Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany. Koç University, Rumelifeneri Yolu, Sarıyer, Istanbul 34450, Turkey.
J Phys Condens Matter. 2014 Dec 3;26(48):485801. doi: 10.1088/0953-8984/26/48/485801. Epub 2014 Nov 6.
Polycrystalline samples of the type-I clathrate Ba(8)Ni(x)Ge(46-x-y)□(y) were synthesized for 0.2 ⩽ x ⩽ 3.5 by melt quenching and for 3.5<x ⩽ 6.0 by melting with subsequent annealing at 700 °C. The maximum Ni content in the clathrate framework at this temperature was found to be x ≈ 4.2 atoms per unit cell. Thermoelectric and thermodynamic properties of the type-I clathrate were investigated from 300 to 700 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. As the Ni content increases, the electronic properties gradually evolve from a metallic character (x < 3.5) towards a highly doped semiconducting state (x ⩾ 3.5). Below x ≈ 4.0 transport is dominated by electrons, while further addition of Ni (x ≈ 4.2) switches the electrical conduction to p-type. Maximum value of the dimensionless thermoelectric figure of merit ZT ≈ 0.2 was achieved at 500 K and 650 K for x ≈ 2.0 and x ≈ 3.8, respectively.
I 型笼型化合物 Ba(8)Ni(x)Ge(46-x-y)□(y)的多晶样品通过熔体淬火在 0.2 ⩽ x ⩽ 3.5 范围内合成，在 3.5<x ⩽ 6.0 范围内通过熔融随后在 700°C 下退火合成。在该温度下，笼型骨架中 Ni 的最大含量被发现为 x ≈ 4.2 个原子/单位晶胞。通过电阻、热电势、热导率和比热测量，在 300 至 700 K 的范围内研究了 I 型笼型化合物的热电和热力学性质。随着 Ni 含量的增加，电子性质逐渐从金属特性（x < 3.5）演变为高度掺杂的半导体状态（x ⩾ 3.5）。在 x ≈ 4.0 以下，输运主要由电子主导，而进一步添加 Ni（x ≈ 4.2）将电传导切换为 p 型。在 x ≈ 2.0 和 x ≈ 3.8 时，无量纲热电优值 ZT 的最大值分别在 500 K 和 650 K 时达到约 0.2。
