La5.4MoO11.1 proton conductors with different
metal doping (Ca2+, Sr2+, Ba2+, Ti4+, Zr4+, and Nb5+) have
been prepared and structurally and electrically characterized.
Different polymorphs are stabilized depending on the doping
and cooling rate used during the synthesis process. The most
interesting results are obtained for Nb-doping,
La5.4Mo1−xNbxO11.1−x/2, where single compounds are obtained
in the compositional range 0 ≤ x ≤ 0.2. These materials are
fully characterized by structural techniques such as X-ray and
neutron powder diffraction and transmission electron microscopy, which independently confirm the changes of polymorphism.
Scanning electron microscopy and impedance spectroscopy measurements in dry/wet gases (N2, O2, and 5% H2−Ar) showed
an enhancement of the sinterability and electrical properties of the materials after Nb-doping. Conductivity measurements
under very reducing conditions revealed that these materials are mixed ionic-electronic conductors, making them potential
candidates for hydrogen separation membranes.
