Short-Range Order and Origin of the Low Thermal Conductivity in Compositionally Complex Rare-Earth Niobates and Tantalates
Short-Range Order and Origin of the Low Thermal Conductivity in Compositionally Complex Rare-Earth Niobates and Tantalates
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DOI：
10.1016/j.actamat.2022.118056
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发表时间：
2021-04
期刊：
影响因子：
9.4
通讯作者：
Andrew J. Wright;Qingyang Wang;Yichi Yeh;Dawei Zhang;M. Everett;J. Neuefeind;Renkun Chen;Jian Luo-Ji
中科院分区：
文献类型：
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作者：
Andrew J. Wright;Qingyang Wang;Yichi Yeh;Dawei Zhang;M. Everett;J. Neuefeind;Renkun Chen;Jian Luo-Ji
稀土铌酸盐和钽酸盐具有低的导热系数，在高熵成分中可以进一步降低导热系数。在这里，我们合成了大量的40个化合物来研究低导热系数的原因。其中29个具有单一的(名义上为立方的)萤石相，其中大多数是新的成分复杂(中或高熵)的组成。此外，掺杂2%的轻元素阳离子还可以进一步降低导热系数。这一庞大的数据集使人们能够发现3+/5+阳离子的导热系数与平均半径比之间的负相关性。虽然这一比值仍低于形成长程有序韦伯来石型相的阈值，但这种关联表明导热系数的降低与短程韦伯来石型相有关，这一点确实从X射线衍射和中子总散射中的扩散散射中得到了揭示。具体地说，中子总散射被用来表征五个选定的样品。在纳米尺度上发现了更适合韦伯利石型结构的方法。在更绝缘的材料中，特征长度(磁区大小)似乎更大。当它接近Ioffe-Regel极限时，声子极限被破坏，“扩散子”产生了观察到的非晶态热导率。
Rare-earth niobates and tantalates possess low thermal conductivities, which can be further reduced in high-entropy compositions. Here, a large number of 40 compositions are synthesized to investigate the origin of low thermal conductivity. Of these, 29 possess single (nominally cubic) fluorite phases and most of them are new compositionally complex (medium- or high-entropy) compositions. Furthermore, doping 2% of light element cations can further reduce thermal conductivity. This large data set enables the discovery of a negative correlation between the thermal conductivity and averaged radius ratio of the 3+/5+ cations. While this ratio is still below the threshold for forming long-range ordered weberite-type phases, this correlation suggests the reduced thermal conductivity is related to short-range weberite-type order, which is indeed revealed by diffuse scattering in X-ray diffraction and neutron total scattering. Specifically, neutron total scattering is used to characterize five selected specimens. A better fit to a weberite-type structure is found at the nanoscale. The characteristic length (domain size) is appears to be larger in more insulative materials. As it approaches the Ioffe-Regel limit, the phonon limit breaks down and “diffusons” give rise to the observed amorphous-like thermal conductivity.