Sains Malaysiana 47(1)(2018): 181–187

http://dx.doi.org/10.17576/jsm-2018-4701-21

Enhancement of Thermoelectric Properties of Yb_0.25Co₄Sb₁₂ Skutterudites through Ni Substitution

(Peningkatan Sifat Termoelektrik bagi Bahan Skuterudit Yb_0.25Co₄Sb₁₂ melalui Penggantian Ni)

MOHAMED BASHIR ALI BASHIR¹, SUHANA MOHD SAID^2*, MOHD FAIZUL MOHD SABRI², YUZURU MIYAZAKI³, DHAFER ABDUL AMEER SHNAWAH², MASANORI SHIMADA³ & MOHAMED HAMID ELSHEIKH⁴

¹Department of Mechanical Engineering, Faculty of Engineering, Eldaein University, 63312 Eldaein, Sudan

²University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

³Tohoku University, 2 Chome-1-1 Katahira, Aoba Ward, Sendai, Miyagi Prefecture 980-8577, Japan

⁴R&D, Cree Inc., Durham, NC 27703, USA

Received: 28 November 2016/Accepted: 9 June 2017

ABSTRACT

In this work, we investigate the effects of Ni doping on the thermoelectric (TE) properties of Yb_0.25Co₄Sb₁₂ sample. Yb_0.25Co_4-xN_ixSb₁₂ (0 ≤ x ≤ 0.5) samples were prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The morphology of consolidated samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The thermoelectric properties of bulk samples were measured from room temperature to 800 K. The XRD analysis confirmed that, the successful formation of the Co₄Sb₁₂ skutterudite phase and Ni is substituted into Co site of the skutterudite crystal lattice. Moreover, the electrical resistivity decreased to 14.6 μΩm at 785 K for Yb_0.25Co_3.5Ni_0.5Sb₁₂ sample, due to increase of the electron concentration by Ni-addition. The absolute Seebeck coefficient reached the highest value of 223 μV/K at 592 K for Yb_0.25Co_3.7Ni_0.3Sb₁₂ sample, thus yielding a maximum value of power factor of 2.41 × 10_-3 W/mK₂ at 592 K. The highest dimensionless thermoelectric figure of merit value ZT of 0.49 at 692 K has been achieved for the Yb_0.25Co_3.7Ni_0.3Sb₁₂ sample, compared to ZT=0.06 for the Yb_0.25Co₄Sb₁₂ sample at same temperature. This work indicates a strategy to improve the thermoelectric performance by Ni substitution of Co sites in the Yb_0.25Co₄Sb₁₂ skutterudite through simultaneous improvement of its electrical conductivity, Seebeck coefficient and reduction of its thermal conductivity.

Keywords: Mechanical alloying; Ni-doping; skutterudite; thermoelectric

ABSTRAK

Dalam kajian ini, kesan pendopan Ni ke atas sifat Yb_0.25Co₄Sb₁₂ telah dikaji. Sampel Yb_0.25Co_4-xNixSb₁₂ (0 ≤ x ≤ 0.5) telah disediakan dengan kaedah pengaloian mekanikal dan seterusnya digabungkan dengan pensinteran pencucuh plasma. Morfologi untuk sampel gabungan telah dicirikan oleh pembelauan sinar-X (XRD) dan imbasan mikroskop elektron berserta tenaga serakan X-ray spektroskopi (SEM-EDS). Ciri termoelektrik sampel telah diukur daripada suhu bilik ke 800 K. Analisis XRD mengesahkan bahawa Ni berjaya didopkan ke dalam Yb_0.25Co_4-xN_ixSb₁₂ CoSb₃ dalam fasa skutterudite, dengan Ni menggantikan beberapa lokasi Co dalam kekisi kristal skuterudit. Selain itu, kerintangan elektrik menurun kepada 14.6 μΩm di 785 K bagi sampel Yb_0.25Co_3.5Ni_0.5Sb₁₂, disebabkan oleh peningkatan bilangan pembawa cas elektron oleh Ni. Pekali Seebeck mutlak mencapai nilai tertinggi 223 μV/K pada 592 K bagi sampel Yb_0.25Co_3.7Ni_0.3Sb₁₂ , lalu menghasilkan nilai maksimum faktor kuasa 2.41 × 10_-3 W/MK2 pada 592 K. Angka merit, ZT yang optimum adalah 0.49 pada 692 K telah dicapai untuk sampel Yb_0.25Co_3.7Ni_0.3Sb₁₂. Kajian ini menunjukkan strategi untuk meningkatkan prestasi termoelektrik melalui penggantian Ni pada bahagian Co dalam bahan skutterudite Yb_0.25Co₄Sb₁₂, sekaligus menambahbaik kekonduksian elektrik, pekali Seebeck dan pengurangan kekonduksian haba.

Kata kunci: Ni-dop; pengaloian mekanikal; skuterudit; termoelektrik

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*Corresponding author; email: smsaid@um.edu.my