Centre for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, DK-8000 Århus C, Denmark.
Inorg Chem. 2010 Oct 18;49(20):9343-9. doi: 10.1021/ic100990a.
The hexagonal polymorph of CeMnNi(4) has been synthesized using cold crucible, high-frequency induction melting with subsequent Czochralski crystal pulling. Single-crystal X-ray diffraction, multitemperature synchrotron powder X-ray diffraction (90 to 600 K), and neutron powder diffraction data have been measured to establish the detailed crystal structure and in particular the location of the Mn atoms. The neutron diffraction data provide sufficient scattering contrast between Mn and Ni to establish that the 2c site has an occupancy of 13% Mn atoms, while the 3g site has an occupancy of 25% Mn atoms. Thus, the crystal structure is complex with considerable disorder. Rietveld refinement of the multitemperature synchrotron data establishes a near linear thermal expansion coefficient of 13.9(3) × 10(-6) K(-1) and 14.9(3) × 10(-6) K(-1) for the a and c axes, respectively. Atomic Hirshfeld surfaces are introduced as a new tool to investigate the atomic coordination and interactions in intermetallic compounds. The atomic displacement parameters (ADPs) are observed to be much larger for the heavy Ce atom than for the lighter Mn and Ni atoms, and this correlates with the large atomic Hirshfeld volume of Ce relative to Mn and Ni. The fit of a Debye model to the ADPs gives θ(D) = 312(3) K. Magnetic susceptibility data measured between 2 and 350 K indicate ferromagnetic ordering at 122(2) K (Weiss constant) based on a linear fit of the inverse magnetic susceptibility in the paramagnetic region. Transport properties were measured on a polycrystalline sample containing CeO(2) (2.8%) and Ni (7.7%) impurities. The electrical conductivity is observed to be metallic with a distinct kink in the data around 120 K coinciding with the observed Curie temperature. The lattice thermal conductivity (κ(L)) increases from 0.5 W/Km at 2 K to 8 W/Km at 50 K, and the relatively moderate value of κ(L) probably reflects the significant structural disorder.
采用冷坩埚、高频感应熔炼和随后的提拉法合成了 CeMnNi(4)的六方多晶型物。测量了单晶 X 射线衍射、多温度同步辐射粉末 X 射线衍射（90 至 600 K）和中子粉末衍射数据，以确定详细的晶体结构，特别是 Mn 原子的位置。中子衍射数据提供了 Mn 和 Ni 之间足够的散射对比，以确定 2c 位的 Mn 原子占据率为 13%，而 3g 位的 Mn 原子占据率为 25%。因此，晶体结构复杂，存在相当大的无序。多温度同步辐射数据的 Rietveld 精修确定了 a 和 c 轴的近线性热膨胀系数分别为 13.9(3)×10(-6)K(-1)和 14.9(3)×10(-6)K(-1)。引入原子 Hirschfeld 表面作为研究金属间化合物中原子配位和相互作用的新工具。观察到重原子 Ce 的原子位移参数（ADPs）比轻原子 Mn 和 Ni 的 ADPs 大得多，这与 Ce 相对于 Mn 和 Ni 的较大原子 Hirschfeld 体积相关。ADPs 的 Debye 模型拟合给出 θ(D)=312(3)K。在 2 至 350 K 之间测量的磁化率数据表明，基于顺磁区倒数磁化率的线性拟合，在 122(2)K（Weiss 常数）处存在铁磁有序。在含有 CeO(2)(2.8%)和 Ni(7.7%)杂质的多晶样品上测量了输运性质。电导率表现为金属性，在 120 K 左右的数据出现明显拐点，与观察到的居里温度一致。晶格热导率(κ(L))从 2 K 时的 0.5 W/Km 增加到 50 K 时的 8 W/Km，κ(L)的相对适中值可能反映了显著的结构无序。
