Study On Preparation,Microstructure And Properties Of Single-crystal Nanocomposites Based On PbTiO₃ Nanoplates

Owing to the unique piezoelectric and ferroelectric properties,the ferroelectric nanocomposites are highly prospective in applications of catalysts,sensing and storage devices,PbTiO₃?PTO?is one of the typical perovskite oxides with high spontaneous polarization and simple structure,which is an ideal material to explore the growth and properties of ferroelectric nanocomposites.In this dissertation,we firstly reviewed the heterostructure,spontaneous polarization of PTO,the surface chemistry arising from the polarization screening and the present status of ferroelectric nanocomposites.Then,we proposed fabricating different types of ferroelectric nanocomposites with the introduction of single-crystal and single-domain 2D PTO nanoplates.We prepared SrTiO₃?STO?-PTO single-crystal heterostructures,CoFe₂O₄?CFO?-PTO single-crystal heterostructures,Pt-PTO single-crystal nanocomposites and Au-PTO single-crystal nanocomposites through a hydrothermal route,a sol-gel route,an oil-bath route and a wet chemistry route,respectively.By using serial characterization approaches,systematic investigations were performed on the morphologies,microstructure of the interfaces as well as the magnetic and catalytic properties of the nanocomposites.The main results are listed as follows:?1?SrTiO₃?STO?-PTO single-crystal heterostructures were prepared by a hydrothermal route.The HAADF-STEM investigation suggested that STO selectively and epitaxially grew on the positive polar facet?{001}?and four lateral planes?{100}?of PTO nanoplate,with {100}STO parallel to {100}PTO.PTO and STO are both single crystals and the interface of STO and PTO are atomic-level smooth.The growth of STO is controlled by the polarization screening of PTO.In details,negatively charged STO particles would be preferentially absorbed on the positive polar facet of PTO to compensate the positive charges until the screening is completely established,during which,STO formed an epitaxially-grown film and the thickness of the film increased and reached a saturation value at a certain temperature eventually.?2?Free-standing PTO nanoplates were used as substrate to fabricate 0-2 type CoFe₂O₄?CFO?-PTO multiferroic heterostructures by a sol-gel route.Spinel cubic phase CFO and perovskite PTO are characterized to be single crystals.CFO nanodots have been revealed to epitaxially grow on the {001} planes of the PTO nanoplate,forming well-defined pyramidal-like morphologies,with { 200}CFO parallel to {100}PTO.Such heterostructures demonstrated a magnetic anisotropy along and perpendicular to the {001} plane of PTO nanoplate,with an obvious difference?40%?in saturation magnetization.More interestingly,the heterostructures showed an instinct magnetoelectric?ME?coupling with the magnetization dropping by 7.6%around 710 K when the temperature cooled down,which could be attributed to the absence of clamping effect as well as the large-area and high-quality interface.?3?By using KBr as modifier,Pt-PTO nanocomposites were obtained through an oil-bath route.Pt nanoparticles were characterized to be single-crystal cubic strucure enclosed by ?100} planes,with a size of?20 nm.Then,Au-PTO nanocomposites were prepared by a wet chemistry route with the Au particles being single-crystal particles,with a size of?5 nm.The results of CO oxidation reactions showed that the completing temperature of CO oxidation for Pt-PTO prepared by the oil-bath route,Au-PTO,Pt-PTO and Pt-STO-PTO fabricated through a wet chemistry route are 250 ?,230 ?,150? and 120 ? respectively.