Pressure induced lattice effects in pure and near optimally doped La2−xSrxCuO4

Abstract

The effect of hydrostatic pressure on La2−xSrxCuO4 has been examined by synchrotron angle-resolved powder XRD (at RT and at 20 K for x = 0.0 and 0.15) with two pressure transmitting media (methanol-ethanol and neon) and by Raman spectroscopy (at RT for x = 0.05, 0.15, 0.24, and 0.45). The XRD data from the two transmitting media for the undoped La2CuO4 compound deviate above ∼6.5–7 GPa but they clearly show that at RT the orthorhombic to tetragonal (O–T) phase transition occurs at ≈3.1 GPa, and is shifted to a much higher value (≈10 GPa) at 20 K. La1.85Sr0.15CuO4 appears in the tetragonal phase in the whole pressure region studied (up to 13 GPa). Both La2−xSrxCuO4 compounds show an isostructural modification in the pressure dependence of the LaO and CuO bond lengths around ∼2 GPa. As in other cuprates, hydrostatic pressure Raman measurements of La2−xSrxCuO4 indicate anomalies in phonon characteristics at about the same pressure and to an amount that strongly depends on doping in close agreement with XRD data. This phonon anomaly is not related with any intercalation of organic material into the structure, but as the bond length variation with pressure indicates with an apparent charge redistribution.