超导体Ba_2YCu_3O_(6.92)晶格中不同位置氧的热稳定性

引人注目的Ba_2YCu_3O_(6.0+x)(0.3相似文献   

水对甲醇在电解银上氧化反应的影响

本文运用超高真空程序升温反应谱(TPRS),结合瞬变应答和同位素交换方法研究了电解银上氧致甲醇吸附和反应的机理以及水对甲醇氧化的影响.实验结果表明:吸附态的氧能显著增加甲醇的吸附并和甲醇反应生成水;水中的氧来源于吸附态氧,氢来源于甲醇中的甲基氢和羟基氢且以甲基氢居多.水和氧在电解银表面上存在着竞争吸附,水的加入能抑制甲醇氧化为甲醛的副产物CO_2的产生,提高反应选择性.此结果与活性数据一致.     

超导体Ba2YCu3O6.92晶格中不同位置氧的热稳定性

Studies on high-T_c superconductor Ba_2YCu_3O_(6.92) using thermogravimetry, temperature programmed decomposition, oxygen isotopic exchange method are reported. There are six steps in the thermogavimetric graph of Ba_2YCu_3O_(6.92). At the first step, 0.40 oxygen atom per unit cell is released, the amount of which corresponds to that of the oxygen released from the CuO_4 square plane when the oxidation number of copper reduced from +3 to +2. This amount of oxygen plays a key role on the influence on the T_c of superconductor. At the is 0.45, corresponding to the amount of oxygen released from CuO_4 when the oxidation number of copper changed from +2 to +1. The oxygen atom released totally at the last three steps is 1.07 per unit cell, which correspondes to the oxygen released from CuO_5 square pyramid when the oxidation number of copper changed from +2 to +1. The first three steps are almost continuous, so in TPD curve there is only one peak at 514 ℃ with respect to the three steps in TG curve and the decomposition heat of this one is 171±8 kJ mol~(-1). Another peak which is over 900 ℃ on TPD curve is the result of the loss of oxygen from the last three steps in TG curve. The sample released oxygen can recover its supeconductivity after reabsorbing oxygen. Oxygen isotopic exchange method shows that the oxygen atoms of CuO_4 and CuO_5 groups can be interexchanged under certain temperature and indicates that there is some bonding between CuO_4 square plane and CuO_5 square pyramidal groups in the crystal lattice of Ba_2YCu_3O_(6.92).     

4:2钼, 钨过氧配合物的热稳定性研究

用热分析、程序升温超高真空质谱、真空原红外光谱等技术研究属于VskaIIb4:2钼、钨过氧配合物K~4M~4O~1~2(O~2)~1、K~4W~4O~1~2(O~2)~2.4H~2O的热分解行为, 前者中两个过氧基同时分解(278℃), 后者分两步进行(180和342℃), 每步分解一个过氧基, 4:2钨过氧配合物出现在180℃分解的原因是由于结晶水的作用。比较钼、钨过氧配合物分解温度, 发现VaskaIIb型配合物的热稳定性都比VaskaIIa 型的高。     

用卢瑟福背散射和核反应技术测定Y-Ba-Cu-O超导体的元素配比

本文报道了用卢瑟福背散射和核反应~(16)O(d,P_1)~(17)O测定超导Y-Ba-Cu-O体系元素配比的实验结果。发现在煅烧后成为超导体的样品,其实际组分中Y和O的含量均低于煅烧后为非超导体的样品,且在煅烧时与氧气充分接触的部分,其实际组分中氧含量反而较小。本工作还提示了要得到性能良好的薄膜或提高电流负载,必须对各种工艺条件下生成的超导体中所有元素的实际配比进行测定而不能依赖于名义值。