Superconducting Properties of FeSe 1-x S x Crystals for x up to 0.19

We report on the transport properties of FeSe $$_{1-x}$$ S $$_{x}$$ single crystals for x = 0.04, 0.09, and 0.19. These compounds show a consequent increase in the superconducting transition temperature to about 10.5 K for x = 0.04 and 0.09 followed by a decrease to 8.5 K for x = 0.19, completing the superconducting dome of the FeSe $$_{1-x}$$ S $$_{x}$$ series phase diagram. The sample with the highest substitution level x = 0.19 shows no transition to an orthorhombic phase at low temperatures. Therefore, the suppression of the low temperature structural transition in FeSe $$_{1-x}$$ S $$_{x}$$ coincides with the start of the steep decrease in the superconducting transition temperature.