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Tham khảo tài liệu 'ferroelectrics physical effects part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 350 Ferroelectrics - Physical Effects A HITACHI S2600N scanning electron microscope SEM coupled with EDX was used to analyze the ceramics microstructure. The solid-oxide electrolyte galvanic cells method was employed to obtain the thermodynamic properties of the samples. As shown in previous papers Tanasescu 1998 2003 2009 the thermodynamic stability limits of the ABOs-s perovskite-type oxides are conveniently situated within the range of oxygen chemical potentials that can be measured using galvanic cells containing 12.84 wt. yttria stabilized zirconia solid electrolyte and an iron-wustite reference electrode. The design of the apparatus as well as the theoretical and experimental considerations related to the applied method was previously described Tanasescu 1998 2011 . The measurements were performed in two principal different ways Under the open circuit conditions keeping constant all the intensive parameters when the electromotive force EMF measurements give information about the change in the Gibbs free energy for the virtual cell reaction. The EMF measurements were performed in vacuum at a residual gas pressure of 10-7 atm. The free energy change of the cell is given by the expression AG cell u. u . 4FE 1 where E is the steady state EMF of the cell in volts uO2 uO2 f are respectively the oxygen chemical potentials of the sample and the reference electrode and F is the Faraday constant F 96.508 kJ V equiv. . By using the experimental values of the electromotive force of the cell and knowing the free energy change of the reference electrode Charette 1968 Kelley 1960 1961 the values of the relative partial molar free energy of the solution of oxygen in the perovskite phase and hence the pressures of oxygen in equilibrium with the solid can be calculated ago2 RTln Po2 2 The relative partial molar enthalpies and entropies were obtained according to the known relationships Tanasescu 1998 2011 AGO2 d T AH O2 dT T2 3 AGo2 AHo2 - TASo2 4 The overall uncertainty due .
