Disorder Of Ions Research Articles

The Significance of Ion Conduction in a Hybrid Organic–Inorganic Lead‐Iodide‐Based Perovskite Photosensitizer

AbstractThe success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid‐state properties, these materials surprised by anomalies such as a huge apparent low‐frequency dielectric constant and pronounced hysteretic current–voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build‐up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic–inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.

The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead-Iodide-Based Perovskite Photosensitizer.

The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid-state properties, these materials surprised by anomalies such as a huge apparent low-frequency dielectric constant and pronounced hysteretic current-voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build-up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic-inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.

Protocolo diagnóstico de las alteraciones hidroelectrolíticas en el paciente pluripatológico

Nowadays we usually face pluripathological patients, with chronic treatments. These patients show many electrolyte disorders, which can depend on their chronic disease and their treatments, anintercurrent acute condition or both. Patients with chronic renal failure are the prototype of pluripathological patient with electrolyte disorders, because it can not only cause a large number of disorders itself but also it is usually associated with other diseases. However other frequent pathologies can also present ionic disorders such as hyponatremia in heart failure or hypokalemia in patients suffering arterial hypertension and treated with furosemide or thiazides. Other pathologies can also be diagnosed because of their ionic disorder, as it happens in diabetic patients, where we find metabolic acidosis in relation to hyperglycemic conditions. Poisoning by certain substances, for example metformin or lithium, can also cause ionic disorders.

Critical behavior and change in universality of La0.67Ba0.22Sr0.11Mn1−x Co x O3 manganites

The critical properties of the manganese perovskite La0.67Ba0.22Sr0.11Mn1−xCoxO3 (x = 0.0, 0.2 and 1.0) were investigated by analyzing the magnetic data and determining the critical exponents using different techniques such as Arrott–Noakes plots, plots of Kouvel–Fisher critical isotherms and scale analysis. The analysis indicated that the experimentally determined critical exponents of the compound La0.67Ba0.22Sr0.11MnO3 belong to the three-dimensional Heisenberg universality. However, the samples doped with Co (x = 0.2 and 1.0) were characterized by critical exponents belonging to the universality class of the long-range mean field theory. The observed transition in the universality of the manganite perovskite upon doping with Co could be due to the development of long-range dipolar interactions between the spins instigated by ionic disorder, and the increase in the number of localized eg and t2g electrons. The doping also resulted in progressive breaking Mn4+–O–Mn3+ links at the substituted sites as the Co concentration increased, resulting in a significant reduction in the saturation magnetization and the ferromagnetic correlation length.

Effects of different annealing atmospheres on magnetic properties in La2CoMnO6 single crystals

We have successfully synthesized the high-quality single crystals of double perovskite La2CoMnO6 by flux method and investigated the effects of different annealing conditions on the magnetic properties. In an as-grown crystal, ferromagnetic order along the c axis arises below 204 K, and the spin-glass-type behavior inherent from ionic disorders is also observed. Upon annealing in different gas environments, the reconstructed magnetic states induce a metamagnetic transition (after Ar annealing), and increase Curie temperature (after O2 annealing). After quenching, the magnetic transition temperature decreases significantly, comprising lots of defects and disorders. Our results provide adequate procedures to control magnetic properties of double-perovskite compounds.

Dielectric Properties and Relaxation of Bi2Ti2O7

The dielectric properties of Bi2Ti2O7 were explored as a function of temperature and frequency. A comparison between the dielectric response of the well‐known Bi1.5Zn0.92Nb1.5O6.92 (BZN) pyrochlore and the recently available Bi2Ti2O7 sintered ceramic revealed considerable differences, which indicate that chemical disorder, and not atomic displacement on its own, is chiefly responsible for the dielectric relaxation in bismuth pyrochlores. A low‐frequency (<10 kHz) and relatively high‐temperature (~125 K) dielectric relaxation was observed in Bi2Ti2O7. An Arrhenius function was used to model the relaxation behavior and yielded an activation energy of 0.162 eV and an attempt jump frequency of ~1 MHz. This response is consistent with space charge polarization and not the result of dipolar or ionic disorder.

Action of Gaseous Nitric Oxide on Some Physical and Chemical Parameters of Human Blood Samples

We studied the metabolic changes induced by gaseous nitric oxide in whole blood samples in vitro. Blood samples were collected from healthy donors (Nizhny Novgorod station of blood transfusion). We carried out the direct bubbling of blood samples (n = 14) with gaseous flow with NO in a special appliance. We modeled standard conditions using the apparatus “Plazon” (concentration NO 800 mcg/l). Middle power of gas flow was used. The blood sparging time was 2 min, and exposition time lasted 3 min. Every blood sample volume was 5 ml. All the parameters were controlled before and after blood processing with NO. We tested lactate dehydrogenase activity in direct and reverse reactions spectrometrically by G. A. Kochetov’s method. Aldehyde dehydrogenase activity was examined by B. M. Kershnhots’s and E. V. Serkina’s methods, superoxide dismutase—by T. V. Sirota’s technology. Total protein level was examined by modified Louri’s method. The concentration of lactate was tested with the automatic analyzer “SuperGL Ambulance”. The indices of acidbase balance and blood gases partial pressure were estimated with special analyzer “ABL-77”. Additional control of energy metabolism changes was accomplished with derivative parameters, such as coefficient of energy reaction balance and coefficient of substrate provision. Different changes of blood physical and chemical parameters are induced by NO-processing which was fixed in our experiments. There is an inhibition of erythrocytes energy metabolism, decreasing of plasma antioxidant reserves, moderate ionic disorders and of acid-base misbalance in blood samples in vitro. Besides, according to the indirect signs, the used regimen of NO-processing mainly affected erythrocytes, and stipulated methemoglobin formation. These data testify that the used dose of gaseous nitric oxide is too high for investigated human blood. In our opinion, registered negative effects of free NO may be eliminated by bound nitric oxide use (first of all in its natural form—dinitrosyl-iron complexes).

Influence of Ce substitution on the order-to-disorder structural transition, thermal expansion and electrical properties in Sm2Zr2−xCexO7 system

Cerium substituted rare earth zirconates of the form Sm2Zr2−xCexO7 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized via solid state reaction route. Structural, morphological and electrical characterizations were conducted using high temperature X-ray diffraction, FT Raman spectroscopy, thermo-mechanical analysis, scanning electron microscopy and impedance spectroscopy techniques. Addition of Ce ions into the crystal induced structural disorder to both cationic and anionic sublattices, gradually transforming the unit cell from an ordered pyrochlore to a defect fluorite structure. Substitution of bigger Ce ions to the Zr sites led to an increase in the lattice parameter and a decrease in thermal expansion coefficient of the material. The ionic disorder led to a decreased energy barrier for the thermally activated conduction process thereby increasing the overall conductivity of the materials. The maximum value of total conductivity observed in this study is 3.93 × 10−3 S cm−1 at 1023 K, which is higher than the recently reported values in a similar Sm2Zr2O7 system. Beyond x = 0.4, the ion–ion interaction in the disordered lattice began to dominate, leading to an increased activation energy and decreased total conductivity. The results demonstrate that the thermal expansion of these oxides is predominantly influenced by the B–O bond energy rather than the Madelung binding energy.

Neutron powder diffraction and molecular dynamics study of superionic SrBr2

The nature of the dynamic ionic disorder within the high-temperature superionic phase of strontium bromide, β-SrBr2, has been investigated using reverse Monte Carlo (RMC) modelling of neutron powder diffraction data and complementary ab initio molecular dynamics (MD) simulations. The RMC and MD results are in good agreement and indicate the presence of extensive dynamic disorder within the Br− sublattice of the cubic fluorite structure. Rapid anion diffusion predominantly occurs as hops between nearest neighbour sites in the 〈100〉 directions, though the trajectories are markedly curved and pass through the peripheries of the octahedral voids in the cation sublattice. In addition, there are extensive correlations between the motions of individual Br−, often leading to the formation of a short-lived square antiprism co-ordination environment around the Sr2+. Such polyhedra are observed within the (ambient temperature) ordered tetragonal crystal structure of α-SrBr2. The nature of the ionic disorder in SrBr2 is of particular interest because it is the only known example of a Br−-ion superionic. Owing to the large size of this anion, a comparison with the behaviour of other superionic phases gives an insight into the role of ionic size on the conducting properties within these materials.

Low prevalence of hyponatremia codification in departments of internal medicine and its prognostic implications

Objective:Hyponatremia is the most frequent ionic disorder among ambulatory and hospitalized populations. The aim of the study is to describe the profile of patients admitted to internal medicine departments of Spanish hospitals with a diagnostic codification of hyponatremia in their discharge sheets.Methods:Data from the Minimum Basic Data Set (MBDS) of discharged patients from all departments of internal medicine (IM) of the Spanish National Health System (NHS) between 2007 and 2010 were analyzed to describe the profile of patients with diagnostic codification of hyponatremia.Results:A total of 2,134,363 admittances were analyzed, identifying 31,933 (1.5%) with a diagnostic code of hyponatremia (18.3% as principal diagnosis and 81.7% as secondary diagnosis). Mortality among patients with codified hyponatremia was markedly higher than in patients without this condition (13.1% vs 9.8% [OR 1.38; 95% CI 1.33–1.41]). Hyponatremia codification was independently associated with a higher risk of readmission (OR 1.33 CI 95% 1.29–1.38). Average length of stay for patients with hyponatremia was 11.67 days (SD 13.01), compared to 9.84 days (SD 11.61) among the general population admitted to IM (p < 0.001). Mean cost per admission in the presence of codified hyponatremia was €4023 (SD €2531), compared to €3537 (SD €2858.02); p < 0.001. Hyponatremia was more prevalent among patients with the following conditions: dementia, chronic and acute renal failure, hepatic cirrhosis, pressure ulcers, heart failure, and depression.Conclusions:We found an extremely low prevalence of hyponatremia codification in our series (1.5%). Hyponatremia is underreported and undertreated although numerous studies have shown its devastating impact on hospital admittance. The first step in order to improve this situation is to raise awareness among physicians about a problem that despite its high prevalence is still overlooked.

Estimation of some molecular effects of gaseous nitrogen oxide on human blood in vitro

The aim of this work is complex estimation of the nitric oxide action on whole blood of healthy people. We tested the reaction of whole human blood (n=14) to the processing of it with cold NO-containing plasma. We performed direct sparging of blood samples by gaseous flow with NO in a special plant. Cold NO-containing plasma was generated by apparatus "Plazon" (Russia). We tested lactate dehydrogenase activity in direct and reverse reactions, aldehyde dehydrogenase and superoxide dismutase activity, total protein and lactate level, acid-base balance and the partial pressure of gases in blood. For integral assessment of energy metabolism changes a number of derivative parameters (coefficients of energy reaction balance and substrate provision) were used. Our experiments showed, that the processing of whole human blood with NO-containing gas flow (NO concentration--800 ppm) results in significant changes of its physical and chemical parameters. This exposure leads to inhibition of erythrocytes energy metabolism, decreasing plasma antioxidant reserves, developing moderate ionic disorders and acid-base disbalance in blood samples in vitro.

Limits to Doping of Wide Band Gap Semiconductors

The role of defects in materials is one of the long-standing issues in solid-state chemistry and physics. On one hand, intrinsic ionic disorder involving stoichiometric amounts of lattice vacancies and interstitials is known to form in highly ionic crystals. There is a substantial literature on defect formation and the phenomenological limits of doping in this class of materials; in particular, involving the application of predictive quantum mechanical electronic structure computations. Most wide band gap materials conduct only electrons and few conduct holes, but rarely are both modes of conduction accessible in a single chemical system. The energies of electrons and holes are taken from the vertical ionization potentials and electron affinities; polaronic trapping of carriers is excluded. While the focus here is defect energetics, the atomic and electronic structures have been carefully examined in all cases to ensure physical results were obtained.

Multiferroicity in Mn-deficient Ca3CoMnO6: The consequence of Fe substitution

We present careful experiments on the multiferroicity in Ca3CoMn0.92O6 by Fe substitution of Mn. It is revealed that a proper Fe substitution modulates the Co/Mn spin order, favoring the ferroelectricity. The multifold interactions between the intra-chain spins and inter-chain spins are analyzed. It is suggested that the Mn deficiency and Fe substitution can break the inter-chain interactions to some extent, resulting in the delicate competition between these mutual interactions. The modulation of the ionic (charge) disorder and spin frustration order is the core physics for improving the ferroelectric performance.

Pressure-Controlled Neutral–Ionic Transition and Disordering of NH···N Hydrogen Bonds in Pyrazole

Pyrazole exhibits exceptional effects of temperature and pressure for H-disorder in hydrogen bonds NH···N. Under normal conditions, α-pyrazole is polar (orthorhombic space group Pna21), but the structure is pseudo-centrosymmetric. Two symmetry-independent molecules differently favor the H-sites at their amine nitrogen atoms. The asymmetric disorder of protons in hydrogen bonds NH···N leads to the disproportionation favoring the cations at one site and anions at the other. High temperature increases distortions of the structure from the centrosymmetric symmetry, activates the disproportionation defects, and stabilizes the averaged ionic disparity of symmetry-independent molecules at the ±0.1 e level. Critical pressure Pc = 0.45 GPa induces a transition to centrosymmetric phase β, space group Pnab. This transition involves the 50:50 H-disordering in NH···N hydrogen bonds and eliminates molecular displacements as well as the favored H-sites. The NH···N bonds are hardly compressed at Pc in pyrazole, and they...

The mechanism of ultrafast structural switching in superionic copper (I) sulphide nanocrystals

Superionic materials are multi-component solids with simultaneous characteristics of both a solid and a liquid. Above a critical temperature associated with a structural phase transition, they exhibit liquid-like ionic conductivities and dynamic disorder within a rigid crystalline structure. Broad applications as electrochemical storage materials and resistive switching devices follow from this abrupt change in ionic mobility, but the microscopic pathways and speed limits associated with this switching process are largely unknown. Here we use ultrafast X-ray spectroscopy and scattering techniques to obtain an atomic-level, real-time view of the transition state in copper sulphide nanocrystals. We observe the transformation to occur on a twenty picosecond timescale and show that this is determined by the ionic hopping time.

Cathodoluminescence insights into the ionic disorder of photocatalytic anatase films

The nature of ionic disorder and the effect of structural defects on the photocatalytic function of anatase are revisited in the light of direct experimental evidence retrieved on the molecular scale by cathodoluminescence (CL) spectroscopy. CL spectra, collected on different types of photocatalytically efficient or inefficient anatase films, embodied a composite optical response of electron-compensating majority types of ionic disorder in the anatase lattice. This paper describes the dual experimental output obtained by systematically monitoring optically active off-stoichiometry sites, as follows: (i) quantitative analyses of film stoichiometry including the interactions of different lattice-defect populations; and (ii) stability/evolution of off-stoichiometry sites upon post-fabrication annealing cycles and their effects on the photocatalytic activity of the films. CL experiments provided us with direct access to the structural state of the defective anatase lattice, thus unfolding some missing detail about the complex physicochemical interactions behind its photocatalytic efficiency.

Magnetic Properties of the Double Perovskites (Sr1-xLax)2CoMO6 with M = Sb, Nb, and Ta

We have investigated the crystalline structure and the magnetic properties of (Sr 1- x La x ) 2 Co M O 6 with M = Sb, Nb, and Ta. For M = Sb, an almost completely ordered double perovskite structure was realized for all x . On the other hand for M = Nb and Ta, the ionic disorder of Co and M ions occurs for x ≤0.1, while the ionic order increases with increasing Co 2+ content resulting from La 3+ substitution. The magnetic susceptibility (χ) for M = Sb showed a Curie–Weiss-like temperature dependence for all x values, suggesting the high-spin (HS) or the intermediate-spin (IS) state as the ground state of Co-3 d electrons. For M = Nb and Ta with x ≤0.1, the spin state of Co ions is interpreted as a mixture of Co ions with LS and IS (and/or HS) states, and a spin-glass-like freezing of the magnetic Co ions occurs below 20 K. For x ≥0.2, HS or IS states becomes dominant with increasing the ionic order of Co and M . We infer that the difference in the covalent character between M 5+ –O 2- bond for M = Sb and that for M = Nb or Ta is the origin of both the difference of the ionic order and the difference of the spin state of Co ions through the crystalline field around them.

Multiferroic properties in orthorhombic perovskite manganites: Monte Carlo simulation

In this work, a random field method (based on Mochizuki-Furukawa model) is used to study the effect of the R-site ionic disorder and inhomogeneity on the multiferroic behavior in orthorhombic manganites. It is shown that both the R-site ionic disorder and inhomogeneity can drive the reorientation of the plane in which cycloidal spin order takes place and actually lead to the flop of the spins from the ab-plane to the bc-plane. The simulated results can be understood as the consequence of the competition between exchange interactions and spin-orbit coupling.

Lead‐Free Relaxor Ferroelectrics

Feature size is a natural determinant of material properties. Its design offers the technological perspectives for material improvement. Grain size, crystallite size, domain width, and structural defects of different nature constitute the classical design elements. Common ferroelectric ceramics contain micrometer grain sizes and submicrometer domain widths. Domain wall mobility is a major contribution to their macroscopic material properties providing approximately half of the macroscopic output in optimized materials. The extension into the dynamic nanoworld is provided by relaxor ferroelectrics. Ionic and nanoscale field disorders form the base to a state with natural nanometer‐size polar structures even in bulk materials. These polar structures are highly mobile and can dynamically change over several orders of magnitude in time and space being extremely sensitive to external stimuli. This yields among the largest dielectric and piezoelectric constants known. In this feature article, we want to outline how lead‐free relaxors will offer a route to an environmentally safer option in this outstanding material class. Properties of uniaxial, planar, and volumetric relaxor compositions will be discussed. They provide a broader and more interesting scope of physical properties and features than the classical lead‐containing relaxor compositions.

Raman and IR studies of TaWO5.5, ASbWO6 (A = K, Rb, Cs, Tl), and ASbWO6·H2O (A = H, NH4, Li, Na) pyrochlore oxides

AbstractRaman and infrared (IR) spectra of defect pyrochlores TaWO5.5, NH4SbWO6·H2O, HSbWO6·H2O, LiSbWO6·H2O, NaSbWO6·H2O, KSbWO6, RbSbWO6, CsSbWO6, and TlSbWO6 were measured. The obtained spectra are discussed using the factor group approach for the cubic Fd‐3m space group, and assignment of bands to respective motions of atoms is proposed. Our results show that the phonon properties of the pyrochlores are strongly affected by disorder, and therefore Raman and IR spectroscopies are very useful tools in studying disorder in this family of compounds. In particular, our studies have shown that in these ionic conductors disorder at sites occupied by NH$_{4}^{+}$, H+, or alkali‐metal ions decreases with increasing size and mass of these ions. Copyright © 2010 John Wiley &amp; Sons, Ltd.