“…Also, many double substitutions at the V-site or Bi/V have been reported in the literature [10,[20][21][22][23]. Some studies have been focused on Bi4V1.8M0,1M'0,1O11-d solid solutions (where M is a divalent element and M' is tetra or pentavalent cations) with the aim of an enhancement of the ionic conductivity by some ''synergic effect'' [12,20].…”