The potential of
calcium-doped layered perovskite compounds, BaNd
1–
x
Ca
x
InO
4–
x
/2
(where
x
is
the excess Ca content), as protonic conductors was experimentally
investigated. The acceptor-doped ceramics exhibit improved total conductivities
that were 1–2 orders of magnitude higher than those of the
pristine material, BaNdInO
4
. The highest total conductivity
of 2.6 × 10
–3
S cm
–1
was
obtained in the BaNd
0.8
Ca
0.2
InO
3.90
sample at a temperature of 750 °C in air. Electrochemical impedance
spectroscopy measurements of the
x
= 0.1 and
x
= 0.2 substituted samples showed higher total conductivity
under humid environments than those measured in a dry environment
over a large temperature range (250–750 °C). At 500 °C,
the total conductivity of the 20% substituted sample in humid air
(∼3% H
2
O) was 1.3 × 10
–4
S
cm
–1
. The incorporation of water vapor decreased
the activation energies of the bulk conductivity of the BaNd
0.8
Ca
0.2
InO
3.90
sample from 0.755(2) to 0.678(2)
eV in air. The saturated BaNd
0.8
Ca
0.2
InO
3.90
sample contained 2.2 mol % protonic defects, which caused
an expansion in the lattice according to the high-temperature X-ray
diffraction data. Combining the studies of the impedance behavior
with four-probe DC conductivity measurements obtained in humid air,
which showed a decrease in the resistance of the
x
= 0.2 sample, we conclude that experimental evidence indicates that
BaNd
1–
x
Ca
x
InO
4–
x
/2
is a fast proton
conductor.
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