Enhanced superconducting properties in

We report an enhancement of the superconducting transition temperature ( T c ) when chromium (Cr) is substituted in excess at the iron (Fe) site (FeCrxSe, x = 0.01 , 0.02 and 0.03). There is a corresponding increase in the superconducting volume fraction with T c attaining a value of 11.2 K on 2% Cr substitution when compared to a T c of 8.5 K for the conventional tetragonal Fe-excess sample Fe1+xSe. The results point to the role of chemical pressure (introduced via ionic size variation at the Fe site upon Cr substitution in excess) on superconducting properties.