Alcohol-hydrothermal Synthesis Of Tetragonal Barium Titanate Powders

Tetragonal barium titanate （BaTiO3） with high dielectric constant and loss dielectricloss, can be widely applied in the field of electronic ceramics. So the preparation of highcontent tetragonal barium titanate powder became more important. The crystal structure,barium titanate c/a, dispersion, particle size and the grain morphology are importantindicators for barium titanate powder.This topic about Ba（OH）2·8H2O and Ti（OC₄H₉）₄as raw materials, tetragonal phasebarium titanate powder from the hydrothermal synthesis. Analyzed alcohol types in thesolvents（ethanol, isopropyly alcohol, butanol, ethylene glycol,1,4-butanediol）, the contentof ethanol, reactant Ba/Ti, reaction time, reaction temperature, concentration of rawmaterial, source of titanium and washing process and so on to influence synthesis bariumtitanate of tetragonal phase, the powder were characterized by XRD, DSC, TEM, SEM, IRand laser nano particle size analysis. Summary the process conditions of barium titanatepowder of tetragonal phase with high content, doped rare-earth La on this basis, analysisthe effect of dielectric properties of barium titanate with doping La of different content.Results show that barium titanate powder synthesized with alcohol/water mixturesolvent as dispersion medium, solvent type has significant effect on crystal phase ofbarium titanate, the long carbon chain more disadvantageous to synthesize barium titanateof tetragonal phase, decreased the c/a of barium titanate, under the same conditions bariumtitanate synthesized with ethylene glycol as solvent have more impurities, usingethanol/water mixture solvent as the dispersing medium, more conducive to synthesizebarium titanate of tetragonal phase of high content, tetragonal phase content reaches ashigh as73%; adding a moderate amount of ethanol to synthesize barium titanate powder oftetragonal phase, when adding50%ethanol, barium titanate synthesized with maximumc/a of barium titanate, it can reach1.0074, tetragonal phase content is52%; increasedreactant Ba/Ti, longer reaction time, rise reaction temperature, can promote powder fromcubic change to tetragonal phase, increased tetragonality c/a; With the increasing of the concentration of raw materials, powder particle size and c/a of barium titanate are reduced;barium titanate powder of high c/a synthesized with titanium dioxide, tetragonal phasewith high content, but powders have more impurity, pure barium titanate powdersynthesized with terabutyl titanate as the source; compared with unheated, barium titanatesynthesized with heating titanium alcohol solution, increased c/a of barium titanate, canpromote the crystal phase of barium titanate from cubic change to tetragonal; bariumtitanate for alcohol-wash heating can remove OH-, barium titanate have high c/a value, canreach1.0093, tetragonal phase content of barium titanate can reach86%. Comprehensiveexperiment results obtained optimum reaction conditions is that Ba（OH）2·8H2O andTi（OC₄H₉）₄as raw materials, fixed barium titanium molar ratio2.0, in ethanol/watermixture solvent, of whith50%ethanol content, the titanium alcohol mixed solution heating,at180℃with120h, prepared barium titanate pulp for alcohol wash heating to synthesisebarium titanate powder with tetragonal phase of86%.Barium titanate had heat treatment at800℃,900℃,950℃,1000℃, it reduced c/a ofbarium titanate, heat treatment that prompted crystal phase of barium titanate changed, it isnot conducive to synthesise barium titanate of tetragonal phase.Barium titanate of tetragonal phase of high content, with rare earth La as modifyingagent, found that doping La does not change the main crystal phase structure of bariumtitanate, along with the La content increased, cell volume of barium titanate reduced; Lamolar content is less than0.3%, barium titanate dielectric constant greatly improved; Lacontent is0.3%, water absorption rate and apparent porosity reached a minimum,effectively inhibiting abnormal crystal growth at barium titanate sintering process whendoping La. The doping the La barium titanate powder by950℃presintering, comparedwith not presintering powder, dielectric constant of barium titanate decreased, dielectricloss increased.