• Yaseen Iqbal

      Articles written in Bulletin of Materials Science

    • Effect of fluxing additive on sintering temperature, microstructure and properties of BaTiO3

      Yaseen Iqbal Asad Jamal Riaz Ullah M Naeem Khan Rick Ubic

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      Various fluxing materials are added to technical ceramics in an attempt to lower their sintering temperatures and make their processing economical. The effect of 0.3wt%Li2CO3 addition on the phase, microstructure, phase transition temperatures and dielectric properties of BaTiO3 was investigated in the present study. The addition of 0.3wt% Li2CO3 was observed to lower the optimum sintering temperature by ∼200°C with no second phase formation and cause a five-fold reduction in grain size. Rhombohedral-to-orthorhombic and tetragonal-to-cubic phase transitions at the expected temperatures were evident from the Raman spectra, but the orthorhombic-totetragonal phase transition was not clearly discernible. The persistence of various phase(s) at higher temperatures in the flux-added materials indicated that the phase transitions occurred relatively slowly. A decrease in dielectric constant of Li2O-added BaTiO3 in comparison to pure BaTiO3 may be due to the diminished dielectric polarizability of Li+ in comparison to Ba2+.

    • Improvement in the microwave dielectric properties of SrCa4Nb4TiO17 ceramics by Ba substitution

      Abdul Manan Yaseen Iqbal

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      Microwave dielectric ceramics in the Sr1–𝑥Ba𝑥Ca4Nb4TiO17 (0 ≤ 𝑥 ≤ 0.75) composition series were fabricated via a solid-state mixed oxide route. All the compositions formed single phase in Sr1–𝑥Ba𝑥Ca4Nb4TiO17 (0 ≤ 𝑥 ≤ 0.75) solid solutions within the detection limit of in-house X-ray diffraction (XRD). The sintered microstructure of these ceramics comprised densely packed elongated and plate-like grains. The dielectric properties varied linearly with 𝑥. Relative permittivity (𝜀r) increased from 47.2 to 54.5, unloaded quality factor multiplying the resonant frequency (𝑄u 𝑓o) decreased from 11,984 to 9345 GHz and temperature coefficient of resonant frequency (𝜏f) increased from –78.6 to 20 ppm/°C with an increase in x from 0 to 0.75. In the present study, 𝜀r ≈ 51.6, 𝑄u 𝑓o ≈ 10,160 GHz (5.37 GHz) and 𝜏f ≈ –13.5 ppm/°C were achieved for Sr0.5Ba0.5Ca4Nb4TiO17 (𝑥 = 0.5) ceramics.

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      Posted on October 12, 2020

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      Chemical Sciences 2020

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