ECI Digital Archives

Title

Pressure-induced defects in zirconates

Authors

Hitoshi Takamura, Department of Materials Science, Graduate School of Engineering, Tohoku UniversityFollow
Yushi Ohno, Department of Materials Science, Graduate School of Engineering, Tohoku University
Kazutoshi Nakajima, Department of Materials Science, Graduate School of Engineering, Tohoku University
Akimitsu Ota, Department of Materials Science, Graduate School of Engineering, Tohoku University
Itaru Oikawa, Department of Materials Science, Graduate School of Engineering, Tohoku University

Conference Dates

September 4-8, 2016

Abstract

Defects, e.g. vacancies and interstitials, play an important role on the physical properties of oxides, especially on their ionic transport. Those defects in oxides are generally controlled and analyzed as functions of dopant concentration, c, temperature, T, and oxygen chemical potential, _O2, but not of total pressure, P. This is not surprising given that a molar volume, V_m, of solids is much smaller than that of gas phase by a factor of ≈1/1000. Meanwhile, under high pressure such as several GPa, the effect of total pressure on free energy, i.e. V_mP, reaches 20~100 kJ/mol, which is high enough to affect the defect formation and migration in solids. In fact, pressure-induced phenomena are recently of great interest in solid state ionics. In this study, we focus on the pressure effects on the defect formation in some stabilized ZrO₂ and acceptor-doped BaZrO₃.

For Y-stabilized ZrO₂, reduction was found to be enhanced under high pressure. Figure 1 shows the lattice constant of 8YSZ electrochemically reduced under high pressure as a function of oxygen deficiency introduced. Under high pressure such as 1 to 6 GPa, 8YSZ was easily reduced even at 3V_DC at 500°C. The oxygen deficiency reaches  = 0.05. Unlike reduced CeO₂ which shows lattice expansion, the reduced 8YSZ shows 0.5% smaller lattice constant. The lattice shrinkage was also confirmed by DFT calculations. This supports that applying high pressure, which in general enhances a reaction with negative volume change, enhances the reducing reaction of cubic ZrO₂. Figure 2 shows the temperature dependence of electrical conductivity of reduced 8YSZ. The reduced 8YSZ appears to show mixed ionic and electronic conduction; major carrier is electrons. Acceptor-doped BaZrO₃ was also subjected to high pressure on the order of GPa. Their defect equilibrium and proton conductivity will be also discussed.

Please click Additional Files below to see the full abstract.

Recommended Citation

Hitoshi Takamura, Yushi Ohno, Kazutoshi Nakajima, Akimitsu Ota, and Itaru Oikawa, "Pressure-induced defects in zirconates" in "Nonstoichiometric Compounds VI", ECI Symposium Series, (2016). https://dc.engconfintl.org/nonstoichiometric_vi/19