SOME ANOMALIES DUE TO THE LOW-TEMPERATURE STRUCTURAL TRANSITION AROUND X=0.12 IN LA2-XBAXCUO4

Anomalies of heat capacity and thermal expansion have been observed near x = 0.12 in La2-xBa(x)CuO4. The anomalies are ascribed to the low-temperature structural transition. We determine accurately the phase baundary as a function of x. Widely broadened Cu-NQR spectra for x < 0.14 show that the local charged states of the CuO2 plane are largely distributed in the low-temperature phase. The phase diagram and its relation with the suppression of superconductivity around x = 0.12 are briefly discussed.