Gd^(3+)掺杂La_(1-x)Gd_xMgAl_(11)O_(19)(x=0～1)陶瓷的制备及热学性能

PREPARATION OF Gd^(3+)-DOPED La_(1-x)Gd_xMgAl_(11)O_(19)(x = 0-1) CERAMICS AND ITS THERMAL PROPERTIES

以Al(OH)3,La2O3,Gd2O3和4MgCO3·Mg(OH)2·5H2O为原料,采用固相反应法在1500℃保温4h合成了镁基六铝酸镧钆(La1-xGdxMgAl11O19,x=0～1,LGMA)粉体。结果表明:合成的LGMA粉体具有畸变的磁铅石型晶体结构,形成一种镧钆共掺镁基六铝酸盐固溶体,LGMA晶粒发育良好,呈板片状,晶粒平均厚度约为350nm。采用无压烧结法在1700℃保温6h后LGMA陶瓷仍能保持其稳定的磁铅石结构。在LaMgAl11O19晶格中掺入钆离子能显著降低LGMA陶瓷的高温热导率,在800℃,GdMgAl11O19陶瓷的最低热导率为1.78W/(m·K),200～1200℃范围的平均线性热膨胀系数为9.39×10-6/K。GMA陶瓷具有较低热导率的主要原因是:在LaMgAl11O19晶格中原子质量较重的Gd3+取代La3+能够增强声子散射作用,Gd3+掺入后引起的晶格畸变对声子散射也具有重要作用。

Lanthanum-gadolinium magnesium hexaluminate（La1-xGdxMgAl11O19,x = 0-1,LGMA） powders were synthesized at 1 500 ℃ for 4 h using Al（OH）3,La2O3,Gd2O3 and 4MgCO3·Mg（OH）2·5H2O as raw materials via a solid state reaction method.The results show that the LGMA powders exhibit a distorted magnetoplumbite-type（MP） crystal structure and forms a solid solution of co-doped lanthanum-gadolinium magnesium hexaluminate,and the morphology of LaMgAl11O19 particles appears plate-like with a clear edge and well-developed faces,and the average crystalline grain size of the LGMA powders is about 350 nm.The LGMA ceramic pressureless sintered at 1 700 ℃ for 6 h could maintain the stable MP crystal structure.The incorporation of Gd3＋ into the lattice could reduce the high-temperature thermal conductivities of the LGMA ceramic.The thermal conductivity at 800 ℃ of GdMgAl11O19 ceramic is 1.78 W/（m·K）,and its linear thermal expansion coefficient from 200 to 1 200 ℃ is 9.39 × 10-6/K.The main reason of low thermal conductivity of LGMA ceramics is due to the enhanced phonon scattering effects caused by the heavy rare-earth Gd3＋ replacing La3＋ in the lattice of LaMgAl11O19.The lattice distortion induced by the dopping Gd3＋ also plays an important role on phonon scattering.