HIGH PRESSURE AND LOW TEMPERATURE STUDY OF THE LTO TO LTT PHASE TRANSITION IN La_1.875Ba_0.125CuO₄. R. L. Harlow, M. K. Crawford, E. M. McCarron, CRD, The DuPont Company, Wilmington, DE 19880-0228; S. W. Tozer, NHFML, Florida State University, Tallahassee, FL 32306-4005; D.E. Cox, Q. Zhu, T. Vogt, Dept. of Physics, Brookhaven National Laboratory, Upton, NY 11973; J. D. Jorgensen, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439

We have performed a high pressure, low temperature x-ray diffraction study of the LTO (Bmab) to LTT (P4₂/ncm) structural transition in La_1.875Ba_0.125CuO₄. This phase transition leads to a drastic suppression of superconductivity which is not yet understood. The reported partial restoration of superconductivity under pressure stimulated our study. The stuctural work was performed using a Merrill-Bassett diamond anvil cell with a 4:1 methanol to ethanol pressure medium. The hydrostatic nature of this medium at pressures as high as 68 kbar and temperatures as low as 15 K was confirmed by the fact that the diffraction linewidths were limited by the position-sensitive detector resolution of 0.04 degrees. Measurements at a number of temperatures and pressures suggest that pressure first stabilizes a Pccn low-temperature phase. Higher pressures lead to the I₄/mmm (HTT) high temperature phase becoming stable at all temperatures from 300 K to 15 K. The results suggest that there is no suppression of superconductivity in the HTT phase at a doping level of 1/8 hole per Cu atom.