Synthesis and properties of SmO0.5F0.5BiS2 and enhancement in Tc in La1-ySmyO0.5F0.5BiS2.

The crystal structure and properties of a new member of the oxybismuth sulfide family SmO(0.5)F(0.5)BiS(2) are reported here. The compounds SmO(1-x)F(x)BiS(2) (x = 0.0 and 0.5) are isostructural with LaOBiS(2) and crystallize in the CeOBiS(2)-type structure (P4/nmm). Sm substitution in LaO(0.5)F(0.5)BiS(2) (La1-ySmyO(0.5)F(0.5)BiS(2)) leads to a gradual decrease in the a-lattice constant; however, the c-lattice constant does not show such a gradual trend. Enhancement in T(c) is achieved upon partial substitution of La by the smaller Sm ion. A maximum T(c) ∼ 4.6 K was observed for composition with y = 0.8. Disobeying this trend, Tc disappears unexpectedly in the composition SmO(0.5)F(0.5)BiS(2) (y = 1.0). Both the undoped and F-doped (x = 0.0 and 0.5) compounds are paramagnetic, exhibiting semiconducting behavior down to 2 K.