Electronic origin of the incommensurate modulation in the structure of phosphorus IV

An incommensurate modulated structure was found recently in a light group V element phosphorous in the phase P-IV stable in the pressure range 107-137 GPa. We consider configurations of the Brillouin zone and Fermi sphere within a nearly-free-electron model in order to analyze the importance of these configurations for the crystal structure energy. For the phase P-IV with the base-centered orthorhombic structure, oC2, we consider a commensurate approximant with an 11-fold supercell along the c-axis and a modulation wave vector equal 3/11 which is close to the experimentally observed value of 0.267. Atomic shifts due to the modulation result in appearance of satellite reflections and hence in a formation of additional Brillouin zone planes. The stability of this structure is attributed to the lowering of the electronic band structure energy due to Brillouin zone - Fermi surface interactions

Transformations of Phosphorus under Pressure from Simple Cubic to Simple Hexagonal Structures via Incommensurately Modulations: Electronic Origin

The lighter group-V element phosphorus forms the As-type (hR2) structure under pressure, above 5 GPa, and at 10 GPa transforms to the simple cubic structure (cP1), similar to arsenic. Despite of its low packing density, the simple cubic structure is stable in phosphorus over a very wide pressure range up to 103 GPa. On further pressure increase, the simple cubic structure transforms to a simple hexagonal structure (hP1) via a complex phase that was solved recently as incommensurately modulated. Structural transformations of phosphorus are connected with the changes of physical properties. Above 5 GPa phosphorus shows superconductivity with Tc reaching ~9.5K at 32GPa. The crystal structures and properties of high-pressure phases for phosphorus are discussed within the model of the Fermi sphere and Brillouin zone interactions.Comment: 6 page, 6 figures, the 1st International Electronic Conference on Crystals 21-31 May 2018. arXiv admin note: substantial text overlap with arXiv:0911.240

Structure stability in the simple element sodium under pressure

The simple alkali metal Na, that crystallizes in a body-centred cubic structure at ambient pressure, exhibits a wealth of complex phases at extreme conditions as found by experimental studies. The analysis of the mechanism of stabilization of some of these phases, namely, the low-temperature Sm-type phase and the high-pressure cI16 and oP8 phases, shows that they satisfy the criteria for the Hume-Rothery mechanism. These phases appear to be stabilized due to a formation of numerous planes in a Brillouin-Jones zone in the vicinity of the Fermi sphere of Na, which leads to the reduction of the overall electronic energy. For the oP8 phase, this mechanism seems to be working if one assumes that Na becomes divalent metal at this density. The oP8 phase of Na is analysed in comparison with the MnP-type oP8 phases known in binary compounds, as well as in relation to the hP4 structure of the NiAs-type

Effect of pressure on the Raman modes of antimony

The effect of pressure on the zone-center optical phonon modes of antimony in the A7 structure has been investigated by Raman spectroscopy. The A_g and E_g frequencies exhibit a pronounced softening with increasing pressure, the effect being related to a gradual suppression of the Peierls-like distortion of the A7 phase relative to a cubic primitive lattice. Also, both Raman modes broaden significantly under pressure. Spectra taken at low temperature indicate that the broadening is at least partly caused by phonon-phonon interactions. We also report results of ab initio frozen-phonon calculations of the A_g and E_g mode frequencies. Presence of strong anharmonicity is clearly apparent in calculated total energy versus atom displacement relations. Pronounced nonlinearities in the force versus displacement relations are observed. Structural instabilities of the Sb-A7 phase are briefly addressed in the Appendix.Comment: 10 pages, 8 figure

ВОЗМОЖНОСТИ СОВРЕМЕННОЙ ДИАГНОСТИКИ ГЕРПЕСВИРУСНЫХ ИНФЕКЦИЙ У ДЕТЕЙ

Medical history, clinical and laboratory data were studied in 828 children aged from 2 months to 14 years. All of them had different clinical forms of herpesvirus infections (HVI). The combination of the information allows to form the etiologic diagnosis timely and to evaluate the activity of the current infection. Given the polymorphism of clinical symptoms of HVI, it was very important to determine herpesvirus genomes in three media (blood, saliva, urine) by PCR, and high titers of G-antibodies (439 u for CMV and 212.3 u for HHV-6). У 828 детей в возрасте от 2 месяцев до 14 лет с различными клиническими формами герпесвирусных инфекций (ГВИ) были исследованы анамнестические, клинические и лабораторные данные, сочетание которых позволяет своевременно ставить этиологический диагноз и оценивать активность текущего инфекционного процесса. Учитывая полиморфизм клинических симптомов ГВИ, была показана высокая диагностическая значимость определения геномов герпесвирусов в трех средах (кровь, слюна, моча) методом ПЦР и высоких титров G-антител (439 ед. для ЦМВ и 212,3 ед. для ВГЧ-6).