• K Ahmadi

      Articles written in Bulletin of Materials Science

    • 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.

    • Synthesis and characterization of ZnO/TiO2 composite core/shell nanorod arrays by sol–gel method for organic solar cell applications

      K Ahmadi Ali Abdolahzadeh Ziabari K Mirabbaszadeh A Ahadpour Shal

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      ZnO/TiO2 core/shell nanorod arrays were deposited on indium tin oxide (ITO) substrate via a facile sol–gel dip-coating process. Effects of solution pH for ZnO, annealing temperature, growth time and temperature on the physical properties of nanorods have been investigated. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were employed to characterize the structural and morphological properties of the prepared composite nanorods. XRD result revealed wurtzite structure of ZnO with a mixed anatase and rutile structure phase for TiO2. Energy-dispersive X-ray (EDX) and UV–vis spectroscopy were used to study the chemical composition and optical properties of the films, respectively. Electrical resistivity of the films was also investigated. The optical and electrical properties of the bare TiO2 thin film and core/shell composite were compared together. The results showed that owing to smaller band gap and lower resistivity, the core/shell structure as an electron transport layer for inverted photovoltaic devices is more suitable than bare TiO2 thin film.

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