Structure at low temperature of oxygen isotope exchanged La$_{1.8875}$Sr$_{0.1125}$CuO$_{4}$

The crystal structures at low temperatures of oxygen isotope-exchanged pairs of La$_{1.8875}$Sr$_{0.1125}$CuO$_{4}$ were examined using high resolution synchrotron powder x-ray diffraction at NSLS X7A. This study was designed to examine the possibility that small structural differences might contribute to the observed superconducting isotope effects. The x-ray diffraction regions about the orthorhombic (200),(020) peaks of $^{16}$O and $^{18}$O isotope-exchanged pairs were studied in detail. There is no significant difference in orthorhombic lattice parameters at any temperature. A minority ($\sim $10{\%}) tetragonal (LTT) phase is also necessary to adequately account for the observed intensities at low temperatures. The fraction of LTT phase does not differ perceptibly with oxygen isotope exchange. We conclude, based on direct measurement of crystal structure at low temperatures, that the observed differences in superconductivity of oxygen isotope exchanged pairs are likely intrinsic effects.