Browsing by Author "Cancarevic, Marija"

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    Thermodynamic optimization of the PbO-ZrO2-TiO2 (PZT) system and its application to the processing of composites of PZT ceramics and copper
    (2007) Cancarevic, Marija; Aldinger, Fritz (Prof. Dr. rer. nat.)
    PbZrxTi1-xO3 (PZT) or modified PZT solid solutions are of great interest for technological applications, which result from their piezoelectric, ferroelectric and pyroelectric properties. Although extensive experimental studies of the PZT system have been carried out in the past little attention was paid to phase equilibria and thermodynamics of the system Pb-Zr-Ti-O, which are important for the optimization of manufacturing and sintering conditions of the PZT ceramics as well as for tailoring their physical properties. In view of using copper for conductor lines in hybrid systems the compatibility between Cu and PZT become of special interest which requires an understanding also the multicomponent Cu-Pb-Zr-Ti-O system. The aim of this thesis was to obtain a consistent set of thermodynamic data for the Cu-Pb-Zr-Ti-O system, by means of the CALPHAD method, and then to calculate phase equlibria and chemical potential diagrams, which are relevant to the processing of actuators based on PZT ceramics and copper. The thermodynamic properties were described using the compound energy formalism (CEF) as well as the substitutional solution model for various solid phases and the associate model for the liquid phase, while the Redlich-Kister series were used to account for the interactions between species. Associate solution model adopted for the description of the liquid phase in the multicomponent Cu-Pb-Zr-Ti-O system was found to be superior for calculating the relevant phase equilibria in comparison with the two-sublattice ionic model, although both models can be successfully applied to the binary systems (Zr-O, Ti-O, Cu-O, Pb-O). The ternary Cu-Pb-O, Cu-Ti-O and Cu-Zr-O systems were assessed for the first time. The binary Cu-O and Pb-O systems were taken from literature with some modifications of the Pb-O system in the liquid phase region, while the binary Ti-O system was completely reassessed in the present work. The ternary Cu-Pb-O system shows a large liquid miscibility gap of peculiar shape, which connects to the miscibility gaps in each of the binary sub-systems. The ternary compound Cu2PbO2 was modelled as a stoichiometric compound. Its thermodynamic properties were estimated by experiments. In the modelling of the ternary Cu-Ti-O system the three ternary compounds, Cu3Ti3O, Cu2Ti4O and Cu3TiO4 were taken as stoichiometric compounds. In the Cu-Zr-O system the literature data show no existence of ternary compounds and it was experimentally proved in this work. The quasibinary PbO-ZrO2, PbO-TiO2 and ZrO2-TiO2 systems, the edges of the quasiternary PbO-ZrO2-TiO2 (PZT) system, were reassessed on the basis of most recent literature data. Thermodynamic properties of the end-members, ZrO2 and PbO have been taken from the literature, while those of TiO2 were evaluated in the present work. Due to limited experimental information, PbTiO3 (tetragonal and cubic forms) and PbZrO3 (cubic form) were considered as stoichiometric compounds in the PbO-TiO2 and PbO-ZrO2 systems, while the tetragonal and orthorhombic PbO solid solutions were described by a substitutional model. The perovskite solid solution series, PbZrxTi1-xO3 was modelled as high temperature cubic form using the substitutional model. Calculated phase diagrams, i.e., predicted phase relations in the multicomponent Cu-Pb-Zr-Ti-O system (isobaric-isothermal sections and chemical potential diagrams) were checked experimentally. Experimental points were chosen based on CALPHAD approach and all compositions were prepared by solid state reaction. For the verification of the phase relations and invariant reactions in the oxide rich part (Cu2O-CuO-PbO-TiO2 and Cu2O-CuO-PbO-ZrO2 isotherms) experiments were done in air. The investigation of the reactivity between Cu and PbTiO3, PbZrO3 or PZT in the solid state was performed at the carefully controlled partial pressure of oxygen using different kinds of buffers (Ni/NiO, Cu/Cu2O) at 1073 and 1173 K. Microstructural characterization of the samples was done by X-ray, DTA, SEM and EDX analysis. The database evaluated in this thesis is reliable for extrapolating calculations in the oxygen-rich part of the multicomponent Cu-Pb-Zr-Ti-O system, i.e., in the PbO-ZrO2-TiO2, Cu2O-CuO-PbO-ZrO2, Cu2O-CuO-PbO-TiO2 and Cu2O-CuO-ZrO2-TiO2 sub-systems. In addition, it can be used for prediction of reactions between metals and oxides, i.e. between Cu and PZT ceramics (Cu-PbO-ZrO2-TiO2 system), for which purpose it was mainly developed, but not for calculations in the Cu-Pb-Zr-Ti system and corresponding subsystems. The phase diagrams of the multicomponent Cu-Pb-Zr-Ti-O system calculated in this thesis were found to be well consistent with the experimentally obtained results, which clearly show the chemical stability of copper and PZT ceramic at temperatures below 1273 K in reducing atmosphere. The reactivity between copper and PbTiO3, PbZrO3 or PbZrxTi1-xO3 (x=0.44, 0.5) was not observed using the characterization methods applied in this work. Detailed investigation of the feasibility of using copper in piezoelectric actuators based on PZT solid solutions requires the application of additional characterization methods such as measurements of electrical and polarization properties. In addition, detailed investigation of the kinetics of PbO evaporation seems to be of fundamental importance in optimization of the processing conditions (temperature and time) for PZT-based ceramics.