ELECTRONIC AND STRUCTURAL INSTABILITIES OF SINGLE-CRYSTALLINE LA2-X-YNDYSRXCUO4 NEAR 1 8-DOPING/

We have performed ultrasonic measurements, X-ray diffraction, resistiv ity and susceptibility measurements in order to investigate the correl ation between the structural instability and the electronic states in the normal state of single-crystalline La2-x-yNdySrxCuO4 with x=1/8 an d y=0.4. There exist two structural phase transitions at low temperatu res, one of which is of the 2nd order (OMT-OLT) and the other is of th e 1st order (OLT-TLT). The phase transition to the TLT phase appears t o couple to the electronic instability leading to the local suppressio n of superconductivity.