Electrical conductivity measurements have been performed on the pyroch
lore compounds Y2Ti2O7, Gd2Ti2O7 and Sm2Ti2O7 as a function of tempera
ture, oxygen fugacity and aliovalent dopant concentration. Both the ma
gnitude and type of conduction (ionic and/or electronic) were found to
be influenced by dopant size, site location (''A'' or ''B'' cation su
blattice) and net dopant density. While Ca doping on the ''A'' cation
sublattice (Ca'(Gd,sm,Y)) was found to increase the ionic conductivity
by as much as two and half orders of magnitude, Sr and Mg dopants wit
h larger dopant-host size mismatch induced a drop in ionic and an enha
ncement in electronic conductivity. Acceptor doping on the ''B'' catio
n sublattice, e.g. Al'(Ti), increased the ionic conduction only at low
dopant levels, while RU(TI) enhanced electronic conduction at high P-
O2 Trends in ionic and electronic conduction as a function of T, P-O2,
and dopant density are analyzed with the aid of a defect chemical mod
el.