Structural analysis and physical properties of High-Pressure and Low-Temperature Phases of Solid Oxygen

利用单色同步x射线衍射技术研究了固体氧在19k、180k和240k低温和12gpa高压下的相变，并根据结构数据揭示了α-、β-δ-和ε-0_2的相关系。单斜相α-0_2在19K时，随着压力的增加，在7.6 Gpa时直接转变为ε-0_2。α-δ相边界位于240 K以上的高温区，α-0_2相在较宽的压力和温度范围内稳定。晶格常数的b/a比在19 K时随压强单调增加，在7.6 GPa时达到0.708，但由于α-ε跃迁，b/a比急剧下降至0.690。从压缩率的各向异性来看，在7.2 Gpa压力下，α-0_2相存在共线反铁磁序。测定了α-0_2相在19k时的状态方程。在277 K和300 K下研究了β-0_2相的结构和晶格压缩。从粉末中得到的晶格常数a和c的压力依赖性表明，a的可压缩性几乎是c的7倍。a的大线性可压缩性可能归因于基面上的反铁磁相互作用。α-δ和α-β相变之间的晶格变形的类比也提示了δ相的磁序。在100 Gpa以上，金属ζ - pnase的结构为单斜晶格（SG: P2/m）， Z=2。这个晶格由0个分子组成。因此，该相为分子半金属相。在室温下对β、δ和ε-0_2相的单晶生长进行了研究，并对其结构进行了分析。样品质量很好，半最大值时的全宽度约为0.005^o。数据收集是通过几种方法进行的。发现基面上的热参数_<11>相当大。少

The phase transition of solid oxygen has been investigated at low-temperatures of 19 K, 180 K and 240 K and at high-pressures of up to 12 Gpa using monochromatic synchrotron x-ray diffraction techniques, and the phase relation among α-,β-δ-, and ε-0_2 has been revealed, based on the structural data. The monoclinic α-0_2 phase at 19K, with increasing pressure, directly transformed to theε-0_2 phase at 7.6 Gpa. The α-δ phase boundary was located on a higher temperature region than 240 K and the α-0_2 phase was stable over a wide pressure and temperature range. The b/a ratio of the lattice constants at 19 K exhibited a monotonic increase with pressure and reached 0.708 at 7.6 GPa, while it abruptly decreased to 0.690 by the α-ε transition. From the anisotropy of compressibility, the existence of a collinear antiferromagnetic order in the α-0_2 phase was confirmed at pressure up to 7.2 Gpa. The equation of state of the α-0_2 phase at 19 K has also been determined.The structure and lattice … More compression of β-0_2 phase have been studied at 277 K and 300 K. The pressure dependence of lattice constants, a and c, obtained from a powder indicated an anisotropic compressibility, a is almost seven times as compressible as c.This large linear compressibility of a may be attributed to the antiferromagnetic interaction in the basal plane. An analogy of the lattice deformation between the α-δ and α-β phase transitions was also suggestive of the magnetic order in theδ phase.The structure of the metallic ζpnase above 100 Gpa was determined to be a monoclinic lattice (SG : P2/m) with Z=2. This lattice consisted of 0_2 molecules. Therefore, this phase was concluded to be molecular semi metallic.The single crystal growth of β, δ, and ε-0_2 phases and the structure analyses of these crystals were carried out at room temperature. The sample quality was very good and the full width at half maximum was about 0.005^o. The data collection was carried out by several methods. It is found that the thermal parameter in basal planeβ_<11>, was considerably large. Less