Atomic-Scale Observation of Spontaneous Hole Doping and Concomitant Lattice Instabilities in Strained Nickelate Films

Thin oxide films are of vast opportunities for modern electronics and can facilitate emergent phenomena by factors absent in the bulk counterparts, such as the ubiquitous epitaxial strain and interfacial charge doping. Here, we demonstrate the twisting of intended bulk-metallic phases in 10-unit-cell LaNiO3, PrNiO3, and NdNiO3 films on (001)-oriented SrTiO3 into distinct charge-lattice entangled states by epitaxial strains. Using atomically-resolved electron microscopy and spectroscopy, the interfacial electron doping into SrTiO3 in the conventional context of band alignments are discounted. Instead, spontaneously doped holes that are localized and at the order of 1013 cm-2 are atomically unraveled across all three heterointerfaces and associated with strain mitigations by the accompanied atomic intermixing with various ionic radii. The epitaxial strains also lead to condensations of monoclinic-C2/c lattice instabilities, which are hidden to the bulk phase diagram. The group-theoretical analysis of characteristic transition pathways unveils the strain resurrection of the hidden C2/c symmetry. While this strain-induced monoclinic phase in LaNiO3 remains metallic at room temperature, those in PrNiO3 and NdNiO3 turn out to be insulating. Such strain-induced monoclinic lattice instabilities and parasitic localized holes go beyond the classical elastic deformations of films upon epitaxial strains and hint on plausible hidden orders in versatile oxide heterostructures with unexpected properties, of which the exploration is only at the infancy and full of potentials.

Interaction of Th(IV), Pu(IV) and Fe(III) with ferritin protein: how similar?

Ferritin is the main protein of Fe storage in eukaryote and prokaryote cells. It is a large multifunctional, multi-subunit protein consisting of heavy H and light L subunits. In the field of nuclear toxicology, it has been suggested that some actinide elements, such as thorium and plutonium at oxidation state +IV, have a comparable `biochemistry' to iron at oxidation state +III owing to their very high tendency for hydrolysis and somewhat comparable ionic radii. Therefore, the possible mechanisms of interaction of such actinide elements with the Fe storage protein is a fundamental question of bio-actinidic chemistry. We recently described the complexation of Pu(IV) and Th(IV) with horse spleen ferritin (composed mainly of L subunits). In this article, we bring another viewpoint to this question by further combining modeling with our previous EXAFS data for Pu(IV) and Th(IV). As a result, the interaction between the L subunits and both actinides appears to be non-specific but driven only by the density of the presence of Asp and Glu residues on the protein shell. The formation of an oxyhydroxide Th or Pu core has not been observed under the experimental conditions here, nor the interaction of Th or Pu with the ferric oxyhydroxide core.

Исследование структурного совершенства монокристаллов ниобата лития разного состава и генезиса методом ИК спектроскопии в области валентных колебаний водородных связей

We have analyzed complex defects due to the presence of hydrogen bonds in the crystal structure in nominally pure lithium niobate crystals with different Li/Nb ratio, in crystals alloyed with magnesium and zinc in a wide concentration range (LiNbO3 : Mg (0.19-5.91 mol.% MgO) and LiNbO3 : Zn (0.04-6.5 mol. % ZnO)) and in the double-alloyed crystals (LiNbO3 : Y(0.24) : Mg(0.63 wt. %) and LiNbO3 : Gd (0.25) : Mg(0.75 wt. %)), obtained by technology of direct melt alloying, and also in the double-alloyed crystal (LiNbO3 : Mg(5. 05 mol.% MgO) : Fe(0.009 mol.% Fe2O3)) grown from a charge synthesized using the technology of homogeneous alloying with magnesium and iron Nb2O5. We revealed the influence of doping impurities on the concentration of OH-groups, the type and localization of complex defects in the crystal structure. The change in the number of hydrogen atom positions in the structure of the LiNbO3 crystal allow us to judge with sufficient accuracy whether the crystal composition is stoichiometric or congruent. For doped crystals of different compositions data were obtained testifying to changes in the character of complexation of OH-groups with point defects of the cationic sublattice with formation of defects: MеLi-OH-, MеLi-MеNb-OН. A change in the mechanism of entry of the dopant cation into the structure dramatically affects the change in the properties of the crystal.The difference in the frequencies (and, correspondingly, in the values of the quasi-elastic constants of the O-H bonds) in the spectrum of a congruent crystal and doped crystals can also be contributed by differences in the electronegativity and ionic radii of the principal and doping cations.

COMPARATIVE ANALYSIS OF THE INFLUENCE OF DOPING IONS OF YTTRIUM AND BORON FORMATION OF DEFECTS IN LITHIUM NIOBATE CRYSTALS

Кристалл ниобата лития, являющийся широко используемым и весьма востребованным в настоящее время нелинейно-оптическим материалом, примечателен своей способностью к варьирования широкого спектра сегнетоэлектрических и нелинейно-оптических характеристик в зависимости от типа и концентрации примесного иона, а также от соотношения Li / Nb . На основе разработанного нами подхода к моделированию кластеров в кристалле ниобата лития, в котором рост кластера идёт не элементарными ячейками, а кислородными октаэдрами, проведён сравнительный анализ особенностей внедрения в кристалл примесных ионов иттрия и бора с одинаковым зарядом +3 . Показано, что встраивание, вследствие различного ионного радиуса, идёт по двум механизмам: если для металла иттрия действует обычный механизм, когда примесной ион локализуется внутри кислородного октаэдра, то ион неметаллического элемента бора встраивается в тетраэдрические пустоты структуры, а именно в кислородные плоскости, образующие октаэдр. При этом влияние данных примесных ионов на одну из важнейших характеристик ниобата лития оказывается диаметрально противоположным: иттрий усиливает фоторефрактивный эффект, бор -понижает, что необходимо учитывать при направлении целевого использования кристаллов ниобата лития. Lithium niobate crystals, which are a widely used and highly demanded as nonlinear optical material, are remarkable for their ability to vary a wide range of ferroelectric and nonlinear optical characteristics depending on the type and concentration of the impurity ion, as well as on the Li / Nb ratio. Based on our approach to modeling clusters in the lithium niobate crystal, in which the cluster grows not by unit cells, but by oxygen octahedra, we have carried out a comparative analysis of the features of the incorporation of impurity ions of yttrium and boron with the same charge +3 into the crystal. It is shown that due to the different ionic radii the incorporation proceeds by to two mechanisms. If for yttrium the usual mechanism operates, when the impurity ion is localized inside the oxygen octahedron. The ion of boron, i.e. a nonmetallic element, is incorporated into the tetrahedral voids of the structure, namely, into the oxygen planes forming the octahedron. In this case, the influence of these impurity ions on one of the most important characteristics of lithium niobate turns out to be diametrically opposite: yttrium enhances the photorefractive effect, boron decreases it, which must be taken into account in the direction of targeted use of lithium niobate crystals.

HYDROGEN BONDS IN LITHIUM NIOBATE CRYSTALS OF DIFFERENT COMPOSITION

Методом ИК-спектроскопии в области валентных колебаний OH - групп выполнен анализ комплексных дефектов, обусловленных наличием в структуре кристалла водородных связей, в номинально чистых кристаллах ниобата лития конгруэнтного и стехиометрического состава с разным отношением Li / Nb, а также в кристаллах LiNbO: Zn(0,04 - 6,5 мол.% ZnO), легированных цинком в широком диапазоне концентраций, полученным по технологии прямого легирования расплава. Выявлено влияние легирующих примесей на концентрацию OH - групп, вид и локализацию комплексных дефектов в структуре кристалла. Показано, что изменение количества позиций атомов водорода в структуре кристалла LiNbO позволяет с достаточной точностью судить о соответствии его состава стехиометрическому или конгруэнтному составу. Для легированных кристаллов LiNbO : Zn(0,04 - 6,5 мол.% ZnO) получены данные, свидетельствующие об изменении при прохождении концентрационных порогов характера комплексообразования OH - групп с точечными дефектами катионной подрешетки. При этом, вследствие изменения механизма вхождения легирующего катиона в структуру кардинально изменяются свойства кристалла. Вклад в различие частот (и, соответственно, в значение квазиупругих постоянных связей OH -) в спектре конгруэнтного кристалла и легированных кристаллов может вносить также различие электроотрицательностей и ионных радиусов основных и легирующих катионов. An analysis of complex defects was carried out by IR-spectroscopy method in the area of OH - groups stretching vibrations. The defects are caused by hydrogen bonds present in the structure of nominally pure congruent lithium niobate crystals, crystals of stoichiometric composition with a different Li / Nb ratio, as well as in LiNbO: Zn(0,04 - 6,5 мол.% ZnO) crystals doped in a wide range of concentrations due to direct doping of the melt method. Dopants were determined to influence OH - groups concentration, type and localization of complex defects in the crystals structure. A change in the amount of hydrogen sites in the LiNbO crystals structure was shown to evaluate the composition either stoichiometric or congruent. The character of OH - groups complexing with cation sublattice point defects was shown to change when doped crystals LiNbO: Zn(0,04 - 6,5 мол.% ZnO) trespass concentration thresholds. Dopant incorporation mechanism changes at this drastically, thus crystal properties also change quite sharply. Frequencies (as well as quasi-elastic constants of OH - bonds) change in congruent and doped crystals due to a difference in electronegativities and ionic radii of the main and dopant cations.

Effect of Yttrium Oxide in Hydroxyapatite Biocomposite Materials: Electrical and Antimicrobial Evaluation

Synthesis and characterization of biocomposite materials of hydroxyapatite (HA) and yttrium oxide (Y2O3) were investigated. HA nanoparticles powder was obtained from mussel shells via a wet chemical precipitation routine. HA powder was doped with 1 and 2 wt% of Y2O3 . For microstructural examination, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) coupled with energy dispersive X-rays (EDX) were used. In addition, the dielectric and electrical properties and antimicrobial activities were investigated. XRD patterns reveal the crystallization of the oxyapatite. The peak intensities of pristine HA are inferior compared to the yttrium containing HA composites, thus suggesting that the addition of yttrium promotes the crystallization of HA due to the variance in their ionic radii. FT-IR shows a variation in the phosphate wavenumber, indicating the integration of yttrium into the HA matrix. SEM reveals nanorod- or worm-like crystals arose in clusters. With increasing Y2O3, from 1 to 2 wt%, the DC conductivity reduces from 16 to 9.3 nS/cm, which confirms that high amounts of Y3+ substitute Ca2+ in the HA matrix. In the high-frequency range, the AC conductivity linearly increases with increasing frequency following the universal power law. Further, antimicrobial activity results showed that the addition of yttrium in HA improves the antimicrobial effects against pathogenic bacteria and fungi. Additional research is needed to investigate the doping concentration of yttrium ions, and an anticipated property could be comprehended for several forthcoming biomedical applications

Hydrothermal synthesis of ABi2Ta2O9Aurivillius phase: A comparative study of A-site cation size on structure, dielectric, optical properties

In this study, the double-layered Aurivillius phases CaBi2Ta2O9 (CBT) and PbBi2Ta2O9 (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an [Formula: see text]21am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca[Formula: see text] compared to Pb[Formula: see text]. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of [Formula: see text]-site cations (Ca[Formula: see text] and Pb[Formula: see text] strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca[Formula: see text] cations induced a higher structural distortion, which resulted in higher bandgap ([Formula: see text] energy and ferroelectric transition temperature ([Formula: see text] of CBT, compared to those of PBT.

IMPACT OF NEODYMIUM AND SCANDIUM IONIC RADII ON SORPTION DYNAMICS OF AMBERLITE IR120 AND AB-17-8 REMOTE INTERACTION

The aim of this research work is comparative study of influence of ionic radii of heavy metal ions of neodymium and scandium on their sorption process from corresponding water solutions of sulfates by sorbents such as individual ion-exchangers Amberlite IR120, AB-17-8 and mixture of these sorbents related to interpolymer system Amberlite IR120-AB-17-8 at the various molar relations. Laboratory experiments of this work of sorption heavy ions of neodymium and scandium were carried out and inves-tigated by using the following physico-chemical methods of analysis: conductometry-based on the electrical conductor, pH-metry-based on the concentration of hydrogen ions, colorimetry, atomic-emission spectro-scopy. Ion-exchangers in the interpolymer system undergo remote interaction with further transition into highly ionized state. There is formation of optimal conformation in structure of the initial ion- exchangers. Significant increase of ionization of the ion-exchange resins occurs at molar ratio Amberlite IR120:AB-17-8 = 5:1. Significant increase of sorption properties is observed at this ratio due to mutual activation of ion-exchangers. The extraction rate of Nd3+ ions in 48 hours is 42.32%, and the extraction rate of Sc3+ ions is 38.06%. A possible reason for higher sorption of neodymium ions in comparison with scandium ions is maximum conformity of globes of internode links of Amberlite IR120 and AB-17-8 after activation to sizes of neodymium sulfate in an aqueous medium.

Theoretical Insight Into Diamond Doping and Its Possible Effect on Diamond Tool Wear During Cutting of Steel

Natural diamond tools experience wear during cutting of steel. As reported in our previous work, Ga doping of diamond has an effect on suppressing graphitization of diamond which is a major route of wear. We investigate interstitial and substitutional dopants of different valence and different ionic radii (Ga, B, and He) to achieve a deeper understanding of inhibiting graphitization. In this study, ab initio calculations are used to explore the effects of three dopants that might affect the diamond wear. We consider mechanical effects via possible solution strengthening and electronic effects via dopant-induced modifications of the electronic structure. We find that the bulk modulus difference between pristine and doped diamond is clearly related to strain energies. Furthermore, boron doping makes the resulting graphite with stable sp2 hybridization more perfect than diamond, but Ga-doped diamond needs 2.49 eV to form the two graphene-like layers than only one layer, which would result in the suppressed graphitization and reduced chemical wear of the diamond tool.

Synthesis and Structural Characterisation of Yttrium-Doped α-Zirconium Phosphate

There has been a considerable amount of interest in the ion-exchange properties of layered zirconium phosphates. Potential applications in the remediation of nuclear waste have renewed interest in these inorganic materials, due to their high stability under the acidic conditions typically found in legacy waste pools. It has been well documented that the substitution of metals with different ionic radii into the frameworks of inorganic materials can alter the chemical properties including ion-exchange selectivity. The work presented here focusses on the synthesis and characterisation of yttrium-doped α-zirconium phosphates which are reported for the first time. Two different synthetic methods were used, reflux and hydrothermal syntheses, and the products were characterised by various methods such as powdered X-ray diffraction, MAS-NMR and scanning electron microscopy. It was found that up to 15% of zirconium could be replaced by yttrium before any noticeable impurity phases could be observed. Rietveld refinement from the doping showed that the products did not obey the Vegard’s law. However, the ion-exchange results clearly showed enhanced capacities and selectivity towards Co2+ ions for the substituted materials.