Rock Salt Layers Research Articles

A Natural 2D Heterostructure [Pb3.1Sb0.9S4][Au xTe2- x] with Large Transverse Nonsaturating Negative Magnetoresistance and High Electron Mobility.

We report the two-dimensional (2D) natural heterostructure [Pb3.1Sb0.9S4][Au xTe2- x] ( x = 0.52-0.36) which shows anomalous, transverse nonsaturating negative magnetoresistance (MR). For x = 0.52, the material has a commensurately modulated structure with alternating [Pb3.1Sb0.9S4] rocksalt layers and atomically thin [Au xTe2- x] sheets, as determined by single-crystal X-ray diffraction using a (3 + 1)-dimensional space group; for other x compositions, the modulated structure is absent and the Au and Te atoms are disordered. The transport properties in this system at low temperature (<100 K) are dominated by an unusual 2D hopping mechanism, while at room temperature a high carrier mobility of ∼1352 cm2 V-1 s-1 is obtained ( x = 0.36). The confined electrons within the [Au xTe2- x] layers are also exposed to interlayer coupling with the insulating [Pb3.1Sb0.9S4] layers, and as a result, the properties of the heterostructures emerge not only from the constituent layers but also the interactions between them. Furthermore, the various Au and Te coordination patterns found in the [Au xTe2- x] sheets as a function of x further contribute to a unique electronic structure that leads to the anomalous nonsaturating negative MR with different field dependent behaviors. First-principles calculations indicate that the [Au xTe2- x] sheets are responsible for the unusual electrical transport properties in this 2D system.

Thin Film Fabrication and Characterization of Layered Rock Salt LiCoO2 on Quartz Glass Spray-Coated with an Aqueous Ammonia Solution Involving Metal Acetates

A LiCoO2 thin film on a quartz glass substrate was fabricated by a wet process involving heat treatment of a precursor film spray-coated with an aqueous ammonia solution containing LiCH3COO and Co(CH3COO)2. The precursor film formed onto the substrate at 180 °C in air, and was heat treated at 500 °C in air for 0.5 h. The obtained film was spin-coated further with an ethanol-based precursor solution containing identical metal acetates, and heat treated at 500 °C in air for 0.5 h. The X-ray diffraction pattern of the resultant film showed only peaks assignable to the layered-rock-salt LiCoO2. Raman spectroscopy measurements revealed vibrational modes assignable to layered rock salt LiCoO2, with minor content of less than 5 mol% of spinel-type Co3O4. The field emission scanning electron microscopy images indicated that the resultant film was 0.21 μm thick, had no voids, and was a combination of small rounded grains measuring 18 nm in diameter and hexagonal grains larger than 0.2 μm in length. The Hall effect measurements indicated that the resultant thin film was a p-type semiconductor with electrical resistivity of 35(2) Ω·cm and a carrier concentration and carrier mobility of 8(2) × 1016 cm−3 and 2(1) cm2·V−1·s−1, respectively.

Use of Alternative Hydrogeological Conceptual Models to Assess the Potential Impact of Climate Change on Groundwater Sustainable Yield in Central Huai Luang Basin, Northeast Thailand

Sustainable management of groundwater resources is essential for sound groundwater development, especially in sensitive salt-affected areas. In Northeast Thailand, the Central Huai Luang Basin, underlain by rock salt, is the source of groundwater and soil salinity. The future sustainable groundwater development yield was assessed under the plausible uncertainty of hydrogeological and projected climate scenarios that could impact the groundwater system. The SEAWAT and HELP3 models were used to simulate groundwater system. The four alternative scenarios of hydrogeological conceptual models were formulated to determine the impact on groundwater system and sustainable groundwater yield. In addition, impacts of projected climate conditions on each alternative model were explored. The results indicate that variable depths and thicknesses of rock salt layers have a higher impact on groundwater salinity distribution and sustainable yield estimations than model boundary conditions. Groundwater salinity, shallow water table areas, and sustainable yield projections vary substantially depending on the possible conceptual model scenarios. It is clear that the variable hydrogeological models affect groundwater sustainable yields.

A novel synthetic route of micrometer-sized LiCoMnO4 as 5 V cathode material for advanced lithium ion batteries

We synthesized micrometer-sized LiCoMnO4 with spinel structure by heating ion-exchanged LixCo0.5Mn0.5O2 with O6-type layered rocksalt structure at 600 °C. In this synthetic route, we first synthesized micrometer-sized NaxCo0.5Mn0.5O2 with P2-type layered rocksalt structure at 900 °C. Then, we prepared O6-LixCo0.5Mn0.5O2 by ion-exchange of Na+ for Li+ using LiNO3 at 280 °C. The structural transformation from layered rocksalt to spinel structure was confirmed at about 600 °C by the DTA curve. The average particle size of about 5 μm was almost the same as that of the starting P2-NaxCo0.5Mn0.5O2. The discharge capacity–voltage curves of the present LiCoMnO4 showed a maximum discharge capacity of about 105 mA h g−1 between 3.0 and 5.2 V vs. Li/Li+ at 25 °C, in spite of large micrometer-sized particles. We believe that micrometer-sized LiCoMnO4 would be important as one of 5 V cathode materials to achieve its higher compressed density of the electrode for advanced lithium ion batteries (LIBs), such as all solid-state LIB application.

Unusual synergistic effect in layered Ruddlesden\u2212Popper oxide enables ultrafast hydrogen evolution

Efficient electrocatalysts for hydrogen evolution reaction are key to realize clean hydrogen production through water splitting. As an important family of functional materials, transition metal oxides are generally believed inactive towards hydrogen evolution reaction, although many of them show high activity for oxygen evolution reaction. Here we report the remarkable electrocatalytic activity for hydrogen evolution reaction of a layered metal oxide, Ruddlesden−Popper-type Sr2RuO4 with alternative perovskite layer and rock-salt SrO layer, in an alkaline solution, which is comparable to those of the best electrocatalysts ever reported. By theoretical calculations, such excellent activity is attributed mainly to an unusual synergistic effect in the layered structure, whereby the (001) SrO-terminated surface cleaved in rock-salt layer facilitates a barrier-free water dissociation while the active apical oxygen site in perovskite layer promotes favorable hydrogen adsorption and evolution. Moreover, the activity of such layered oxide can be further improved by electrochemistry-induced activation.

Resistance Growth in Lithium-Ion Pouch Cells with LiNi0.80Co0.15Al0.05O2 Positive Electrodes and Proposed Mechanism for Voltage Dependent Charge-Transfer Resistance

High nickel content positive electrode materials, like LiNi0.80Co0.15Al0.05O2 (NCA), have been observed to lose capacity due to impedance growth when cycled above 4.1 V vs. Li/Li+. In this paper, we tested pouch cells with NCA positive electrodes and graphite, graphite-SiO, or graphite-SiC negative electrodes. In each case the pouch cells show high resistance at high voltage for every cycle, and resistance growth during cycling that is in part responsible for capacity loss. Symmetric cell experiments were used to show that the high resistance does, in fact, come from the positive electrode charge transfer resistance which is attributed to a thickening rock salt layer on the positive electrode (seen by other researchers). We propose a mechanism to explain why the charge transfer resistance depends on voltage for the positive electrode.

Structure and Electrochemical Properties of α-NaFeO2 Obtained under Various Hydrothermal Conditions

High-crystallinity α-NaFeO2 samples can be obtained from α-FeOOH in highly concentrated NaOH solution under various hydrothermal conditions. The electrochemical performance of the process depends on the hydrothermal condition: selecting a higher treatment temperature engenders better cycle performance. The cycle performance can also be changed by adding small amounts of KOH or LiOH·H2O to the NaOH solution. Better cycle performance is obtainable for a sample with added KOH. X-ray Rietveld analysis revealed a metastable structure: Na and Fe ion sites (3a and 3b sites) were not fully occupied in a hexagonal layered rock salt structure (Rm). The electrochemical cycle performance depends strongly on the crystal structure: conversion to nearly ideal α-NaFeO2 structure with small lattice parameters is effective to attain better cycle performance. Growing-up primary particle size was also important strategy to obtain the sample with better cycle performance.

Reversible operation of La0·8Sr0·2MnO3 oxygen electrode infiltrated with Ruddlesden-Popper and perovskite lanthanum nickel cobaltite

The electrochemical performance and stability of La0·8Sr0·2MnO3 oxygen electrodes infiltrated with La2Ni0·5Co0·5O4 (Ruddlesden-Popper) and LaNi0·5Co0·5O3 (perovskite) nano-particles were studied under cyclic solid oxide electrolysis cell and solid oxide fuel cell modes. Electrochemical impedance spectroscopy and analysis of distribution of relaxation times were utilized to investigate the effect of addition of catalysts with Ruddlesden-Popper and perovskite structures on the reversible operation of electrochemical cells. Results indicated that addition of La2Ni0·5Co0·5O4 nanoparticles has more impact on polarization resistance reduction as compared to LaNi0·5Co0·5O3 in cyclic operation, probably due to the facile oxygen transport in the rock salt layer of Ruddlesden-Popper structure. Analysis of the polarization resistance fluctuations shows a better stability in Ruddlesden-Popper structure-infiltrated electrodes as compared to perovskite structure. The difference between maximum and minimum of polarization resistances (i.e. fluctuations) in cyclic operation is reduced significantly by introducing Ruddlesden-Popper-structured lanthanum nickel cobaltite nanoparticles.

Ruddlesden-Popper phases Sr3Ni2–xAlxO7–δ and some doped derivatives: Synthesis, oxygen nonstoichiometry and electrical properties

The Ruddlesden-Popper phases Sr3Ni2–xAlxO7–δ (0.5 < х ≤ 0.75) were synthesized in the system Sr–Al–Ni–O for the first time. They show 2P/RS structure, in which two perovskite layers (P) are stacked in between rock-salt layers (RS). The composition Sr3Ni2–xAlxO7–δ with x = 0.5 was stabilized by partial substitution of Sr2+ for Ba2+ to give Sr2.8Ba0.2Ni1.5Al0.5O7–δ. This substitution allowed to reduce the synthesis duration and to lower its temperature. The study of specific electrical resistivity of Sr3Ni2–xAlxO7–δ (0.5 < х ≤ 0.75) and Sr2.8Ba0.2Ni1.5Al0.5O7–δ (x = 0.5) showed that it decreased with decreasing aluminum content. The specific resistivity of yttrium-modified phases Sr2.8–yYyBa0.2Ni1.5Al0.5O7–δ was found to decrease with increasing y and reaches a minimum value for у = 0.1. Oxygen nonstoichiometry of limiting representatives in single phase range 0.5 < x ≤ 0.75 was estimated by iodometric titration at 20 °C, which gave the oxygen deficiency δ of 1.02 (x = 0.75) and 0.78 (x = 0.5), showing the decrease of δ with decreasing aluminum content. The temperature range of semiconductor-to-metal transition (350–450 °C) was determined by thermal analysis and electrical measurements. All synthesized compounds were analyzed by X-ray powder diffraction for identification of crystalline phases.

Reversible Structural Changes and High-Rate Capability of Li3PO4-Modified Li2RuO3 for Lithium-Rich Layered Rocksalt Oxide Cathodes

Lithium-rich layered rocksalt oxides are promising cathode materials for lithium-ion batteries, owing to their high charge–discharge capacities of over 250 mA h g–1. However, their poor rate capability remains to be addressed. Here, we investigate the effects of surface modification by amorphous Li3PO4 on the structures and electrochemical reactions in the surface region of an epitaxial Li2RuO3(010) film electrode fabricated by pulsed laser deposition. Structural characterization using surface X-ray diffraction (XRD), hard X-ray photoemission spectroscopy, and neutron reflectometry shows that surface modification by 3 nm thick Li3PO4 resulted in the partial substitution of P for Li in the surface region of Li2RuO3. The modified (010) surface exhibits better rate capability at 20 C (41% of the discharge capacity at 0.3 C) compared to the unmodified surface (5% of that at 0.3 C). In situ surface XRD confirmed that highly reversible structural changes occurred at the modified surface during lithium (de)inter...

Галогенные отложения уфимского яруса в пределах Соликамской впадины

The paleogeographic and tectonic conditions of the accumulation of Ufimian deposits (Lower Permian) were reconstructed on the basis of study more than 2000 wells within the Solikamsk depression. The most complete cross-section of the salt-marl formation (9 large layers of rock salt and gypsum rock) was studied. On this basis, the modified scheme of stratification of the salt-marl layer was proposed. The stratum was dismembered, both with complete and partial preservation of the salt layers. The stratum is divided into 3 large cyclothemes in this scheme, the cyclothemes - into series of cyclites. Each cyclite has a complete cycle of the evaporate sedimentation. The maps were constructed for each salt layer. The maps show the configuration of the salt lagoon and the migration of its depocenter within the Solikamsk depression (Ufimian age). The study of the cross-section shows the vertical change of the composition. The salt-bearing rocks are replaced by carbonate rocks - it corresponds to a general transgression in the region. For upper layers of salt-marl strata the facial replacement of the salt by gypsum rocks has been revealed. The analysis of the configuration of the reconstructed lagoon at the geological time demonstrates its connection with the regional tectonic events and salt tectonics in the Kungur sediments.

Potential impact of climate change on groundwater resources in the Central Huai Luang Basin, Northeast Thailand

The Central Huai Luang Basin is one of the important rice producing areas of Udon Thani Province in Northeastern Thailand. The basin is underlain by the rock salt layers of the Maha Sarakham Formation and is the source of saline groundwater and soil salinity. The regional and local groundwater flow systems are the major mechanisms responsible for spreading saline groundwater and saline soils in this basin. Climate change may have an impact on groundwater recharge, on water table depth and the consequences of waterlogging, and on the distribution of soil salinity in this basin. Six future climate conditions from the SEACAM and CanESM2 models were downscaled to investigate the potential impact of future climate conditions on groundwater quantity and quality in this basin. The potential impact was investigated by using a set of numerical models, namely HELP3 and SEAWAT, to estimate the groundwater recharge and flow and the salt transport of groundwater simulation, respectively. The results revealed that within next 30years (2045), the future average annual temperature is projected to increase by 3.1°C and 2.2°C under SEACAM and CanESM2 models, respectively, while the future precipitation is projected to decrease by 20.85% under SEACAM and increase by 18.35% under the CanESM2. Groundwater recharge is projected to increase under the CanESM2 model and to slightly decrease under the SEACAM model. Moreover, for all future climate conditions, the depths of the groundwater water table are projected to continuously increase. The results showed the impact of climate change on salinity distribution for both the deep and shallow groundwater systems. The salinity distribution areas are projected to increase by about 8.08% and 56.92% in the deep and shallow groundwater systems, respectively. The waterlogging areas are also projected to expand by about 63.65% from the baseline period.

Fundamental Insight into Zr Modification of Li- and Mn-Rich Cathodes: Combined Transmission Electron Microscopy and Electrochemical Impedance Spectroscopy Study

While zirconium-based coatings are known to improve the cycling stability of a number of lithium ion battery cathodes, the microstructural origin of this enhancement remains uncertain. Here we combine advanced transmission electron microscopy (high-resolution transmission electron microscopy, high-angle annular dark field, electron energy loss spectroscopy, and energy-dispersive X-ray spectroscopy) with electrochemical impedance analysis to provide new insight into the dramatic role of Zr surface modification on the electrochemical performance of Li- and Mn-rich (LMR) cathodes (Li[Li0.2Ni0.13Co0.13Mn0.54]O2). It is demonstrated that a Zr-based rock-salt structure layer with a thickness of 1–2 nm is formed on the surface of the LMR. This layer is effective in suppressing the deleterious phase transformation of LMR from initial layered composite combining Li2MO3 and LiMO2 to the disordered rock-salt phase, leading to an enhanced long-term cycling performance and rate capability. Electrochemical impedance sp...

La2Pr2Ni3O10±δ Ruddlesden-Popper phase as potential intermediate temperature-solid oxide fuel cell cathodes

Ruddlesden-Popper phases are layered oxides composed of nABO3 perovskite layers sandwiched between two AO rock-salt layers. Herein a new composition of n = 3 Ruddlesden-Popper phases, La2Pr2Ni3O10±δ, synthesised by the citrate sol-gel method is reported. A preliminary microstructure investigation combined with studies of the electrochemical performance of this new composition, La2Pr2Ni3O10±δ as a potential cathode material in both symmetrical and single cell configurations is reported. The area specific resistance of the La2Pr2Ni3O10±δ cathode was found to be 0.34 Ω cm2 at 800 °C, which is significantly better than previous reports for the La4Ni3O10±δ analogue under similar conditions. A modest peak power density of 0.19 W cm−2 at 800 °C was found, whilst electrode adhesion was identified as contributing to the modest performance.

Non-precious transition metal oxide calcium cobaltite: Effect of dopant on oxygen/hydrogen evolution reaction and thermoelectric properties

We report here structural, thermoelectric and electrocatalytic performance of the undoped and doped Calcium Cobaltite: Ca3Co4-xMoxO9 (x = 0, 0.1, 0.2, 0.3 and 0.4) series. The Calcium cobaltite (CCO) crystallizes in a layered structure with alternate rock salt (RS) type arrangement and CoO2 layer stacked along the c axis having monoclinic symmetry with a mis-fit between RS and CoO2 layer along the b axis. Rietveld refinement confirms the formation of the similar crystal structure with no impurity phases for all the doped composites. XPS and FTIR data reveal that at an initial stage, Mo enters RS structure and at higher concentrations of doping Mo may exist in both the layers. Multivalent Mo acts as an electron dopant that reduces hole concentration resulting in an increase in seebeck coefficient (S). In addition to thermoelectric performances, the electrocatalytic behaviour of undoped and doped CCO toward the oxygen/hydrogen evolution reaction (OER/HER) has been demonstrated. We presume that the as-synthesized doped material has a potential to become a future electrocatalyst material.

Facet-Dependent Rock-Salt Reconstruction on the Surface of Layered Oxide Cathodes

The surface configuration of pristine layered oxide cathode particles for Li-ion batteries significantly affects the electrochemical behavior, which is generally considered to be a thin rock-salt layer in the surface. Unfortunately, aside from its thin nature and spatial location on the surface, the true structural nature of this surface rock-salt layer remains largely unknown, creating the need to understand its configuration and the underlying mechanisms of formation. Using scanning transmission electron microscopy, we have found a correlation between the surface rock-salt formation and the crystal facets on pristine LiNi0.80Co0.15Al0.05O2 primary particles. It is found that the originally (014) and (003) surfaces of the layered phase result in two kinds of rock-salt reconstructions: the (002) and (111) rock-salt surfaces, respectively. Stepped surface configurations are generated for both reconstructions. The (002) configuration is relatively flat with monatomic steps while the (111) configuration sho...

New Insights into Hydride Bonding, Dynamics, and Migration in La2LiHO3 Oxyhydride.

Hydride anion-conducting oxyhydrides have recently emerged as a brand new class of ionic conductors. Here we shed a first light onto their local vibrations, bonding mechanisms, and anion migration properties using the powerful combination of high-resolution inelastic neutron scattering and a set of rigorously experimentally validated density functional theory calculations. By means of charge-density analysis we establish the bonding to be strongly anisotropic; ionic in the perovskite layer and covalent in the rock salt layer. Climbing nudged elastic band calculations allow us to predict the hydride migration paths, which crucially we are able to link to the observed exotic ionic-covalent hybrid bonding nature. In particular, hydride migration in the rock salt layer is seen to be greatly hindered by the presence of covalent bonding, forcing in-plane hydride migration in the perovskite layer to be the dominant transport mechanism. On the basis of this microscopic insight into the transport and bonding, we are able to propose future candidates for materials that are likely to show enhanced hydride conductivity.

Ruddlesden-Popper type La2NiO4+δ oxide as a pseudocapacitor electrode

Ruddlesden-Popper type La2NiO4+δ (LNO) oxide was investigated as a novel pseudocapacitive electrode and performed high performance with the capacitance of 657.4 F g−1 under the scan rate of 2 mV s−1 in 3 M KOH electrolyte. Two cathodic peaks and one anodic peak in CV curves of LNO in KOH electrolyte indicate the special oxygen insertion/extrusion processes because its structure alternates with perovskite LaNiO3 layers and LaO rock-salt layers in succession. Cycle performance of LNO at a relatively high current density of 10 A g−1 is approximately 96.2% after 500 cycles in 3 M KOH electrolyte, showing good cycling stability. This confirms LNO as a potential candidate for high performance pseudocapacitor electrodes.

New, Efficient, and Reliable Air Electrode Material for Proton-Conducting Reversible Solid Oxide Cells.

Driven by the demand to minimize fluctuation in common renewable energies, reversible solid oxide cells (RSOCs) have drawn increasing attention for they can operate either as fuel cells to produce electricity or as electrolysis cells to store electricity. Unfortunately, development of proton-conducting RSOCs (P-RSOCs) faces a major challenge of poor reliability because of the high content of steam involved in air electrode reactions, which could seriously decay the lifetime of air electrode materials. In this work, a very stable and efficient air electrode, SrEu2Fe1.8Co0.2O7-δ (SEFC) with layer structure, is designed and deployed in P-RSOCs. X-ray diffraction analysis and High-angle annular dark-filed scanning transmission electron microscopy images of SEFC reveal that Sr atoms occupy the center of perovskite slabs, whereas Eu atoms arrange orderly in the rock-salt layer. Such a special structure of SEFC largely depresses its Lewis basicity and therefore its reactivity with steam. Applying the SEFC air electrode, our button switches smoothly between both fuel cell and electrolysis cell (EC) modes with no obvious degradation over a 135 h long-term test under wet H2 (∼3% H2O) and 10% H2O-air atmospheres. A record of over 230 h is achieved in the long-term stability test in the EC mode, doubling the longest test that had been previously reported. Besides good stability, SEFC demonstrates great catalytic activity toward air electrode reactions when compared with traditional La0.6Sr0.4Co0.2Fe0.8O3-δ air electrodes. This research highlights the potential of stable and efficient P-RSOCs as an important part in a sustainable new energy power system.

Electrostatic Interactions versus Second Order Jahn–Teller Distortion as the Source of Structural Diversity in Li3MO4 Compounds (M = Ru, Nb, Sb and Ta)

With the advent of layered rocksalt oxides showing anionic redox activity toward Li, there has been an increased focus on designing new rocksalt structures and, more particularly, compounds pertaining to the Li3MO4 family. The structural richness of this family is nested in its ability to host many different cations, leading to the formation of superstructure patterns whose predictability is still limited. Thus, there is a need to understand the formation of such superstructures, as cationic arrangements have a crucial effect on their physical properties. Herein we propose a combined experimental and theoretical approach to understand the interactions governing cation ordering in binary systems of general composition given by Li3MyM′1–yO4 (M and M′ being Ru, Nb, Sb, and Ta). Through complementary X-ray diffraction and X-ray absorption spectroscopy techniques, we reveal a solid-solution behavior for the Li3RuySb1–yO4 system, as opposed to Li3SbyNb1–yO4 that enlists four rocksalt structures with different cation orderings. We use DFT calculations to rationalize such a structural diversity and find that it is controlled by a delicate balance between electrostatic interactions and charge transfer due to a second order Jahn–Teller distortion. This insight provides a new viewpoint for understanding cationic arrangements in rocksalt structures and guidelines to design novel phases for applications such as Li-ion batteries or ionic conductors.