Component Tailoring And Process Modification Of Bismuth Layer-structured Ferroelectrics

Bismuth layered-structure oxides are one class of the most important ferroelectric materials.They feature many excellent characters benefiting from their layered-structure,such as higher Curie temperature and good resistance of polarization towards temperature,high resistance to high voltage,low dielectric loss and outstanding fatigue performance,etc.,thus are promising candidates for non-violate random access memories,high-temperature sensors and so on.While limited by the layered-structure,the ferroelectric domains within the grains are difficult to follow the applied electric field and resulting a poor ferroelectric performance;In addition,the connection between the microstructure and their photocatalytic behavior is still need to be further studied.(B_1/3/Nb_2/3)?B=Mg,Zn,Cu?co-substituting for Ti⁴⁺in B-site of Bi₄Ti₃O₁₂-based Aurivillius ceramics were prepared to improve the piezoelectric properties.The electrical properties and conduction mechanisms of them was investigated.The activation energy related with the electrical relaxation determined from the electric modulus spectra was 0.71 eV and the electrical conductivity decreased dramatically by(Mg_1/3/Nb_2/3)-doping,due to the enhanced structural distortion and the decrease in oxygen vacancy concentration.The(Mg_1/3/Nb_2/3)-substituted specimen with a Curie point of 686°C and a large field-induced strain of 0.061%as well as a higher remnant polarization of 12.9?C/cm² could be a promising material for high-temperature lead-free piezoelectric applications.Aurivillius Bi₅Ti₃FeO₁₅?BTF?multiferroic?MF?nanofibers?NFs?of about 400 nm were fab-ricated by electrospinning and calcination.The BTF NFs exhibit an effective mi-cro-piezoelectriccoefficientof35pm/Vandbenignmicro-ferroelectricity.Macro-ferroelectric and magnetoelectric coupling behavior were investigated in detail by non-sintering and pressing for the first time,which is smaller than that of the BTF ceramic or film due to the adverse effects of filled air.A magnetoelectric?ME?voltage coefficient as large as 14 mVcm^-1Oe^-1 can be achieved.Weak ferromagnetism was also realized at RT.Al-though the sintering temperature was only 600°C,MF BTF NFs as multiferroic materials were successfully obtained,which offers new insights into the design and application of promising lead-free MF materials for novel devices.Bi_5-xLa_xTi₃FeO₁₅?x=0,1?nanofibers?NFs?toward wool keratin-based biocompatible piezo-electric NGs are demonstrated.The refined structure of Bi₄LaTi₃FeO₁₅?BLTF?NFs by the Rietveld method was confirmed to be a four-layer Aurivillius oxide with an orthorhombic space group A21am.Wool keratin was extracted by using the oxidizing and subsequent de-oxidizing reaction process.BLTF NFs are biocompatible in bio-environment as regards the mice pre-osteoblasts MC3T3-E1.BLTF NFs NG can generate an output voltage of 0.14 V and output current of 41 n A(with a current density of 20.5 nA cm^-2),with quite reproducible power generation.The prominent power generation of BLTF NFs NG is partly originated from the La³⁺substitution for the A-site Bi³⁺,which decreases the number of oxygen vacan-cies in the perovskite layers.Furthermore,piezoelectric NFs as exceptional fillers coupled sufficient connectivity,larger degree of crystallinity and Young's modulus of the system to-gether in the keratin matrix also contribute to enhanced piezoelectric power generation.Be-sides,one mechanism responsible for the optimal BLTF NFs NG was proposed.It is demonstrated a ternary heterostructured photocatalyst polymeric graphitic carbon nitride?for simplicity,g-C₃N₄?coupled with Bi₄Ti₃O₁₂/Bi₂Ti₂O₇?BTO?by a simple route of electrospinning/calcination.This optimal photocatalyst shows efficient reproducible hydrogen evolution(638?molh^-1g^-1)under visible light,which is about 8.6times higher than BTO and 1.55 times higher than g-C₃N₄.The optimal loading of BTO nanorods on g-C₃N₄ increases light absorption to generate more photoelectrons and simultaneously promotes separation and transfer of photoinduced electrons and holes,which arises from the intrinsic electric field formed between the?Bi₂O₂?²⁺slabs and the(Bim-1TiO_3m+1)units in Bi₂Ti₂O₇ and Bi₄Ti₃O₁₂.On the basis of further obtained temperature dependent experimental results through the Arrhenius relationship,mechanism of temperature dependent spontaneous polarization is proposed.