Evidence for a high-pressure isostructural transition in nitrogen

Understanding the high-pressure behaviors of diatomic molecules (H2, O2, N2, etc) is one of the most basic as well as important objective in high-pressure physics. Under high pressure diatomic molecule solids often exhibit rich crystal polymorphs. High-pressure isostructural transitions (HPIT) in solid hydrogen and oxygen, involving considerable technical challenges, have been experimentally documented, suggesting a possible prevailing pressure-driven molecular-symmetry breaking pathway. In spite of extensive efforts, however, HPIT in nitrogen has not been observed so far. Here we present a monoclinic-to-monoclinic isostructural phase transition (λ→λ’) in solid nitrogen at approximately 50 GPa accompanied with anomalies in lattice parameter, atomic volume and Raman vibron modes. Further ab initio calculations strongly confirmed the HPIT in nitrogen, showing the weak distortion of orientation and slight rotation in nitrogen molecules possibly drive the low-pressure phase, λ-N2, to an isostructural high-pressure phase, λ’-N2 without changing crystal symmetry. In addition, we probed in detail the phase stability and revisited the pressure-temperature (P-T) phase diagram of nitrogen, discovering a new high-pressure amorphous phase, η’-N2.

Структура, зеренное строение и диэлектрические свойства керамик твердых растворов YCu-=SUB=-x-=/SUB=-Mn-=SUB=-1-x-=/SUB=-O-=SUB=-3-=/SUB=-

Solid solution ceramics of the YCuxMn1-xO3 system at x = 0.05; 0.10; 0.15 were prepared by solid-phase reactions followed by sintering using conventional ceramic technology. The study of their structure, microstructure and dielectric properties including of temperature and frequencies investigation of dielectric permittivity, conductivity and tangent of dielectric loses is carried out. It is established that hexagonal phase is predominantly formed in the ceramics. Its grain structure is unhomogenius, while synthesis is performed with the formation of liquid phases of eutectic origin. It is shown that anomalous behavior of dielectric characteristics at Т=30-200 ºС connected to interlayer polarization effects, while features at Т = 222 ºС (x = 0.05), 234 ºС (x = 0.10) and 247 ºС (x = 0.15) we connected to “isostructural” phase transition that is intermediate between the ferroelectric and paraelectric phases.

Supramolecular [Na(15-crown-5)]+ cations anchored to face sharing octahedral lead bromide chains featuring a rotor in a one-dimensional perovskite with a reversible isostructural phase transition near room temperature

Crystal engineering study aims at a better understanding of the correlation between the components and crystal structures, so that the desired crystal structure and functionality will be acquired. In this...