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Configuration and Rearrangement Rate of Excess Oxygen Atoms in Transition-Metal Oxides Related to Superconductors

超导体相关过渡金属氧化物中过量氧原子的构型和重排率

基本信息

批准号：
08454208
负责人：
OGUNI Masaharu
金额：
$ 5.06万
依托单位：
Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Both La_2NiO_<4+delta> and La_2CuO_<4+delta> crystals have atomic arrangements of a K_2NiF_4 type, and the latter crystal only with excess oxygen atoms shows superconductivity at low temperatures. The configurational structure and rearrangement rate of the excess oxygen atoms as functions of delta, affecting the superconducting properties in the latter copper crystals, are attractive. Heat capacity, resistivity and thermoelectric power were measured for the both crystals in the present work.1) High-precision adiabatic calorimeter was constructed which works in the temperature range between 13 K and 500 K.2) Nickel compound with delta=0.00 showed remarkable two-dimensional nature in the magnetic interaction between electronic spins of nickel atoms. The possibility was indicated that the phase transitions at 80 K and 120 K are of the (super-lattice commensurate) -incommensurate- (normal commensurate) type. It was also indicated that the crystals in the delta range between 0.047 and 0.150 show different delta-T phase relations depending on the size of crystal particles. Low-temperature stable compounds were found to be formed at around delta=0.07 and 0.10, and peritectic or eutectic disordering phenomena of excess oxygen atoms were found to take place in the delta ranges between the compositions of stable compounds. Glass transition phenomena due to the freezing-in of diffusional motion of excess oxygen atoms were found.3) Copper compounds with 0<delta<0.035 showed three structural phase transitions below 320 K.It was indicated that the phase separation with respect to the composition of excess oxygen atoms take place above room temperature, and that the phase transitions are ascribed to the tilt of CuO_6 octahedra. A glass transition was observed for delta-0.05 and 0.07 crystals, and interpreted as due to freezing of the short-range rearrangement (not diffusional motion) of excess oxygen atoms.

La_2NiO_4+Delta和La_2CuO_4+Delta&gt；晶体都具有K_2NiF_4型原子排列，而后者只有过量氧原子才表现出低温超导电性。过剩氧原子的构型结构和重排速率是影响后一种铜晶体超导性质的主要因素。测量了两种晶体的热容、电阻率和温差电势。1)研制了工作在13K-500K温度范围内的高精度绝热量热计。2)化合物镍原子的电子自旋之间的磁相互作用具有明显的二维性质。80K和120K的相变可能是(超晶格公度)-无公度-(正常公度)型的。研究还表明，在0.047~0.150范围内的晶体，随晶体颗粒尺寸的不同，表现出不同的Delta-T相关系。在δ=0.07和0.10附近形成了低温稳定化合物，在稳定化合物的组成之间的增量范围内出现了过剩氧原子的包晶或共晶无序现象。发现了由于过剩氧原子扩散运动的冻结而导致的玻璃化转变现象。3)在320K以下，具有0&lt；δ&lt；0.035的铜化合物发生了三次结构相变。结果表明，相对于过剩氧原子组成的相分离发生在室温以上，并且相变归因于CuO_6八面体的倾斜。在Delta-0.05和0.07晶体中观察到了玻璃化转变，并解释为由于过剩氧原子的短程重排冻结(而不是扩散运动)。