Study On Synthesis And Properties Of Inorganic Functional Oxides

The relationship between structure and properties of a compound is an important topic in solid state chemistry.Based on the research in this relationship and analysis of the inside mechanism,researchers can adjust the parameters of composition,crystal structure,microstructure and electron structure,to change or tune properties of a compound.A compound with some remarkable property can be taken as a functional material.Oxides have rich composition,structure,and property,which is a main subject to many disciplines like solid state chemistry,solid state physics,and material chemistry etc.Considering the various preparation methods,rich composition,remarkable properties and wide application of oxides,it is both academic and applied significance to tune the morphology and micro-structure of an oxide to evaluate the optical,electrical,and magnetic properties.Spinel oxide is an important industrial material,which is land mineral-rich and preparation diversity.Transition metal oxides with spinel structure AB₂O₄,where A occupies one-eighth of the tetrahedral sites（T_d）and B occupies half of the octahedral sites in a face-centered cubic close-packed oxygen sublattice（O_h）.Besides the normal spinel structure,the structure can be defined as inversed spinel structure if the divalent cations fully occupy on O_h sites or mixed spinel structure once the divalent partly occupy on O_h sites.Diversity of structure and composition make the properties complicated.Spinel aluminates take the advantage of spinel structure and chemical composition,showing characters of high temperature tolerance,high hardness,acid and base tolerance.Depending on the alkaline earth or transition element in A site,Spinel aluminates are used as photocatalysts,buffer layers,pigments,phosphors,refractories.There are many methods to prepare the spinel aluminates:solid state method,sol-gel,co-precipitation,hydrothermal technology,and solution combustion method,etc.We studied various preparation method for spinel oxides and choose the solution combustion method to prepare the spinel aluminates.Several spinel aluminates were prepared,which’s structure and property were further characterized.Combined the structural adjustion and solution combustion method,we focus on the luminance property of MgAl₂O₄:Eu³⁺phosphor and gain the following results.（1）A series of spinel aluminate nanopigments（MgAl₂O₄,CoAl₂O₄,NiAl₂O₄,CuAl₂O₄,and ZnAl₂O₄）were synthesized with an easy solution combustion method and the structure and property were characterized.An aqueous solution containing stoichiometric amount of nitrates and glycine as fuel is heated above 400℃rapidly,then the solution boils and burns.The compound is formed during the combustion process due to the flashily released heat.As-prepared combustion products need secondary heat treatment to further crystallize and remove the carbon deposition.MgAl₂O₄ and CoAl₂O₄ are formed as white powder;the CoAl₂O₄ is blue;NiAl₂O₄ is light green;CuAl₂O₄ is brown.From the XRD patterns,no impure phases are observed and all these as-prepared samples are crystalized in the designed spinel phase.SEM show all the samples were composed by aggregated nanoparticles with the character of porous structure.XPS analysis suggests that the Al³⁺cations occupy these two different positions due to site inversion effect.It seems that the Al³⁺cations are more easily to occupy the O_h sites if the radius of the divalent metal cations are close to that value of Al³⁺in the combustion method.The magnetic properties of CoAl₂O₄,NiAl₂O₄,and CuAl₂O₄ were characterized.Both CoAl₂O₄ and CuAl₂O₄show frustrated magnetic property.However,NiAl₂O₄ show antiferromagnetic property.Heat capacities of these compounds are further studied and evidence the strong spin frustration in CoAl₂O₄ and CuAl₂O₄,which give the corresponding Debye temperature,Einstein temperature,and magnetic entropy.It helps us to better understand the relationship between structure and property of these spinels.（2）Base on the work mentioned above,we found the spinel structure has strong tolerance for foreign element doping.To investigate the influence of annealing temperature on the structural rigidity and photoluminescence,Eu³⁺doped MgAl₂O₄ceramics have been synthesized by a solution combustion reaction and thermally treated at various temperature.Powder XRD indicate that pure spinels were synthesized and the crystallinity increased with the increase of the heat treatment temperature.Low temperature heat capacities of sample show the structural rigidity has positive relationship with the calcine temperature.The SEM show spongy structure of the particles formed due to the exhausting the large amount of gases during the short solution combustion process.The porosity increased with the rise of the secondary treatment temperature.These phosphors exhibit hypersensitive red emission peaking at 613 nm when excited by 274 nm and 394 nm light.Moreover,the emission excited by 394 nm is stronger than that excited by 274 nm.The MgAl₂O₄:Eu³⁺calcined at 900℃shows the best performance and the effective emission excited by near-UV 394 nm.The photoluminescence not solely depends on the structural rigidity but needs some balance between the disorder caused by Eu³⁺doping and long range order of the structure.（3）During the research on hydrothermal preparation of spinel oxides.A new complex AgCu（IO₃）₃ is synthesized and characterized by single crystal X-ray diffraction and magnetization measurement.AgCu（IO₃）₃ is isostructral with AgPb（IO₃）.The crystal structure of AgCu（IO₃）₃ consists of two crystallographically distinct distorted octahedral CuO₆ groups,three different pyramidal IO₃ groups and an irregular AgO₇ polyhedron.The Cu（1）O₆ and Cu（2）O₆ octahedra alternate and share a common oxygen corner O（1）to form a zigzag chains.The magnetization data suggests the weak antiferromagnetic interaction dominates the magnetic property of the compound,although there are coexistence of antiferromagnetic interaction and ferromagnetic interaction.By studying the structure and properties of functional oxide,this paper explores the experimental methods to control the physical properties of materials and further discusse the relationship among the preparation,structure,and property.This experimental results enrich the inorganic synthesis and preparative chemistry and also provide some new viewpoints and experimental cases for the development of solid state chemsitry.