Enhanced 119Sn Moessbauer quadrupole interactions below the magnetic phase transition of UPt2Sn

119Sn Moessbauer effect measurements (4.2 K < T < 300 K) have been performed on the antiferromagnetic (AF) intermetallic compounds UPt2Sn and UCu2Sn. For temperatures above TN we find that the quadrupole splitting (ΔEQ) in UPt2Sn is about 3 times larger than in UCu2Sn. This difference in ΔEQ is suggested to be due to a large electronic contribution from the Pt-ligands in UPt2Sn. Upon decreasing temperature below TN, we find only in UPt2Sn an anomalous increase of ΔEQ relative to the extrapolated ΔEQ values in the paramagnetic phase (4% increase at 4.2 K). In addition, we have measured the thermal expansion coefficient (α) of a polycrystalline UPt2Snsample (4.2 K < T < 200 K) using a high-resolution capacitive dilatometer. We find a jump in α at TN of Δα ∼ 1.1 x 10-6 K-1. It is shown that the enhancement of ΔEQ is of electronic origin and related to the onset of AF order in UPt2Sn. (orig.)