Cubic stabilized zirconia

The fast-ion ceramic conductors of interest here are cubic stabilized zirconia (CSZ), an oxygen ion conductor, and a sodium aluminate (/f -alumina), a sodium ion conductor. Both are discussed in detail below. The overview by T.A. Ramanarayanan et al. [8] covering CSZ and its applications is recommended. 

Cubic stabilized zirconia (CSZ) Pure zirconia (Zr02) is either chemically extracted and purified from the mineral zircon (ZrSi04) or purified from baddeleyite. It occurs as three crystalline polymorphs with monoclinic, tetragonal and cubic structures. The monoclinic form is stable up to 1170°C... 

Electrolyte-cubic stabilized zironia Almost without exception cubic stabilized zirconia is the chosen ceramic for the electrolyte in SOFCs. This is because of its adequate conductivity and almost total absence of electronic conductivity, and because it is stable against the wide range of oxygen partial pressures ( 1 atm. to 10 20 atm.) encountered in a fuel cell. Also, because of a combination of availability and cost the favoured compound is yttria-stabilized zirconia, ZrO2+8-10mol.% Y203 (YSZ). 

Sensing oxygen with cubic stabilized zirconia... 

The tracer diffusion coefficient for oxygen ions in a particular cubic stabilized zirconia is measured and found to fit the relationship... 

The ionic transport in solids is attributed to the hopping of ionic carriers between the equivalent positions in the crystal lattice. This mechanism is known as lattice diffusion and depends on the jumping distance and frequency of moved ions. The understanding of the influence of these factors on the ionic conductivity is very important for the development of material with enhanced ionic transport. The question of what is the limit of ionic conductivity in solids will be addressed by analyzing the ionic transport in cubic stabilized zirconia systems with different acceptor dopants. 

Welberry. T.R. Withers. R.L. Mayo, S.C. A modulation wave approach to understanding the disordered structure of cubic stabilized zirconias (CSZs). J. Solid State Chem. 

Cubic stabilized zirconia (Zr02) is used as a furnace element allowing temperatures >2000°C to be achieved. Because of the low conductivity of Zr02 at room temperature, it requires preheating by gas or conventional resistance elements to reduce the resistance to a level at which... 

Cubic stabilized zirconia stabilized usually with either CaO or Y2O3. 

The main difference between the two types is in the electrolyte. The MCFC uses a molten carbonate immobilized in a porous LiA102 matrix. The SOFC uses a ceramic membrane of cubic stabilized zirconia. An illustration of the operation of a SOFC is shown in Figure 30.22. 

The parent structure of the anion-deficient fluorite structure phases is the cubic fluorite structure (Fig. 4.7). As in the case of the anion-excess fluorite-related phases, diffraction patterns from typical samples reveals that the defect structure is complex, and the true defect structure is still far from resolved for even the most studied materials. For example, in one of the best known of these, yttria-stabilized zirconia, early studies were interpreted as suggesting that the anions around vacancies were displaced along < 111 > to form local clusters, rather as in the Willis 2 2 2 cluster described in the previous section, Recently, the structure has been described in terms of anion modulation (Section 4.10). In addition, simulations indicate that oxygen vacancies prefer to be located as second nearest neighbors to Y3+ dopant ions, to form triangular clusters (Fig. 4.11). Note that these suggestions are not... 

Stabilized zirconia refers to a solid solution of zirconium oxide with one or more of a number of stabilizing oxides (CaO, MgO, 20, or others) to form a cubic fluorite structure. This... 

Cubic fluorite-structure (Fm3m) zirconia-based solid solution, (Zr,ACT,REE)02 x, exhibi ts significant compositional flexibility to incorporate high concentrations of Pu, neutron absorbers, and impurities contained in Pu-bearing wastes (Gong et al. 1999). The phase has excellent radiation stability. No amorphization was observed under ion irradiation at room temperature to a dose corresponding to 200 dpa, and at 20 K to a dose of 25 dpa. Irradiation with I+ and Sr+ up to 300 dpa produced defect clusters in Y-stabilized zirconia, but did not cause amorphization. Amorphization... 

FIGURE 5.11 Phase diagram of the pseudobinaiy CaO-ZrOz system. The cubic calcia-stabilized zirconia phase occupies the central band in the diagram and is stable to about 2400°C. 

As an attempt to solve this problem, zirconia is "stabilized" in the cubic phase by alloying it with an appropriate amount of di-or tri-valent oxide of cubic symmetry such as CaO, MgO or Y203. This results in a lowering of the temperature for the two lowest temperature transitions. These alloys are called partially stabilized zirconia, PSZ and they are a mixture of cubic and monoclinic or tetragonal phases and fully stabilized zirconia (all cubic phase) depending upon the concentration of the "dopant" or added metal oxide. 

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