Influence Of Nonstoichiometry Research Articles

Influence of Nonstoichiometry on the Magnetic Properties of CeFe2:Mn Alloys

Influence of Nonstoichiometry on the Magnetic Properties of CeFe2:Mn Alloys

Influence of Nonstoichiometry on the Viscoelastic Properties of a Polyelectrolyte Complex

Influence of Nonstoichiometry on the Viscoelastic Properties of a Polyelectrolyte Complex

High-energy ball milling of nonstoichiometric compounds

The preparation of nanocrystalline powders of nonstoichiometric compounds such as carbides and oxides by high-energy milling is considered. The modern state of milling models for nonstoichiometric compounds is described. The influence of nonstoichiometry on the particle size of the produced nanopowders is discussed. The model dependences of the size of nanopowder particles on the duration of milling and the composition of nonstoichiometric compounds are compared with the literature experimental results on the milling of nonstoichiometric carbides and oxides. Diffraction methods for the certification of nanopowders according to the size of the nanoparticles, the magnitude of microstrains, and the uniformity of the microstructure are considered in detail. The importance of taking into account the anisotropy of microstrains in milled nanopowders is shown.

(Invited) Functional Defects By Design—a High-Throughput Approach to Energy Materials Discovery

Defects and impurities introduce localized heterogeneities in solids and decisively control the behavior of a wide range of energy technologies. Fuel cell materials, especially proton conducting fuel cells, are a quintessential example in this regard. Designing and developing solid oxide materials that can selectively transport protons will enable us to develop the next generation proton conducting solid oxide fuel cells. Protons require less activation energy compared to oxygen ions which results in a lower operating temperature, higher operating efficiency and better material reliability. In this work [1,2,3,4] we focus obtaining fundamental insights on how properties of host material structure along with dopants, disorder and strain influences proton transport properties in solid oxides by coupling high-throughput computations with functional imaging, neutron spectroscopy and transport measurements.We initially focus on the perovskite family of compounds (such as doped BaZrO3). We benchmark our calculations against a wide range of experimental measurements such as kelvin probe force microscopy (KPFM), inelastic neutron scattering (INS) and atom probe tomography (APT). To obtain better insights on why certain cubic perovskite/dopant combinations are better at conducting protons compared to others, we developed a high-throughput framework to perform ab initio calculations. The high-throughput framework can scale massively to tens of thousands of nodes to fully exploit the computational capability of the Oak Ridge Leadership Computing facility. We employ this approach to calculate proton transport properties in several cubic perovskite materials with different host atoms and dopants. The results obtained from these calculations enables us to obtain better insights on how material structure – such as atomic properties (electronegativity, ionic radius) and lattice properties (sub-lattice distortion) influences proton transport. The results obtained from this high-throughput analysis is being employed to develop a machine learning framework to predict structure-property correlations on a larger set of perovskites materials. Finally, we explore the role of disorder on proton transport by studying for example fluorite based lanthanum tungstate materials. [1] “Defect Genome of Cubic Perovskites for Fuel Cell Applications”, Journal of Physical Chemistry C, 121, 26637 (2017)[2] “The Influence of Local Distortions on Proton Mobility in Acceptor Doped Perovskites”, Chemistry of Materials, 2018, 30 (15), pp 4919–4925[3]“The Influence of the Local Structure on Proton Transport in a Solid Oxide Proton Conductor La0.8Ba1.2GaO3.9”, J. Mat. Chem. A, 5, 15507 (2017)[4] “Influence of Non-Stoichiometry on Proton Conductivity in Thin Film Yttrium-doped Barium Zirconate”, ACS Appl. Mater. Interfaces, 2018, 10 (5), pp 4816–4823

Influence of Nonstoichiometry in Fluoride Phase on the Ionic Conductivity of Composite Fluoride‒Oxide Materials 90PrF3 · 10Al2O3 and 90Pr0.95Sr0.05F2.95 · 10Al2O3

The two-phase fluoride oxide composite 90Pr0.95Sr0.05F2.95 · 10Al2O3 (mol %) composed of a highly conductive fluoride matrix with a tysonite structure (LaF3) and aluminium oxide is of interest as a solid electrolyte membrane in a potentiometric oxygen sensor with an auxiliary electrode. The ionic conductivity of the composite 90Pr0.95Sr0.05F2.95 · 10Al2O3 has been determined by impedance spectroscopy in vacuum (~0.1 Pa) in the temperature range of 293‒700 K. Its dominant component is the conducting non-stoichiometric tysonite phase Pr0.95Sr0.05F2.95. To estimate the contribution of this phase to the composite conductivity, the conductivities of the single-phase (single-crystal) PrF3 and Pr0.95Sr0.05F2.95 bases and a twophase composite 90PrF3 · 10Al2O3 with a stoichiometric fluoride matrix PrF3 have been investigated. The use of the nonstoichiometric phase Pr0.95Sr0.05F2.95 as a composite matrix instead of PrF3 leads to an improvement of ionic conductivity by a factor of ~200: to 5 × 10–3 S/cm at 400°C.

Influence of Nonstoichiometry on Proton Conductivity in Thin-Film Yttrium-Doped Barium Zirconate.

Proton-conducting perovskites have been widely studied because of their potential application as solid electrolytes in intermediate temperature solid oxide fuel cells. Structural and chemical heterogeneities can develop during synthesis, device fabrication, or service, which can profoundly affect proton transport. Here, we use time-resolved Kelvin probe force microscopy, scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations to intentionally introduce Ba-deficient planar and spherical defects and link the resultant atomic structure with proton transport behavior in both stoichiometric and nonstoichiometric epitaxial, yttrium-doped barium zirconate thin films. The defects were intentionally induced through high-temperature annealing treatment, while maintaining the epitaxial single crystalline structure of the films, with an overall relaxation in the atomic structure. The annealed samples showed smaller magnitudes of local lattice distortions because of the formation of proton polarons, thereby leading to decreased proton-trapping effect. This resulted in a decrease in the activation energy for proton transport, leading to faster proton transport.

Влияние нестехиометричности карбидной фазы системы Fe—Al—C на её электронную структуру и магнитные свойства

Влияние нестехиометричности карбидной фазы системы Fe—Al—C на её электронную структуру и магнитные свойства

The influence of nonstoichiometry on elastic characteristics of metastable β-WC1–x phase in ion plasma condensates

The dependence of elastic moduli for different directions on the nonstoichiometry with respect to carbon atoms in octahedral interstices of face-centered cubic crystalline lattice is established for the first time for metastable tungsten carbide (β-WC1–x phase). It is shown that with decreasing content of carbon atoms in the tungsten carbide lattice it is compressed, which is accompanied by the growth of the contribution of metallic component, thus determining higher density of the coating material and change of elastic characteristics for different crystallographic directions. This makes it possible to obtain carbide coatings with the required ratio of elastic constants via corresponding technological regimes, which is especially important in formation of coatings with predominant crystallite growth orientation.

Investigation of the influence of nonstoichiometry and doping with carbon and nitrogen on the electronic spectrum of rutile by the coherent potential method

The electronic spectra and magnetic properties of rutile (TiO2), nonstoichiometric rutile (TiO2 − δ), and stoichiometric and nonstoichiometric rutiles doped with carbon or nitrogen (TiO2 − y − δCy and TiO2 − y − δNy, y(δ) = 0, 0.03, 0.06) have been calculated using the coherent potential method. The used method of investigation has made it possible for the first time to calculate the disordered arrangement of impurity atoms and vacancies in the oxygen sublattice with their arbitrary concentration. The changes in the electronic spectrum and magnetic properties with variations in the concentration of dopants have been investigated. The possible photocatalytic activity of considered compositions has been analyzed.

The influence of nonstoichiometry on LaMnO3 perovskite for catalytic NO oxidation

A series of structural modified LaxMnO3 (x=0.9, 0.95, 1, 1.05, 1.11) perovskites used for NO oxidation was synthesized by a sol–gel method and characterized by XRD, BET, XPS, EPR and H2-TPR. La0.9MnO3 sample exhibits superior activity, and a 50% NO conversion at 250°C is obtained. XPS and EPR results reveal a higher Mn4+/Mn3+ ratio in Mn-rich samples, which induce more active oxygen bonding to Mn4+ due to the need for balancing the chemical states and stabilizing the structure. Easily regenerated oxygen associated with Mn4+ catalyzes the low-temperature NO oxidation. The constant activation energy (44.8kJ/mol) obtained in the kinetics tests indicates the same mechanism of NO oxidation operated on all the samples.

Influence of Nonstoichiometry on Extrinsic Electrical Conduction and Microwave Dielectric Loss of BaCo1/3Nb2/3O3Ceramics

The microwave (MW) dielectric loss (or quality factor,Q) of BaCo1/3Nb2/3O3(BCN) ceramics exhibits a strong dependence on sample‐processing conditions and is not always consistent with the degree of 1:2 B‐site cation ordering. Impedance spectroscopy results reveal that these BCN ceramics exhibit remarkably different electrical properties due to low levels of nonstoichiometry induced during ceramic processing. These compositional changes are difficult to detect by common chemical techniques but can have a significant influence on the electrical properties, and in particular on the extrinsic electrical conduction andQ. The influence of extrinsic conduction induced by ceramic processing should therefore be considered when optimizingQin MW dielectric ceramics.

The Influence of Non-Stoichiometry on the Corrosion Kinetics of Uranium Dioxide

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Ionic conduction in Ba xCe 0.8Pr 0.2O 3–α

Ba x Ce 0.8Pr 0.2O 3– α ( x=0.98–1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500–900 °C. The influence of nonstoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba 1.03Ce 0.8Pr 0.2O 3– α was a pure protonic conductor, and Ba 0.98Ce 0.8Pr 0.2O 3– α was a mixed conductor of protons and electrons in wet hydrogen at 500–900 °C. BaCe 0.8Pr 0.2O 3– α was a pure protonic conductor in 500–600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500–900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.

Influence of nonstoichiometry on ferroelectric phase transition in BaTiO3

The ferroelectric phase transition behavior in equilibrated nonstoichiometric BaTiO3 powder samples was characterized by a differential scanning calorimeter. The transition temperature (TC) and enthalpy of transition (ΔHTC) between the paraelectric and ferroelectric phases were varied systematically with defect concentrations through the Ba∕Ti ratio, temperature, and oxygen partial pressure [p(O2)]. It was observed that the different defects such as titanium, barium, and oxygen vacancies all contribute to the changes of TC and ΔHTC. The TC decreased with increasing concentration of TiO2 partial Schottky defects and BaO partial Schottky defects. The annealing temperature increased the TC due to a complex mechanism with the increase of full Schottky defect reactions. In terms of p(O2), TC is constant in the ionic compensation region, and increases with the nonstoichiometry in the electronically compensated p(O2) region.

Mixed Conduction in Tb2O3 Doped BaCeO3

AbstractBaxCe0.8Tb0.2O3−α (x=0.98–1.03) solid electrolytes were synthesized and characterized by using X‐ray diffraction (XRD). By using AC impedance spectroscopy and gas concentration cell electromotive force (EMF) measurements, the electrical conduction behavior of the specimens was investigated in different gases during 500–1000 °C. The influence of nonstoichiometry in the specimens with x≠1 on conduction properties was studied and compared with that in the specimen with x=1. The results show that the specimens are all of perovskite‐type orthorhombic structure. In 500–1000 °C, electronic hole conduction is dominant in dry and wet oxygen, air or nitrogen. Protonic conduction is dominant in wet hydrogen and it is about two orders of magnitude higher than that in hydrogen‐free atmospheres (oxygen, air and nitrogen). The electrical conductivity of the same specimen in water vapor‐saturated oxygen, air or nitrogen is slightly higher than that in corresponding gas without water vapor. The electrical conductivities of the nonstoichiometric specimens are higher than those of the stoichiometric one.

Ionic conduction in Ba xCe 0.8Er 0.2O 3− α

Ba x Ce 0.8Er 0.2O 3− α ( x=0.98–1.03) solid electrolytes were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the specimens were a single perovskite-type orthorhombic phase. The conduction properties of the specimens were studied electrochemically in the temperature range of 600–1000 °C. The influence of nonstoichiometry in the specimens with x≠1 on conduction properties was investigated and compared with that in the specimen with x=1. These three specimens showed a good protonic conduction under wet hydrogen, a mixed conduction of oxide-ion and electronic hole under dry higher oxygen partial pressure, and a mixed conduction of proton, oxide-ion and electronic hole under wet higher oxygen partial pressure. Both of the protonic and oxide-ionic conductivities increased with increasing barium content in the specimens under wet hydrogen and dry air, respectively.

Influence of nonstoichiometry on long-range order and its measurement in (GaAs)1−xGe2x and related alloys

The influence of nonstoichiometry on long-range order in metastable alloys of GaAs with Ge has been studied using Monte Carlo simulations and analytic approximations based on the Davis–Holloway stochastic growth model applied to a 〈111〉 growth direction. The results show that the direct effects of nonstoichiometry on long-range order are relatively small. However, deviations from stoichiometry comparable to those reported previously can introduce significant errors into x-ray measurements of the order parameter. It is shown that discrepancies between measured order parameters and those calculated using the growth model can be explained as arising from the unrecognized effects of nonstoichiometry on the x-ray measurements. An incidental result of the analysis is that the long-range order predicted by the Davis-Holloway model arises entirely from its prohibition of Ga-Ga nearest-neighbor pairs. Identical results are obtained with and without the additional prohibition of As-As nearest-neighbor pairs.

Influence of Nonstoichiometry and Iron Doping on Optical Absorption in KNbO 3 Single Crystals

Single crystals of KNbO 3 and KNbO 3 : Fe have been grown from the K 2 CO 3 -Nb 2 O 5 melted solution at various technological conditions. The investigations of optical absorption of these crystals were carried out. Marked influence of technological conditions and doping with iron on optical absorption has been found. Observed changes of the absorption spectra are associated with lattice defects arising due to nonstoichiometry and/or doping.

Electrical properties of Na1/2Bi1/2TiO3–BaTiO3 ceramics

Abstract Lead-free Na 1/2 Bi 1/2 TiO 3 –BaTiO 3 piezoelectric ceramics with perovskite structure were studied. The piezoelectric properties of (1− x )Na 1/2 Bi 1/2 TiO 3 – x BaTiO 3 ( x =0.02, 0.04, 0.06, 0.08, 0.10) ceramics were reported and their piezoelectric properties reach extreme values near the MPB (about x =0.06). Influences of nonstoichiometry and doping on the structures and piezoelectric properties of (Na 1/2 Bi 1/2 ) 0.92 Ba 0.08 TiO 3 ceramics were further studied. The relationship between piezoelectric constant and depolarization temperature of nonstoichiometric and doped ceramics was also investigated. It was found that in most of Na 1/2 Bi 1/2 TiO 3 –BaTiO 3 ceramics studied, their depolarization temperatures were much lower than maximum temperatures of dielectric constant–temperature curves; the origin of this phenomenon was discussed.

Nonstoichiometry and critical temperature of MgB2

The influence of nonstoichiometry of the new high-temperature superconductor MgB2 on its critical temperature was studied by the direct magnetooptical observations of the penetration and trapping of magnetic flux. To preclude the possible influence of accidental factors, a special sample with transition from pure boron to the MgB2 with an excess of Mg was synthesized. In a narrow region near the unreacted boron, the magnetic-field trapping and screening disappear at a temperature 1.5 K higher than in the dominant stoichiometric region of the sample.