Spinel solid solutions

In addition to the extremely wide variety of simple binary spinels, it is possible to prepare many solid solutions series. The major advantage of forming solid solutions is that their physical properties vary continuously with composition, thus leading to the possibility of material design for specific applications. The cations forming spinel solid solutions appear in Table 2.4. Solid solutions involving the substitution of one divalent cation by another, or by a combination of divalent cations, are first discussed. 

A classical, extensively studied example is the so-called Ni-Zn ferrites, with the general formula  

These ferrites are the basis for many applications. The lattice parameter varies linearly with composition, x, as shown in Fig. 210. The cation radius ratio for tetrahedral sites is large (in four-fold symmetry, the Zn radius is 0.60 A, while that of Fe is 0.49 A (Shannon, 1976)), and has the strongest influence on the lattice parameter, as well as on the magnetic properties of these solid solutions (Globus, Pascard Cagan, 1977). 

Substitutions of Fe have also been extensively studied. Blasse (1964) has reported the cation distribution in Me Fe2 A1 04, with Me = Fe, Co, Mg, Cu, Ni. The amount of A1 on tetrahedral sites, y, is plotted as a function of x on Fig. 2.11, to show the cation distribution. In the case of Fe Fe2lj Al,t04, for instance, the cation distribution is  

The spinel systems containing Mn offer an additional complication the energy difference between Mn and Mn is very small, and the following equilibrium exists  

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This is also valid for the more complex spinel solid solutions of FejO, Mn304 and CO3O4, in which electron exchange occurs in addition to substitutional disorder (2). 

Under non-equilibrium conditions, it is possible to prepare the complete defect-spinel solid solution Fe3 x04, x < 0.33 The iron vacancies are mainly on the B sites, so the end member y-Fe203 may be written as Fe [Fe5/3ni/3]04. 

Ulmer, G. White, W. B. (1966) Existence of chromous ion in the spinel solid solution series FeCr204-MgCr204. J. Amer. Ceram. Soc., 49,50-1. 

C. A. Leech and L. E. Campbell, in Spinel Solid Solution Catalysts for Automotive Applications , Am. Chem. Soc. Spring Meeting, Los Angeles, California, 1974. 

Harrison RJ, Putnis A (1995) Magnetic properties of the magnetite-spinel solid solution Saturation magnetization and cation distributions. Am Mineral 80 213-221 Harrison RJ, Putnis A (1997) The coupling between magnetic and cation ordering A macroscopic approach. Eur J Mineral 9 1115-1130... 

Harrison RJ, Putnis A (1999a) The magnetic properties and crystal chemistry of oxide spinel solid solutions. Surveys Geophys 19 461-520... 

O Neill HSC, Navrotsky A (1984) Cation distributions and thermodynamic properties of binaiy spinel solid solutions. Am Mineral 69 733-753... 

Sasamoto et al. [413] determined the Mg partial pressures over the MgO/AljOj spinel solid solution sjfstem (see Table 18) by the use of W Knudsen cells with a ThOj liner. Chemical activities of MgO were evaluated by comparing the Mg pressures over the solid solution with those obtained on vaporizing MgO(s) from the same cell. 

In a typical spinel, solid solutions, quenching, and redox equilibria can very rapidly complicate the simple analysis presented here. Additional Reading contains a number of references that the interested reader can consult. 

Spinel Solid Solution Catalysts for Automotive Applications... 

Table V. Surface Area and Porosity of Celcor Substrates and Celcor Substrates Impregnated with Spinel Solid Solutions...

Figure 3. Carbon monoxide oxidation with various spinel solid solutions as a function of temperature and space velocity.

The thermal behaviour of the initial permeability is important for many applications. In a representative spinel solid solution series, Ni-Zn ferrites, the relative permeability can be varied from 20 for NiFe204, to 8000 for Zno.7Nio.3Fe204, Fig. 4.47. As stated by Eq. (4.59), the initial permeability varies as Since anisotropy decreases faster than... 

Zie] Cation disordering calculations < 600°C, metastable miscibility gap in the spinel solid solution... 

Kat] Katsura, T, Wakihara, M., Kara, S.I., Sugihara, T, Some Thermodynamic Properties in Spinel Solid Solutions with the Fe304 Componenf , J. Solid State Chem., 13(1-2), 107-113 (1975) (Calculation, Experimental, Phase Diagram, Thermodyn., 11)... 

Fig. 1. Cu-Fe-O. Lattice parameter of the Fe304-CuFe204 spinel solid solution...

Yam] Yamaguchi, T., Shiraishi, T., Eutectoid Decomposition of CuFc204-Fe304 Spinel Solid Solution Including CuFesOg , J. Am. Ceram. Soc., 52(7), 401 (1969) (Crys. Stmcture, Phase Relations, Kinetics, 6)... 

Jac] Jacob, K.T., Fitzner, K., Alcock, C.B., Activities in the Spinel Solid Solution, Phase Equi-hbria and Thermodynamic Properties of Ternary Phases in the System Cu-Fe-O , Metall Trans. B, 8B(3), 451-460 (1977) (Experimental, Phase Diagram, Phase Relations, Thermodyn., 43)... 

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