磁铅石结构LaMgAl11O19粉体制备及其晶格热膨胀

Preparation and lattice thermal expansion of lanthanum magnesium hexaaluminate powder with magnetoplumbite structure

摘要:

采用反向化学共沉淀-高温煅烧法制备了镁基六铝酸镧(LaMgAl₁₁O₁₉)粉体。利用X射线衍射、场发射扫描电子显微镜、高温原位X射线衍射及Rietveld晶体结构精修法对粉体的物相组成、显微形貌、晶体结构及晶格热膨胀行为进行了研究。结果表明,反向化学共沉淀制备的氢氧化物前驱体经1600 ℃热处理后完全转变为磁铅石结构的LaMgAl₁₁O₁₉,呈规则六方板片状,晶面光滑平整。采用高温原位XRD技术及Rietveld晶体结构精修系统研究了镁基六铝酸镧材料的晶格热膨胀行为。随着温度的升高,镁基六铝酸镧(LaMgAl₁₁O₁₉)晶格热膨胀表现出各向异性,晶胞参数a和c随温度变化关系为：a_T=5.5821+1.625×10_-5T+1.757×10_-8T₂+4.24×10_-12T₃,c_T=21.9189+1.1952×10_-4T+4.587×10_-8T₂+5.463×10_-11T₃。室温~1300 ℃,//a平均热膨胀系数为8.42×10_-6/℃,//c平均热膨胀系数为12.54×10_-6/℃。La-O键各向异性热膨胀是LaMgAl₁₁O₁₉晶格热膨胀各向异性的主要原因。

Abstract:

The lanthanum magnesium hexaaluminate (LaMgAl₁₁O₁₉) powder was prepared via reverse chemical coprecipitation and high-temperature calcination method. The phase composition, microstructure, crystal structure and anisotropic lattice thermal expansion were ananlyzed using X-ray diffractometer (XRD), field emission scanning electron microscope (FSEM), in-situ high temperature X-ray diffraction (HD-XRD) and Rietveld refnement. The results showed that the precursors were final transformed to LaMgAl₁₁O₁₉ at sintering temperature of 1600 _oC, in which the hexagonal plane was regular and smooth. Anisotropic lattice thermal expansion of LaMgAl₁₁O₁₉ was investigated by HD-XRD using rietveld refnement method. The influence of temperature-related parameter on cell parameters was analyzed, of which a_T=5.5821+1.625×10_-5T+1.757×10_-8T₂+4.24×10_-12T₃ and c_T=21.9189+1.1952×10_-4T+4.587×10_-8T₂+5.463×10_-11T₃. Lattice thermal expansion of LaMgAl₁₁O₁₉ presented anisotropic characteristics. At ambient temperature to 1300 ℃, average coefficient of thermal expansion of LMA were obtained with TECs(//a)= 8.42×10_-6 /℃, TECs(//c)=12.54×10_-6 /℃. The variation of lattice thermall expansion of LaMgAl₁₁O₁₉ mainly due to the changes of La-O bond caused by temperatute.