Enhanced High-Temperature Thermoelectric Performance of Yb_{14–<i>x</i>}Ca_<i>x</i>MnSb₁₁

The high temperature p-type thermoelectric material Yb14MnSb11 has been of increasing research interest since its high temperature thermoelectric properties were first measured in 2006. Subsequent substitutions of Zn, Al, and La into the structure have shown that this material can be further optimized by altering the carrier concentration or by reduction of spin-disorder scattering. Here the properties of the Yb14–xCaxMnSb11 solid solution series where isovalent Ca2+ is substituted for Yb2+ will be presented. Crystals of the Yb14–xCaxMnSb11 solid solution series were made by Sn-flux (x = 2, 4, 6, 8) with the following ratio of elements: (14–x)­Yb: xCa: 6 Mn: 11Sb: 86Sn, and their structures determined by single crystal X-ray diffraction. The density of the material significantly decreases by over 2 g/cm3 as more Ca is added (from x = 1 to 8), because of the lighter mass of Ca. The resulting lower density is beneficial from a device manufacturing perspective where there is often a trade-off with the specific power per kilogram. The compounds crystallize in the Ca14AlSb11 structure type. The Ca substitution contributes to systematic lengthening the Mn–Sb bond while shortening the Sb–Sb bond in the 3 atom linear unit with increasing amounts of Ca. Temperature dependent thermoelectric properties, Seebeck, electrical resistivity, and thermal conductivity were measured from room temperature to 1273 K. Substitution of Yb with Ca improves the Seebeck coefficient while decreasing the thermal conductivity, along with decreasing the carrier concentration in this p-type material resulting in an enhanced thermoelectric figure of merit, zT, compared to Yb14MnSb11.高温p型热电材料（p-type thermoelectric material）Yb₁₄MnSb₁₁自2006年首次测得其高温热电性能以来，相关研究关注度持续提升。后续通过将Zn、Al、La引入该结构进行掺杂取代的研究证实，可通过调控载流子浓度或抑制自旋无序散射（spin-disorder scattering），进一步优化该材料的热电性能。本文将报道以等价态Ca²⁺取代Yb²⁺所制备的Yb₁₄₋ₓCaₓMnSb₁₁固溶体（solid solution）系列的相关性能。本研究采用锡助熔剂法（Sn-flux）制备了x取值为2、4、6、8的Yb₁₄₋ₓCaₓMnSb₁₁固溶体系列晶体，所用元素摩尔比为(14–x)Yb : xCa : 6Mn : 11Sb : 86Sn，并通过单晶X射线衍射（single crystal X-ray diffraction）表征了其晶体结构。由于Ca的原子量小于Yb，随着Ca掺杂量从x=1提升至x=8，材料的密度显著降低，降幅超过2 g/cm³。从器件制备的视角来看，更低的密度具备显著优势——因为器件开发中往往需要在单位千克比功率与其他性能间进行权衡。该系列化合物均采用Ca₁₄AlSb₁₁结构型结晶。随着Ca掺杂量的增加，Ca取代会使3原子线性单元中的Mn-Sb键系统性延长，同时缩短Sb-Sb键。研究测试了该材料从室温至1273 K范围内的温度依赖性热电性能，涵盖塞贝克系数（Seebeck coefficient）、电阻率与热导率。相较于原始的Yb₁₄MnSb₁₁材料，以Ca取代Yb可提升该p型材料的塞贝克系数，同时降低热导率与载流子浓度，最终使热电优值（thermoelectric figure of merit）zT得到显著提升。