• G Kavei

      Articles written in Bulletin of Materials Science

    • Fabrication and characterization of the 𝑝-type (Bi2Te3)𝑥(Sb2Te3)1–𝑥 thermoelectric crystals prepared via zone melting

      G Kavei M A Karami

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      In the present study, 𝑝-type (Bi2Te3)𝑥(Sb2Te3)1–𝑥 crystals with various chemical compositions (𝑥 = 0.2, 0.22, 0.235, 0.25, 0.265, 0.28 and 0.3) were fabricated through the zone melting method. Thermoelectric properties, including Seebeck coefficient (𝛼), electrical conductivity (𝜎), thermal conductivity (𝜅) and Hall constants, were measured at room temperature, 300 K. The influence of the variations of Bi2Te3 content (𝑥) on the thermoelectric properties was studied. The increase of Bi2Te3 content (𝑥) caused a decrease in (carrier) hole concentration and thus a decrease of 𝜎 and an increase of 𝛼. The maximum figure of merit (𝑍 = 𝛼2\𝜎/𝜅) of 2.7 × 10-3 K-1 was obtained at about 300 K for the composition of 25% Bi2Te3–75% Sb2Te3 with 3wt% excess of Te.

    • Hot pressing effect on (Bi0.25Sb0.75)2Te3 mechanical and thermoelectric properties

      G Kavei K Ahmadi A Seyyedi

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      (Bi0.25Sb0.75)2Te3 thermoelectric material is a well known 𝑝 type of compound that has higher figure of merit than other stoichiometries. The crystal of this compound was prepared, pulverized in a particle size ratio of 64% with a mesh of 80 (200 𝜇m2) and 36% with a mesh of 60 (250 𝜇m2). The powder was sintered in a heat up to 350–500°C under pressure of 500 MPa (hot pressing). To find out the temperature effects on thermal conductivity of the sample it was systematically investigated in nano-scale intrinsic structures by systems of X-ray diffraction, scanning electron microscopy and, for only once successful attempt, atomic force microscopy. The acquired images ensured to show homogeneous structures for hot pressed samples. In terms of thermal conductivity and with regard to the figure of merit (𝑍), optimum sintering temperature hovers at around 500°C, which leads to a maximum 𝑍 value of around 1.53 K-1.

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