  We report the crystal structures and physical properties of trilayer
nickelates Nd$_4$Ni$_3$O$_{10}$ and Nd$_4$Ni$_3$O$_8$. Measurements of
magnetization and electrical resistivity display contrasting behaviors in the
two compounds. Nd$_4$Ni$_3$O$_{10}$ shows a paramagnetic metallic behavior with
a metal to metal phase transition($T^{\ast}$) at about 162 K, as revealed by
both magnetic susceptibility and resistivity. Further magnetoresistance and
Hall coefficient results show a negative magnetoresistance at low temperatures
and the carrier type of Nd$_4$Ni$_3$O$_{10}$ is dominated by hole-type charge
carriers. The significant enhancement of Hall coefficient and resistivity below
$T^{\ast}$ suggest that effective charge carrier density decreases when cooling
through the transition temperature. In contrast, Nd$_4$Ni$_3$O$_8$ shows an
insulating behavior despite small value of resistivity at room temperature. The
compound shows paramagnetic behavior, with the similar magnetic moments as in
Nd$_4$Ni$_3$O$_{10}$ derived from the Curie-Weiss fitting. This may suggest
that the magnetic moments in both systems are contributed by the Nd ions. By
applying pressures up to about 49 GPa, the insulating behavior is still present
and becomes even stronger. Our results suggest that the different Ni
configurations ($Ni^{1+/2+}$ or $Ni^{2+/3+}$) and competition between localized
and itinerant electrons may account for the contrasting behaviors in trilayer
nickelates Nd$_4$Ni$_3$O$_{10}$ and Nd$_4$Ni$_3$O$_8$.

Materials Science;Superconductivity