2D−3D crossover of the in-plane paraconductivity in optimal doped ReBa₂Cu₃O₇₋δ (Re = Y, Ho) single crystals

The effect of the fluctuation paraconductivity in optimal oxygen-doped ReBa₂Cu₃O₇₋δ (Re = Y, Ho) single crystals has been investigated. The results indicate that the theoretical model of Aslamazov–Larkin (AL) describes the temperature dependence of fluctuation paraconductivity (FP) near the critical temperature (Tc). At temperatures above the temperature of the 2D−3D crossover this dependence is appropriately described by the Lawrence–Doniach (LD) theory. The extended linear dependence of ρab(Т), in the crystal with the minimum critical temperature indicates that we have a high defect concentration in this sample. This in turn causes negative processes into forming fluctuation pairs

Atomistic models for R1–xPrxBa2Cu3O7–δ (R = Y and lanthanides) and related oxides

We report the results of defect structures studies of silicon implanted at different temperatures with Mn ions (Si:Mn) and of GaMnAs layers, next annealed under ambient and high pressures. An influence of annealing conditions on structural properties of Si:Mn and GaMnAs layers was investigated. It has been confirmed that annealing of the Si:Mn samples after implantation results in crystallization of silicon inside the buried postimplanted layer, as well as in the formation of ferromagnetic Mn4Si7 precipitates. A change of strain in the GaMnAs layer, from the compressive to the tensile one, related to a creation of nanoclustered MnAs, was found to be dependent on processing conditions and primary existing structural defects, while independent of the Mn concentration. An influence of primary defects on the structural transformations of the GaMnAs layer is discussed.Атомістичні методи імітаційного моделювання, основані на принципі мінімізації енергії, використані для вивчення структурних параметрів ряду орторомбічних R1–xPrxBa2Cu3O6.5 і пов'язаних з ними сполук. Нові міжатомні потенційні параметри взаємодії одержані для широкого діапазону оксидів, таких як CuO, R2O3, RBa2Cu3O6.5 і R1–xPrxBa2Cu3O6.5 (всього 62 сполуки). Одержані дані знаходяться в доброму узгoдженні з попередніми результатами експериментальних і теоретичних досліджень. Мета даної роботи – прогнозування решіточних потенціалів взаємодії, що можуть бути надалі використані як основа для теоретичного вивчення дефектної хімії надпровідних купратів та інших технологічно важливих оксидів

Atomistic studies of Li+ migration in Y₂O₃ and the structure of related oxides

Atomistic computer simulation techniques based on energy minimization have been employed to predict the equilibrium lattice parameters and volumes of a series of rare-earth sesquioxides and their polymorphs. The results have been found in agreement with experimental data and ab initio studies given in the literature. To demonstrate the applicability of the computational methodology the migration of lithium ions (Li⁺) in yttria (Y₂O₃) has been considered.Атомістичні методи комп’ютерного моделювання, основані на принципі мінімізації енергії, використані для прогнозування рівноважних параметрів і об’єма кристалічної гратки ряда рідкоземельних оксидів та їх поліморф. Результати моделювання знаходяться в доброму узгoдженні з експериментальними і літературними даними. Для демонстрації запропонованої обчислювальної методики розглянутo міграцію іонів літія (Li⁺) в оксиді ітрія (Y₂O₃).Атомистические методы компьютерного моделирования, основанные на принципе минимизации энергии, использованы для предсказания равновесных параметров и объема кристаллической решетки ряда редкоземельных оксидов и их полиморф. Результаты моделирования находятся в хорошем согласии с экспериментальными и литературными данными. Для демонстрации применимости предложенной вычислительной методики рассмотрена миграция ионов лития (Li⁺) в оксиде иттрия (Y₂O₃)

Aluminium-vacancy complexx in Ge₁₋ₓCₓ

A brief review on the potential importance of Ge₁₋ₓCₓ for electro-optic applications and ab initio calculations of the aluminium-vacancy complexes are presented. The stability and geometry of aluminium-vacancy complexes has been examined within the frame of density functional theory and the use of the pseudopotential plane-wave method. The predictions highlight the preference of the cluster geometry on the energetics in Ge₁₋ₓCₓ and the effect of carbon concentration on the stability of clusters

Condictivity anisotropy and pseudogap state evolution in HoBa₂Cu₃O₇₋δ single crystals of a present flat defect topology at decreasing oxygen concentration

The temperature dependences of electrical resistance along the c-axis and in the abplane for HoBa₂Cu₃O₇₋δ single crystals with various oxygen content have been measured. The temperature dependences of the pseudogap value have been determined. These dependences have been shown to be described satisfactority within the frame of crossover (BSC-BEK) theory. The intensification of localization effects results in depression of the pseudogap state. A considerable anisotropy of the superconductive properties has been observed when measuring the temperature dependences of electrical resistance along and across the basis plane

Optimizing oxygen diffusion in cathode materials for solid oxide fuel cells

Recent investigations have revealed that the Ruddlesden–Popper series ( A n+1 B n O 3n+1) and the layered perovskite Ln BaCo 2 O 5+δ (Ln = rare-earth cations) are promising as cathodes for intermediate temperature solid oxide fuel cells. For these to be economical the oxygen diffusion must be maximized. Based on atomistic simulations, we propose strategies for optimizing oxygen diffusion in these materials by modifying the oxygen stoichiometry, the composition and cation disorder. The present investigation is focused on La 2 CoO 4+δ and GdBaCo 2 O 5+δ and the results are discussed in view of recent experimental and theoretical studies. </jats:p

Transport anisotropy and pseudo-gap state in oxygen deficient ReBa₂Cu₃O_7-δ (Re = Y, Ho) single crystals

The temperature dependence of the transport anisotropy of ReBa2Cu3O7-δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals. oxygen deficiency results to uneven oxygen distribution Within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δc increases, the value of the pseudo-gap Δ*ab decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of he localization effects. In distinction to YBa2Cu3O7-δ, the temperature dependence of the anisotropy of the resistivity ρdρab(T) for the HoBa2Cu3O7-δ samples is well described, by the universal "law of 1/2" for the thermally activated hopping conductivity

Effect of high pressure on temperature dependences of the resistivity in the ab-plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals

In the present work, we investigated the influence of high hydrostatic pressure up to 11 kbar on the conductivity in the basal ab-plane of medium-doped with praseodymium (x≈0.23) single-crystal Y1-xPrxBa2Cu3O7-δ samples. It was determined that, in contrast to the pure YBa2Cu3O7-δsamples with the optimal oxygen content, the application of high pressure leads to the formation of phase separation in the basal plane of Y0.77Pr0.23Ba2Cu3O7-δ single crystals. Possible mechanisms of the effect of Pr doping and high pressure on the two-step resistive transition to the superconducting state are discussed. It was determined that in the normal state, the conductivity is metallic and is limited by phonons scattering (Bloch-Grüneisen regime) and defects. The fluctuation conductivity is considered within the Lorentz-Doniach model. Hydrostatic pressure, accompanied by a decrease in anisotropy, leads to a decrease in the residual and phonon resistances. Debye temperature and coherence length are independent of pressure. The applicability of the McMillan formula in the presence of significant anisotropy is discussed. © 2022, The Author(s)

Superconductivity suppression at twin boundaries and longitudinal and transversal transport anisotropy in oxygen deficient YBa₂Cu₃O₇₋ₓ single crystals

The temperature dependences of the conductivity along and across the basis plane have been measured in YBa₂Cu₃O₇₋ₓ single crystals with different oxygen non-stoichiometry. In the oxygen-deficit samples, an inhomogeneous oxygen distribution within the crystal bulk is found, that results in the formation of phases with different critical of superconducting transition temperatures. The accordance of the experimental results with the predictions of different theoretical models has been considered. It has been revealed that the anisotropy of the normal resistivity pc/pab(T) is described well using the universal "law of 1/2", for thermal activation of the hopping conductivity