Compressibility of the high-$T_c$ superconductor ${\mathrm{La}}_{1.7}$${\mathrm{Ba}}_{0.3}$${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$

We report on x-ray diffraction measurements of the pressure dependence of the cell parameters of ${\mathrm{La}}_{1.7}$ ${\mathrm{Ba}}_{0.3}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{y}}$ at room temperature up to 45 kbar. The compressibility κ≊5.6×${10}^{\mathrm{-}4}$ ${\mathrm{kbar}}^{\mathrm{-}1}$, and is nearly isotropic above 7 kbar. However, the contraction of the basal plane a lattice parameter appears to be negligible at lower pressure, indicating a possible structural change near 7 kbar which may be associated with a previously reported anomaly in the pressure dependence on $T_c$.