Pure Rock Salt Research Articles

Salt Mining and Salt Miners at Talkherud–Douzlākh, Northwestern Iran: From Landscape to Resource-Scape

The Douzlākh salt deposit (region: Māhneshān, Zanjān Province, Iran) is unique for its pure and crystal rock salt and was an important supplier of culinary (‘table’) salt in Achaemenid, Sassanid and Middle Islamic times. At the same time, the site was of central importance to the economic life of the rural populations in the Talkherud Basin. This article focuses on the question of which strategies were decisive for the exploitation of the salt mountain and how a potential supra-regional interest in the culinary salt was perhaps reciprocally connected with a rural hinterland. This hinterland was recently investigated in greater detail by our ongoing research. Did a resource-scape based on salt develop with specific economic and social strategies and practices around the Douzlākh? And was this development triggered by state or imperial control and demand? These questions are being pursued from a perspective utilising a variety of subjects and methods in archaeology, archaeobiology, archaeometry and geoarchaeology. In addition to a detailed on-site artefact study, several on- and off-site datasets have been collected and analysed within a multidisciplinary framework. This article synthesises the results of a major 12-year project to identify the organisational principles and daily practices within this specific salt-scape. The sensational finds of the Douzlākh salt mummies, along with the generally outstanding preservation of organic ecofacts and artefacts, allow insights into antique lifeworlds that are otherwise hard to come by. The multidisciplinary study of on- and off-site data allows far-reaching insights into interdisciplinary topics, such as the social system, supply and logistics, or the presence of non-local or non-indigenous populations.

Analysis of structural, electronic and optical properties of Er-doped rock salt AlN using ab-initio calculations.

This investigation includes the structural and optoelectronic characteristics of both pure and Er-doped rock salt aluminium nitride (AlN). Upon introducing Er doping into the AlN host, the calculations reveal a rise in the atomic parameter. Incorporating Er into the system leads to enhancements in the static dielectric coefficient ɛ1(0), static reflectivity R(0), as well as static refractive index n(0), at zero frequency. After doping, the peaks of imaginary dielectric tensor, extinction coefficient and absorption coefficient shift towards lower energy levels. Various exchange correlation potentials are incorporated to compare the results of electronic and optical characteristics. We employed the full potential linearized augmented plane wave (FP-LAPW) approach with WIEN2k code in conjunction with the density functional theory (DFT). To explore the optoelectronic characteristics of both pure as well as doped systems, three distinct exchange correlation potentials are utilized: the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA), Modified Becke Johnson Generalized Gradient Approximations (mBJ + GGA) and Hubbard potential (GGA + U).

Role of Mg–O on phase stabilization in solution combustion processed rocksalt structured high entropy oxide (CoCuMgZnNi)O with high dielectric performance

High entropy oxide (CoCuMgZnNi)O with a phase pure rocksalt was synthesized using low-temperature solution combustion. The precursors were found to combust at 270 °C and 400 °C was considered to be the formation temperature. The high entropy rocksalt oxide (HERO) fully stabilized at 1000 °C shows a single-phase, fcc rocksalt structure with an Fm-3m space group. HERO displays one of its parent oxide Mg–O structural properties as both belong to the cubic family and had lattice parameters very close to each other. The lower cation systems exhibited a transition from spinel to rocksalt structure with the addition of Mg–O. Raman of HERO affirmed a completely disordered occupancy of various metal cations, the formation of HERO at 400 °C, and phase stabilization at 1000 °C. Dielectric measurements at room temperature showed high permittivity (κ) with magnitudes ∼1.9 × 103, 4.7× 101, and 0.9 × 101 at 100, 1k, and 100k Hz.

Li[Ni0.6Mn0.2Co0.2]O2 Made From Crystalline Rock Salt Oxide Precursors

Layered lithium nickel manganese cobalt oxide or NMC type cathode materials dominate the lithium-ion battery market. However, the production of their precursor involves the use of large amounts of water and can create waste. All-dry synthesis methods are attractive as they are potentially cheaper and greener. However, it remains a challenge to achieve atomic scale mixing of the precursor elements by dry methods. Here, we report an alternative route to achieve atomic scale mixing by employing thermal interdiffusion to produce a phase pure rock salt structure precursor for NMC cathode materials, which can significantly shorten the preparation time and may further reduce cost. The complications and applicability of using a thermally synthesized precursor to make layered cathode material are presented in detail.

Study on long-term uniaxial compression creep mechanical behavior of rocksalt-mudstone combined body

Rocksalt and mudstone are usually under common stress in salt storage caverns, resulting in different mechanical properties from pure rocksalt and mudstone. To accurately obtain the creep mechanical characteristics of rocksalt-mudstone combined body, we have made three different combinations. The long-term creep experiment of bedded rocks can more closely reflect the long-term mechanical behavior of surrounding rock of salt storage caverns. The experimental results indicated that the long-term creep curve of the combined body includes initial and steady creep stages, and even includes accelerated creep stage. The strain of mudstone layer in the combined body was lower than that of rocksalt because of the higher strength. With the increase of the height ratio of mudstone, the creep strain of the combined body and each rock layer decreased, but the creep rate increased. A new nonlinear creep-damage constitutive model was proposed, which can well describe the creep evolution characteristics of the experiment. Compared with the fitting curves of classical Burgers and Nishihara creep constitutive models, it is revealed that the proposed model is most consistent with the experimental data. The duration of the long-term creep experiment under lower stress has a highly significant effect on the accuracy of predicting rock creep results. This research will contribute to a deeper understanding of the long-term creep characteristics of bedded rocks in salt storage caverns.

A New Testing Method for the Characterization of the Tension-Compression Cyclic Behavior of Rock Salt

Abstract To improve the stability of salt cavern gas storage, the tension-compression cyclic behavior of surrounding rock must be correctly characterized. This article proposes a new tension-compression cyclic testing method in which a rock specimen–fixing device with position-limit spring components is provided. The fixing device can both bear compressive stress and direct tensile stress, that is, the new testing method implements a completely reversed stress condition: direct tensile stress and compressive stress. Investigations on the tension-compression cyclic behavior of pure rock salt and impure rock salt were undertaken using this method. In the experiment, four cycles of tension-compression alternation loading were carried out first, then a tensile stress was applied until the occurrence of rock failure. The axial stress-strain curve of pure rock salt shows hysteretic behavior within each cycle. The damage evolution process induced by the tension-compression cyclic stress was illustrated by the spatial distribution of acoustic emission (AE) events and the variation of AE cumulative counts. The experimental results indicate that the developed method can be easily applied to investigate the tension-compression cyclic behavior of rock material.

Cu2+–Mn2+-Co-doped CdO nanocrystallites: comprehensive research on phase, morphology and optoelectronic properties

In this study, firstly cadmium hydroxide nanopowder was evolved by cost-effective wet chemical co-precipitation method. The transformation of nanocrystalline Cu2+–Mn2+-co-doped CdO occurred via thermal decomposition of the obtained hydroxide at 750 °C. The structural, optical and electrical behavior of nanocrystallites was analyzed by different complementary measuring tools. DTA of the as-prepared sample exhibited an endothermic peak at 240 °C attributed to crystallization. XRD analysis depicted a multiphase structure in the as-prepared sample, and pure rocksalt structure was obtained after annealing. Cu2+–Mn2+-co-doped cubic CdO has been achieved first time which was further confirmed by FTIR with various stretching and bending vibrations of Cd–O at 720, 625 and 460 cm−1. SEM–TEM images demonstrated the brain-like morphology of different hexagonal and spherical nanocrystallites with an average size of ~ 35 nm. In addition, optical band gap energy was found in the range 2.14–2.44 eV by Tauc’s plot. In photoluminescence results, emission spectra have many bands at 420, 480, 550 nm originated from excitonic transition, structural defects and oxygen vacancies, while intense peak at 450, 520 nm may be ascribed to Cu2+ and Mn2+ dopants, respectively. Hall measurements demonstrated that the Cu2+–Mn2+-co-doped CdO with a pure cubic phase has superior semiconducting behavior. The homogeneous codoping of Cu2+–Mn2+ leads to efficient modification in structural, optical and electrical parameters of CdO which would make such materials attractive for semiconductor and photovoltaic industry, etc.

Structure and microwave dielectric properties of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 ceramics

Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al1/2Nb1/2)4+ substitution on the dielectric properties of Li2Mg3TiO6 ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al1/2Nb1/2)4+ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (εr) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τf|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li2Mg3Ti0.92(Al1/2Nb1/2)0.08O6 sample exhibited outstanding dielectric characteristics:εr = 15.256, Q × f = 174,300 GHz and τf = −19.97 ppm/°C.

Study on Brazilian Splitting Mechanics and Acoustic Emission Characteristics of Impure Salt Rocks

In order to study the mechanical and acoustic emission characteristics of salt rock under indirect tension, we conducted indirect tension cyclic loading and unloading tests and acoustic emission monitoring on pure salt rock and impure salt rock respectively by using MTS815 Flex Test GT rock mechanics test system and PCI-II acoustic emission (AE) three-dimensional positioning system. The results show that: (1) Both salt rocks show strong plastic deformation characteristics, but the plastic deformation ability of salt rocks is weakened by impurities, which is 79% of the average deformation ability of pure salt rocks. (2) The peak load and tensile strength of impure salt rock are higher than those of pure salt rock. The average peak value is 11.18KN and the average tensile strength is 1.81MPa, which are 1.55 times and 1.60 times of pure salt rock respectively. (3) The indirect tensile deformation characteristics of salt rock can be divided into three stages: damage stage at contact site, tensile deformation stage and post-peak deformation stage. (4) The acoustic emission signal is the most intense near the peak value, but the maximum ring counting rate and energy rate of impure salt rock are higher than those of pure salt rock. (5) When salt rock is destroyed, the whole crack surface is destroyed by tension, but the crack area of pure salt rock is much larger than that of impure salt rock.

The rock mechanics and acoustic emission characteristics of rock salt under tension-compression alternating

In order to study the stress state and acoustic emission characteristics of salt rock energy storage during high frequency injection and production of compressed. the self-developed spring specimen limit tension and compression cycle test rock specimen fixing device based on the MTS815 Flex Test GT rock mechanics test system and acoustic emission (AE) three-dimensional positioning real-time monitoring system was used to study on mechanical characteristics and AE characteristics of pure salt rock and impurity salt rock under tension-compression alternating tests for the first time. The test results show that: (1) Under the stress path of tension-compression alternating, the tensile strength of pure salt rock is 0.95 MPa, impurity salt rock tensile strength increased by 47.37% compared with pure salt rock, axial deformation of impurity salt rock is 0.25mm, while pure salt rock is 1.40 times of it. (2) During the compression stage, AE signals with uniform distribution are produced by the effect of mutual dislocation, slip and micro-defect closure in salt rock, which has a certain end-restraint effect; In the stretching stage, the development of intercrystalline cracks is the main cause of AE signals in tensile stage, and AE signal followed hysteresis phenomenon. (3) Comparing with impurity salt rock, the cumulative ringing counts of the four compression loading and unloading stages are 3.13 times higher than impurity salt rock, AE signal of pure salt rock is weaker during tension loading and unloading, the cumulative ringing count increases slightly, a large number of acoustic emission signals accompany only the final tensile failure process. Under the condition of tension-compression alternating, AE signals of pure salt rock with the same tensile or compressive stress levels are more active than those of impurity salt rock, and the number of AE events in compression stage is larger than that in tension stage.

Structural, spectral and optical properties of rocksalt Al,Mn-doped CdO: experimental and DFT studies

Nano-crystalline Cd0.95−x Mn0.05 Alx O (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) semiconductors were synthesized by sol-gel technique. These samples are characterized via X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR) methods. XRD analyses show that the samples have pure rocksalt structure, which is typical for cadmium oxide (CdO). SEM micrographs show that the Al,Mn-doped CdO nanoparticles are cubic with rocksalt structures. The presence of bands at 499, 615 and 660 cm−1 observed in the FTIR spectrum correspond to the stretching of CdO. In addition, the optical properties of nanoparticles were performed as experimentally and theoretically. The optical band gaps of nanoparticles were measured between 1.87 and 2.34 eV, while calculated as 1.19 eV for Mn-doped CdO nanoparticle and 2.13 eV for Mn,Al-doped CdO nanoparticle at lanl2dz and pm6 basis sets. The optical studies showed that the Mn-doped reduces band gap, while Al-doped increases.

Experimental and DEM investigations of temperature effect on pure and interbedded rock salt

Rock salt is considered as a favorable host rock material for natural gas storage due to its low permeability, fast self-healing ability and unique creep behavior. Characterizing engineering properties of rock salt especially interbedded salt under complicated geological storage conditions associated with temperature variations remains challenging. This research integrates physical and numerical experiments to investigate the temperature effect on the engineering behavior of pure and interbedded salt. Thermo-mechanical coupled triaxial compression tests are carried out on both pure (Ash-grey Rock Salt and Charcoal-grey Rock Salt) and impure (Rock Salt with Mudstone interbedded) rock salt specimens. To reveal the underlying mechanism of thermal-induced deformation and cracking of salt at grain scale, we configure a discrete element model and incorporate smooth-joint contacts to capture the interfacial behavior in the bedded salt. Experimental results indicate that the compressive strength and failure mode of rock salt is highly susceptible to temperature. The increasing temperature enhances the ductility of salt whereas lowers its peak compressive strength. Numerical results provide a micromechanical explanation that the attenuated compressive strength of salt under high temperature is attributed to the evolution of micro-cracks. The presence of the mudstone layer increases the overall material strength, confines the crack propagation orientations, and therefore limits the transverse deformation of the bedded salt. This study is expected to bring new insights into the micro-mechanical study of bedded salt and improve the long-term assessment of geological storage facilities.

Synthetic Rock Analogue for Permeability Studies of Rock Salt with Mudstone

Knowledge about the permeability of surrounding rock (salt rock and mudstone interlayer) is an important topic, which acts as a key parameter to characterize the tightness of gas storage. The goal of experiments that test the permeability of gas storage facilities in rock salt is to develop a synthetic analogue to use as a permeability model. To address the permeability of a mudstone/salt layered and mixed rock mass in Jintan, Jiangsu Province, synthetic mixed and layered specimens using the mudstone and the salt were fabricated for permeability testing. Because of the gas “slippage effect”, test results are corrected by the Klinkenberg method, and the permeability of specimens is obtained by regression fitting. The results show that the permeability of synthetic pure rock salt is 6.9 × 10−20 m2, and its porosity is 3.8%. The permeability of synthetic mudstone rock is 2.97 × 10−18 m2, with a porosity 17.8%. These results are close to those obtained from intact natural specimens. We also find that with the same mudstone content, the permeability of mixed specimens is about 40% higher than for the layered specimens, and with an increase in the mudstone content, the Klinkenberg permeability increases for both types of specimens. The permeability and mudstone content have a strong exponential relationship. When the mudstone content is below 40%, the permeability increases only slightly with mudstone content, whereas above this threshold, the permeability increases rapidly with mudstone content. The results of the study are of use in the assessment of the tightness of natural gas storage facilities in mudstone-rich rock salt formations in China.

Impact of solid second phases on deformation mechanisms of naturally deformed salt rocks (Kuh-e-Namak, Dashti, Iran) and rheological stratification of the Hormuz Salt Formation

Viscosity contrasts displayed in flow structures of a mountain namakier (Kuh-e-Namak - Dashti), between ‘weak’ second phase bearing rock salt and ‘strong’ pure rock salt types are studied for deformation mechanisms using detailed quantitative microstructural study. While the solid inclusions rich (“dirty”) rock salts contain disaggregated siltstone and dolomite interlayers, “clean” salts reveal microscopic hematite and remnants of abundant fluid inclusions in non-recrystallized cores of porphyroclasts. Although the flow in both, the recrystallized “dirty” and “clean” salt types is accommodated by combined mechanisms of pressure-solution creep (PS), grain boundary sliding (GBS), transgranular microcracking and dislocation creep accommodated grain boundary migration (GBM), their viscosity contrasts observed in the field outcrops are explained by: 1) enhanced ductility of “dirty” salts due to increased diffusion rates along the solid inclusion-halite contacts than along halite–halite contacts, and 2) slow rates of intergranular diffusion due to dissolved iron and inhibited dislocation creep due to hematite inclusions for “clean” salt types Rheological contrasts inferred by microstructural analysis between both salt rock classes apply in general for the “dirty” salt forming Lower Hormuz and the “clean” salt forming the Upper Hormuz of the Hormuz Formation and imply strain rate gradients or decoupling along horizons of mobilized salt types of different composition and microstructure.

Stabilization of Rock Salt ZnO Nanocrystals by Low-Energy Surfaces and Mg Additions: A First-Principles Study

Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, nanoscale ZnO was recently synthesized in the rock salt structure by addition of Mg. Using first-principles methods, we investigated two stabilization routes for accessing rock salt ZnO. The first route is stabilization by Mg addition, which was investigated by considering ZnO–MgO mixed phases. The second route is through size effects, as surface energies become dominant for small nanocrystal sizes. We discovered that the surface energy of rock salt ZnO is surprisingly low at 0.63 J m–2, which is lower than those of wurtzite and zinc blende ZnO and lower than that of rock salt MgO. We predict that pure rock salt ZnO is stable for nanocrystals smaller than 1.6 nm, and that Mg additions can greatly extend the size range in which the rock salt phase is stable. Both mixed-phase and core–shell models were considered in the calculations. The present approach could be applied to predict the stabilization of many other nanocrystal phases in de...

Structural Changes and Thermal Decomposition of Ni Based Cathode Materials for Li-Ion Batteries Studied By in-Situ XRD

The three-component system Li[NixCoyMnz]O2 has outstanding electrochemical properties due to advantage of the high capacity of LiNiO2, thermal stability and low cost of manganese in LiMnO2 and layered characteristics of LiCoO2. While capacity of Li[NixCoyMnz]O2 is similar to capacity of LiCoO2, it is a promising alternative in terms of performance, safety and cost. Various material combinations are being developed to achieve the higher capacity by increasing Ni content while retaining its advantages. Although higher Ni content contributes to better capacity in Li[NixCoyMnz]O2, but on the other hand, it tends to decrease the thermal stability of electrode material. Safety is one of the most important considerations in EV and HEV. First experimental condition is same state of charge with different Ni contents. Interesting phase transition behavior during heating is observed in Li0.66Ni0.5Co0.2Mn0.3O2 cathode material. Li0.66Ni0.5Co0.2Mn0.3O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 415 ºC. Upon further heating, M3O4-type spinel (Fd-3m) appears and co-exists with LiM2O4-type spinel (Fd-3m) from 497 ºC and remains in this structure up to 600 ºC. In the absence of electrolyte, no peaks of MO-type rock salt phase (Fm-3m) appear until 600 ºC whereas in the presence of electrolyte, further phase transition from M3O4-type spinel (Fd-3m) to MO-type rock salt phase (Fm-3m) takes place above 415 ºC. The electrolyte accelerates the thermal decomposition of charged cathode materials. The presence of electrolyte alters the paths of structural changes and lowers the onset temperatures of thermal decomposition reactions. In case of Li0.66Ni0.5Co0.2Mn0.3O2with electrolyte, more dramatic structural changes are observed in comparison with the one in the absence of electrolyte. The sample with electrolyte shows the structural decomposition to MO-type rock salt phase at 415 ºC, in the early stage of heating. Thermal behavior of Li0.33Ni0.6Co0.2Mn0.2O2 cathode material is similar to the one of Li0.66Ni0.5Co0.2Mn0.3O2. Li0.33Ni0.6Co0.2Mn0.2O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 374 ºC. Upon further heating, M3O4-type spinel (Fd-3m) co-exists with LiM2O4-type spinel (Fd-3m) from 497 ºC and maintains this structure up to 600 ºC. Presence of electrolyte initiates additional phase transitions in this cathode material. M3O4-type spinel (Fd-3m) starts to convert into MO-type rock salt phase (Fm-3m) at 374 ºC. Above 579 ºC, pure MO-type rock salt phase (Fm-3m) is observed. Second condition is same Ni contents in electrode material with different state of charge. The thermal behavior of Li0.66Ni0.5Co0.2Mn0.3O2 cathode material is mentioned above. Li0.33Ni0.6Co0.2Mn0.2O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 340 ºC. Upon further heating, M3O4-type spinel (Fd-3m) co-exists with LiM2O4-type spinel (Fd-3m) from 449 ºC and maintains this structure up to 600 ºC. Presence of electrolyte initiates additional phase transitions in this cathode material. M3O4-type spinel (Fd-3m) starts to convert into MO-type rock salt phase (Fm-3m) at 436 ºC. Above 560 ºC, pure MO-type rock salt phase (Fm-3m) is observed. In the presence of electrolyte, thermal induced phase transition of Li0.33Ni0.6Co0.2Mn0.2O2 shows conversion from LiM2O4-type spinel (Fd-3m) through M3O4-type spinel (Fd-3m) to MO-type rock salt phase (Fm-3m) step by step. On the other hand, thermal decomposition behavior of Li0.66Ni0.6Co0.2Mn0.2O2 shows phase transition to M3O4-type spinel (Fd-3m) and MO-type rock salt phase (Fm-3m) at the same time. This result of different thermal behavior of Li0.66Ni0.6Co0.2Mn0.2O2 and Li0.33Ni0.6Co0.2Mn0.2O2contributes towards better understanding for thermal stability of Ni-based cathode materials. Working on other samples and more detailed discussion will be presented at the time of meeting.Fig1. In-situ XRD patterns of the (a) 33% (b) 66% SOC LiNi0.6Co0.2Mn0.2O2 in the presence of electrolyte heated from 25℃ to 600℃

High pressure phase transition of ZnO/SiO2 core/shell nanospheres

The structural phase transition of ZnO/SiO2 core/shell nanospheres was studied under high pressure using synchrotron X-ray diffraction. The results indicated that the wurtzite structure of the ZnO core is stable up to 11.5 GPa, and then transforms into rocksalt phase. The onset transition pressure is higher than those of the bulk and nano ZnO. It is worth noting that the phase transition from wurtzite to rocksalt is irreversible, which is obviously different from the uncapped bulk and nano ZnO. The pure rocksalt structure ZnO was first obtained at ambient conditions without catalyst or high temperature treatment. We suggested that the SiO2 shells play important roles in the phase transition of inner ZnO cores. The effects of the SiO2 shells on the phase transition of ZnO cores were discussed.

Syntheses and Characterization of Wurtzite CoO, Rocksalt CoO, and Spinel Co3O4 Nanocrystals: Their Interconversion and Tuning of Phase and Morphology

Pure rocksalt (c-CoO) and wurtzite (h-CoO) phases of cobaltous oxide (CoO) have been selectively prepared through thermodynamically and kinetically controlled reactions of a single molecular precursor Co(acac)3 (acac: acetylacetonate), respectively. Changing thermal decomposition conditions of the precursor produces different phases and distinct morphologies of the cobaltous oxides. Hexagonal pyramidal shaped h-CoO nanocrystals have been formed by a flash heating of the reaction mixture (185 °C for 2 h, kinetic control condition), whereas cube shaped c-CoO nanocrystals have been produced by a prolonged heating at a relatively low temperature (130 °C for 12 h, thermodynamic control condition). Addition of o-Dichlorobenzene (o-DCB) to the reaction mixture alters the reaction condition to the thermodynamic control regime by slowing down the decomposition rate of the precursor. Further increase of the concentration of o-DCB in the reaction mixture changes the morphology of product from h-CoO hexagonal pyramids to h-CoO nanorods with various aspect ratios and finally to c-CoO nanocrystals. Air oxidation at 240 °C for 5 h of either h-CoO or c-CoO nanocrystals yields spinel Co3O4 nanocrystals with retention of the original crystal morphology. During the oxidation process, the h-CoO phase has been converted into Co3O4 via formation of the c-CoO phase, but the c-CoO phase has been directly oxidized to Co3O4. The electrochemical properties of the h-CoO, c-CoO, and spinel Co3O4 nanocrystals toward lithium exhibit characteristic features reflecting their Gibbs free energies. This work allows understanding of the detailed mechanism and energetics of selective formation, phase transformation, morphology control, and electrochemical properties in the closely related nanostructured cobalt oxides.

Controlled growth of Zn-polar ZnO film on MgAl2O4 (1 1 1) substrate using MgO buffer layer

A pure rocksalt MgO buffer layer was used to modify the surface structure of MgAl2O4 (1 1 1) substrates to achieve growth of a Zn-polar ZnO film by radio frequency plasma-assisted molecular beam epitaxy. It is found that this pure rocksalt MgO buffer layer plays a crucial role in 30° rotation domain elimination, surface morphology improvement and Zn-polarity control of the ZnO film, as demonstrated by in situ reflection high-energy electron diffraction and ex situ transmission electron microscopy. Atomic force microscopy observation also illustrates a smooth surface for the ZnO film.

Temperature-dependent photoluminescence of CdZnO thin films grown by molecular-beam epitaxy

Large-Cd-concentration ( E g <3.0 eV) CdZnO thin films were grown using molecular-beam epitaxy. Variable-temperature photoluminescence measurements were performed on three typical CdZnO samples having pure wurtzite, pure rocksalt, and wurtzite–rocksalt mixture structures, respectively. The temperature dependence of the CdZnO bandgap shrinkage was investigated and analyzed based on the empirical Varshni and Bose–Einstein fitting on the near-band-edge photoluminescence peak positions. The temperature dependence of the integral PL intensity in the CdZnO samples was also fitted, where fitting equation with hopping term included shows a closer fit to the experimental data. The possible hopping processes in the CdZnO thin films may be related to the band tail states due to alloying effect and Cd distribution nonuniformity in the CdZnO samples.