Solid-solution formation, electrical properties and zero-resistance behaviour in the spinel system Mg2TiO4–MgTi2O4

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Abstract
A range of solid solutions in the system Mg2 –yTi1 +yO4 with average Ti valence x, x=(4 + 2y)/(1 +y), have been prepared for 3.2 < x < 4.0. The lattice parameter varied smoothly with composition, increasing from a value of 8.443 Å for x= 4.0 to 8.484 Å for x= 3.2. Room-temperature resistance was found to be a minimum for compositions between x= 3.25 and 3.3. On cooling from room temperature to 100 K, resistivity rose by several orders of magnitude for compositions with x > 3.3. For compositions with x < 3.25, the temperature dependence of resistivity was much less, with a rise of only one order of magnitude between 300 and 20 K. For compositions between x= 3.25 and 3.3, transitions from semiconducting to zero-resistance behaviour were observed at ca. 50 K. This zero-resistance behaviour was lost on standing, except when the sample was stored in vacuum.