自旋1/2梯状结构化合物Sr_（14-x）Ca_xCu_（24）O_（41）的制备、物相分析和物性研究
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摘要
作为目前强关联电子系统的一个重要研究对象,Sr_(14-x)Ca_xCu_(24)O_(41)具有奇异的结构形式和丰富的电荷与自旋有序的物理现象,对其深入研究,不仅有助于对其本身,而且将加深对包括高温超导在内的其他强关联电子系统的认识。本论文首先慨述了关于梯状化合物主要是Sr_(14-x)Ca_xCu_(24)O_(41)的研究情况,然后从材料学和物理学两方面开展了下述研究工作:
1.借助于XRD和DTA技术研究了(14-x)SrCO_3-xCaCO_3-24CuO体系(x=0,0.4,2.8,5.6,8.4,11.2,13.6和14)在环境压力下固态合成Sr_(14-x)Ca_xCu_(24)O_(41)过程中物相的演变,有助于优化Sr_(14-x)Ca_xCu_(24)O_(41)的合成工艺。
详细研究了(14-x)SrCO_3-xCaCO_3-24CuO体系的热行为与合成纯相Sr_(14-x)Ca_xCu_(24)O_(41)的关系,得出了结论:根据体系的DTA曲线可以确定固态合成其单相的成份区域及温度区域。
2.Sr_(14-x)Ca_xCu_(24)O_(41)特殊的物理性质均与其电子结构密切相关,因此,测量了该化合物(x<9)的Cu 2p_(3/2)、O 1s、Ca 2p_(3/2)和Sr 3d_(5/2)的芯能级光电子发射谱,初步研究了它的电子结构:Ca替代A位Sr对B位Cu芯能级的影响,Cu~(2+)和Cu~(3+)的质量分数及其变化,该体系中Cu、Ca和Sr离子的平均化合价的估算。
3.在外加磁场H=1T,3T和5T时测量了Sr_(14-x)Ca_xCu_(24)O_(41)(x=0,3.5,6,8.4)在10-300K温度范围内的磁化率温度特性,考察了外加磁场和Ca掺杂对它的影响,采用“独立自旋—dimer模型”分析了观测到的磁化率数据,从拟合参数获得了较系统的关于该化合物电子结构的信息。
4.测量了零磁场和外加磁场H=3T条件下未掺杂的Sr_(14)Cu_(24)O_(41)和掺杂的样品Sr_(10.5)Ca_(3.5)Cu_(24)O_(41)的低温(2-12K)磁比热温度关系曲线,得到了有关晶格振动的特征量德拜温度(?)_D、电子态特征量费米温度T_F与费米能级E_F等物理量,考察了比热的磁场效应和Ca掺杂效应。
在50-90K中温区,测量了Sr_(14)Cu_(24)O_(41)在零磁场和H=3T时的磁比热以
As a typical strongly correlated electronic system, S=1/2 spin-ladder compound Sr_14-xCa_xCu_24O_41 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)SrCO_3-xCaCO_3-24CuO system to form Sr_14-xCa_xCu_24O_41 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 Sr_14-xCa_xCu_24O_41 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 2p_3/2, O 1s, Ca 2p and Sr 3d_5/2 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 Sr_14-xCa_xCu_24O_41 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 the
electronic 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.
1.借助于XRD和DTA技术研究了(14-x)SrCO_3-xCaCO_3-24CuO体系(x=0,0.4,2.8,5.6,8.4,11.2,13.6和14)在环境压力下固态合成Sr_(14-x)Ca_xCu_(24)O_(41)过程中物相的演变,有助于优化Sr_(14-x)Ca_xCu_(24)O_(41)的合成工艺。
详细研究了(14-x)SrCO_3-xCaCO_3-24CuO体系的热行为与合成纯相Sr_(14-x)Ca_xCu_(24)O_(41)的关系,得出了结论:根据体系的DTA曲线可以确定固态合成其单相的成份区域及温度区域。
2.Sr_(14-x)Ca_xCu_(24)O_(41)特殊的物理性质均与其电子结构密切相关,因此,测量了该化合物(x<9)的Cu 2p_(3/2)、O 1s、Ca 2p_(3/2)和Sr 3d_(5/2)的芯能级光电子发射谱,初步研究了它的电子结构:Ca替代A位Sr对B位Cu芯能级的影响,Cu~(2+)和Cu~(3+)的质量分数及其变化,该体系中Cu、Ca和Sr离子的平均化合价的估算。
3.在外加磁场H=1T,3T和5T时测量了Sr_(14-x)Ca_xCu_(24)O_(41)(x=0,3.5,6,8.4)在10-300K温度范围内的磁化率温度特性,考察了外加磁场和Ca掺杂对它的影响,采用“独立自旋—dimer模型”分析了观测到的磁化率数据,从拟合参数获得了较系统的关于该化合物电子结构的信息。
4.测量了零磁场和外加磁场H=3T条件下未掺杂的Sr_(14)Cu_(24)O_(41)和掺杂的样品Sr_(10.5)Ca_(3.5)Cu_(24)O_(41)的低温(2-12K)磁比热温度关系曲线,得到了有关晶格振动的特征量德拜温度(?)_D、电子态特征量费米温度T_F与费米能级E_F等物理量,考察了比热的磁场效应和Ca掺杂效应。
在50-90K中温区,测量了Sr_(14)Cu_(24)O_(41)在零磁场和H=3T时的磁比热以
As a typical strongly correlated electronic system, S=1/2 spin-ladder compound Sr_14-xCa_xCu_24O_41 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)SrCO_3-xCaCO_3-24CuO system to form Sr_14-xCa_xCu_24O_41 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 Sr_14-xCa_xCu_24O_41 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 2p_3/2, O 1s, Ca 2p and Sr 3d_5/2 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 Sr_14-xCa_xCu_24O_41 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 the
electronic 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.
引文
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