Study On Preparation, Phase Analysis And Physical Properties Of The Spin-1/2 Ladder Compound Sr_14-xCa_xCu₂₄O₄₁

As a typical strongly correlated electronic system, S=1/2 spin-ladder compound Sr₁4-xCa_xCu₂4O₄1 has a unique layered structure and has showed rich physical phenomena related to the charge ordering and spin ordering. The intensive study on it should promote the knowledge of not only itself but also other strongly correlated electronic systems including high-Tc superconductor. As a result several sets of its experimental investigations are presented in this dissertation.1. The phase evolution under ambient atmosphere during the solid state reaction of (14-x)SrCO₃-xCaCO₃-24CuO system to form Sr₁4-xCa_xCu₂4O₄1 has been studied by means of XRD and DTA techniques. It helps to optimize the process of the synthesis of the compound. The relation between the thermal behavior of the system and the formation of the single-phase Sr₁4-xCa_xCu₂4O₄1 has been disclosed. On grounds of DTA curves of the system, an economical and convenient method has been found for determining the composition or temperature regions during which the single-phase can be obtained.2. For the compound with x<9, its Cu 2p₃/2, O 1s, Ca 2p and Sr 3d₅/2 core-level spectra have been measured and analyzed for better understanding the influence of Ca substitution on the electronic structure, which is closely related to its physical properties.3. For Sr₁4-xCa_xCu₂4O₄1 with x=0, 3.5, 6 and 8.4, the temperature dependence of the magnetic susceptibility, x(T), has been measured underthe applied magnetic field (H=1 T, 3 T and 5 T) in the temperature region of 10-300 K. The effects of both the applied magnetic field and the Ca substitutionon x(T) have been studied, respectively. The x(T) curves were fitted based on the independent spin-dimer model and the significant information about theelectronic structure was obtained from the fitting parameters.4. For Sr14_xCaxCu24O4i with x=0 and 3.5, the magnetic specific heat Cp under the applied magnetic fields (H=0 and 3 T) has been measured in the temperature regions of 2-12 K and 50-90 K, respectively. At low temperature(2-12 K) some physical parameters, such as Debye temperature QD, Fermitemperature TF and Fermi energy EF, were calculated by means of datacurve fitting. In the Cp-T curves at medium temperature (50-90 K) the specific heat anomaly was observed in the temperature region of 60-85 K, during which the %(T) curve has been known to show a broad peak concerned with thespin-gap of CuC>2 chain. The effects of both the applied magnetic field and the Ca substitution on the specific heat were studied, respectively.5. The temperature dependence of the DC resistance of Sri4Cu2404i was reinvestigated and analyzed in the temperature region of 80-280 K. Anabnormal broad peak has been observed around the temperature Tp=210 K in the dlnp/d(l/T)-T curve. The relation between this abnormal peak and the electronic structure was discussed and remains to be clarified.