Abstract
Here we report pressure effects on the superconducting transition temperature (Tc) of the ReFeAsO0.85 (Re=Sm and Nd) system without fluorine doping. In situ measurements under high pressure showed that Tc of the two compounds decreases monotonously over the pressure range investigated. The pressure coefficients dTc/dP in SmFeAsO0.85 and NdFeAsO0.85 were different, revealing the important influence of the deformation in layers on Tc. Theoretical calculations suggested that the electron density of states decreases with increasing pressure, following the same trend of experimental data.