unchanged.Moreover,the Mn₃Ga_1-x Ge_xN and Mn₃Ga_1-x Sn_xN compounds show nearly zero expansion behavior in the temperature rangeof423K⁴75K??T=52K?and480K⁵13K??T=33K?.TheNTE operation-temperature of Mn₃Ga_1-xSn_x compounds moves gradually to low temperature,and the negative thermal expansion rate decreases gradually with the increase of Sn doping content,but the NTE operation-temperature is basically unchanged.And the near zero expansion behavior of composite Mn₃Ga_0.85Si_0.15N/Cu was obtained.Magnetic measurements show that the Mn₃Ga_1-xGe_xN?x=0,0.1,0.2?compounds show that the the magnetic phase transition from ferromagnetic?AFM?to paramagnetic?PM?in the magnetic transition point,while the Mn₃Ga_1-xGe_xN?x=0.3,0.4,0.5?compounds show that the the magnetic phase transition from ferromagnetic?FM?to paramagnetic?PM?.Unlike Mn₃Ga_1-xGe_xN,the Mn₃Ga_1-xSn_xN compounds always show that the the magnetic phase transition from ferromagnetic?AFM?to paramagnetic?PM?.The analysis of the electronic structure of the Mn₃Ga_1-xGe_xN shows that the 3d orbital of Mn and the 2p orbital of N are hybridized to form a narrow band near the Fermi surface;and with the increase of Ge doping,the local lattice distortion is more and more serious,disrupting?^5g antiferromagnetic structure nearest neighbor Mn-Mn moment exchange interaction,leading to local Mn ion magnetic moment decreases,suppresses the magnetic volume effect?MVE?,and ultimately controls the negative thermal expansion of the material behavior.The zero expansion behavior of the composites accords with the ROM model.The interaction between Mn₃Ga_0.85Si_0.15N and Cu shows zero expansion behavior and the structure is stable.