Materials Department, Department of Chemistry and Biochemistry and Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA.
J Phys Condens Matter. 2013 May 8;25(18):186004. doi: 10.1088/0953-8984/25/18/186004. Epub 2013 Apr 16.
Polycrystalline Nd2Ru2O7 samples have been prepared and examined using a combination of structural, magnetic, and electrical and thermal transport studies. Analysis of synchrotron x-ray and neutron diffraction patterns suggests some site disorder on the A-site in the pyrochlore sublattice: Ru substitutes on the Nd-site up to 7.0(3)%, regardless of the different preparative conditions explored. Intrinsic magnetic and electrical transport properties have been measured. Ru 4d spins order antiferromagnetically at 143 K, as seen both in the susceptibility and in the specific heat, and there is a corresponding change in the electrical resistivity. The onset of a second antiferromagnetic ordering transition seen below 5 K is attributed to ordering of Nd 4f spins. Nd2Ru2O7 is an electrical insulator, and this behaviour is believed to be independent of the Ru-antisite disorder on the Nd-site. The electrical properties of Nd2Ru2O7 are presented in the light of data published on all A2Ru2O7 pyrochlores, and we emphasize the special structural role that Bi(3+) ions on the A-site play in driving metallic behaviour. High-temperature thermoelectric properties have also been measured. When considered in the context of known thermoelectric materials with useful figures-of-merit, it is clear that Nd2Ru2O7 has excessively high electrical resistivity which prevents it from being an effective thermoelectric. A method for screening candidate thermoelectrics is suggested.
多晶 Nd2Ru2O7 样品已通过结构、磁性、电学和热输运研究的组合进行了制备和研究。同步加速器 X 射线和中子衍射图谱的分析表明，在钙钛矿亚晶格的 A 位存在一定程度的位错：Ru 取代了 Nd 位，取代度高达 7.0(3)%，与所探索的不同制备条件无关。已经测量了固有磁和电输运性质。Ru 4d 自旋在 143 K 时反铁磁有序，这在磁化率和比热中都可以看到，并且电阻率也相应发生变化。在 5 K 以下观察到的第二个反铁磁有序相变的开始归因于 Nd 4f 自旋的有序。Nd2Ru2O7 是一种电绝缘体，这种行为被认为与 Nd 位上 Ru 反位错无关。Nd2Ru2O7 的电学性质是根据所有 A2Ru2O7 钙钛矿的已发表数据提出的，我们强调了 A 位上 Bi(3+)离子在驱动金属行为方面的特殊结构作用。还测量了高温热电性质。当将其与具有有用优值的已知热电材料进行比较时，很明显，Nd2Ru2O7 的电阻率过高，使其无法成为有效的热电材料。提出了一种筛选候选热电材料的方法。
