Numerical Approach in Superconductivity: An Advanced Study

The dependence of the critical temperature $T_c$ of high-temperature superconductors of various families on their composition and structure is proposed. A clear dependence of the critical temperature of high-temperature superconductors (hydrides, Hg- and Y-based cuprates) on the serial number of the constituent elements, their valence and crystal lattice structure has been revealed. For cuprates, it is shown that it is possible to obtain even higher temperatures of superconducting transitions at normal pressure by implanting mercury atoms into the crystal lattice of cuprate.

Oscillatory Changes in Structural Characteristics in Multicomponent Ceramics, YBCO

The structural characteristics of samples of a four-component superconducting material (YBCO) after exposure to X-ray irradiation during a long time are investigated. The effect of X-ray beam processing on angular positions (corresponding parameters of the crystal lattice) and the width of Bragg reflections is established. The phenomenon of oscillatory behavior in the unit cell dimension with long-time irradiation is found. The analysis of the profiles of reflection also demonstrates the presence of reversible changes phase composition with the exposure time. The observed phenomena reflect the presence of a nontrivial and specific process of compression and expansion of the unit cell due to the accumulation and then disengagement outside of ionized oxygen, which is formed under such irradiation exposure on the surface of the samples.

STRUCTURE CHANGING OF SUBMICRON PZT FILMS WITH A FINE VARIATION OF THE COMPOSITION CORRESPONDING TO MORPHOTROPIC PHASE BOUNDARY

В работе обсуждаются возможности тонкого варьирования состава субмикронных сегнетоэлектрических пленок твердых растворов цирконата-титаната свинца, соответствующих области морфотропной фазовой границы. Варьирование состава осуществлялось путем изменения расстояния от мишени до подложки в диапазоне 30 - 70 мм в установке высокочастотного магнетронного распыления керамической мишени при осаждении пленок на «холодную» подложку платинированного кремния. Это позволило изменять состав осаждаемых пленок (т.е., элементное соотношение атомов Zr и Ti) в диапазоне 0 -1,5% при сохранении однофазности сформированных перовскитовых пленок в процессе отжига при 580°C. При этом пленки характеризовались элементной неоднородностью состава по толщине, достигающей нескольких процентов. Толщина тонких слоев цирконата-титаната свинца составляла 500 нм. Исследовались изменения микроструктуры и параметров кристаллической решетки. Изменения состава пленок сопровождались существенными изменениями характера сферолитовой микроструктуры и ростовой текстуры. Был обнаружен резкий скачок квазикубического параметра кристаллической решетки, причиной которого может являться фазовая трансформация сегнетоэлектрической фазы - от ромбоэдрической модификации к двухфазному состоянию, предположительно состоящему из моноклинной и тетрагональной модификаций. The paper discusses the possibility of a fine variation in the composition of submicron ferroelectric films of lead zirconate titanate solid solutions corresponding to a morphotropic phase boundary. Composition was varied by changing the distance from the target to the substrate in the range of 30 - 70 mm in an installation for radio-frequency magnetron sputtering of a ceramic target, in which films deposition occurred on a «cold» platinized silicon substrate. This made it possible to change the composition of the deposited films (i.e., the elemental ratio of Zr and Ti atoms) in the range of 0 - 1,5% while maintaining the single-phase perovskite films annealed at 580 °С. In this case, the films were characterized by elemental inhomogeneity of the composition over the thickness, reaching several percents. The thickness of thin lead zirconate titanate layers was 500 nm. Changes in the microstructure and crystal lattice parameters were studied. The change in the composition of the films was accompanied by significant changes in the nature of the spherulite microstructure and growth texture. A sharp jump in the quasi-cubic crystal lattice parameter was discovered, which may be caused by the phase transformation of the ferroelectric phase - from the rhombohedral modification to the two-phase state, presumably consisting of monoclinic and tetragonal modifications.

COMPOSITES BASED ON CALCIUM PHOSPHATES AND COPPER NANOPARTICLES

Боргидридным методом с использованием полимерных стабилизаторов (полиэтиленгликоля, поливинилпирролидона) синтезированы наночастицы меди. Методом оптической спектроскопии установлено, что наибольшей стабильностью (до 1,5 месяца) обладают наночастицы меди, полученные при мольном соотношении Cu /полимер 1:3 - 6. Показано, что в отсутствии полимера либо при его небольшом содержании (мольное соотношение Cu /полимер 1:1) происходит агрегирование образующихся наночастиц и выпадение осадка, содержащего медь и ее оксиды (CuO, CuO). Механическим смешиванием аморфизированных фосфатов кальция (в порошковой и гелевой форме) и наночастиц меди (в виде коллоидного раствора) получен порошковый композит, содержащий фазы CaCuH(PO) и CuPOOH . Выявлено, что при совместном осаждении фосфатов кальция и наночастиц меди происходит встраивание ионов меди в кристаллическую решетку фосфатов кальция с образованием смешанных кислых и средних солей. Copper nanoparticles were synthesized by the borohydride method using polymer stabilizers (polyethylene glycol, polyvinylpyrrolidone). It was found by optical spectroscopy that copper nanoparticles obtained at a molar ratio Cu / polymer of 1: (3 - 6) have the highest stability (up to 1.5 months). It was shown that in the absence of polymer or at its low content (molar ratio Cu / polymer 1:1), the resulting nanoparticles aggregate and a precipitate forms containing copper and its oxides (CuO, CuO). By mechanical mixing of amorphized calcium phosphates (in powder and gel form) and copper nanoparticles (in the form of a colloidal solution), a powder composite containing CaCuH(PO) and CuPOOH phases was obtained. It was shown that during the coprecipitation of calcium phosphates and copper nanoparticles, copper ions are incorporated into the crystal lattice of calcium phosphates with the formation of mixed acidic and medium salts.

INFLUENCE OF POLYMORPHIC TRANSFORMATIONS ON ANISOTROPY OF THE SURFACE ENERGY AND THE WORK FUNCTION OF THE ELECTRON OF LITHIUM

На базе электронно-статистического метода показана связь и проведена оценка поверхностной энергии и работы выхода электрона граней кристаллов лития с учетом дисперсионного, поляризационного и осцилляционного взаимодействия атомов поверхностного слоя. Считалось, что кристаллическая решетка не имеет дефектов. Модифицированы выражения поправок и аналитического соотношения, связывающего работу выхода электрона и поверхностную энергию с учетом типа кристаллической решетки и ориентации граней. Рассчитана работа выхода электрона и поверхностная энергия гладких граней при предельных температурах существования полиморфных фаз лития. Установлено влияние полиморфных превращений и температуры на анизотропию. Температурный коэффициент работы выхода электрона бездефектного кристалла положителен и составляет порядка 0,1-1 мэВ. Результаты расчетов хорошо согласуются с экспериментальными данными для поликристаллов. On the basis of the electronic-statistical method, a relationship is obtained and the surface energy and the work function of the electron of the faces of lithium crystals are estimated, taking into account the dispersion, polarization, and oscillatory interactions of the atoms of the surface layer. It was assumed that the crystal lattice has no defects. The expressions for the corrections and an analytical relationship between the work function of the electron and the surface energy are modified taking into account the type of the crystal lattice and the orientation of the faces. The work function of the electron and the surface energy of smooth faces are calculated at the limiting temperatures of the existence of polymorphic lithium phases. The influence of polymorphic transformations and temperature on the anisotropy is established. The temperature coefficient of the work function of an electron in a defect-free crystal is positive and amounts to about 0,1-1 meV. The calculation results are in good agreement with the experimental data for polycrystals.

Synthesis and study of some properties of colloidal quantum dots of indium antimonide

Colloidal quantum dots of indium antimonide have been synthesized by a known technique. The shape and average diameters of quantum dots have been investigated by transmission electron microscopy using a transmission microscope. Controlling the size and shape of colloidal QDs provides information on the formation of the crystal structure of nanoparticles and their possible physical and optical properties. It has been found that InSb quantum dots are characterized by a polygonal shape. The results obtained for QDs correspond to the crystal lattice system of a semiconductor with a cubic crystal lattice structure. Elemental analysis of nanoparticles has been monitored by X-ray microanalysis. The experimental determination error was no more than one percent. The percentages of indium and antimony in QDs according to X-ray microanalysis data corresponded to the theoretical stoichiometry In: Sb = 1:1. Impurities of other elements constituted the level of trace amounts, which confirmed the chemical purity of the synthesized InSb QDs. The fluorescent properties of indium antimonide nanoparticles have been studied. It has been found that the luminescence intensity of InSb nanoparticles at room temperature is insignificant, which is in agreement with the literature data. The quantum yield does not exceed 1%, and the luminescence maximum lies in the range of 1040 nm.

X-RAY studies of ferroelectric lithium niobate crystals doped with rare earth elements

The lattice structural distortions of LiNbO3 crystals doped with samarium with a concentration of 1.0, 1.9, 2.5 mol. % were studied by X-ray diffraction methods. It was found that the samarium atoms and some of the niobium atoms occupied the vacant positions of lithium in the crystal lattice, and some of the niobium atoms were located in the empty octahedron. The octahedra of SmLiO6 was distorted more strongly than octahedra of NbLiO6 when niobium atoms entered the vacant positions of lithium. The smallest changes in the bond lengths in the octahedra of the main motif and in the defect region as well as along the polar axis in the lithium niobate lattice were observed in the sample with a samarium concentration of 2.5 mol. %.

Solid-State Dispersions of Platinum in the SnO2 and Fe2O3 Nanomaterials

The dispersion of platinum (Pt) on metal oxide supports is important for catalytic and gas sensing applications. In this work, we used mechanochemical dispersion and compatible Fe(II) acetate, Sn(II) acetate and Pt(II) acetylacetonate powders to better disperse Pt in Fe2O3 and SnO2. The dispersion of platinum in SnO2 is significantly different from the dispersion of Pt over Fe2O3. Electron microscopy has shown that the elements Sn, O and Pt are homogeneously dispersed in α-SnO2 (cassiterite), indicating the formation of a (Pt,Sn)O2 solid solution. In contrast, platinum is dispersed in α-Fe2O3 (hematite) mainly in the form of isolated Pt nanoparticles despite the oxidative conditions during annealing. The size of the dispersed Pt nanoparticles over α-Fe2O3 can be controlled by changing the experimental conditions and is set to 2.2, 1.2 and 0.8 nm. The rather different Pt dispersion in α-SnO2 and α-Fe2O3 is due to the fact that Pt4+ can be stabilized in the α-SnO2 structure by replacing Sn4+ with Pt4+ in the crystal lattice, while the substitution of Fe3+ with Pt4+ is unfavorable and Pt4+ is mainly expelled from the lattice at the surface of α-Fe2O3 to form isolated platinum nanoparticles.

Simulating Nonlinear Dynamics of a 3D Crystal Lattice of Metals

Oscillations of crystal lattices determine important material properties such as thermal conductivity, heat capacity, thermal expansion, and many others; therefore, their study is an urgent and important problem. Along with experimental studies of the nonlinear dynamics of a crystal lattice, effective computer simulation techniques such as ab initio simulation and the molecular dynamics method are widely used. Mathematical simulation is less commonly used since the calculation error there can reach 10 %. Herewith, it is the least computationally intensive. This paper describes the process and results of mathematical simulation of the nonlinear dynamics of a 3D crystal lattice of metals using the Lennard-Jones potential in the MatLab software package, which is well-proven for solving technical computing problems. The following main results have been obtained: 3D distribution of atoms over the computational cell has been plotted, proving the possibility of displacement to up to five interatomic distances; the frequency response has been evaluated using the Welch method with a relative RMS error not exceeding 30 %; a graphical dependence between the model and the reference cohesive energy data for a metal HCP cell has been obtained with an error of slightly more than 3 %; an optimal model for piecewise-linear approximation has been calculated, and its 3D interpolation built. All studies performed show good applicability of mathematical simulation to the problems of studying dynamic processes in crystal physics.

Preparation of triclinic alite with short soakings in a small experimental high-temperature furnace

The article deals with a laboratory preparation of triclinic modification of clinker mineral tricalcium silicate. A substantial part of the article is devoted to the technology and technique of firing a sample of tricalcium silicate, which would in the future allow the study of the development of the crystal lattice structure of this clinker mineral at short isothermal durations, in the order of minutes. As part of the research, a small high-temperature experimental furnace was designed and constructed. Based on the results, we can express the suitability and applicability of this furnace for the study of the formation of triclinic tricalcium silicate at short soakings.