  Measurements of electrical resistivity were performed between 3 and 300 K at
various pressures up to 2.8 GPa on the BiS2-based superconductors
LnO0.5F0.5BiS2 (Ln = Pr, Nd). At lower pressures, PrO0.5F0.5BiS2 and
NdO0.5F0.5BiS2 exhibit superconductivity with critical temperatures Tc of 3.5
and3.9 K, respectively. As pressure is increased, both compounds undergo a
transition at a pressure Pt from a low Tc superconducting phase to a high Tc
superconducting phase in which Tc reaches maximum values of 7.6 and 6.4 K for
PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2, respectively. The pressure-induced
transition is characterized by a rapid increase in Tc within a small range in
pressure of ~0.3 GPa for both compounds. In the normal state of PrO0.5F0.5BiS2,
the transition pressure Pt correlates with the pressure where the suppression
of semiconducting behaviour saturates. In the normal state of NdO0.5F0.5BiS2,
Pt is coincident with a semiconductor-metal transition. This behaviour is
similar to the results recently reported for the LnO0.5F0.5BiS2 (Ln = La, Ce)
compounds. We observe that Pt and the size of the jump in Tc between the two
superconducting phases both scale with the lanthanide element in LnO0.5F0.5BiS2
(Ln = La, Ce, Pr, Nd).
