Cation Interdiffusion Research Articles

Facile synthesis of wurtzite copper–zinc–tin sulfidenanocrystals from plasmonic djurleite nuclei

The present research demonstrates a facile one-pot heating process without injection to synthesize an important light harvesting quaternary nanocrystal: wurtzite copper–zinc–tin sulfide (w-CZTS). High quality w-CZTS nanocrystals can be easily obtained by mixing all the precursors and simply heating to the reaction temperature. The nano-crystal formation mechanism is thoroughly investigated and resolved by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). It starts with the nucleation of plasmonic djurleite Cu1.94S, subsequent growth of CZTS–Cu1.94S heterostructures and inter-diffusion of cations and then finally leads to single phase and single crystal w-CZTS nanocrystals. The mechanism of nanocrystal formation can be applied universally regardless of the type of zinc and tin precursor for high quality w-CZTS nanocrystals. The in-depth interpretations of the reaction mechanism of this process significantly advance the current knowledge of multi-component nanocrystal formation. The developed method is scalable for high throughput and low cost w-CZTS suspensions which await practical photovoltaic applications.

Efficient dual layer interconnect coating for high temperature electrochemical devices

Effects of novel dual layer coatings Co3O4/La0.85Sr0.15MnO3−δ on high temperature oxidation behaviour of candidate steels for interconnects are studied at 1123 K in flowing simulated ambient air (air + 1% H2O) and oxygen. Four alloys are investigated: Crofer 22 APU, Crofer 22 H, E-Brite and AL 29-4C. The reaction kinetics is followed by measuring the mass increase of the samples over time. The oxide scale microstructure and chemical composition are investigated by scanning electron microscopy/energy dispersive spectroscopy. The kinetic data follow the parabolic rate law. It is found that the oxidation reaction is limited by outward Cr3+ diffusion in the chromia scale. The coating effectively reduces the oxidation rate. Reactions and cation inter-diffusion between the coating and the oxide scale are observed. Long term effects of these interactions are discussed and practical implications for interconnect electrochemical performance are suggested.

Synthesis, crystal stability, and electrical behaviors of La0.7Sr0.3Cr0.4Mn0.6O3−δ–XCu0.75Ni0.25 for its possible application as SOFC anode

La0.7Sr0.3Cr0.4Mn0.6O3−δ (perovskite-type) nanocomposites impregnated with XCu0.75Ni0.25 have been synthesized by sol–gel method. Crystal structure of LSCM–Cu0.75Ni0.25 composites were refined by the Rietveld method. Crystal symmetry of CuO and NiO nanoparticles have monoclinic $$ C12/c $$ and cubic $$ Fm\bar{3}m $$ symmetry, respectively, but after sintering at 1,200 °C and reducing the temperature to 600 °C, it’s transformed into a new Cu0.75Ni0.25 intermetallic solid solution without secondary phase. We have detected a cationic inter-diffusion in Cu ↔ Ni interphase crystals during this reduction process; however, when sintering time exceeds 2 h at 1,200 °C this reaction mechanism is interrupted by a sublimation phenomenon; which causes Cu2O cubic structure segregation from monoclinic CuO structure. This leads to Cu precipitation from the Cu1−x Ni x solid solution. Cu0.75Ni0.25 inhibits the LSCM perovskite-type grain growth (t ≈ 220 nm). Electrical conductivity indicates the presence of semiconductor and metallic-type behaviors with a maximum electrical conductivity (800 °C) >4.5 (log σ, Sm cm−1). When Cu0.75Ni0.25 concentration was 25 and 35 %, semiconductor behavior were dominated. Thermal expansion coefficients showed a linear dependence inversely proportional to Cu0.75Ni0.25 concentration. Electrical conductivity, Rietveld analysis, Porosity, TEC, and E a behaviors lead to the conclusion that the anodes between 25 and 35 % (Cu0.75Ni0.25) are closer to applications at SOFC.

Interplay between magnetism and chemical structure at spinel-spinel interfaces

By utilizing a graded wedge sample geometry in combination with surface sensitive soft x-ray techniques, we explain the enhanced magnetic properties observed at the interface between two dissimilar magnetic spinel oxide thin films in terms of the chemical and magnetic character of the constituent cations. Through x-ray absorption spectroscopy and magnetic circular dichroism studies, we find that the interfacial cations exhibit chemical valences and site-occupancies which differ remarkably from the bulk of either film. This results in enhanced magnetic properties localized to the interface region. While this phenomena likely arises from cation interdiffusion of 1–2 nm near the interface due to the open spinel crystal structure, this dramatic change in the magnetic properties localized to a thin interface region may provide a route to obtaining isolated interfacial properties in other spinel-structured heterostructures.

Interdiffusion of divalent cations in carbonates: Experimental measurements and implications for timescales of equilibration and retention of compositional signatures

Diffusive element exchange between co-existing carbonate phases was investigated experimentally over the temperature range 400–625°C at 1-atmosphere pressure. Thin films were deposited on natural crystals of pure dolomite to produce diffusion couples of dolomite and siderite, rhodochrosite and carbonate solid solutions. The near-surface compositions of samples following diffusion anneals were measured using Rutherford backscattering spectroscopy (RBS), and diffusion coefficients were extracted by fitting the resulting composition vs. depth profiles. Coupled diffusion leading to element exchange between dolomite and carbonates of pure end-member composition (siderite and rhodochrosite) can be described by a single Arrhenius relation in the investigated range of temperatures. In contrast, the quasi-binary exchange between dolomite and Ca-rich carbonate solid solutions yields diffusivities that display a change in slope (a kink) in the Arrhenius relation at ∼525°C. This kink is interpreted to be the result of the initiation of an order–disorder phenomenon rather than a transition from an extrinsic to intrinsic diffusion regime. Experimental results yield the following Arrhenius relations for binary and mulitcomponent interdiffusion couples (in m2/s): DMn-(Mg+Ca)=9.77×10-17exp(-63±5kJ/mol/RT)T=525-625°CDFe-(Mg+Ca)=9.33×10-14exp(-123±10kJ/mol/RT)T=525-625°CDMn-Mg=2.57×10-20exp(-23±4kJ/mol/RT)T=400-525°CDMn-Mg=7.41×10-11exp(-168±15kJ/mol/RT)T=525-625°CDFe-Mg=9.12×10-20exp(-34±10kJ/mol/RT)T=400-525°CDFe-Mg=3.47×10-10exp(-183±14kJ/mol/RT)T=525-625°CKnowledge of these diffusion parameters is valuable for estimating timescales of equilibration between co-existing carbonates or the duration over which a compositional zoning pattern might be preserved. We present simple model calculations for temperatures at which diffusive closure can be expected in natural systems and discuss the implications for geothermometry. It is shown that the presence of a kink in the Arrhenius relation, together with the shallow slope at low temperatures, sets strict limits for maximum times of retention or equilibration for a given grain size. As a result, natural carbonate grains are likely to preserve information not only on the conditions of formation but also on subsequent adjustments during metamorphic events at low to medium temperatures on timescales typical of contact or regional metamorphism. This new information makes major and trace-element composition in carbonates a promising candidate for deciphering kinetically-controlled processes—including crystal growth, metamorphic overprint and the rates and durations of these phenomena.

Cation inter-diffusion between LaMnO 3 and LaCoO 3 materials

Cation inter-diffusion between polycrystalline LaMnO 3 and LaCoO 3 pellets has been studied at 1373–1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman–Matano method from Mn 3+ to Co 3+ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O 3 solid solution suggested. Cation diffusion coefficients in the end members LaMnO 3 and LaCoO 3 were estimated. Cation mobility in LaMnO 3 is higher than in LaCoO 3. It is suggested that higher cation diffusion in LaMnO 3 is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn 4+). The results are compared to previous reports on cation diffusion in perovskite oxides.

Key Issues in Processing Metal-Supported Proton Conducting Anodes for SOFCs Applications

BaCe0.65Zr0.2Y0.15O3-δ (BCZY) have been recently proposed for IT-SOFCs due to its high proton conductivity. On the other hand considerable efforts are directed towards the development of metal-supported cells. The combination of the potential advantages offered by either proton conductors based cells and metal supported configuration has never been explored. In this work the technological issues to produce proton conducting BCZY-Ni anodes stainless steel-supported were carefully investigated. A tailored porous metal support was produced by tape casting. Afterwards the anode was deposited by screen printing and the resulting bilayer sintered in reducing atmosphere. Each step of the production process was thoroughly investigated. A cations interdiffusion between the metallic support and the anodic layer was observed in all range of temperatures considered. The influence of a CeO2 barrier layer and anode thickness on the cations diffusion and a successful production of planar crack-free anode was deeply analyzed.

Comparison of Ferrous Calcium Silicate Slag and Calcium Ferrite Slag Interactions with Magnesia-Chrome Refractories

The cost of maintaining and eventually replacing refractories as a result of slag attack is a significant cost component in the copper industry. Converting matte to blister copper takes place in reactors lined with direct-bonded magnesia-chrome refractories, and several continuous converting operations use calcium ferrite slag. Unfortunately, the low viscosity of calcium ferrite slag makes it aggressive toward the refractories. Ferrous calcium silicate (FCS) slag has been proposed as a replacement; however, the effect of this slag on magnesia-chrome refractories has not been studied. In this work, the interactions between FCS slag and magnesia-chrome refractory at 1573 K (1300 °C) with an oxygen partial pressure of 10−6 atm were studied and compared with that experienced with calcium ferrite slag under the same conditions. Both slags penetrated the pores in the refractory and caused compositional change in the chromite spinel intergranular bonding phase through cation interdiffusion, which resulted in cracking and debonding of periclase grains. It was observed that the refractory was penetrated much more deeply by calcium ferrite slag than FCS slag because of the higher surface tension and lower viscosity of calcium ferrite slag. As a result, the refractory was attacked less by FCS slag than it was by calcium ferrite slag. It is concluded that the use of FCS slag in continuous copper converting is likely to extend refractory life.

Epitaxial growth of Fe/BaTiO3 heterostructures

The realization of epitaxial heterostructures involving ferroelectric (FE) and ferromagnetic (FM) materials is one of the possible routes towards the realization of devices exploiting sizable magnetoelectric effects. In this paper we demonstrate the epitaxial growth of Fe on BaTiO 3(001) as this system represents a prototypical example of interface between well known FE and FM materials with bcc and perovskite structure respectively, both with Curie temperature well above 300 K. Fe grows on BaTiO 3 with 45° rotation of its cubic lattice with respect to that of the substrate in order to reduce the lattice mismatch. Negligible interdiffusion of Ba and Ti cations or Fe atoms is found by X-ray photoemission spectroscopy, while a sizable Fe oxidation occurs within an interfacial layer with thicknesses thinner than 3 nm.

Lanthanum Germanate‐Based Apatites as Electrolyte for SOFCs

AbstractGermanate apatites with composition La10–xGe5.5Al0.5O26.75–3x/2 have been evaluated for the first time as possible electrolytes for solid oxide fuel cells (SOFCs). Different electrode materials have been considered in this study, i.e. manganite, ferrite, nickelates and cobaltite as cathode materials; and NiO–CGO composite and chromium–manganite as anodes. The chemical compatibility and electrochemical performance of these electrodes with La9.8Ge5.5Al0.5O26.45 have been studied by X‐ray powder diffraction (XRPD) and impedance spectroscopy. The XRPD analysis did not reveal appreciable bulk reactivity with the formation of reaction products between the germanate electrolyte and these electrodes up to 1,200 °C. However, a significant cation interdiffusion was observed by energy dispersive spectroscopy (EDS) at the electrode/electrolyte interface, which leads to a significant decrease of the performance of these electrodes.

Modification of optical properties in ZnO particles by surface deposition and anchoring of NiO nanoparticles

Nanodispersion of NiO nanoparticles on the surface of ZnO microparticles has been carried out by means of a low energy dry mixing method. This method keeps the shape and size of the ZnO microparticles that served as support to hold the NiO nanoparticles. The dispersion and anchoring of the NiO nanoparticles takes place by means of an electrochemical reaction with the OH-groups present at the ZnO surface. The process took place at room temperature and cation interdiffusion between ZnO and NiO have not been detected by structural analysis. Nevertheless, changes in the optical properties of semiconductor ZnO particles have been observed due to the deposition of the nanoparticles. These changes correlate with the amount of NiO nanoparticles at the ZnO particle surface. The amount of defects, i.e. oxygen vacancies, interstitial oxygen and zinc vacancies, rises with the increasing NiO content.

Structural features of p-type semiconducting NiO as a co-catalyst for photocatalytic water splitting

Abstract Perovskite-like NaTaO 3 photocatalysts, synthesized by sol–gel and solid-state methods, were loaded with NiO co-catalyst to enhance water splitting activity under UV illumination. Activity increased significantly with NiO loading and reached a maximum at 3 and 0.7 wt%, respectively, for the sol–gel and solid-state synthesized NaTaO 3 . Beyond this point, photocatalytic activity decreased with further loading. Analysis using X-ray diffraction, high-resolution transmission electron microscopy, and diffuse reflectance spectroscopy shows that the interdiffusion of Na + and Ni 2+ cations created a solid–solution transition zone on the outer sphere of NaTaO 3 . For NiO contents less than 3 wt%, no NiO clusters appeared on the NaTaO 3 surface, and the reduction/oxidation pretreatment did not enhance photocatalytic activity. The high activity resulting from a low NiO loading suggests that the interdiffusion of cations heavily doped the p-type NiO and n-type NaTaO 3 , reducing the depletion widths and facilitating charge transfers through the interface barrier.

Effect of starting powders on the sintering of nanostructured ZrO2 ceramics by colloidal processing

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50 μm zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering.

Octahedral Cation Exchange in (Co0.21Mg0.79)2SiO4Olivine at High Temperatures: Kinetics, Point Defect Chemistry, and Cation Diffusion

The potential applications of transition metal-containing olivines, (M,Mg) 2 SiO 4 , in environmental sustainability and renewable energy rely on a better understanding of their internal structure, defect chemistry, and sublattice processes at high temperatures. In the olivine crystal structure, divalent cations occupy two nonequivalent octahedral sites. The kinetics of octahedral cation exchange between the two sites in a (Co 0.21 Mg 0.79 ) 2 SiO 4 single crystal has been studied from 500 to 700 °C by means of time-resolved optical relaxation spectroscopy upon rapid temperature-jumps. Our experiments show that the cation distribution in the two octahedral sites changes toward a random distribution with increasing temperature and that the exchange kinetics is strongly temperature dependent. Modeling of experimental relaxation data using a kinetic equation of cation exchange yields relaxation times of about 12 300 s at 500 °C and about 6 s at 700 °C, respectively, and an activation energy of about 230 ± 12 kJ/mol for the cation exchange reaction in the (Co 0.21 Mg 0.79 ) 2 SiO 4 olivine. Calculations of vacancy concentrations based on a defect model and impurity levels in the (Co 0.21 Mg 0.79 ) 2 SiO 4 single crystal have been used to interpret the experimentally observed dependence on oxygen activity. We developed as well a formula to correlate experimental relaxation times to the cation diffusion coefficient along the b-axis in olivines. Such a relation allows one to estimate Mg self-diffusion coefficients D Mg b as well as Co-Mg interdiffusion coefficients D b along the b-axis, especially at low temperatures, for example, D Mg b = 4.78 x 10 -23 m 2 /s and D b = 9.33 × 10 -23 m 2 /s at 600 °C. Cation interdiffusion coefficients from the extrapolation of our diffusion data to high temperatures are in agreement with available literature data from Co-Mg interdiffusion experiments.

Performance of perovskite-related oxide cathodes in contact with lanthanum silicate electrolyte

The cathodic performance of selected mixed-conducting electrodes, including perovskite-type SrMn 0.6Nb 0.4O 3 − δ , Sr 0.7Ce 0.3Mn 0.9Cr 0.1O 3 − δ and Gd 0.6Ca 0.4Mn 0.9Ni 0.1O 3 − δ , and Ruddlesden–Popper La 2Ni 0.5Cu 0.5O 4 + δ , LaSr 2Mn 1.6Ni 0.4O 7 − δ , La 4Ni 3 − x Cu x O 10 − δ ( x = 0–0.1) and La 3.95Sr 0.05Ni 2CoO 10 − δ , was evaluated in contact with apatite-type La 10Si 5AlO 26.5 solid electrolyte at 873–1073 K and atmospheric oxygen pressure. The electrochemical activity of porous nickelate-based layers was found to correlate with the concentration of mobile ionic charge carriers and bulk oxygen transport, thus lowering in the series La 4Ni 2.9Cu 0.1O 10 − δ > La 4Ni 3O 10 − δ > La 3.95Sr 0.05Ni 2CoO 10 − δ and decreasing on copper doping in K 2NiF 4-type La 2Ni 1 − x Cu x O 4 − δ . The relatively high overpotentials of nickelate-based cathodes, varying in the range − 240 to − 370 mV at 1073 K and current density of − 200 mA/cm 2, are primarily associated with surface diffusion of silica from La 10Si 5AlO 26.5, which partially blocks the electrochemical reaction zone. As compared to the intergrowth nickelate materials, the manganite-based electrodes exhibit substantially worse electrochemical properties, in correlation with the level of oxygen-ionic and electronic conduction in Mn-containing phases. The effects of cation interdiffusion between the cell components as a performance-deteriorating factor are briefly discussed.

Chemical and thermomechanical compatibility between neodymium manganites and electrolytes based on ceria

The goal of this work was to study the thermal expansion behaviour of NdMe 0.5Mn 0.5O 3 (Me = Ni, Co) solid solutions and to establish the phase relations between them, used as cathodes, and two electrolytes based on Ce 0.9Gd 0.1O 1.95. The electrolyte was doped with 1.0 wt% Bi 2O 3 in order to improve the final densification. Intimate mixtures of the cathode and electrolyte powders were reacted at several temperatures for studying the possible reaction products. Cathode–electrolyte pairs were obtained by isostatic pressing of constituent powders and subsequent sintering in the temperature range 1350–1400 °C for 2 h to observe the interphase compatibility. The sintering conditions were optimized to obtain highly densified electrolytes and well-developed cathode–electrolyte interfaces. Scanning electron microscopy observation with EDAX analysis was performed in cathode–electrolyte interfacial regions in order to characterize the obtained microstructures and to determine possible cation interdiffusion between the cathode and the electrolyte. The nickel-doped manganite, NdNi 0.5Mn 0.5O 3, is chemically and thermo-mechanically compatible with both electrolytes without formation of new phases up to 1400 °C even during long treatment times. On the other hand, NdCo 0.5Mn 0.5O 3 perovskite not had a good behaviour with none of the electrolytes.

Morphological stability of solid-liquid interface during melt crystallization of M 1−x R x F2+x solid solutions

The physicochemical fundamentals of solid solutions M1 − xRxF2 + x (where M = Ca, Sr, Ba, Cd, and R is rare-earth element) with optical quality without a growth-induced cell substructure are considered. The stability of the plane crystallization front to concentration undercooling without account of released crystallization heat is considered. A modified method of stability functions calculation of the crystallization front using phase diagrams is proposed. For MF-RF3 systems, a critical analysis of experimental data on phase equilibria in the region of existence of 55 fluorite solid solutions M1 − xRxF2 + x is performed and the stability functions are calculated. Coefficients of cation interdiffusion in the melt are estimated by growing concentration series of single crystals.

Mixed conductivity, stability and electrochemical behavior of perovskite-type (Sr 0.7Ce 0.3) 1 − xMn 1 − yCr yO 3 − δ

The total conductivity, Seebeck coefficient, thermal and chemical expansions, and steady-state oxygen permeability of Sr 0.7Ce 0.3Mn 1 − y Cr y O 3 − δ ( y = 0−0.5) with tetragonal perovskite structure were analyzed in the oxygen partial pressure range 10 − 16 to 0.3 atm at 600–1270 K. The oxygen permeation fluxes, governed by both surface exchange kinetics and bulk ionic transport limited by low oxygen-vacancy concentration, are 10–30 times higher compared to (La,Sr)MnO 3 − δ . While the perovskite lattice of (Sr 0.7Ce 0.3) 1 − x MnO 3 − δ ( x = 0−0.05) is almost intolerant with respect to A-site cation deficiency, the stability limits of Sr 0.7Ce 0.3Mn 1 − y Cr y O 3 − δ in reducing atmospheres are essentially unaffected by Cr doping and correspond to oxygen partial pressures of (0.4−1.5) × 10 − 11 atm at 1223 K. The substitution of chromium for manganese decreases p-type electronic conduction predominant in the whole phase stability domain, suppresses chemical expansion on reducing p(O 2) due to lowering oxygen stoichiometry variations, but leads also to moderately higher thermal expansion. The electrical properties indicate strong hole trapping by chromium cations and progressive charge-carrier localization. The steady-state polarization studies of porous Sr 0.7Ce 0.3Mn 0.9Cr 0.1O 3 − δ electrodes in contact with two apatite-type silicate electrolytes, La 10Si 5AlO 26.5 and La 6.83Pr 3Si 4.5Fe 1.5O 26 + δ , showed a relatively poor electrochemical performance, which may be partly associated with microstructural degradation and cation interdiffusion between the cell components.

High-temperature transport properties, thermal expansion and cathodic performance of Ni-substituted LaSr 2Mn 2O 7−δ

The substitution of manganese with nickel in LaSr 2Mn 2O 7− δ , where the solubility limit corresponds to approximately 25% Mn sites, enhances the Ruddlesden–Popper phase stability at elevated temperatures and atmospheric oxygen pressure. The total conductivity of LaSr 2Mn 2− y Ni y O 7− δ ( y=0–0.4) decreases with nickel additions, whilst the average thermal expansion coefficients calculated from dilatometric data in the temperature range 300–1370 K increase from (11.4–13.7)×10 −6 K −1 at y=0 up to (12.5–14.4)×10 −6 K −1 at y=0.4. The conductivity and Seebeck coefficient of LaSr 2Mn 1.6Ni 0.4O 7− δ , analyzed in the oxygen partial pressure range 10 −15–0.3 atm at 600–1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism. Reductive decomposition is observed at the oxygen pressures close to Ni/NiO boundary, namely ∼2.3×10 −11 atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O 2)-independent. The steady-state oxygen permeability of dense LaSr 2Mn 1.6Ni 0.4O 7− δ membranes is higher than that of (La,Sr)MnO 3− δ , but lower if compared to perovskite-like (Sr,Ce)MnO 3− δ . Porous LaSr 2Mn 1.6Ni 0.4O 7− δ cathodes in contact with apatite-type La 10Si 5AlO 26.5 solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials.

Structural and magnetic properties of magnetite-containing epitaxial iron oxide films grown on MgO(001) substrates

The structural and magnetic properties of three kinds of Fe oxide films—Fe3O4, a berthollide type of Fe oxide, and a composite of Fe3O4 and FeO—grown on MgO(001) substrates epitaxially at 423K by pulsed laser deposition were investigated by magnetoresistance measurement and grazing incidence x-ray diffraction. The Fe3O4 film had the largest negative magnetoresistance and the roughest film-substrate interface. The very close lattice matching of single-phase Fe3O4 and MgO facilitates the formation of antiphase boundaries due to natural growth defects and of a rough interface probably due to cation interdiffusion.