Zirconia solid-state diffusion

Historically, stabilized (and partially stabilized) zirconia ceramics were prepared from powders in which the component oxides are mechanically blended prior to forming and sintering. Because solid state diffusion is sluggish, firing temperatures in excess of 1800°C are normally required. Furthermore, the dopant was nonuniformly distributed, leading to inferior electrical properties. Trace impurities in the raw materials can also lead to enhancement of electronic conductivity in certain temperature ranges, which is also undesirable. To overcome these problems, several procedures have been developed to prepare reactive (small particle size) and chemically pure and homogeneous precursor powders for both fully stabilized and partially stabilized material. Two of these are alkoxide synthesis and hydroxide coprecipitation. 

A number of oxides with the fluorite structure are used in solid-state electrochemical systems. They have formulas A02 xCaO or A02 xM203, where A is typically Zr, Hf, and Th, and M is usually La, Sm, Y, Yb, or Sc. Calcia-stabilized zirconia, ZrC)2.xCaO, typifies the group. The technological importance of these materials lies in the fact that they are fast ion conductors for oxygen ions at moderate temperatures and are stable to high temperatures. This property is enhanced by the fact that there is negligible cation diffusion or electronic conductivity in these materials, which makes them ideal for use in a diverse variety of batteries and sensors. 

Horita, T., Yamaji, K., Sakai, N., Yokokawa, H., Kawada, T., Kato, T. Oxygen reduction sites and diffusion paths at Lao <>Sro iMnO j x/yttria-stabilizcd zirconia interface for different cathodic overvoltages by secondary-ion mass spectrometry. Solid State Ionics 2000,127, 55-65. 

S. Dou, C.R. Masson and P.D. Pacey, Chemical diffusion in calcia-stabilized zirconia ceramic. Solid State Ionics, 18/19 (1986) 736-740. 

Although the emphasis here will, by necessity, be placed on more recent data, several key reviews of transport in nanocrystalline ionic materials have been presented, the details of which will be outlined first. An international workshop on interfacially controlled functional materials was conducted in 2000, the proceedings of which were published in the journal Solid State Ionics (Volume 131), focusing on the topic of atomic transport. In this issue, Maier [29] considered point defect thermodynamics and particle size, and Tuller [239] critically reviewed the available transport data for three oxides, namely cubic zirconia, ceria, and titania. Subsequently, in 2003, Heitjans and Indris [210] reviewed the diffusion and ionic conductivity data in nanoionics, and included some useful tabulations of data. A review of nanocrystalline ceria and zirconia electrolytes was recently published [240], as have extensive reviews of the mechanical behavior (hardness and plasticity) of both metals and ceramics [13, 234]. 

Poulsen, F. W. (2000). Defect chemistry modelling of oxygen stoichiometry, vacancy concentrations, and conductivity of (Lai xSrx)j,Mn03+j. Solid State Ionics 129 143-162. Mizusaki,., Saito, T., and Tagawa, H. (1996). A chemical diffusion-controlled electrode reaction at the compact Lai- Sr MnOa-stabilized zirconia interface in oxygen atmospheres. J. Electrochem. Soc. 143 3063-3073. 

As mentioned earlier, the first diffusion measurements utilizing solid state electrolytes involved calcia or yttria stabilized zirconia to transport oxygen into a electrode material which exhibits solubility for oxygen. The cell is represented by ... 

Araki W, Aral Y (2010) Oxygen diffusion in yttria-stabilized zirconia subjected to rmiaxial stress. Solid State Icmics 181(8-10) 441 146... 

Ji, Y., Kilner, J.A., Carolan, M.F. (2005) Electrical properties and oxygen diffusion in Yttria-stabilised Zirconia (YSZ)-Lao,8Sro,2Mn03+5 (LSM) composites. Solid State Ionics, 176 (9-10), 937-943. 

---