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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+ δ）和La_2CuO_（4+ δ）晶体均具有K_2NiF_4型原子排列，后者仅含过剩氧原子，在低温下具有超导电性。作为δ函数的过剩氧原子的构型结构和重排率，影响后者铜晶体中的超导性质，是有吸引力的。本文测量了这两种晶体的热容、电阻率和热电势。1）建立了工作温度范围为13 ~ 500 K的高精度绝热量热计。2）δ =0.00的镍化合物在镍原子电子自旋间的磁相互作用中表现出显著的二维性质。指出了80 K和120 K的相变是（超晶格公度）-无公度-（正常公度）型的可能性。研究还表明，在0.047和0.150之间的δ范围内的晶体根据晶体颗粒的尺寸表现出不同的δ-T相关系。发现在δ =0.07和0.10附近形成低温稳定的化合物，并且发现过量氧原子的周晶或共晶无序现象发生在稳定化合物的组成之间的δ范围内。3）0<delta<0.035的铜化合物在320 K以下出现了三种结构相变，表明在室温以上发生了与过剩氧原子组成有关的相分离，相变归因于CuO_6八面体的倾斜。玻璃化转变的δ-0.05和0.07晶体中观察到，并解释为由于冻结的短程重排（不扩散运动）的过剩氧原子。