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Phase Stability of Mixed-Cation Alkaline-Earth Hexaborides

机译：混合阳离子碱土己二硼酸盐的相位稳定性

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We present the behavior of multiple solid solutions within ternary (BaxCa1-x)B-6 and (BaxSr1-x)B-6 compounds and demonstrate that nanodomain formation is preferred over uniform solid solutions under certain processing conditions. Instead of the expected single solid solution of M-1 and/or M-2 atoms within the MB6 phase, we note separation into nanodomain regions rich in either M-1 or M-2. This phase separation has been observed from detailed analyses of the shapes of the peaks in X-ray diffraction data, where peak splitting and asymmetry are the result of multiple solid solutions with lattice parameters differing by up to 1.4%. High-resolution transmission electron microscopy confirms the presence of these nanodomains, which are about 2-3 nm in size, and reveals varying degrees of lattice misalignment. We also present X-ray diffraction analysis of (BaxCa1-x)B-6 powders calcined from 1273 to 1973 K and document the enhancement in sample homogeneity as the separated phases merge into a uniform solid solution. As subsequent calcinations at lower temperatures do not result in a re-separation of phases, the nanodomains are deemed metastable. The greatest degree of phase separation is observed in the (BaxCa1-x)B-6 system, which corresponds to the largest difference in cation radii (0.161 vs. 0.134 mn for Ba2+ and Ca2+, respectively). Analysis of the chemical reactions that occur during synthesis suggests that the decomposition of the metal precursors (nitrates and carbonates) to metal oxides may cause selective MB6 phase formation in mixed-cation hexaborides.
机译：我们介绍了三元（BAXCA1-X）B-6和（BAXSR1-X）B-6化合物内多固溶溶液的行为，并证明在某些加工条件下纳米域形成均匀的固溶体。代替MB6相中的M-1和/或M-2原子的预期单固溶溶液，我们注意到富含M-1或M-2的纳米域区分离。已经从X射线衍射数据中的峰的形状进行详细分析来观察到该相分离，其中峰分裂和不对称是多个固体溶液的结果，晶格参数不同达1.4％。高分辨率透射电子显微镜证实了这些纳米染色物的存在，其尺寸约为2-3nm，并揭示了不同程度的晶格未对准。我们还呈现（BAXCA1-X）B-6粉末的X射线衍射分析从1273-1973K煅烧，并将样品均匀性的增强作用，因为分离的相合并成均匀的固溶体。随着较低温度的后续煅烧不会导致重新分离相，纳米染色体被认为是稳定的。在（BaxCa1-X）B-6系统中观察到最大程度的相分离，其对应于阳离子半径的最大差异（分别为Ba2 +和Ca2 +的0.161 vs.0134mN）。分析合成期间发生的化学反应表明，金属前体（硝酸盐和碳酸盐）与金属氧化物的分解可能导致混合阳离子己酯中的选择性MB6相形成。

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  • 来源
    《Crystal growth & design》 |2017年第6期|共12页
  • 作者

    Cahill James T.; Alberga Michael; Bahena Joel; Pisano Christopher; Borja-Urby Raul; Vasquez Victor R.; Edwards Doreen; Misture Scott T.; Graeve Olivia A.;

  • 作者单位

    Univ Calif San Diego Dept Mech &

    Aerosp Engn 9500 Gilman Dr MC 0411 La Jolla CA 92093 USA;

    Alfred Univ Kazuo Inamori Sch Engn 2 Pine St Alfred NY 14802 USA;

    Univ Calif San Diego Dept Mech &

    Aerosp Engn 9500 Gilman Dr MC 0411 La Jolla CA 92093 USA;

    Univ Calif San Diego Dept Mech &

    Aerosp Engn 9500 Gilman Dr MC 0411 La Jolla CA 92093 USA;

    Inst Politecn Nacl Ctr Nanociencias &

    Micro &

    Nanotecnol Ave Luis Enrique Erro S-N Mexico City 07738 DF Mexico;

    Univ Nevada Chem &

    Mat Engn Dept 1664 N Virginia St MS 388 Reno NV 89557 USA;

    Rochester Inst Technol Kate Gleason Coll Engn 77 Lomb Mem Dr Rochester NY 14623 USA;

    Alfred Univ Kazuo Inamori Sch Engn 2 Pine St Alfred NY 14802 USA;

    Univ Calif San Diego Dept Mech &

    Aerosp Engn 9500 Gilman Dr MC 0411 La Jolla CA 92093 USA;

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  • 正文语种 eng
  • 中图分类 晶体学;
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