The electrical conductivity of lithium-manganese spinels is analyzed in sam
ples with different starting Li cationic fraction x. Li-rich spinels, resul
ting from Li-Mn substitution around the stoichiometric value (x = 0.333), s
how conductivity values higher than that observed in stoichiometric LiMn2O4
. Besides, a conductivity drop, associated with a structural phase transiti
on at about 290 K in LiMn2O4,progressively disappears by decreasing x, whil
e it is absent in Li-rich samples. Stoichiometry effects on the concentrati
on of charge carriers and on the available sites for the hopping transport
process are evaluated, as well as the effects due to coexisting insulating
phases. The role of the Jahn-Teller effect on the conductivity behaviour of
stoichiometric and Li-poor spinels is also considered.