Studies of Superconducting Oxides with the Spinel Structure

3 Studies of Superconducting Oxides with the Spinel Structure 

Further adding to the complexity of the spinel structure are three possible arrangements of the metal ions in the cubic close-packed anions. The ordering of divalent metal ions (such as Mg2+) on the proper tetrahedral sites and all the trivalent ions (as Ai3+) in the correct octahedral sites, will give rise to the normal spinel structure. If the divalent ions occupy some of the octahedral sites and half of the trivalent ions move to the tetrahedral sites, the structure is then referred to as the inverse spinel structure. The last case exists when the tetrahedral sites and the octahedral sites are occupied by a mixture of di- and tri-valent ions. This type is known to generate the random spinel structure, and the exact composition and populations in the 

Historical Introduction and Crystal Chemistry o Oxide Superconductors 51 

The data for several Li/Ti/O spinel compositions are presented in Table 9 with their reported transition temperatures. Unfortunately many of these samples were not homogeneous. 

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