The Study of Thermal Equilibrium and Highly Oxygenated State under High Oxygen Pressure

在这项研究中，我们开发了一种新的装置，利用它可以在高压下进行热重和差热分析(TG-DTA)。用该装置研究了高温超导体Rb2Cu3Oy(R=Y，Sm，Er)在高氧压下的氧非化学计量比和相变。我们观察到在室温和10atm以上的300atm C之间发生了可逆的重量变化。从各种实验得出的结论是，这种行为是由于在稠密气体下的浮力造成的。通过考虑浮力的计算对这一行为进行了定量解释。用该计算方法对观察到的热重曲线进行了修正。Bc_2Cu_3O_y表现出从正交相到四方相的转变，这是一种有序-无序转变。目前尚不清楚高氧区的相变是如何发生的。我们首次在这么高的含氧量区域观察到了这一转变。在y=6.75时，YBa2Cu3Oy和SmBa2Cu3Oy的转变温度(T_T)分别在830ﾟC和730ﾟC有饱和趋势，而ErBa2Cu3Oy的转变温度(T_T)在y=6.75以上又有增加的趋势。这些行为表明，在y=6.75附近存在另一种氧空位排列的新相。我们在一些草酸中发现了有趣的热分解压力依赖性。本机适用于氢气气氛。

In this study, we have developed a new apparatus by which thermogravimetry and differential thermal analysis (TG-DTA) can be performed under high gaseous pressure. By using this apparatus, we have investigated oxygen nonstoichiometry and phase transition in high temperature superconductors RBa_2Cu_3O_y (R=Y,Sm, Er) under high oxygen pressure up to 150 atm. We observed a reversible weight change between room temperature and 300ﾟC above 10 atm. From various experiments it was concluded that this behavior is due to buoyancy under a dense gas. The behavior was quantitatively explained by the calculation taking buoyancy into a consideration. The observed TG curves were corrected by using this calculation. RBa_2Cu_3O_y shows a transition from orthorhombic to tetragonal which is a kind of order-disorder transition. It has been unknown how is the transition in the region of high oxygen content. We first observed the transition in such high oxygen content region. The transition temperature (T_t) has a trend to saturate at 830ﾟC in YBa_2Cu_3O_y and 730ﾟC in SmBa_2Cu_3O_y around y=6.75, and in ErBa_2Cu_3O_y it tends to increase again above y=6.75. These behaviors suggest an existence of a new phase with an another arrangement of oxygen vacancies around y=6.75. And we found interesting pressure dependences of thermal decomposition in some oxalic acids. This machine is available for hydrogen atmosphere.