Abstract
Thermo-physical properties of La 2− x NiO 4+ δ have been investigated above room temperature for an excess oxygen phase ( δ = 0.16, x = 0) and a deficient one ( δ = -0.15, x = 0.15). Carefull study of the weight variations in the temperature range 300–1200 K shows clearly that oxygen starts to leave the oxide above 600 K, where the previous transport properties data pointed to a semiconductor → metal transition. However the measurements have not been performed at a constant composition and must be re-interpreted. The departure of oxygen also occurs at a temperature where the tetragonality ration c/a is maximal. This proves a link between this quantity and the Ni +III content also observed in Sr substituted compounds. Finally, the oxygen departure may be correlated with the transformation of the low temperature constrained phase into a high temperature, oxygen deficient one.
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