  We have synthesized tetragonal iron selenide and telluride superconductors
through solid state reaction at 450deg.C and 550deg.C respectively. These
synthesis temperatures have been established by optimization. Electrical
resistivity and magnetic susceptibility measurements (4.2-300 K) confirm
superconductivity with Tc of around 8.5 K in all selenide samples of nominal
composition Fe1+deltaSe (delta=0.02-0.22). However, Scanning Electron
Microscopy/ Energy Dispersive Spectroscopy studies clearly indicate that the
actual stoichiometric ratio of Fe : Se for all the samples synthesized is
around 1:1. Also all the samples exhibit identical phase transition
temperatures from tetragonal to orthorhombic structure below ~ 100 K implying
identical phase composition. The partial substitution of Se by Te leads to an
enhancement of Tc to ~ 13 K. The non-superconducting telluride Fe1.09Te
exhibits a metal-insulator phase transition at ~ 82 K. Substitution studies of
this telluride system by S and Si have in addition been carried out to
investigate if chemical pressure induces superconductivity.
