School of Engineering Sciences and Technology

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Browsing School of Engineering Sciences and Technology by Author "Alam, Mahfooz"
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    High-frequency dielectric characterization of novel lead-free ferroelectrics
    ( 2020-11-01) Sreenu, Gomasu ; Alam, Mahfooz ; Fasquelle, Didier ; Das, Dibakar
    Novel lead-free BFO–STO, BFO–CTO, and BFO–BZO ceramics were fabricated by the conventional method and their structural, microstructural, and dielectric properties were characterized. Dielectric measurements were carried out at room temperature in a large frequency range, from 20 Hz to 1.8 GHz. XRD analysis has demonstrated differences in the crystalline structure of the samples. BFO–STO exhibits a very different behavior compared to BFO–CTO and BFO–BZO ceramics because its XRD pattern contains peaks from diffracting planes of BFO and STO simultaneously. In comparison, the diffraction patterns of BFO–BZO and BFO–CTO are dominated by the peaks from diffracting planes of BZO and CTO, respectively. SEM observation has also revealed important differences in their microstructure. BFO–BZO and BFO–CTO have presented similar values of dielectric constant at low and high frequencies, ε′ ~ 85 from 1 to 100 MHz. The lowest value of the loss tangent was measured on BFO–CTO with tan δ = 5 × 10–3 at f = 50 MHz. The BFO–STO ceramic has given higher values of the dielectric constant, closer to those reported for the bulk STO. Nearly frequency-independent high dielectric constant with very low loss over a broad frequency range (20 Hz to 1.8 GHz) of BFO–STO ceramic makes this material a potential candidate for high-temperature and high-frequency application with superior energy performance.
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    Influence of synthesis methods on structural, piezoelectric, ferroelectric and mechanical properties of lead-free K < inf > 0.5 < /inf > Na < inf > 0.5 < /inf > NbO < inf > 3 < /inf > (KNN) ceramics
    ( 2020-11-05) Alam, Mahfooz ; Khilari, Sukhamoy ; Jai Shree, K. ; Das, Dibakar
    In this work lead free perovskite ferroelectric ceramics, K0.5Na0.5NbO3 (KNN), has been synthesized by two different methods, conventional solid state (SS) and co-precipitation (CPP), from the same starting materials, Nb2O5, Na2CO3 and K2CO3 and their properties have been compared. Double calcination, 700 °C for 7h followed by 850 °C for 6h, of the co-precipitation precursor resulted in single phase perovskite structure (JCPDS card No. 01-077-0038), whereas for solid state precursor a triple calcination, 850 °C for 5h, 1000 °C for 5h followed by 1050 °C for 5h, ended up with producing the cubic perovskite KNN phase. Both samples were sintered at 1120 °C for 2h under atmospheric condition in a muffle furnace. FESEM is used to find the microstructural features. Energy dispersive X-ray spectroscopy is used to confirm the chemical composition of the samples. Evolution of the phase structure and variation in Curie temperature, dielectric constant, piezoelectric voltage coefficient (g33), piezoelectric charge coefficient (d33) as well as mechanical properties such as hardness, stiffnesshave been studied and compared for the KNN samples prepared by two different synthesis methods.
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    Synthesis and characterization for mechanical and electrical properties of lead-free sodium bismuth titanate (Na < inf > 0.5 < /inf > Bi < inf > 0.5 < /inf > TiO < inf > 3 < /inf > ) ceramics
    ( 2020-11-05) Khilari, Sukhamoy ; Alam, Mahfooz ; Jai Shree, K. ; Das, Dibakar
    Lead-free Sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) ferroelectric ceramic was prepared by conventional solid state reaction method. Microstructural, dielectric and mechanical properties were explored. Single perovskite phase is revealed by XRD. Homogeneously compacted microstructure with square shape grain morphology is observed inFESEM. The depolarization temperature and Curie temperature have been found as 160°C and 265°C respectively.The transition of phases from ferroelectric to relaxor ferroelectric occurs at 220°C.Piezoelectric charge coefficient (d33) ofthe sintered sample is 75 pC/N.The hardness value of 706 HV was measured by Vickers Hardness Tester. Nanoindentation test shows the stiffness and hardness of the sintered sample as 922 µN/nm and 2.59 GPa respectively.