Oxygen diffusion in YSZ single crystals at relatively low temperatures

Abstract

The 18O tracer experiments were carried out on two cubic YSZ single crystals at temperatures of T D = 423 K and T D = 473 K. The diffusion profiles were determined by the SIMS technique. The diffusion coefficients, the surface exchange coefficients and the activation enthalpy are discussed together with earlier data at higher temperatures. The present oxygen diffusion data demonstrate that the same diffusion process is operating over a wide temperature range.Yttria stabilized zirconia YSZ is a solid electrolyte with applications as solid oxide fuel cells (SOFC), oxygen sensors and oxygen generators [1]. In this work we study the diffusion coefficient and the exchange rate of YSZ cubic single crystals at 423 K and 473 K to extend earlier data to lower temperature. This is of interest for the assessment of the oxygen diffusion process and for the application of SOFC at temperatures below 1000 K [2].Two cubic single crystal ZrO 2 ⋅ 9.5 mol% Y 2 O 3 (Zirmat, North Billeria, MA) specimens were polished on one side with a 1 µm diamond paste to achieve a surface roughness of <10 nm. The size of the specimens was 2 × 2 × 0.5 mm 3 . The polished surfaces of the crystals are parallel to a (100) plane. The diffusion anneals were performed in a 8 cm 3 sealed glass tube at a 10 kPa pressure of 18 O 2 . The glass tube contains 2.4 × 10 -5 mol 18 O 2 . The amount of gas exchange during the diffusion process is approximately 3 × 10 -9 mol. This is negligibly compared to the initial conditions. The diffusion temperatures and times are given in Table 1. The SIMS (secondary ion mass spectroscopy) measurements were performed using a Cameca IMS-6f facility.

Oxygen Isotope Transport Properties of Yttria‐Stabilized Zirconia (YSZ) in O2‐ and H2O‐Containing Atmospheres

“…The activation enthalpy for tracer diffusion calculated from our data is DH D* = (0.94 ± 0.02) eV. Combining our data with those obtained on 9.5 mol.% YSZ from Manning et al [12] and from Röwer et al [13], we obtain a global expression for the temperature range of Figure 6 shows the surface exchange coefficients k* of the single crystals YSZ as a function of inverse temperature. In general our data for pH 2 [19].…”

“…Much effort has been devoted to characterizing bulk transport in O 2 -containing atmospheres [7][8][9][10][11][12][13], and the behavior is relatively well understood. In H 2 O-containing atmospheres YSZ is known to dissolve water according to [14] …”

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 9: Room temperature

“…5, while the upper limit corresponds to D chem . Figure 5 also shows the oxygen tracer diffusion data for YSZ reported by Kilo et al 11 and Rower et al 12 Of course, the lower limit of bar 2, corresponding to D T , should be used for comparison between the two sets of data (the real value of D T will be somewhere between the values represented by the limits of the bar, since the accelerating effect due to the low concentration of electronic charge carriers in YSZ is lower than that predicted by theory). As can be seen from Fig.…”

A brief review of the ionic conductivity enhancement for selected oxide electrolytes

“…It has been widely reported that impurities such as silica greatly decrease the grain-boundary conductivity in zirconia and ceria [57,61,[63][64][65][66]. Badwal and Rajendran found that the addition of only 0.2 wt.% silica was sufficient to decrease the grain-boundary conductivity of YSZ by a factor greater than 15 [65].…”

“…Therefore, eliminating the effect of impurities on the grain boundary can benefit the ionic conductivity of the electrolyte. A number of strategies have been suggested to control the silica-rich grain boundary, including specialized heat treatments, the application of pressure, and various additives [57,61,[63][64][65][66].…”