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

用单色同步辐射X射线衍射法研究了固体氧在19K、180K、240K低温和高达12 Gpa高压下的相变，并根据结构数据揭示了α-，β-δ-和ε-0_2之间的相关系。在19K时，随着压力的增加，单斜晶系的α-02相直接转变为ε-02相。α-δ相界位于高于240K的温区，α-02相在较宽的压力和温度范围内是稳定的。在19K时，晶格常数的b/a随压力单调增加，在7.6 GPa时达到0.708，而在α-ε相变时，b/a突然下降到0.690。从可压缩性的各向异性确定了α-02相在7.2GPa压力下存在共线反铁磁有序。还测定了α-02相在19K时的状态方程。结构和晶格…在277K和300K下，研究了β-02相的更大压缩。从粉末获得的晶格常数a和c的压力依赖关系表明，a的可压缩性几乎是c的7倍，a的这种大的线性可压缩性可以归因于基面上的反铁磁相互作用。对α-δ相变和α-β相变的晶格形变进行了类比，揭示了δ相中的磁序关系，确定了ζ金属相的结构为Z=2的单斜晶格(SG：P2/m)，该晶格由0_2分子组成。在室温下进行了β，δ、ε-02相的单晶生长和晶体结构分析。样品质量很好，半高全宽约为0.005^o。结果表明，基面β_&lt；11&gt；的热学参数较大。较少

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