Study Of Layered Niobate Salts Obtained By Gel-combustion Chemical Method

Layered niobate salts are a new type of functional materials. Due to the unique layeredstructure and interlayer chemical reactivity, it has wide application in many fields such asluminescence, conductivity, adsorption, ion exchange, light catalysis and so on. These kindsof substances commonly used the high temperature solid-phase synthesis. But it will be mixedwith impurities easily in the milling process and lead to low purity. In this paper, layeredniobate salts are prepared by gel-combustion chemical method. It can solve the problem andget the good uniformity and high purity niobate powers.First, we introduced the research background and significance of the subject and researchprocess in the filed of niobate materials. Structural characteristics and preparation methods ofniobate materials were also summarized.Second, the niobate powders （KNb₃O₈） with layered structure were successfullysynthesized via the citric acid gel-combustion process using KNO₃and Nb₂O₅H₂O as the rawmaterials which are according to a certain stoichiometric ratio. Thermal behavior of theprecursor was determined by TG-DSC techniques. The phase composition and morphology ofthe synthesized samples were characterized by using the X-ray diffraction and scanningtransmission electron microscope. It was found that the amorphous precursor of KNb₃O₈lostphysical adsorption water between100²30℃. Organic compounds of the sample wereoxidized to decompose completely at about500℃. KNb₃O₈phase was crystallized directlyfrom the amorphous precursor at about600℃. The SEM images of the samples showed thatthe particles were bar-like under calcination temperature of600℃. The morphology of theparticles transformed into flakes gradually as the calcination temperature increasing. It is alayered metal oxide with a perovskite structure.Third, we have synthesized KLaNb₂O₇by doping La³⁺in the niobate substrate. The rawmaterials also were KNO₃and Nb₂O₅H2O. It was found that the sample of KLaNb₂O₇lostphysical adsorption water between100²00℃. Organic compounds of the sample wereoxidized to decompose completely at about500℃. KLaNb₂O₇phase was crystallized directlyfrom the amorphous precursor at about800℃. We can obtain KLaNb₂O₇which had theobvious plate structure when the calcination temperature was higher than1000℃. Thecrystallinity of particles ascend with the calcination temperature increasing. The preferablegrowth of crystal was along crystal phase and radial enlargement. However, the morphologyof the products became into molten state when the temperature was more than1300℃.Finally, we have synthesized KLa_0.95Eu_0.05Nb₂O₇by doping Eu³⁺in the niobate substrate（KLaNb₂O₇） via the citric acid gel-combustion process. Through the detection of excitation and emission spectra, luminescent properties were analyzed and characterized. We alsostudied the mechanism of energy transfer between the substrate and rare earth ions. It wasfound that luminescence of rare earth ions mainly came from the effective energy transfer ofsubstrate. The excitation spectra of samples contained f-f transition excitation spectrum ofrare earth ions. It can be inferred that energy was passed by the substrate to the rare earth ionsof Eu³⁺, and the excitation efficiency of the substrate was more than the excitation efficiencyof Eu³⁺own energy levels.