  Polycrystalline samples of LaSr1-xBaxNiO4 show a crossover from a state with
metallic transport properties for x = 0 to an insulating state as x -> 1. The
end member LaBaNiO4 with a nominal nickel Ni 3d7 configuration might therefore
be regarded as a candidate for an antiferromagnetic insulator. However, we do
not observe any magnetic ordering in LaBaNiO4 down to 1.5 K, and despite its
insulating transport properties several other physical properties of LaBaNiO4
resemble those of metallic LaSrNiO4. Based on an analysis of electrical and
thermal-conductivity data as well as magnetic-susceptibility and
low-temperature specific-heat measurements we suggest that LaBaNiO4 is a Fermi
glass with a finite electron density of states at the Fermi level but these
states are localized.
