Övgü Ceyda Yelgel

N- ve P-tip Katkılı Mg2Si1-xSnx Katı alaşımlarının termal iletkenliklerinin teorik calışması

Mg2Si1-xSnx katı alaşımları yüksek termoelektrik verimlilikleri sebebiyle 500 K’den 800 K’e kadar olan orta sıcaklılık aralığı için umut vaadeden termoelektrik materyallerdir. Bu çalışmada hem n- hem p-tip katkılı Mg2Si1-xSnx katı alaşımlarının termal iletkenlikleri teorik olarak detaylıca incelenmesi sunulmuştur. Taşıyıcılardan (elektronlar yada holler), elektron-hole çiftlerinden ve fononlardan kaynaklanan termal iletkenlik katkıları ayrı ayrı göz önüne alınarak ve sırasıyla Wiedeman-Franz kanunu, Price’in teorisi, ve Debye’nin izotropik sürekli modeli uygulanarak hesaplanmıştır. Bütün fonon çarpışma mekanizmaları, kaynağı kristal sınırlarından, kütle bozukluklarından, bozunum potansiyellerinden ve anharmoniklikten olan katı alaşımların hepsi için eksiksiz bir şekilde incelenmiştir. En düşük toplam termal iletkenlik değerleri n-tip katkılı Mg2(Si0.4Sn0.6)0.98Bi0.02 katı alaşım için 700 K’de 2.431 WK-1m-1 olarak, p-tip katkılı Mg2(Si0.3Sn0.7)0.95Ga0.05 katı alaşım için 600 K’de 1.843 WK-1m-1 olarak bulunmuştur buda açıkca öneriyor ki p-tip katkılı Mg2Si1-xSnx tabanlı katı alaşımlar n-tip katkılı katı alaşımlarından termoelektrik cihazlar için daha iyi adaylardır.

Anahtar Kelimeler:

termoelektrik materyaller, termal iletkenlik, fonon termal iletkenlik

Theoretical Study of Thermal Conductivities of n- and p-type Doped Mg2Si1-xSnx Thermoelectric Solid Solutions

Mg2Si1-xSnx solid solutions are a promising class of thermoelectric materials due to their high thermoelectric efficiencies at intermediate temperature range from 500 K to 800 K. Present study presents a theoretical work of the thermal conductivities of both n- and p-type doped Mg2Si1-xSnx solid solutions. The thermal conductivity contributions arising from carriers (electrons or holes), electron-hole pairs, and phonons are taken into account separately by employing the Wiedemann-Franz law, Price's theory, and Debye's isotropic continuum model, respectively. All phonon scattering mechanisms originate from crystal boundaries, mass-defects, deformation potentials, and anharmonicity are investigated rigorously for all solid solutions. The lowest total thermal conductivity values are obtained as 2.431 WK-1m-1 at 700 K for n-type doped Mg2(Si0.4Sn0.6)0.98Bi0.02 solid solution and 1.843 WK-1m-1 at 600 K for p-type doped Mg2(Si0.3Sn0.7)0.95Ga0.05 solid solution which clearly suggest that p-type doped Mg2Si1-xSnx based solid solutions are better candidates for the thermoelectric devices than their n-type doped solid solutions.

Keywords:

thermoelectric materials, thermal conductivity, phonon thermal conductivity,

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