Preparation of infinite-layer cuprate compounds (Sr1−xLax)CuO2 and detailed phonon properties in x = 0

The infinite-layer compounds, (Sr1−xLax)CuO2, having the simplest structure among cuprate high- T c superconductors, were synthesized for x = 0 , 0.075, 0.10, and 0.125, with a careful preparation of precursors and by using the high pressure synthesis technique. To establish macroscopic and microscopic evaluations of phonon properties, specific heat and inelastic X-ray scattering (IXS) were performed in the stoichiometric SrCuO2. Fundamental phonon parameters (the Debye temperature and the average sound velocity) were estimated from the derived phonon density of states (ph-DOS) from the IXS measurement. The Debye temperature independently determined from the specific heat measurement was in good agreement with that from the IXS result. By applying the established method to superconducting compositions, it becomes possible to study phonon behaviors in detail with respect to high- T c superconductivity and/or strong electron correlations.