Structural transitions in a doped lanthanum cuprate

La-139 NMR and relaxation measurements have been performed on La1.8-xEu0.2SrxCuO4 (x = 0.13 and 0.2) single crystals. The temperature dependence of the 139La NMR spectra in all the structural phases [high-temperature tetragonal (HTT) -> low-temperature orthorhombic (LTO) -> low-temperature tetragonal (LTT)] reveals the nonvanishing tilt angle of the CuO6 octahedra in the HTT phase, opposed to the case of La2-xSrxCuO4 where the tilt angle disappears immediately above the transition. Since La-139 relaxation data provide evidence of the thermodynamic critical fluctuations associated with the structural phase transitions, HTT -> LTO and LTO -> LTT, we conclude that the structural transitions in Eu-doped La2-xSrxCuO4 should be of the order-disorder type rather than of the displacive type observed in La2-xSrxCuO4. The change of the nature of the structural transitions caused by doping with Eu appears to be consistent with the LTO -> LTT transition that is absent in La2-xSrxCuO4.