RAMAN-SCATTERING AND WEAK-FERROMAGNETISM STUDIES IN EU2CUO4

We show that there is a subtle instability of the T' structure for the R(2)CuO(4) (R = rare earth) compounds at the center of the R series w ith the boundary at Eu2CuO4. Crystals grown in Pt crucibles and PbQ fl ux show weak ferromagnetism (WF) and two strongly temperature-dependen t forbidden Raman peaks. However crystals grown in alumina crucibles a nd CuO flux do not show WF and the forbidden Raman peaks are much less intense. The observation of WF and forbidden Raman peaks for Eu2CuO4 compounds suggests that the instability of the T' structure may be ass ociated with O(1) displacement in the CuO2 planes.