The Study On Local Structure,Phase Transition And Oxygen Ion Conduction Of ZrO₂ By Eu³⁺ Photoluminescence Spectroscopy

Zirconia has important application value in the fields of structural ceramics,oxygen sensors,oxygen ion conductors,dentistry and biomedicine due to its excellent physical and chemical properties.The advantages and defects of the material mainly depend on the rich crystalline phase structure and the regulation of its local structure.At present,the measurement methods for analyzing the microstructure of materials mainly include XRD,Raman,EXAFS,neutron diffraction,ESR,etc.Most of these test methods require that the sample has a long-range ordered crystal structure so as to obtain the structural information of the sample by diffraction principle.However,due to the existence of defects,the difference between the internal surface and the limitation of synthesis methods,Many samples are difficult to meet the local crystal structure uniformity,therefore,based on the diffraction principle can only obtain the average information of the local structure of the sample.At the same time,for different local environments,most research methods can only give the signal intensity of the corresponding environment according to the number of different environments,so it is difficult to identify a small amount of local structure of the sample.In order to solve the above problems,a method based on Eu³⁺photoluminescent spectroscopy to detect the local crystal structure changes of Zr O₂ based materials is proposed in this thesis.In this thesis,a series of Zr O₂ based materials were synthesized by combustion method.Based on Eu³⁺photoluminescence spectroscopy,the local structure of Zr O₂ based materials was studied in depth,several phase transition mechanisms of Zr O₂ were analyzed,and the unique local structure of Zr O₂ based micro/nano powder synthesized by combustion method and its effect on oxygen ion conduction were studied.And the conductivity concentration quenching mechanism of Zr O₂ based oxygen ion conductor.Specific findings are as follows:First of all,（1）Even for the micro-nanocrystals that have been treated at 1100℃and have very good crystallinity（as proved by XRD）,the photoluminescence spectrum of Eu³⁺confirms the existence of 5 kinds of non-uniform local structures.Based on the excitation selection and spectral reconstruction strategy,the excitation and emission spectra of each environment and the proportion of each environment were obtained.（2）Based on the PL of Eu3+ion,the crystal structure of Zr O₂ with doping concentration x=0.16 and x=0.21 was characterized and compared,and it was found that the sample structure with x=0.21 had higher oxygen vacancy concentration.These results indicate that Eu³⁺can be used as a structure probe to obtain finer and more sensitive local structure information than XRD and Raman methods,and it is expected to be used in the local structure study of materials other than Zr O₂ with multiple local structures.Secondly,this chapter skillfully solves the difficulties in controlling three factors—Y³⁺doping concentration,oxygen vacancy concentration,and average grain size—based on combustion method combined with appropriate atmosphere and temperature treatment,that may affect the phase transformation of Zr O₂.And proposes a new guess that may affect the phase transformation mechanism of Zr O₂.Through combing photoluminescence spectroscopy of Eu³⁺,with XRD,SEM and Raman to verify.It is found that the increase of Y³⁺doping concentration is beneficial to the formation of more symmetric phase.The oxygen vacancies in Zr O₂ are Schottky defects,and the existence of oxygen vacancies will promote the transformation of tetragonal phase to monoclinic phase.Oxygen vacancies can be fully and freely redistributed below 800℃,but it has little effect on the transition of tetragonal phase to monoclinic phase.Even if the average grain size has reached close to hundred nanometers,increasing the average grain size can promote the transition of Zr O₂ from tetragonal to monocline phase.The ideas developed in this chapter can be extended to study the phase transition of other suitable materials as well as to gain a better understanding of the mechanism of Zr O₂ phase transition.Thirdly Zr_0.99Eu_0.01O_2-δnanoparticles with stable mixture of tetragonal and monotropic phases at room temperature were synthesized by combustion method and based on the photoemission spectrum of Eu³⁺,it was found that:（1）the anomalous tetragonal phase was mainly due to the nano size effect,rather than the high concentration of oxygen vacancies generated by the special synthesis process.With the increase of heat treatment tenderness,it will gradually change into monoclinic phase.（2）The difference of local structures of the Zr_0.91Eu_0.01Y_0.08O_2-δpressed tablets sintering into dense ceramics at 1100℃is significantly reduced,although the precursor synthesized by combustion method has significantly difference.Different calcination temperatures have little effect on the grain conductivity,but have great effect on the grain boundary conductivity of ceramic materials.Finally,YSZ electrolyte ceramic materials with different Y³⁺doping concentrations were synthesized by combustion method.The results of AC impedance spectroscopy show that the conduction activation energy of grain increases with the doping concentration.The electrical conductivity of the grains in the low temperature region x=0.08 is the highest,and that in the high temperature region x=0.16 is the highest.The conductivity of YSZ oxygen ion conductor is related not only to the activation energy of grain conduction but also to the degree of defect association and the migration barrier of oxygen vacancy.The photoemission spectra of Eu³⁺show that the concentration of oxygen vacancy increases with the Y³⁺doping concentration rise.Compared with the sample x=0.16,the oxygen vacancy in the sample x=0.21 is more likely to be located around Y³⁺,resulting in enhanced defect association and resulting in concentration quenching of the electrical conductivity of the sample grains.