Impact of Cation Stoichiometry on the Crystalline Structure and Superconductivity in Nickelates

The recent discovery of superconductivity in infinite-layer nickelate films has aroused great interest since it provides a new platform to explore the mechanism of high-temperature superconductivity. However, superconductivity only appears in the thin film form and synthesizing superconducting nickelate films is extremely challenging, limiting the in-depth studies on this compound. Here, we explore the critical parameters in the growth of high-quality nickelate films using molecular beam epitaxy. We found that stoichiometry is crucial in optimizing the crystalline structure and realizing superconductivity in nickelate films. In precursor NdNiO3 films, optimal stoichiometry of cations yields the most compact lattice while off-stoichiometry of cations causes obvious lattice expansion, influencing the subsequent topotactic reduction and the emergence of superconductivity in infinite-layer nickelates. Surprisingly, in-situ reflection high energy electron diffraction indicates that some impurity phases always appear once Sr ions are doped into NdNiO3 although the X-ray diffraction data are of high quality. While these impurity phases do not seem to suppress the superconductivity, their impacts on the electronic and magnetic structure deserve further studies. Our work demonstrates and highlights the significance of cation stoichiometry in the superconducting nickelate family.

PRODUCTION OF SYNTHETIC WOLLASTONITE BASED ON PHOSPHORIC SLAG AND AMORPHOUS SILICA PRODUCED BY "SOLAR" SILICON

В статье приведены результаты исследований по получению синтетического волластонита на основе фосфорного шлаке и аморфного кремнезема от производства солнечного кремния. Установлено, что корректировка электротермофосфорного шлака аморфным кремнеземом от производства «солнечного» кремния облегчает процесс волластонитообразования, смещая его в область более низких температур 800-950оС и минимизирует количество примесных фаз при температурах 1000-1050оС устойчивого существования игольчатого волластонита. The article presents the results of research on the production of synthetic wollastonite based on phosphoric slag and amorphous silica from the production of solar silicon. It is established that the correction of electrothermophosphoric slag with amorphous silica from the production of "solar" silicon facilitates the process of wollastonite formation, shifting it to the region of lower temperatures of 800-950oC and minimizes the number of impurity phases at temperatures of 1000-1050oC for the stable existence of needle wollastonite.

Computationally accelerated discovery of high entropy pyrochlore oxides

High entropy ceramics provide enhanced flexibility for tailoring a wide range of physical properties, emerging from the diverse chemical and configurational degrees of freedom. Expanding upon the endeavors of recently synthesized high entropy ceramics in rock salt, fluorite, spinel and perovskite structures, we explore the relative feasibility of formation of high entropy pyrochlore oxides, A2B2O7, with multi-cation occupancy of the B-site, estimated from first principles based thermodynamic descriptors. Subsequently, we used Monte Carlo simulations to estimate the phase composition, oxygen vacancy concentration and local ionic segregation as a function of temperature and oxygen partial pressure. In parallel, we have investigated the synthesis of several multicomponent oxides with a pyrochlore composition, related to our computational investigations, resulting in several high purity pyrochlore oxides, in some cases with minor impurity phases. Ultimately, our approach allows us to evaluate potential impurity phases, ionic disorder and oxygen vacancy concentration in response to the experimental variables, thereby making realistic predictions that can direct and accelerate experimental synthesis of novel multicomponent ceramics.

Optimizations of the Sintering Temperature to Reduce the Nd3RuO7 Phase and Investigations of their Effect on the Magnetic Properties in Nd2Ru2O7

One of the pyrochlore systems, Nd2Ru2O7, shows unique magnetic properties and can be a candidate of the electrocatalyst material for industrial applications. This system shows magnetic anomalies around 1.8 K, 21 K, and 146 K. The anomaly at 21 K is suggested to be coming from the impurity component of Nd3RuO7 and is still debatable. To investigate the effects of impurities on the magnetic properties of this sample, we synthesized some samples (labelled as Sample-I and II) using the solid-state reaction method with different heat treatment conditions and measured the magnetic susceptibility. We found that low sintering temperatures generated impurity phases of raw materials and Nd3RuO7. We also confirmed that those impurity phases were able to be reduced by optimizing heat treatment conditions. The optimum temperature for the sintering process should not be higher than 1000°C. The higher sintering temperatures yield more Nd3RuO7 impurity phases. Magnetic susceptibility measurements showed that samples with Nd3RuO7 impurity phases exhibited a peak around 21 K in the zero field-cooled condition accompanied by a broad peak around 12 K in the field-cooled condition indicating the appearance of Nd3RuO7.

Особенности катионного распределения и магнитных свойств гексаферритов BaFe-=SUB=-12-x-=/SUB=-Y-=SUB=-x-=/SUB=-О-=SUB=-19-=/SUB=-

BaYxFe12-хO19 (0.1 ≤ x ≤ 1.2) hexaferrites were studied using Mössbauer spectroscopy, magnetometry, and X-ray diffraction. A low isomorphic capacity of hexaferrite is shown, which at x = 0.6 leads to phase separation with the formation of BaFe2O4 and Y3Fe5O12 impurity phases. The data of Mössbauer spectroscopy showed that the Y3 + ions occupied the 12k position with the formation of the nonequivalent position 12k ′ due to the breaking of two magnetic bonds Fe (12k) - O - Fe (12k) in the triad of octahedra 12k with their replacement by Fe (12k ) - O - Y (12k). It is shown that BaYxFe12-хO19 hexaferrites are less magnetically hard than BaFe12-хAlxO19.

Impurity Phases and Optoelectronic Properties of CuSbSe2 Thin Films Prepared by Cosputtering Process for Absorber Layer in Solar Cells

When there is a choice of materials for an application, particular emphasis should be given to the development of those that are low-cost, nontoxic, and Earth-abundant. Chalcostibite CuSbSe2 has gained attention as a potential absorber material for thin-film solar cells, since it exhibits a high absorption coefficient. In this study, CuSbSe2 thin films were deposited by radio frequency magnetron cosputtering with CuSe2 and Sb targets. A series of CuSbxSe2 thin films were prepared with different Sb contents adjusted by sputtering power, followed by rapid thermal annealing. Impurity phases and surface morphology of Cu–Sb–Se systems were directly affected by the Sb sputtering power, with the formation of volatile components. The crystallinity of the CuSbSe2 thin films was also enhanced in the near-stoichiometric system at an Sb sputtering power of 15 W, and considerable degradation in crystallinity occurred with a slight increase over 19 W. Resistivity, carrier mobility, and carrier concentration of the near-stoichiometric thin film were 14.4 Ω-cm, 3.27 cm2/V∙s, and 1.33 × 1017 cm−3, respectively. The optical band gap and absorption coefficient under the same conditions were 1.7 eV and 1.75 × 105 cm−1, which are acceptable for highly efficient thin-film solar cells.