利用XRD和DTA/TG系统地研究了石榴石结构的Li7La3Zr2O12 (LLZO)的形成机制,所用原料为LiOH·H2O.研究发现,LLZO是通过以下化学反应形成的:7Li2O+3La2O3+4ZrO2=2Li7La3Zr2O12.XRD结果表明,LLZO大约在680℃开始生成,这与DTA/TG曲线上的放热峰比较吻合,这个放热峰是由LLZO相生成引起的.LLZO相在比较宽的温度范围内(720～1000℃)能稳定存在.然而,当温度高于1000℃,由于锂元素的严重挥发缺失,LLZO是不稳定的,会分解为焦绿石相的La2Zr2O7.随着煅烧温度的升高,分解产物的量越来越多,LLZO逐渐减少.当反应混合物在较低的煅烧温度时,所生成的物质经鉴定是镧的化合物,这是因为La2O3非常容易吸收水汽和CO2,LLZO粉末在800℃利用固相反应法合成.经研究发现,LLZO晶体属于四方晶系.由扫描电镜观测显示,所制备的LLZO粉末是纳米尺度的.
The formation mechanism of garnet-like Li7La3Zr2O12 (LLZO) phase was investigated using LiOH·H2O as raw materials by XRD and DTA/TG measurements.It is found that the reaction mechanism of the LLZO formation is as follows:7Li2O+3La2O3+4ZrO2=2Li7La3Zr2O12.The LLZO phase forms at about 680 ℃ according to the XRD patterns,which is in agreement with the thermic peak at 700 ℃ in DTA/TG curves,and the peak arises from the formation of LLZO phase.The temperature range of stable LLZO phase is wider,from 720 to 1000 ℃.However,LLZO is thermally unstable at the high temperatures (＞1000 ℃) due to a serious loss of lithium element,and it discomposes into pyrochlore phase La2Zr2O7.And the amount of the decomposed products increases,and LLZO decreases gradually with the increase of the calcination temperature.When the reactant mixture is calcined at low temperature,the produced phases are identified to be lanthanum compounds because La2O3 absorbs moisture and CO2 very easily.The chemical reactions at lower temperature are mainly related with the reactions among lanthanum compounds.LLZO powder could be synthesized by solid state reaction at 800 ℃.It is found that the LLZO crystal belongs to the tetragonal symmetry.SEM observation shows that the obtained LLZO powder is nano-sized.
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