Contribution of the hybrid component to the structure and properties of ceramics based on metastable phases Al2O3

The paper presents results of the study of the effect of doping with yttrium oxide on ceramics of the composition (γ + θ) Al2O3 + nY2O3 (n = 0, 1, 2, 3 wt%), sintered at 1550°C for 2 h, from powders of the specified composition annealed at temperatures of 500 , 800, 1000°С. X-ray diffraction analysis established the formation in ceramics of yttrium aluminum garnet Y3Al5O12 (YAG) and a metastable phase of the same composition with a tetragonal lattice type in powders at temperatures above 1200°C. The effect of YAG on the physical and mechanical properties was established: high properties were demonstrated by ceramics of the composition α-Al2O3 + 2wt% Y2O3, obtained from a powder annealed at 1000°C. In addition, high physical and mechanical properties were observed in ceramics of the composition α-Al2O3 + 0wt% Y2O3, obtained from a powder annealed at 800°C. The effect of the so-called “mutual protection against crystallization” was discovered, which consists in the mutual inhibition of crystallization processes in powders of the Al2O3 – Y2O3 system.

Calculation of the nonstoichiometry area of nanocrystalline palladium (II) oxide films

Nanocrystalline palladium (II) oxide films were synthesised using thermal oxidation in the oxygen atmosphere of the initial ultradispersed metal palladium layers with a thickness of ~ 35 nanometres that were obtained on SiO2/Si (100) substrates using the method of thermal sublimation in high vacuum. Using X-ray analysis, it was established that during thermal oxidation in the oxygen atmosphere within the temperature range T = 670–970 K the values of the a and c parameters of the tetragonal lattice as well as the unit cell volume of nanocrystalline PdO films increased monotonously with the rise of the temperature reaching the maximum values at T = 950–970 K. It was found that the parameters of the tetragonal lattice and the unit cell volume of nanocrystalline PdO films decreased as the oxidation temperature increased up to T > 970 KBased on the ratio of the c/a parameters, it was shown that the main contribution to the deformation phenomena of the tetragonal lattice were mostly due to the increase in the elementary translations along the coordination axes OX and OY. Based on an assumption that the ionic component of the chemical bond is essential to the palladium (II) oxide structure, we suggested a method for the calculation of the range of the nonstoichiometry area for nanocrystalline PdO films, using the reported data on the radii of cation Pd2+ and anion O2- taking into account their coordination environment. The results of the calculations showed that nanocrystalline PdO films synthesised with an oxygen pressure of ~ 105 kPa are characterisedby the two-sided homogeneity region in relation to the stoichiometric ratio of the components. The homogeneity region of nanocrystalline PdO films is characterised by the retrograde solidus line in the range of the temperatures T = 770–1070 K.

The Dirac Cone in Two-Dimensional Tetragonal Silicon Carbide：Ring Coupling Mechanism

The exploration of novel two-Dimensional semimetallic materials is always an attractive topic. We propose a series of two-dimensional silicon carbide with a tetragonal lattice. The band structure of silicon carbide...

Novel two-dimensional ZnO$_2$, CdO$_2$ and HgO$_2$ monolayers: a first-principles-based prediction

In this paper, the existence of monolayers with the chemical formula XO$_2$, where X= Zn, Cd, and Hg with hexagonal and tetragonal lattice structures is theoretically predicted by means of...

STRUCTURE AND STABILITY OF A TETRAGONAL DIAMOND-LIKE LAYER: FIRST-PRINCIPLE CALCULATIONS

Методом теории функционала плотности было выполнено теоретическое исследование нового слоевого полиморфа алмаза DL, состоящего из двух полимеризованных тетрагональных графеновых слоев L. Установлено, что новый алмазоподобный слой имеет двумерную тетрагональную решетку с параметром a = b = 0,3822 нм и толщиной 0,1599 нм. Рассчитанные поверхностная плотность и ширина запрещенной зоны этого слоя равны 0,109 мкг/см и 2,63 эВ, соответственно. Новый слой DL должен быть устойчивым, как минимум, до 220 К. Также установлено, что слой DL может быть получен при сильном одноосном сжатии двух графеновых слоев L при давлении 29,6 ГПа. Using the density functional theory method, a theoretical study of a novel layered DL polymorph of diamond, consisting of two polymerized tetragonal graphene L layers, was performed. It was established that the new diamond-like layer has a two-dimensional tetragonal lattice with the parameter a = b = 0,3822 nm and a thickness of 0,1599 nm. The calculated surface density and band gap of this layer are 0,109 μg/cm and 2,63 eV, respectively. The new DL layer must be stable up to at least 220 K. It was also found that the DL layer can be obtained by strong uniaxial compression of two graphene L layers at a pressure of 29,6 GPa.

The Mottled Capsid of the Salmonella Giant Phage SPN3US, a Likely Maturation Intermediate with a Novel Internal Shell

“Giant” phages have genomes of >200 kbp, confined in correspondingly large capsids whose assembly and maturation are still poorly understood. Nevertheless, the first assembly product is likely to be, as in other tailed phages, a procapsid that subsequently matures and packages the DNA. The associated transformations include the cleavage of many proteins by the phage-encoded protease, as well as the thinning and angularization of the capsid. We exploited an amber mutation in the viral protease gene of the Salmonella giant phage SPN3US, which leads to the accumulation of a population of capsids with distinctive properties. Cryo-electron micrographs reveal patterns of internal density different from those of the DNA-filled heads of virions, leading us to call them “mottled capsids”. Reconstructions show an outer shell with T = 27 symmetry, an embellishment of the HK97 prototype composed of the major capsid protein, gp75, which is similar to some other giant viruses. The mottled capsid has a T = 1 inner icosahedral shell that is a complex network of loosely connected densities composed mainly of the ejection proteins gp53 and gp54. Segmentation of this inner shell indicated that a number of densities (~12 per asymmetric unit) adopt a “twisted hook” conformation. Large patches of a proteinaceous tetragonal lattice with a 67 Å repeat were also present in the cell lysate. The unexpected nature of these novel inner shell and lattice structures poses questions as to their functions in virion assembly.

Novel electronic nematicity in heavily hole-doped iron pnictide superconductors

Electronic nematicity, a correlated state that spontaneously breaks rotational symmetry, is observed in several layered quantum materials. In contrast to their liquid-crystal counterparts, the nematic director cannot usually point in an arbitrary direction (XY nematics), but is locked by the crystal to discrete directions (Ising nematics), resulting in strongly anisotropic fluctuations above the transition. Here, we report on the observation of nearly isotropic XY-nematic fluctuations, via elastoresistance measurements, in hole-doped Ba1−xRbxFe2As2iron-based superconductors. While forx=0, the nematic director points along the in-plane diagonals of the tetragonal lattice, forx=1, it points along the horizontal and vertical axes. Remarkably, for intermediate doping, the susceptibilities of these two symmetry-irreducible nematic channels display comparable Curie–Weiss behavior, thus revealing a nearly XY-nematic state. This opens a route to assess this elusive electronic quantum liquid-crystalline state.

Discovery of a ferroelastic topological insulator in a two-dimensional tetragonal lattice

We found that 2D tetragonal HfC allowed simultaneous presence of ferroelastic and topological orders.