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    Functionally graded Al2O3-based ceramic systems by gel casting method
    (Wiley, 2024) Topates, Gulsum; Akca, Erdem; Tur, Yahya Kemal; Duran, Cihangir
    Functionally graded ceramic systems consisted of Al2O3/(Al2O3-ZrO2) and Al2O3/(Al2O3-Nd2Ti2O7) have been produced by gel casting. In Al2O3/ZrO2 systems, Al2O3 was gathered with three different Al2O3/ZrO2 mixtures with varying ZrO2 contents. For Al2O3/Nd2Ti2O7 system, Al2O3 layer was combined with 3 mol% Nd2Ti2O7-doped Al2O3. All samples sintered at 1480 and 1540 degrees C showed strong adhesion between layers without any crack formation. In the Al2O3/ZrO2 systems, both layers were intact; a distinct separation was observed, whereas a large reaction zone was observed for the Al2O3/Nd2Ti2O7 system as a consequence of reaction between both phases. The separation between layers for both systems was identified by SEM-EDX analyses. The hardness and wear tests of the samples showed that functional grading approach ensures combining various physical properties in a monolithic body.
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    Processing and characterization of < 001 >-textured Pb(Mg1/3Nb2/3)O-3-Pb(Yb1/2Nb1/2)O-3-PbTiO3 ceramics
    (CAMBRIDGE UNIV PRESS, 2017) Duran, Cihangir; Cengiz, Salih; Ecebas, Nazim; Dursun, Sinan; Akca, Erdem
    0.62[0.75(Pb(Mg1/3Nb2/3)O-3)-0.25(Pb(Yb1/2Nb1/2)O-3)]-0.38(PbTiO3) ceramics were successfully textured in [001] via the template grain growth method using 1-7 vol% platelike BaTiO3 (BT) templated (the Lotgering factor of 0.91 at 5 vol% BT). Dielectric spectra indicated a normal ferroelectric behavior without any frequency dispersion and no low-temperature phase transition. The chemically stable BT phase within the matrix gave rise to a composite effect and its relatively inferior properties affected the dielectric and electromechanical properties. The lower T-C of the BT decreased the Curie temperature from 226 to 213 degrees C (with a depolarization temperature of 204 degrees C). Significantly higher levels of strain (0.33%), narrower hysteresis level (7.7%), higher piezoelectric strain coefficient (660 pm/V), and low-field (<5 kV/cm) piezoelectric strain coefficient (1340 pm/V) at 50 kV/cm were achieved at 5 vol% BT addition. These results are very promising for the fabrication of high performance transducer and actuator applications without severe temperature limitations.
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    The role of Nb2O5 polymorphs on processing-structure-property relationship in lead-based perovskite 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 piezoceramics
    (Elsevier Sci Ltd, 2021) Akca, Erdem; Unveroglu, Begum; Tatar, Istek; Duran, Cihangir
    Lead-based niobate piezoceramics with perovskite structure exhibit a wide range of superior dielectric and electromechanical properties and hence are commonly used for potential commercial applications. However, the effect of Nb2O5 with various polymorphs on structure and properties of the lead-based perovskite niobates has not been studied in literature. The aim of this study was to investigate the influence of Nb2O5 with various polymorphs on the processing-structure-property relationship in lead-based perovskite 0.5Pb(Yb1/2Nb1/2)O-3-0.5PbTiO(3) (PYNT) piezoceramics. The polymorphic state of Nb2O5 source dramatically affected densification, phase formation and microstructure evolution of the PYNT ceramics fabricated by applying closely controlled processing routes. Dense and pyrochlore-free PYNT ceramics with a minor amount of residual PbO were produced after sintering at 1100 degrees C for 1 h with using 3 g atmosphere powder. Raman spectroscopy revealed that the PYNT ceramic produced using orthorhombic Nb2O5 had the most homogeneous cation ordering at the B-site as well as the least amount of the unknown phase caused by the Yb/Nb mixed compound, which resulted in up to 17% improvement in the piezoelectric and electromechanical properties with respect to the one produced using a mixture of orthorhombic and monoclinic Nb2O5 . Therefore, care must be taken with initial powder characteristics, especially the crystalline structure of Nb2O5 , for the sake of the fabrication of perovskite lead-based niobates with reproducible as well as enhanced properties.