Effects of Ge Doping on Micromorphology of MnSi in MnSi∼ 1.7 and on Their Thermoelectric Transport Properties

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MnSi layers in Ge-doped MnSi∼ 1.7 increased with increasing Ge content up to $x=0.00133$, began to break at $x=0.00265$ and finally disappeared at $x=0.00530$. An experimental equation for the growth of MnSi was proposed for the interval between the MnSi layers and amount of doped Ge content. The crystallinity of Ge-doped MnSi∼ 1.7 increased initially with increasing doped Ge content and saturated at high Ge content. Thermoelectric transport properties along the $c$-axis of Ge-doped MnSi∼ 1.7 were measured as a function of Ge content at room temperature. Electrical conductivity and thermoelectric power of Ge-doped MnSi∼ 1.7 were compared to those of Al-doped MnSi∼ 1.7 in our previous work. A maximum in the electrical conductivity and a minimum in the thermoelectric power of Ge-doped MnSi∼ 1.7 were observed at $x=0.00133$, reflecting a change in hole density which was influenced by the volume ratio of MnSi. Hole mobility depended on the existence of MnSi layers and/or of interfaces between MnSi∼ 1.7 and MnSi and on the crystallinity of MnSi∼ 1.7. The thermal conductivity of Ge-doped MnSi∼ 1.7 had a maximum at $x=0.00053$. The increase in thermal conductivity at low Ge doping can be explained by the increase in the amount of MnSi segregated in doped MnSi∼ 1.7, while the decrease at high Ge content was caused by the increase in phonon scattering of Ge. A maximum figure of merit of Ge-doped MnSi∼ 1.7 was obtained at $x=0.00974$, reflecting a maximum power factor.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2005-12-15

Effects of Ge Doping on Micromorphology of MnSi in MnSi∼ 1.7 and on Their Thermoelectric Transport Properties

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