The Electric And Optical Properties Of Doped Bi-layer Structure Lead-free Ferroelectric Materials

Bismuth layer-structured ferroelectric (BLSF) ceramics are potential candidate lead-free materials in nonvolatile random access memories, especially at high temperatures and high frequencies device application due to their high remnant polarization, low coercive electric field and low dielectric constant, high Curie temperature etc. In Bi-layer structure ferroelectric material, Bi4Ti3O12 and CaBi4Ti4O15 have been widely investigated in view of the characteristic of high Curie temperature. Otherwise, rare-earth doped powders display many excellent properties based on photoluminescence (PL) and electrical properties due to the unique electron structure of rare-earth, especially photoluminescence properties. In this thesis, the main results are listed as follows.Chapter 2 reports ferroelectric and Eu-doped CaBi4Ti4O15: Nd thin films prepared on Pt/Ti/SiO2/Si substrates by a sol-gel method. All the CBENT films have a polycrystalline bismuth-layered perovskite structure, and a morphotropic phase boundary between orthorhombic phase and tetragonal phase was shown to exist. The thin films are dense and smooth with uniformly distributed grains when x is less than 0.2. When x is larger 0.2, a roughened surface with some pores was obtained. The PL intensity of the CBENT films are significantly dependent on annealing temperature and Eu concentration. The remnant polarization 2Pr values of the Eu-doped CaBi4Ti4O15: Nd thin films with Eu concentrations of x=0, 0.2, 0.5 were approximately 13.2, 30.7 and 25.3μC/cm2, respectively.In chapter 3, the surface photovoltage (SPV) responses was investigated in sol-gol derived Bi4Ti3O12(BiT) thin films of highly c-axis orientation. The remnant polarization (2Pr) and coercive electric field (Ec) of the Au/BiT/FTO capacitor were about 98.8μC/cm2 and 212 kV/cm, respectively. The maximal surface photovoltage value 1.8 mV of the device of FTO/BiT/ITO with dc bias voltage (from -1V to +1V) was observed at room temperature, and it is three times larger than that under the zero bias. The SPV intensity increased with the positive field increasing, and became weaker with a reverse response with the negative field increasing. It is suggested that the SPV with respect to the unpoled and poled films are largely depend on the ferroelectric polarization.Chapter 4 mainly introduces photoluminescence and dielectric properties of CaBi3.75-xEuxNd0.25Ti4O15 ferroelectric ceramics. Their structures and surface morphology were examined by X-ray diffraction, Raman spectrum and scanning electron microscopy, respectively. The morphotropic phase boundary (MPB) between orthorhombic and tetragonal was found located in the range of 0.3