Development of next generation Peltier materials by means of misfit-layered sulfides

为了设计新型的Peltier材料，我们致力于制备能同时实现大的热电功率因数和低的晶格热导率的错配层状硫化物[Ln_2S_2]_PTS_2(Ln：稀土离子，T：过渡金属离子)。首先，探索了一种制备新型p型材料的T=Nb体系。除Ln=Eu和Lu外，包括Y在内的所有稀土离子都形成了[Ln_2S_2]_PNBS_2相。根据离子半径的不同，发现了三种具有不同超空间群的结构。含Ln=La、Ce和Pr的较大离子形成正交的Fm2m(P00)00s，而含Ln=Nd和Sm的样品形成Fm2m(P00)000。对于Ln=Gd，Tb，Dy，Ho，Er，Tm，Yb和Y的小离子，得到了单斜晶系的F2(P0q)相。含Ln=Yb的样品具有最高的热电优值系数Z=3.2x10^-4；K^-1；，在300K附近，塞贝克系数S=60μVk^-1；-1，电阻率ρ=1.4mΩcm，κ=0.80WK^&1；-1&gt；，得到尺寸…。更多的S功绩系数ZT~0.1。Z值仍随温度升高而增加，但Z值的最大值以及可利用的最高极限温度并未详细确定。接下来，我们用Yb-Nb-S化合物作为p型桥臂，以锡-钛-S化合物作为n型桥臂，制作了热电pn结(1对)。用银浆将其固定在铝片上，然后对其进行Peltier性能测量。在开始时，实际上观察到了几个开尔文之间的小温差，但随着电流的进一步施加，温差变得很小，并达到零。这可以归因于两腿的塞贝克系数不足以继续产生温差(~70μvk^&lt；-1&gt；)，因为产生的焦耳热很容易克服温差。因此，有必要进一步研究设计具有更大优值系数的硫化物热电材料。较少

We have focused on preparing misfit-layered sulfides [Ln_2S_2]_pTS_2 (Ln:lanthanide ions, T:transition metal ions), in which a large thermoelectric power factor and a low lattice thermal conductivity can be simultaneously realized, to design novel Peltier materials. First of all, a T=Nb system has been explored to prepare new p-type materials. Except for Ln=Eu and Lu, all the lanthanides ions including Y are found to form [Ln_2S_2]_pNbS_2 phases. Three-types of structure with different superspace group are discovered depending on their ionic radii. Larger ions with Ln=La,Ce and Pr form orthorhombic Fm2m(p00)00s, while the samples with Ln=Nd and Sm form Fm2m(p00)000. For smaller ions with Ln=Gd,Tb,Dy,Ho,Er,Tm,Yb and Y, monoclinic F2(p0q) phases are obtained. The sample with Ln=Yb exhibits the highest thermoelectric figure-of-merit Z=3.2 x 10^<-4> K^<-1>, with the Seebeck coefficient S=60μVK^<-1>, resistivity ρ=1.4 mΩcm and κ=0.80 WK^<-1>m^<-1>, at around 300 K, yielding the dimensionles … More s figure-of-merit ZT〜0.1. The Z value still increases with increasing temperature, but the maximum value of Z as well as the highest limit temperature to be utilized are not determined in detail. Next, we have fabricated a thermoelectric pn junction (1 pair) using a Yb-Nb-S compound as a p-type leg and a Sn-Ti-S compound as an n-type leg. The pn uncouple was attached to an Al sheet on its top with silver paste and then was subjected to the Peltier property measurements. At the beginning, a small temperature difference with several kelvin was in fact observed but the difference became small and reached zero with further applying an electric current. This behavior can be ascribed to the fact that the Seebeck coefficient of the both legs was not enough (〜70μVK^<-1>) to keep generating temperature difference because the generated Joule heat easily overcame the temperature difference. Hence, further study is necessary to design sulfide thermoelectric materials which have larger figure-of-merit. Less