Study On The Synthesis And Properties Of M-doped PbTiO₃ (M=Fe, Co, Ni, Cu) Ferromagnetoelectrics And Lanthanum Hydroxide Nanowires Via Hydrothermal Route

Multiferroic materials show both ferromagnetism and ferroelectricity in the same phase and the coupling between the two properties often occurs.Such materials have attracted intensive interests for potential device applications.Devices controlled by either the electric or the magnetic polarization would provide a method in designing. However,few multiferroic magnetoelectrics exist in nature or have been synthesized in the laboratory due to the theoretical incoordination between ferromagnetism and ferroelectricity.In order to synthesize such materials,the researches on the diluted magnetic semiconductors(DMSs),which are of ferromagnetic and semiconducting properties synchronously,provide us with an inspiration.This motivated us to dope transition metal ions in ferroelectrics to prepare multiferroics synchronously showing ferroelectricity and ferromagnetism.Here,in this thesis PbTiO₃ crystals with ferromagnetism and ferroelectricitism were hydrothermal prepared assisted with PEG by doping transition metal ions in the structure of perovskite ferroelectrics PbTiO₃. We explained the mechanism of oriented attachment and the origin of ferromagnetism in this thesis.In our thesis,lanthanum hydroxide of nanowires was successfully synthesized via hydrothermal method.The mechanism of lanthanum hydroxide nanowires and the effects of response parameters on the morphology of synthesized lanthanum hydroxide powders were also studied.The main results include:1.Tetrabutyl titanate and lead nitrate were used as the starting materials. Analytical grade potassium hydroxide(KOH)and chemical grade PEG were used as mineralizer and surfactant.Self-assembled Fe-doped PbTiO3 with ferroelectricity and ferromagnetism were synthesized by a PEG assisted hydrothermal reaction route.2.The origin of ferromagnetism was explained in this thesis.It is generally accepted that Fe³⁺ions substitute for Ti⁴⁺at B sites of the perovskite ABO₃ lattice.So oxygen vacancies will arise naturally to ensure charge neutrality when a trivalent Fe ion is substituted in B sites of Ti⁴⁺,and the exchange interaction of ferric ions via an electron trapped in a bridging oxygen vacancy constitutes an F center which is regarded as the origination of the ferromagnetism.At the doping amount of 0.5～1 mol%,the synthesized Fe-doped PbTiO₃ is a kind of multiferroic magnetoelectrics. More than 2%,it is to be paramagnetic material.3.We study the effects of PEG on the microscopic morphology and properties of Fe-doped PbTiO₃.PEG offers a relaxant adjustment between the submicron crystals, which leads to oriented attachment of the submicron crystals,and the SAED are of polycrystalline diffraction ring-pattems.The Fe-doped PbTiO₃ shows stronger ferromagnetism as the oriented attachment.4.The introduction of Fe is by a way of the co-precipitation of Ti and Fe. Compared of precursors by different precipitating agents of ammonia and KOH,we found that saturation magnetic moment is stronger when KOH was used as precipitating agents.5.Co,Ni,Cu-doped lead titanate were synthesized,and we study the effects of different doping transition metals on morphology and magnetic properties of PbTiO₃. Co,Ni-doped PbTiO₃ partly self-assembled,and Co-doped PbTiO₃ also have weak ferromagnetism;Cu-doped PbTiO₃ has little oriented attachment.6.Lanthanum hydroxide of nanowires were successfully synthesized by using lanthanum nitrate(La(NO₃)₃·6H₂O)as precursors and KOH as mineralizer via hydrothermal method.The samples display the uniform morphology of nanorods with about 10 nm in width and 10-4000 nm in length.The study indicates that lanthanum hydroxide grows along[100]axis because of great anisotropy.The effects of response parameters on the morphology of synthesized lanthanum hydroxide powders were also studied.