Compact Grains Research Articles

Tailored nanocrystalline Niobium coatings on steel substrates for superior resistance to micro-crack initiation

Fracture of metallic thin films during deformation hampers extensive applications of coated engineering components. In this study, the resistance to micro-crack initiation of Niobium (Nb) coatings deposited on stainless steel substrates is improved remarkably by tuning the substrate bias voltages during unbalanced magnetron sputtering. With the tailored nanocrystalline microstructure, the failure strain for coating fracture is increased to 30 %, which is far greater than that of previous metallic coatings (below 10 %). Microstructure characterizations reveal that intergranular nano-pinholes and amorphous phases can be eliminated effectively with a moderate ions bombardment effect to avoid brittle film fracture. At the same time, compact and homogenous nanocrystalline grains with appropriate intragranular defects are obtained via enhanced atom diffusivity during deposition. Therefore, large plastic deformation can be accommodated through both stress-driven grain coarsening and continuous dislocation plasticity, avoiding fracture of the Nb coatings.

Lead-free BiFeO3-BaTiO3 based high-Tc ferroelectric ceramics: Antiferroelectric chemical modification leading to high energy storage performance

Dielectric capacitors have been widely used in pulsed power devices owing to their ultrahigh power density, fast charge/discharge speed, and excellent stability. However, developing lead-free dielectric materials with a combination of high recoverable energy storage density and efficiency remains a challenge. Herein, a high energy storage density of 7.04 J/cm3 as well as a high efficiency of 80.5% is realized in the antiferroelectric Ag(Nb0.85Ta0.15)O3-modified BiFeO3-BaTiO3 ferroelectric ceramic. This achievement is mainly attributed to the combined effect of a high saturation polarization (Pmax), increased breakdown field (Eb), and reduction of the remnant polarization (Pr). The modification of pseudotetragonal BiFeO3 by Ag(Nb0.85Ta0.15)O3 leads to a high Pmax, and the enhanced relaxor behavior gives rise to a small Pr. The promoted microstructure (such as a dense structure, fine grains, and compact grain boundaries) after modification results in a high breakdown strength. Furthermore, both the recoverable energy density and efficiency exhibit high stability over a broad range of operating frequencies (1–50 Hz) and working temperatures (25–120 °C). These results suggest that the (0.67–x)BiFeO3-0.33BaTiO3-xAg(Nb0.85Ta0.15)O3 ceramics can be highly competitive as a lead-free relaxor for energy storage applications.

Reactions mechanism and mechanical properties of a SiCf/SiC joint affected by Cu/Ni/Ti elements and inhomogeneous composites

PIP-prepared SiCf/SiC composite joints were brazed by using Cu-Ni-Ti filler alloys, composed of region I: Ni16Si7Ti6 +NiSi2/NiSi/Ni3Ti+TiCx +Cu and region II: TiCx +Cu and infiltration region. The individual and coupled reactions between Cu/Ni/Ti elements and SiCf/SiC composites were clarified experimentally and thermodynamically. The infiltration region was first confirmed to be amorphous Cu-Si-C or Si-C matrix, Cu or Cu(C), (Cu, Ni)15Si4, and Ni2Si. The joint strength was related to the carbonization and amorphization in the infiltration region and the compound content in region I. Three interfaces of vertical fiber-seam, parallel fiber-seam, and matrix-seam were different because of the inhomogeneous features of SiCf/SiC composites. The crystallinity of SiC and the residual free carbon affected the reaction kinetics of the Ti element. The PyC coating produced compact TiCx grains that consequently served as a diffusion barrier for the parallel fibers. The topology of the fibers affected the infiltration region by forming a "capillary action".

Low-temperature sintering of PLSZT-based antiferroelectric ceramics in reducing atmosphere for energy storage

Due to their elevated sintering temperature, pure PLZST-based antiferroelectric ceramics are unsuitable for co-firing with copper internal electrodes as MLCC dielectric materials. In this work, PLZST ceramic materials sintered at low temperature in reducing atmosphere were obtained through a unique BASK glass additive and Y3+ co-doping. While the sintering temperature of ceramics is reduced to 1040 °C, stable defect association (YPb∙,YZr′) is formed by Y3+ solution entering A/B site, which effectively inhibits the increase of defect concentration and promotes ceramic sintering. The high breakdown strength of PLSZT ceramics is attributed to their compact grain and excellent insulation resistivity, which enhance their tolerance to electric fields. An ultrahigh recoverable energy density (Wrec) of 4.9 J/cm3 with a high energy storage efficiency (η) of 92.8% are achieved at an electric field of 400 kV/cm. Moreover, the AFE ceramics possess excellent discharge energy storage properties with a high discharge energy density (Wd) of 4.4 J/cm3 and a large power density (Pd) of 125 MW/cm3.

Experimental investigation of mixing railway ballast grains with different form using large-scale direct shear box apparatus

This paper investigates the effect of grain form on the mechanical behaviour of a railway ballast aggregate using large-scale shear box tests. The speciality of the research is that – contrarily to most of the experimental studies, where the shape content of the assemblies are not manipulated – here, the grains were carefully sorted and the ballast samples were assembled with the desired size and form content. A new sorting method was developed for laboratory-scale samples to separate compact and non-compact (flat, elongated or bladed) grains. This method utilises the combination of standard bar sieves and shape index calliper. The geometries of the grains in the resultant assemblies were thoroughly investigated using modern 3D imaging-based shape characterisation methods. With the adequate parameter thresholds, good correspondence was found between the standard industrial and the modern imaging-based methods, which allows the virtual reproduction of the introduced laboratory sorting technique. Three types of andesite railway ballast assemblies were tested experimentally: a fully compact, a fully non-compact and a mixed one. The mixed assembly had the highest internal friction angle which proves that it can be beneficial to mix grains with different types form. The amount of broken mass and the failure modes of the grains were also recorded, and it was found that the non-compact assembly had the highest rate of breakage. The results of the study also serve as a good basis for the calibration of numerical models.

Optimization of Growth Parameters of the RF-Sputtered CuInGaSe2 Thin Films for Photovoltaic Applications

CuInGaSe2 (CIGS) thin films were deposited by RF sputtering using a single quaternary target. The effects of various sputtering parameters, such as substrate temperature, sputtering power, and gas flow rate, were studied systematically. The structural, morphological, compositional, and optical properties of the films were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDAX), and UV–vis-NIR spectroscopy. The samples exhibited the chalcopyrite type tetragonal structure of CIGS, as confirmed by the XRD analysis. Raman spectroscopy represents the presence of Cu poor ordered vacancy compound (OVC) phase in all the present samples. The growth of the sample at a higher substrate temperature resulted in a higher crystalline nature with a suppressed OVC phase and energy bandgap of 1.18 eV. The deposition of CIGS at 160 W sputtering power favors growth towards (112) Bragg crystal plane, suppressing the (220)/(204) plane of CIGS, shows change in preferred orientation with a lower sputtering power at 80 and 120 W. The sample grown at a gas flow rate of 60 standard cubic centimeters per minute (SCCM) exhibited compact grain growth with marginally improved crystallinity. The sample grown at 160 W, 300 °C, and 60 SCCM showed better crystalline and morphological properties, and it can be used as an absorber layer for highly efficient CIGS thin-film solar cells.

Influence of (Zn0.5Ti0.5)3+ substitution on structural evolution, bond characteristics, and microwave dielectric properties of spinel Li(Zn0.5Ti0.5)xGa5-xO8 solid solutions

In this study, the evolution of phase and bond characteristics, as well as the consequent effects on the microwave dielectric properties of Li(Zn0.5Ti0.5)xGa5-xO8 ceramics were investigated. XRD and Rietveld refinement patterns revealed that the sample underwent a transformation from a low-symmetry inverse cubic spinel phase, characterized by the P4332 space group, to a high-symmetry cubic spinel phase associated with the Fd-3m space group. All samples displayed compact grain structures in their surface micro-morphologies, and they achieved high relative densities exceeding 97% when sintered at their respective optimal temperatures. With increasing x value, the dielectric constant increases due to the growth in ionicity and αtheo/Vm. Concurrently, the τf value shifts from −69.29 ppm/°C to −48.73 ppm/°C, a trend that aligns with the bond valence changes at the octahedral position as a function of x. In the range of 0 ≤ x ≤ 3, the Q × f value initially increased due to the change in symmetry, growth in lattice energy, and reduction of Ti3+ content. However, it subsequently decreased as a result of further disruption in ordering and diminishing lattice energy. The optimal microwave dielectric properties were obtained for the x = 3 sample (LiZn1.5Ti1.5Ga2O8) sintered at 1220 °C, displaying characteristics of εr = 16.46, Q × f = 79,268 GHz and τf = −53.36 ppm/°C.

Construction of Cr coatings with different columnar structure on Zircaloy-4 alloys to optimize the high-temperature steam oxidation behavior for accident tolerant fuel claddings

To optimize the oxidation behavior of chromium-coated Zircaloy-4 alloys under 1200 °C high-temperature steam for accident tolerant fuel (ATF) claddings, Cr coatings with different columnar structure are constructed by changing bias voltage using high power impulse magnetron sputtering and corresponding microstructure, mechanical and high-temperature steam oxidation properties are studied systematically. With the bias voltage increase from 0 V to − 150 V, the microstructure of Cr coatings changes from porous columnar structure to compact columnar structure. Especial for bias voltage is − 90 V, the tiny compact grains uniform distribute on the surface micrographs and optimal compact columnar structure are observed on the cross-section micrographs. The hardness and elastic modulus of as-prepared Cr coatings increase firstly and then decrease, the hardness of Cr coatings with optimal compact columnar structure is 8.65 GPa, which is elevated ∼2.28 times than Cr coatings with porous columnar structure. 1200 °C high-temperature steam oxidation test results show an interesting phenomenon that the thickness of Cr layer reduces initial and then increase with the exposure time prolong from 1 h to 4 h. The main steam oxidation mechanism, in the early oxidation stage, is formation the compact Cr2O3 oxide layer. Then, with the exposure time extend, the reduction reaction plays the significant part for steam oxidation mechanism, which is consumption of outmost Cr2O3 oxide layer and formation of subsurface Cr layer. The construction of Cr coatings with compact columnar structure and relevant oxidation mechanism are expected to offer a new idea for improving 1200 °C steam oxidation resistance of chromium-coated Zircaloy-4 alloys.

Optoelectrical Properties of Treated CdSe Thin Films with Variations in Indium Chloride Concentration.

The effect of a nontoxic chloride treatment on the crystallinity and optoelectrical characteristics of a CdSe thin film was studied. A detailed comparative analysis was conducted utilizing four molarities (0.01 M, 0.10 M, 0.15 M, and 0.20 M) of indium (III) chloride (InCl3), where the results showed a notable improvement in CdSe properties. The crystallite size of treated CdSe samples increased from 31.845 nm to 38.819 nm, and the strain in treated films dropped from 4.9 × 10-3 to 4.0 × 10-3, according to XRD measurements. The highest crystallinity resulted from the 0.10 M InCl3-treated CdSe films. The In contents in the prepared samples were verified by compositional analysis, and FESEM images from treated CdSe thin films demonstrated compact and optimal grain arrangements with passivated grain boundaries, which are required for the development of a robust operational solar cell. The UV-Vis plot, similarly, showed that the samples were darkened after treatment and the band gap of 1.7 eV for the as-grown samples fell to roughly 1.5 eV. Furthermore, the Hall effect results suggested that the carrier concentration increased by one order of magnitude for samples treated with 0.10 M of InCl3, but the resistivity remained in the order of 103 ohm/cm2, suggesting that the indium treatment had no considerable effect on resistivity. Hence, despite the deficit in the optical results, samples treated at 0.10 M InCl3 showed promising characteristics as well as the viability of treatment with 0.10 M InCl3 as an alternative to standard CdCl2 treatment.

The Study of Multi-Stage Cold Forming Process for the Manufacture of Relief Valve Regulating Nuts

Cold forging is widely used in many industries. Multi-stage cold forming is usually utilized in forging fasteners. In this study, numerical simulation and experimental investigations were carried out on a five-stage cold-forming process for the manufacturing of low-carbon steel AISI 1010 relief valve regulating nuts. The forming process through five stages included preparation and centering for backward extrusion, backward extrusion over die pin, upset, backward extrusion over a moving punch, and piercing. The formability of the workpiece was studied, such as the effects on forming force response, maximum forming force, effective stress and effective strain distributions, metal flow patterns, and strength. A comparison of the forming forces obtained in the forming experiment with the numerical simulation results of the five-stage cold forming showed a good agreement with the trend of the forming force growth. For the maximum forming force and forming energy, the fourth stage of backward extrusion over the moving punch at the upper face was the largest among the five stages. The total maximum forming forces from the first to the fifth stages were numerically 440.9 kN and experimentally 449.4 kN, meaning the FE simulation and experimental results were in good agreement. The numerically simulated effective strain distributions were consistent with the experimentally tested hardness distributions. Highly compacted grain flow lines also resulted in higher hardness. The overall hardness of the workpiece formed by five-stage cold forming increased by 31% compared to the initial billet. The hardness of the workpiece increased with the forming stages, and the strain-hardening effect was obvious. The strength of the workpiece was significantly increased by five-stage cold forming.

Charge Separation Enhancement Enables Record Photocurrent Density in Cu2ZnSn(S,Se)4 Photocathodes for Efficient Solar Hydrogen Production

AbstractCu2ZnSn(S,Se)4 (CZTSSe) is a promising light absorbing semiconductor for solar energy conversion in photovoltaic cells and photo‐electrochemical (PEC) water‐splitting devices, owing to its earth‐abundant constituents, adjustable band‐gap, and superior absorption coefficient. However, the severe charge carrier recombination and the sluggish charge separation efficiency are the main issues obstructing the enhancement of device performance. In this work, a planar‐type Mo/CZTSSe/CdS/TiO2/Pt photocathode is fabricated. High‐quality CZTSSe film with compact and uniform crystal grains can be obtained via a two‐step process involving solution processed spin coating and thermally processed selenization. When an appropriate film thickness is used, both bulk defects and surface/interface defects are passivated, significantly suppressing the defects‐assisted recombination. Moreover, the benign energy band alignment of CZTSSe/CdS heterojunction is favorable to enhance photo‐generated charge separation and transfer efficiency. A remarkable photocurrent density of 40.40 mA cm−2 (at 0 VRHE) can be achieved, approaching to its theoretical value of 42.85 mA cm−2, and representing the highest value reported to date for kesterites‐based photocathodes. A champion CZTSSe photocathode with half‐cell solar‐to‐hydrogen conversion efficiency of 6.47% suggests a bright future for efficient solar hydrogen production applications.

Chemical, surface, and thermal studies of mixed oxides cupric oxide (CuO), lanthanum oxide (La2O3), and graphene oxide for dye degradation from aqueous solution

Mixed oxy-compositions are lately used for water treatment that might be exploited as photo-catalyst, and adsorptive materials for the disposal of water pollutants. Cupric oxide (CuO), lanthanum oxide (La2O3), and graphene oxide (GO)-based nanocomposites show an interest in water treatment applications owing to the adsorptive feature of carbon-based nanoparticles (NPs), besides low band gap of metal oxides that boosts photo-catalytic process. CuO/La2O3/GO-based nanocomposites are prepared and tested for their thermal stability, and dye removal activity. The change in nanocomposites structure upon the incorporation of CuO and La2O3 into GO nanosheets is inspected via TEM micrographs showing a decline in lanthana rod length to be 200 nm on average. Additionally, the improved roughness structure and the compact grain size appear in SEM micrographs reports CuO grain size reduction reaching an average size of 250 nm. The roughness parameters of CuO/La2O3/GO are extraordinarily heightened in which the supreme value of roughness average is 7.6 nm. Ternary nanocomposite exhibits a maximum value (85%) as a methylene blue (MB) dye removal. Based on these obtained results, the fabricated nanocomposites are recommended for water treatment due to their enriched physicochemical and morphological features as well as the better thermal stability and exerted dye removal activity.

A synergistic two-step optimization design enables high capacitive energy storage in lead-free Sr0.7Bi0.2TiO3-based relaxor ferroelectric ceramics

A two-step design is developed to realize multi-objective synergistic optimizations including high activity/ultrafine PNRs and ultrasmall grain size with compact grain boundaries, showing huge application potential in advanced pulsed power devices.

Comparative study between CZTS and CZTSe thin layers for photovoltaic applications

A comparative study of the thin layer based on copper zinc tin sulphide Cu2ZnSnS4 (CZTS) and that based on copper zinc tin selenide Cu2ZnSnSe4 (CZTSe) was made in order to assess the structural, morphological, optical and electrical qualities. for better use in improving performance of CZTS, CZTSe or CZTSSe based solar cell. CZTS and CZTSe thin films prepared by the spray pyrolysis technique were characterized by X-ray diffraction (XRD) which confirmed their kesterite structure in the tetragonal crystal phase. In addition, the analysis of the surfaces of the thin layers with the scanning electron microscope SEM, showed compact grains, well agglomerated and of appreciable sizes. UV-visible spectroscopy measured the quality of light absorption and located the bandgap energy values between 1.16 eV for CZTSe and 1.69 eV for CZTS i.e. in the range of potential absorbers for CZTS and CZTSe based thin film solar cells.

Synthesis and characterization of Cu-sandwiched Sb2Se3 thin films and numerical simulation of p-Sb2Se3/n-ZnSe heterojunction solar cell

Sb2Se3 and Cu-sandwiched Sb2Se3 thin films were prepared by sequential evaporation of (Sb/Se) × 3 and [(Cu/(Sb/Se) × 3/Cu)] precursor stacks over the glass substrates in a high vacuum using electron beam (e-beam) evaporation followed by annealing in a tubular furnace at various temperatures in Ar atmosphere. The growth of Sb2Se3 and Cu-sandwiched Sb2Se3 films is studied by varying annealing temperature. The Sb2Se3 films grown without copper layers were peeled off from the glass substrates when annealed above 300 °C, whereas the Cu-sandwiched Sb2Se3 films were adherent to substrates up to 450 °C. The XRD of Cu-sandwiched Sb2Se3 films annealed at all temperatures confirms the Sb2Se3 formation with orthorhombic crystal structure. The Cu-sandwiched films annealed at ≤ 250 °C showed the preferred orientation along the (hk0) plane, whereas films annealed at ≥ 300 °C exhibited the (hk1) preferred orientation. The morphology of Cu-sandwiched Sb2Se3 films annealed at 450 °C showed compact and larger grains (∼0.8 μm) with a direct optical band gap of 1.04 eV. Hall effect measurement exhibited a p-type conductivity with a hole concentration of 3.1 × 1015 cm−3. The numerical simulation of the proposed Glass/Ni/p-Sb2Se3/n-ZnSe/ITO/Al heterojunction solar cell showed a power conversion efficiency of 21.51%.

Characterization of Sb2Te3 thin films prepared by electrochemical technique

A conductive and thermally stable material with a high work function is required to produce highly efficient CdTe-based thin film solar cell (TFSC) devices. In this study, we report the growth of layers of polycrystalline, stoichiometric, and compact antimony telluride (Sb2Te3) by using the wet-chemical aqueous electrochemical technique. A three-electrode geometry consisting of a working electrode, a reference electrode, and a counter electrode was used to deposit the Sb2Te3 thin films at a low temperature (60 °C ± 2 °C). The growth potential was optimized through cyclic voltammetric measurements with reference to the Ag/AgCl reference electrode. The structural, morphological, compositional, and electrical properties of the films were studied and correlated. Their prominent Bragg reflections of (103), (016), and (110) verified the growth of the rhombohedral crystal structure of Sb2Te3. The Raman modes Eg and A1g, observed at 119.88 and 161.48 cm−1, respectively, confirmed the formation of the Sb2Te3 compound. Compact grain growth with a void-free and well-adherent layer was observed using scanning electron microscopy. The grain size, surface morphology, and thickness of the Sb2Te3 layers were significantly influenced by variations in the deposition potentials. An EDS analysis of the sample grown at −0.5 V revealed nearly stoichiometric growth (2:3, Sb:Te ratio). The elemental chemical states were studied through XPS analysis. The survey scan confirmed the presence of antimony, tellurium, oxygen, and carbon. The current–voltage characteristics reflected the nearly ohmic nature of the Sb2Te3 thin films. The ideality factor and carrier concentration obtained for the sample grown at −0.5 V exhibited nearly ohmic behaviors, with a high conductivity that was suitable for back-contact between the buffer layer and CdTe for the development of CdS/CdTe solar cells.

Effects of yttrium doping on structural, electrical and optical properties of barium titanate ceramics

In this report, we study the Yttrium-doped Barium Titanate (Y-BT) Ba1 − xYxTiO3 (with x = 0.00, 0.01, 0.03, 0.05, 0.07 mmol) perovskite ceramics synthesized by sol-gel method. The as-made powder samples were pressed into a pellet shape and subsequently sintered at 1300 °C for 5 h in air. The structural, morphological, electrical, and optical properties of the synthesized samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), impedance analyzer, and UV-Vis-NIR Spectroscopy respectively. The XRD study revealed the formations of single phase tetragonal structure of Barium Titanate (BT) with ∼23–33 nm mean crystallite size. The crystallite size increases initially with Y-doping, found at about 33 nm for x = 0.01, and reduces for increase in Y3+ concentration further. The microstructural study from FESEM depicts the uniform distribution of compact and well-faceted grain growth for Y-BT in contrast with undoped barium titanate. The average grain size (∼0.29–0.78 μm) of the Y-BT decreases with increasing doping concentration. Frequency-dependent impedance analyses show enhanced dielectric properties like dielectric constant, quality factor, and conductivity with low dielectric loss in the presence of Yttrium. The optical bandgap energy (∼2.63–3.72 eV) estimated from UV-Vis-NIR diffuse reflection data shows an increasing trend with a higher concentration of yttrium doping.

Structure, segregation and properties of high-alloy Al – Ti – V – Ni alloys

Using optical and electron scanning microscopy, as well as electron probe microanalysis and X-ray diffraction analysis, the authors looked at the structure, segregation and properties (hardness HRA, microhardness HV) of high-alloy Al – Ti – V – Ni alloys. It was established how the structure tends to change and how elements of the structural components of the studied alloys (1–5) tend to distribute as a function of V and Ni concentration. Using electron probe microanalysis, the structural conponents of the studied alloys were identified depending on V and Ni concentration. 1. The initial alloy 1 sees vanadium aluminide Al3(V, Ti) solidify from Al – Ti – V – Ni (wt. %: 24.6 V, 0 Ni), as well as alloyed vanadium carbide. The former solidifies as grey-coloured grains with a minimum size of 25 μm and serves as the base phase, whereas tha latter comes in a spiky shape (<25 μm). A blackish-coloured mixture of Al + Al3Ti + Al21V2 solidifies last. 2. Alloy 2 sees nickel aluminide Al3Ni solidify from Al – Ti – V – Ni (17 wt. % V, 7.2 wt. % Ni) as fine-grained light-coloured inclusions against a background of vanadium aluminate Al2(V, Ti), which is the key structural component of the alloy. Together with the above phases, alloyed titanium carbide (Al, Ti, V)3C forms in the alloy as compact grey-coloured grains. A phase mixture of Al + + Al3Ni + Al3Ti + Al21V2 solidifies last. 3. The following phases solidify in alloys 3–5 from Al – Ti – V – Ni (0–10.7 wt. % V; 13.5–23.8 wt. % Ni): β'-phase – a solid solution of Ni in nickel aluminide AlNi, which comes as fine-grained white-coloured inclusions against a background of nickel aluminide Al3Ni, which is the base phase. The next phase includes compact dark-grey grains of titanium carbide Ti2C. Alloys 4–5 see a new phase form – a complex alloyed titanium aluminide Al3(Ti, V, Ni), which consists of dark-grey oblong-shaped crystals. A phase mixture of Al + Al3Ni + Al3Ti + Al21V2 solidifies last. Even though the stoichiometry of the identified phases fails to match the results of electron probe microanalysis, the results of X-ray diffraction analysis confirms the presence of the key structural components in the studied alloys.This research was carried out using the equipment of the Applied Materials Science Centre at the Pacific National University. It was funded by the Ministry of Education and Science of the Russian Federation under Gove rnmental Assignment No. FEME-2020-0010.

Why do compact grain boundary complexions prevail in rock-salt materials?

Over 40 years of studies of grain boundaries in ionic rock-salt materials have left the community divided. On one hand, numerical simulations systematically predict open, hollow structural units to be the ground state. On the other, most recent experiments report compact structures to be the norm. To reconcile modelling with experimental evidence, we investigate the stability of three high-angle symmetric tilt grain boundaries in magnesium oxide MgO with respect to the presence of charge-neutral vacancy pairs. We demonstrate that although open structural units are energetically the most favourable, they are easily destabilized by vacancies. It follows that open complexions can never be at equilibrium with the surrounding grains at finite temperature. On the contrary, compact structural units can accommodate a wide range of defects concentrations, and are much more resilient with respect to the absorption of vacancies. These results highlight the limitations of studies that consider only the ground state, and stress the importance of accounting for the presence of other defects when modelling grain boundaries in ionic materials.

Fabrication of C12H28ClN-assisted perovskites thin films with micrometer-sized grains via low-temperature hot-casting in ambient air for resistive memory device application

Fabricating perovskite (PVK) films with large grains and compact grain boundaries via solution processability is demanding for efficient electronic and optoelectronic devices. Hot-casting produces dense PVK films with bigger and adjacent grains; however, involves higher temperatures and an inert atmosphere that increases the fabrication cost. Herein, using dodecylammonium chloride (DCl) as an additive, combined with hot-casting is utilized and compact bi-cation PVK films with grain size > 110 µm are synthesized at lower temperature and ambient air. It is revealed that the films have a dense microstructure with no voids among the grains. Also, the films are highly crystalline with preferentially orientated crystals and showed greater hydrophobicity and an extended carrier lifetime. Finally, the films are employed in a resistive-memory storage device, which demonstrated a high ON/OFF ratio of > 106 and lower power consumption. Such high-quality films prepared at ambient conditions could be useful for the realization of other highly efficient optoelectronic devices.