Preparation Of Barium(Strotium) Titanate Nanoparticles And Research On Its Properties Of Phtotocatalysis And Humidity

Barium strontium titanate Ba_1-xSr_xTiO₃（BST in short）has typical perovskite structure,it has excellent dielectric property,low dielectric loss,high dielectric constants,and good thermal stability.The dielectric and optical properties of barium strontium titanate can be continuously adjusted by changing the atomic ratio of strontium in the range of 0～1,which enables barium strontium titanate to be used in the field of electronic device^[1-2].In this thesis the main research tasks are as follows:Firstly,barium strontium titanate powder material is prepared by hydrothermal method.The effect of hydrothermal parameters,including the mole ratio of barium,strontium and titanium in the precursor,the concentration of the reactants in the precursor,the concentration of KOH,ethanol solvent and so on,on the growth of barium strontium titanate was studied.It is found that the ratio of barium,strontium and titanium in the precursor is the key factor for the purity of the hydrothermal product.Pure BST nanopowders without impurity was prepared with the mole ratio 2:1:2 and 2:3:2 of barium,strontium and titanium in the precursor.Increasing the concentration of the reactants in the precursor in helpful for producing pure phase Ba_1-xSr_xTiO₃.The high concentration of KOH results in crystalline phase segregation of barium titanater from barium strontium titanate,2M/L KOH is the suitable concentration for preparation of pure phase barium strontium titanate.Barium strontium titanate hollowsphere particles are prepared with the mole ratio of barium,strontium and titanium as 2:3:2 in the precursor.Using water as solvent will promote the growth of BST hollowspheres,while using ethanol and water mixture as solvent will suppress the growth of hollowspheres,barium strontium titanate nanosheets are prepared in the mixture solvent.Barium titanate（BT）and strontium titanate（ST）particles prepared with the same procedure as that to prepared Ba_1-xSr_xTiO₃ are larger and agglomerate seriously,it is concluded that adulteration of strontium cation in Ba_1-xSr_xTiO₃ can decrease the size of nanoparticles and modify the dispersibility of nanoparticles.Secondly,Ba_1-xSr_xTiO₃ nanoparticles,prepared by the hydrothermal method are applied in the photocatalylic degradation of methylene blue solution.The photocatalytic activity of Ba_1-xSr_xTiO₃ nanoparticles are better than that of barium titanate and strontium titanate.The photocatalytic activity of the sample Ba_0.11Sr_0.89TiO₃ is similar to that of strontium titanate with the help of its hollowspere structure.Ba_0.11Sr_0.89TiO₃ mixed with P25 have a synergistic effect on methylene blue solution degradation,which could be attributed to a multistep band structure.As a result,their photocatalytic activity has been enhanced,prior to the single ingredient P25 or Ba_0.11Sr_0.89TiO₃.In the hydrothermal process,adding surfacant PEG is very helpful for decrease the size of BST nanoparticles.PEG has better effect on modifying the property of BST（2:1:2）than that of BST（2:3:2）.Adding surfacant PVP is also helpful for decrease the size of Ba_0.54Sr_0.46TiO₃ nanoparticles in the BST（2:1:2） sample and largely enhances the photocatalytic activity of the BST（2:1:2） sample,but is inclined to increase the size of the BST（2:3:2） sample,resists the formation of hollowsphere nanoparticles in the BST（2:3:2） sample,resulting in its photocatalytic activity declining.Comparing to the BST（2:3:2） sample,adding the surfacant PEG or PVP has a positive effect on modifying photocatalytic activity of the BST（2:1:2） sample.The concentration of strontium cation,the size of the nanoparticles,hollowsphere structure and dispersibility of the photocatalyst in the solution,all together determine the photocatalytic activity of Ba_1-xSr_xTiO₃.Finally,the prepared Ba_1-xSr_xTiO₃ nanoparticles are pressed into thin tablets with the help of binder.Remove the binder from the tablets at certain temperature before they are annealed.Pt electrodes are deposited on the tablets and humidity sensitivity of the tablets are investigated.It is found that the component of the samples,post annealing,and the thickness of electrodes sputtered on the Ba_1-xSr_xTiO₃ samples all have effect on the humidity sensitivity of the sample.BT,ST annealed at 600℃or700℃have good humidity sensitivity in high humid environment,BT annealed at700℃has better humidity sensitivity while longer recovery time.As to the BST（2:1:2） sample,it has shorter the average response time and recovery time,1163s and904s respectively,when it is annealed at 600℃.BST（2:1:2） demonstrates the best humidity sensing performance after annealed at 600℃.It has the best overall performance,with good humidity resolution,high sensitivity,reasonable response and recovery time.A proper amount of strontium doping into Ba TiO₃effectively enhances the humidity sensing properties of the Ba_1-xSr_xTiO₃samples such as BST（2:1:2）,while excessive doping of strontium cation into Ba_1-xSr_xTiO₃ decreases humidity sensitivity,lengthen the response time and recovery time like BST（2:3:2）.After doping of strontium cation into Ba_1-xSr_xTiO₃,the resistance of Ba_1-xSr_xTiO₃ samples has decrease to one magnitude comparing to that of Ba TiO₃.Increasing the electrode thickness on the samples can modify the contact between the electrode Pt and the samples,which can decline the noise disturbance,make the humidity sensitivity testing line more smooth,and decrease the resistance of the samples.Increasing the electrode thickness on the samples is also helpful for eliminating humidity hysteresis of the sample,but has little effect on the humidity sensing characteristic properties such as sensitivity,response resistance and recovery resistance of the samples.The devices made of Ba_1-xSr_xTiO₃ material has high humidity sensitivity,but their response time and the recovery time needs to be further decreased.In future,these characteristic properties of the devices can be modified by optimizing the structure of the devices as well as further adjusting the property of Ba_1-xSr_xTiO₃ material.