Study On Structure Design And Conduction Mechanism Of NiMn-based NTC Thermistor And Fe-based Perovskite Material

Spinel NiMn₂O₄?NMO? as a negative temperature coefficient thermistor, due to the best sensitivity and accuracy and the lowest-cost advantage occupy a large market. It has been widely used in the aerospace, deep-sea exploration, low temperature control, temperature measurements, circuit compensation, voltage stability, flow velocity measurements and time delays et al. This paper outlines the research background and research status NiMn₂O₄ and BiFeO₃, introduces the background of theoretical knowledge first-principles based on density functional theory and two-dimensional correlation analysis technique. O n this basis, the use of first-principles and two-dimensional correlation analysis technique to quantitatively study the process of temperature-dependent electron transfer mechanism of the N iMn-based spinel and Fe-based perovskite material.First, in the large temperature range?50¹500 K?, we used the first-principles calculate method, the generalized gradient approximation GGA+U and augmented plane wave method to calculate the temperature-dependent electron transfer mechanism of the transition metals V/Nb/Ta substituted cation and nonmetallic F/Cl/Br/I substituent oxygen of the spinel NiMn₂O₄. And we use the two-dimensional correlation analysis technique quantitative analysis the heat accumulation on the static orbital fluctuations of Spinal NMO. The results showed that: V/Nb/Ta octahedral substitution reduces the spin-polarized d orbital and promotes the original d-p ?*?Mn-O? orbital hybridization transform to the d-p?Nb/Ta-O? ?* and ?* hybrid orbital; V/Nb/Ta tetrahedral substitution not only keeps the Mn-3d-O-2p d-p orbital hybridization in the Octahedral, but also enhances the V-3d-O-2p d-p orbital hybridization in the Toctahedral, thereby enhancing the electron transfer rate?0.09?0.11 e?; F/Cl/Br/I O-substituted form the F/Cl/Br/I-2p-O-2p p-p hybrid orbitals, inducing the formation of oxygen vacancies and prompting Mn charge disproportionation Mn3+?Mn4+-Mn3+.Secondly, in order to calculate late simulate complex?spinel-perovskite? electron transfer properties, in a large temperature range?50¹500 K?, we using first principles and two-dimensional correlation analysis techniques quantitative research t he electron transfer characteristics of Fe-based perovskite BiFeO₃ in different temperature reagion; and temperature-depedent electron transfer mechanism of transition metal V/Nb/Ta and non- metallic F/Cl/Br/I substituent BFO. The results show that: the heat accumulation accelerates the O-2p orbital splitting, causing the Fe-charge disproportionation Fe-3d⁵? Fe-3d⁵-d0(Fe³⁺? Fe²⁺-Fe³⁺). With the temperature increasing, the temperature-dependent electron transfer change from triplet degenerate t2 g orbital?ferromagnetic phase? to two- fold degenerate eg orbital?anti- ferromagnetic phase?. V/Nb/Ta cation substituent BFO reduce the spin polarization of d orbital, prompting the original p-p?Bi-O? and the d-p?Mn-O? ?* and ?* orbital hybridization change to the?Bi-O? p-p and?Nb/Ta-O? d-p ?* orbital hybridization, the electrical properties change the conductor to the semiconductor; F/Cl/Br/I substitute effectively controlled the strong covalent hybridization between the d⁰ and O-2p⁴ orbitals. The forming of X-p⁵-O-2p⁴ hybrid orbital led to the Fe charge disproportionation Fe³⁺-3d⁵-Fe²⁺-3d⁵-d⁰, resulting ferromagnetic-antiferromagnetic transition phase.Finally, the calculation results of the previous simulation spinel-perovskite heterojunction. However, it is diffic ult to optimize the Mn based spinel and Fe based perovskite composite interface in the simulation calculation, and it is difficult to synthesize the Mn-based spinel Fe-based perovskite in the experimental process. To this end, for the spinel-type ferrite Fe₃O₄ semiconductor?band gap:1.9 2.7eV? is preferably biocompatible, combined with the excellent optical properties of perovskite type BiFeO₃ film. The controllable components?XZn?Fe₂O₄-BiFeO₃ heterojunction was prepared use the method of microbial synthesis, by improving efficiency of the photogenerated electron-hole pairs to prepared the high fluorescent composite material of. To this end, we verified the fluorescence enhancement mechanism of the surface of spinel-perovskite type?XZn?Fe₂O₄-BiFeO₃ by the first principle calculation method. The results showed that: spinel?XZn?Fe₂O₄ ferrite embedded perovskite type BiFeO₃ film, since the interfacial coupling of the Fe-O-O-Bi and the Fe-O-Fe. That not only reducing the band gapof?XZn?Fe₂O₄ ferrite?1.56 e V? by increasing the carrier mobility and the recombination of the photo-generated carriers, but also broadening the light emitting area? extended to 100 nm? of fluorescence intensity by expanding the surface area of the iron-based heterojunction?XZn?Fe₂O₄-BiFeO₃.