Thoretical Study on Electronic Structures and Pressure-Induced Composite Phase Transitions of Solid Oxygen

From band structure calculations using full-potential(FP)-LMTO method for molecular phases of oxygen we have obtained the following important results：1.At ambient pressure the most stable state is the AF state.2。Pressure-induced insulator-metal transition occurs by band overlapping which closes the indirect energy gap.At the transition volume V I D 2 M I D 2=25.98 A D 13 I D 1，the magnetic moment still remains in each molecule.3.With farther decreasing the volume the magnetic moment disappears and the paramagnetic metallic phase is realized at V ii D2=11.36埃D13 ii D1 which corresponds to theζ-phase at 116.In order to see a possibility that the observed metallization is realized in a monatomic phase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of theζ-phase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of theζ-phase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of theζphase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of theζphase of solid oxygen we have performed band calculations of monatomic phasing to that of the zetomic phase of thase 116 GPa D 11)。As the crystal structure we have chosen theβ-Po type because it is the monatomic structure realized first under high p…More ressures in other VI-b elements.Theβ-Po type structure is rhombohedral and the sc，bcc and fcc structures are realized for special values of c/a ofβ-Po type structure.We have found that the total energy ofβ-Po oxygen is higher than that of the molecularζ(Monoclinic)phase obtained for the same volume。Therefore，judging from all the results of our calculations it is strongly suggested that a paramagnetic metallic state is realized in molecular solid oxygen under high pressures higher than about100 GPa.We investigated also pressure-induced superconductivity ofβ-Po Se(60 Gpa&lt；P&lt；150 Gpa)and of bcc Se(150 Gpa&lt；P)in the frame work of Allen-Dynes formalism.In the bcc phase the superconducting transition temperature T I D 2c ii increases considerably with decreasing pressure，and T I D 2 c i D 2 reaches more than 10 K at the transition from bcc toβ-Po.The origin of this remarkable increase of T I D2c IED2is mainly attributed to phonon anomaly in the middle of the aunline。Inβ-Po phase，on the other hand，T I D 2 c D 2 is almost pressure independent(~5K)and there is a large jump in T I D 2 at the transition fromβ-Po to bcc.Less：Less

From band structure calculations using full-potential (FP)-LMTO method for molecular phases of oxygen we have obtained the following important results:1. At ambient pressure the most stable state is the AF state.2. Pressure-induced insulator-metal transition occurs by band overlapping which closes the indirect energy gap. At the transition volume VィイD2MィエD2=25.98 ÅィイD13ィエD1, the magnetic moment still remains in each molecule.3. With farther decreasing the volume the magnetic moment disappears and the paramagnetic metallic phase is realized at VィイD2MィエD2=11.36 ÅィイD13ィエD1 which corresponds to the ζ-phase at 116 GPa.In order to see a possibility that the observed metallization is realized in a monatomic phase of solid oxygen we have performed band calculations of monatomic phases for the volume corresponding to that of the ζ-phase at 116 GPa(VィイD2MィエD2=11.36 ÅィイD13ィエD1). As the crystal structure we have chosen the β-Po type because it is the monatomic structure realized first under high p … More ressures in other VI-b elements. The β-Po type structure is rhombohedral and the sc, bcc and fcc structures are realized for special values of c/a of β-Po type structure. We have found that the total energy of β-Po oxygen is higher than that of the molecular ζ(monoclinic) phase obtained for the same volume. Therefore, judging from all the results of our calculations it is strongly suggested that a paramagnetic metallic state is realized in molecular solid oxygen under high pressures higher than about 100 GPa.We investigated also pressure-induced superconductivity of β-Po Se (60 Gpa < P < 150 Gpa) and of bcc Se (150 Gpa < P) in the frame work of Allen-Dynes formalism. In the bcc phase the superconducting transition temperature TィイD2cィエD2 increases considerably with decreasing pressure, and TィイD2cィエD2 reaches more than 10 K at the transition from bcc to β-Po. The origin of this remarkable increase of TィイD2cィエD2 is mainly attributed to phonon anomaly in the middle of the ГN line. In β-Po phase, on the other hand, TィイD2cィエD2 is almost pressure independent (〜5K) and there is a large jump in TィイD2cィエD2 at the transition from β-Po to bcc. Less