Preparation And Physical Properties Of Lanthanum-praseodymium Calcium Manganese Oxide Nanofibers And Graphene

In recent years,the research of nanomaterials has become a hotspot in the fields of materials science and condensed matter physics,and the related technologies have developed rapidly.Compared with conventional size materials,nanomaterials have superior physical properties and exhibit some novel effects.They have been applied to many fields such as electronic devices,photocatalysis,fuel cells,filtration,and biomedicine.Therefore,preparing nanomaterials and exploring their microstructure and properties have great significance to enhance theoretical understanding and design novel electronic devices.In this paper,LaPrCaMnO and graphene nanomaterials were prepared,their composition,microstructure,and electromagnetic properties were characterized,and related mechanism studies were carried out.Nanomaterials in various dimensions were studied.Chapter 2 studied one-dimensional LPCMO nanofibers.Chapter 3 studied graphene,characterized the electromagnetic properties and conducted the conductive mechanism of the two-dimensional graphene paper and three-dimensional graphene aerogel fiber.Chapter 4 introduced the application of three-dimensional graphene aerogel fibers.The main research contents were as follows:1.The structure,magnetic properties,resistance,magnetoresistance,volt-ampere characteristic curves and differential resistance at low temperatures of the La0.33Pr0.34Ca0.33MnO3?LPCMO?nanowires prepared by electrospun and calcination were studied.Magnetic studies found that the LPCMO underwent a transition from paramagnetic phase to ferromagnetic phase and formed cluster-spin glass state at low temperatures.The resistance and magnetoresistance studies indicated the presence of metal-insulator transitions and magnetoresistance effects,and the high-temperature behaviors were explained by Mott's1 dimensional variable range hopping model.The nonlinear I-V curves at low temperatures indicated that the LPCMO had threshold voltage and zero bias conductance,which represented the existence of Coulomb blockage.The differential resistance curves at low temperatures indicate complex phase competition.These phenomena were attributed to the electronic phase separation in LPCMO.2.Graphene is a two-dimensional material with good physical properties.Its excellent charge transport characteristics have promoted extensive exploration of graphene-based electronic devices.In order to determine the effect of the mesostructure on the electromagnetic transport properties of graphene,the temperature-dependent resistance and the magnetoresistance of reduced graphene oxide paper and reduced graphene oxide aerogel fiber were measured.The graphene paper and aerogel fiber were in accordance with Mott's two-dimensional and three-dimensional variable range hopping models.As the temperature decreased,graphene had a transition from small-negative to large-positive magnetoresistance.For negative MR,MR?H².For positive MR,ln[R?H?/R?0?]?H².In the framework of hopping conduction,the effects of wave function contraction and quantum interference on positive and negative magnetoresistance were discussed.3.Light-weight conductors have important value for wearable electronic devices.This work reported the flexible and light-weight multi-functional composite cable based on graphene aerogel fiber.The graphene aerogel fibers filled with polyethylene glycol were prepared by wet spinning and supercritical drying methods.The fibers had good mechanical property,thermal stability,and electrical conductivity in 10-380 K(4.85×10³ S·m^-1 at 300 K).The fibers had a pronounced thermal response to both electrical and light stimulation in cold environments.The polydimethylsiloxane and the fluorocarbon were coated on the surface as the insulating layer and the super-hydrophobic layer,making the fibers had self-cleaning function.These fibers can be used as conductive cables.