The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba_8−xR_xCu₁₆P₃₀, with the smallest pentagonal dodecahedral cages encapsulating La³⁺ and Ce³⁺. Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

三价稀土阳离子与它们的碱和碱土同伴之间最显着的区别是存在局部4 f电子。将三价稀土阳离子放置在富勒烯分子内部或金属间化合物的嵌段之间已产生了许多令人着迷的特性和材料。长期以来尚未发现的材料是一种带有稀土阳离子的半导体化合物，该化合物位于三维框架的超大型多面体笼体内。在这项工作中，我们提出了非常规包合物Ba _{8− x} R _x Cu ₁₆ P ₃₀的合成，其包封了La ³⁺和Ce的最小五边形十二面体笼³⁺。通过同步加速器粉末衍射，飞行时间中子粉末衍射，扫描透射电子显微镜和电子能量损失谱的组合明确地确定了它们的组成和晶体结构。我们的量子力学计算和实验表征表明，稀土阳离子的掺入可显着提高空穴迁移率并降低空穴浓度，从而导致热电性能急剧提高（700％）。