Distortion Of Geometry Research Articles

A Lithium Complex Ferroelectric with High Curie Temperature: [Li(1,10-Phenanthroline)2]I.

Paraelectric-ferroelectric phase transitions have been mainly acknowledged by the order-disorder type in most molecular ferroelectrics or the displacive type in inorganic ferroelectrics. However, reports regarding symmetry-breaking ferroelectric phase transitions induced by distortion in the coordination geometry have been scarce. In this study, we present a lithium complex molecular ferroelectric [Li(1,10-phenanthroline)2]I, which undergoes an Aizu mmmFmm2 type symmetry-breaking ferroelectric phase transition at 371 K. Its ferroelectricity has been identified by the geometric distortion of the lithium ions coordination environment and the concomitant directional movement of iodide ions. Besides, the ferroelectric loop of [Li(1,10-phenanthroline)2]I can be readily obtained from a polarized polycrystalline pellet at room temperature; in addition, its nonlinear optical signal is comparable to that of KH2PO4 (KDP). To the best of our knowledge, [Li(1,10-phenanthroline)2]I represents the first lithium-based organic complex ferroelectric exhibiting a coordination geometry-triggered symmetry-breaking ferroelectric phase transition. This work will provide significant inspiration for the design of novel molecular ferroelectrics.

Fine-Tuning the Anisotropies of Air-Stable Single-Molecule Magnets Based on Macrocycle Ligands.

Air-stable single-molecule magnets (SMMs) can be obtained by confining DyIII ion in a D6h coordination environment; however, most of the current efforts were focused on modifying the rigidity of the macrocycle ligand. Herein, we attempt to assemble air-stable SMMs based on macrocycles with a replaceable coordination site. By using an in situ 1 + 1 Schiff-base reaction of dialdehyde with diamine, three air-stable SMMs have been obtained in which one of the equatorial coordination sites can be varied from -NH- (for Dy-NH), -O- (for Dy-O), and -NMe- (for Dy-NMe). Complex Dy-NH shows a less distorted D6h symmetry and an anisotropy energy barrier of 1270 K. For complex Dy-O, the coordination site of -O- gives a relatively longer coordination bond but a comparable energy barrier in contrast with that of Dy-NH. In the case of complex Dy-NMe, although the -NMe-group gives a very long coordination bond, the large steric effect on the -NMe- group enforces a larger distortion of the D6h coordination geometry, resulting in the fast quantum tunneling of the magnetization that shortcuts the thermal relaxation process; therefore, Dy-NMe shows a lower energy barrier. This study provides a new strategy for modifying the coordinate site on the equatorial plane of D6h symmetry to fine-tune the structure and magnetic anisotropy of SMMs.

Coordination geometry flexibility driving supramolecular isomerism of Cu/Mo pillared-layer hybrid networks.

Hydrothermal synthesis led to four novel 3D pillared-layer metal-organic frameworks: [Cu4(4,4'-bipy)4(MoO4)4·0.3H2O]n (1), [Cu(4,4'-bipy)0.5(MoO4)·0.25H2O]n (2), [Cu(4,4'-bipy)(MoO4)·0.1H2O]n (3), and [{Cu(4,4'-bipy)}2(Mo8O26)0.5]n (4). These compounds exhibit diverse supramolecular isomerism within their 3D coordination networks, each incorporating bimetallic {CuMoO} layers linked by 4,4'-bipyridine, demonstrating a remarkable structural diversity. Compound 1 features a 3D network derived from conformational supramolecular isomerism. Its bimetallic layer comprises fused 16-membered {Cu4Mo4O8} and eight-membered {Cu2Mo2O4} rings, with varying O-Cu-O bond angles affecting the network puckering and Cu-Cu distances. In contrast, the coordination networks observed in 2, 3, and 4 correspond to structural supramolecular isomers from the earlier stated networks. In 2, centrosymmetric Cu2+ dimers with distorted square-pyramidal geometry are linked along the c axis by 4,4'-bipyridine, forming 1D {Cu2(4,4'-bipy)}n chains with a Cu-Cu distance of 2.95 Å. Its oxide substructure comprises bilayers of fused 12-membered {Cu3Mo3O6} rings. Crystal structures 3 and 4 are particularly notable for their construction at the Cu+ centers. In compound 4, this isomerism is further influenced by the interplay between the distortion of the coordination geometry of both the Cu and Mo ions. The propensity to form these supramolecular isomers primarily stems from the flexible coordination environment of copper ions. Electron paramagnetic resonance measurements corroborated the structural descriptions of the paramagnetic compounds 1 and 2.

Symmetry Breaking of Electronic Structure upon the π→π* Excitation in Anthranilic Acid Homodimer.

The main purpose of this study is to characterize the nature of the low-energy singlet excited states of the anthranilic acid homodimer (AA2) and their changes (symmetry breaking) caused by deformation of the centrosymmetric, ground state structure of AA2 towards the geometry of the S1 state. We employ both the correlated ab initio methods (approximate Coupled Clusters Singles and Doubles-CC2 and CASSCF/NEVPT2) as well as the DFT/TDDFT calculations with two exchange-correlation functionals, i.e., B3LYP and CAM-B3LYP. The composition of the wavefunctions is investigated using the one-electron transition density matrix and difference density maps. We demonstrate that in the case of AA2, small asymmetric distortions of geometry bring about unproportionally large changes in the excited state wavefunctions. We further provide comprehensive characterization of the AA2 electronic structure, showing that the excitation is nearly completely localized on one of the monomers, which stands in agreement with the experimental evidence. The excitation increases the π-electronic coupling of the substituents and the aromatic ring, but only in the excited monomer, while the changes in the electronic structure of the unexcited monomer are negligible (after geometry relaxation). The increased electronic density strengthens both intra- and intermolecular hydrogen bonds formed by the carbonyl oxygen atom of the excited monomer, making them significantly stronger than in the ground state. Although the overall pattern of changes remains qualitatively consistent across all methods employed, CC2 predicts more pronounced excitation-induced modifications of the electronic structure compared to the more routinely used TDDFT approach. The most important deficiency of the B3LYP functional in the present context is locating two charge-transfer states at erroneously low energies, in close proximity of the S1 and S2 states. The range-corrected CAM-B3LYP exchange-correlation functional gives a considerably improved description of the CT states at the price of overshot excitation energies.

Local Structure‐Induced Selective Interactions Enables High‐Performance and Burn‐in‐Free Organic Photovoltaics

AbstractOligomeric acceptors (OAs) have attracted considerable attention in the organic photovoltaics (OPV) field owing to their capacity in balancing the merits from both monomeric and polymeric acceptors. A delicate control over the distortion between blocks of OAs usually determines the performance and stability of relevant OPV devices. However, it imposes great complexity to realize a controllable degree of distortion by tuning the skeleton of blocks and the position of linker between blocks. Herein, we developed a facile strategy to rationally control the geometry distortion of OAs via a straightforward substitution of alkoxy side‐chains on their blocks. This helps elucidate the integrated influences of molecular distortion and non‐bonded contacts on the selective interactions between OA molecules and between OA and host acceptor in ternary blend. We demonstrate the alkoxy‐OA molecules having stronger self‐interactions would mitigate their interactions with host acceptor, therefore alleviating the kinetic diffusion and excessive aggregation of total acceptors. Combining with a composite‐interlayer strategy by introducing a phenyl‐substituted self‐assembled monolayer to enhance the doping with polyoxometalate, an impressive efficiency of 20.1 % is achieved accompanied by a negligible burn‐in loss against physical aging. This study demonstrates the validation of tuning of selective interactions towards high‐performance and burn‐in‐free OPV.

Local Structure-Induced Selective Interactions Enables High-Performance and Burn-in-Free Organic Photovoltaics.

Oligomeric acceptors (OAs) have attracted considerable attention in the organic photovoltaics (OPV) field owing to their capacity in balancing the merits from both monomeric and polymeric acceptors. A delicate control over the distortion between blocks of OAs usually determines the performance and stability of relevant OPV devices. However, it imposes great complexity to realize a controllable degree of distortion by tuning the skeleton of blocks and the position of linker between blocks. Herein, we developed a facile strategy to rationally control the geometry distortion of OAs via a straightforward substitution of alkoxy side-chains on their blocks. This helps elucidate the integrated influences of molecular distortion and non-bonded contacts on the selective interactions between OA molecules and between OA and host acceptor in ternary blend. We demonstrate the alkoxy-OA molecules having stronger self-interactions would mitigate their interactions with host acceptor, therefore alleviating the kinetic diffusion and excessive aggregation of total acceptors. Combining with a composite-interlayer strategy by introducing a phenyl-substituted self-assembled monolayer to enhance the doping with polyoxometalate, an impressive efficiency of 20.1 % is achieved accompanied by a negligible burn-in loss against physical aging. This study demonstrates the validation of tuning of selective interactions towards high-performance and burn-in-free OPV.

Unveiling Chirality Transfer between Chiral Centers and Metal Halides in Chiral Organic-Inorganic Hybrid Metal Halides.

Chirality transfer refers to the process in which chiral cations compel the crystallization of the inorganic component into the Sohncke group. Enhancing the chirality of the inorganic component in chiral organic-inorganic hybrid metal halides (OIHMHs) through chirality transfer, aimed at improving chiroptical and spintronic properties, remains challenging due to the complexity of the underlying mechanism. To investigate this, we propose a novel concept─chirality transfer coefficient─as a means of quantifying the strength of chirality transfer in OIHMHs. A comparative study of OIHMHs with varying dimensionality, metal ions, and chiral centers was conducted to elucidate this mechanism. By analyzing factors such as hydrogen bonding, the number of chiral centers, dimensionality, helical geometry, and structural distortions, we found that chirality transfer is influenced by a combination of structural dimensions and the number of chiral centers. Importantly, our findings reveal that 0D, and 1D OIHMHs, particularly 1D with a zigzag chain configuration, exhibit stronger chirality transfer than their 2D counterparts. Moreover, in 2D OIHMHs, a reduction in the number of chiral centers enhances chirality transfer. However, no direct correlation was observed between chirality transfer and spin splitting. These insights contribute to a more comprehensive understanding of chirality transfer mechanisms and provide a strategic approach for enhancing the chirality transfer and associated physical properties in OIHMHs.

Theoretical and experimental studies on the effect of the 1,2-diketone group on geometry distortion for phenacene-type polycyclic aromatic compounds

Abstract This paper addresses the geometry distortion of orthoquinone-containing phenacene-type compounds by comparing the structures of phenanthrene-9,10-dione, chrysene-5,6-dione, and picene-13,14-dione. Interestingly, the calculated geometry of chrysene-5,6-dione under the isolated state was drastically different from the experimental one observed by single-crystal X-ray analysis. Theoretical calculations suggested that the molecular geometry of the o-quinone derivatives was sensitive not only to the sterically intramolecular proximity between the carbonyl oxygen and the hydrogen atoms of the benzene rings but also to intermolecular interactions. The twist distortion affects properties such as oscillator strength and 1-electron transitions, for low-lying excited states.

Electronic and adsorption properties of halogen molecule X2 (X=F, Cl) adsorbed arsenene: First-principles study

The geometry, electronic structure, and adsorption properties of halogen molecule X2(X = F, Cl) on arsenene were investigated using first-principles calculations. The adsorption of molecules was considered at various sites and in various orientations on the pristine arsenene (p-As) surface. Both molecules show chemisorption and the crystal orbital Hamiltonian population (COHP) analysis reveals the formation of strong X-As bonds. In particular, the adsorbed molecules spontaneously dissociate into atomic halogen atoms, with a diffusion barrier of 1.91 (1.72) eV for F2(Cl2). The adsorbed X2 molecules induced distortions in the local geometry due to strong interaction with arsenene. Importantly, the formation of X-As bonding remarkably changed the electronic properties, evidenced by the decrease of the actual band gap due to the emergence of defect states within the band gap. For instance, the F2 adsorbed arsenene system (F2-As) exhibited an average band gap of 1.17 eV, and Cl2 adsorbed arsenene (Cl2-As) showed an average band gap of 0.83 eV. In particular, indirect to direct band gap transition was observed for some adsorption configurations. The reduction in band gap resulted in the enhancement of electrical conductivity. These findings suggest that the electronic properties of arsenene can be tuned by halogen decoration.

Discerning the Structure-Photophysical Property Correlation in Zero-Dimensional Antimony(III)-Doped Indium(III) Halide Hybrids.

Zero-dimensional (0D) metal halide hybrids incorporating optically emissive Sb3+ dopants have received huge research attention as a result of dopant-based visible emission for lighting and scintillation applications. Indeed, there have been a plethora of reports on Sb3+ doping of indium halide (In-X)-based 0D hybrids that show strong dopant emission with varied emission wavelengths (λem) and photoluminescence quantum yields (PLQYs). However, discerning the structure-luminescence relation in these 0D-doped hybrids remains challenging because it necessitates exquisite synthetic control on the local metal (dopant) halide geometry/site asymmetry. Demonstrated here is synthetic control that allows tuning of the local metal halide geometry of the Sb3+ dopants in 0D In-X hybrids utilizing five different organic cations. Experimental analysis of the series of Sb3+-doped In-X hybrids reveals a strong correlation between the extent of local metal halide geometry distortion and their photophysical properties (λem and PLQY). Density functional theory calculations of the doped compounds, characterizing ground- and excited-state structural distortions and energetics, reveal the origin of the extent of luminescence behavior. The experimental-computational results reported herein unravel the operative structure-luminescence relation in 0D Sb3+-doped In-X hybrids, provide insight into the emission mechanism, and open up avenues toward rational synthesis of strongly emissive materials with desired emission color for targeted applications.

Investigation of the Relationship between Quantum Yield, Charge-Transfer State, and Structure of the Ligands in Red-Emitting Heteroleptic Iridium(III) Complexes.

Iridium(III) organometallic complexes have been a key component in commercialization of organic light-emitting diodes, but the direct relationship between their structural features and photophysical properties has not yet been fully established. Here, combined experimental and theoretical studies are carried out to elucidate the main factors governing the quantum efficiency of red phosphorescent emitters by using two heteroleptic iridium(III) complexes with high geometrical similarity. It is found that two red-emitting heteroleptic iridium complexes differing only in the steric direction of phenylquinoline (pq) and phenylisoquinoline (piq) ligands, annotated Red-pq and Red-piq, show clearly different degrees of distortion of the ligand geometry in the excited state, which leads to the higher quantum yield of Red-piq than that of Red-pq. This larger distortion of the piq ligand causes more suppressed nonradiative decay of Red-piq than that of Red-pq which is the important factor governing the higher quantum yield of Red-piq.

Asymmetric nanofracture in WS2 for its local toughness anisotropy

Fracture in crystal lattices usually occurs with discrete atomic bond breakages around the crack tip. WS2 involves three-layer atomic structures, where the atomic stress near the crack front exhibits thickness dependence and significantly relies on the local distortion of lattice geometry. We show that the T-stress obtained by over-deterministic methods, and the continuum circumferential stress, are limited in predicting the nanocrack kinking of WS2 strips by molecular dynamics simulations. As the far-field displacement loads, the T-stress initially increases in negative, followed by a slight jump at the initiation of kinking, and the continuum circumferential stress cannot accurately capture the variation of atomic stresses at the crack tip. This can be attributed to the local anisotropy in atomic lattices, and the crack preferentially extends in the zigzag direction of the local maximum energy release rate. Our work might provide insights into the fabrication and assembly of WS2 nanodevices.

New Catalyst Systems for the Polymerization of Norbornene and Its Derivatives Based on Cationic Palladium Cyclopentadienyl Complexes

The catalytic properties of systems based on [Pd(Cp)(L)n]m[BF₄]m (where Cp = η5-C5H5; n = 2, m = 1: L = tris(orthomethoxyphenyl)phosphine, triphenylphosphine, tris(2-furyl)phosphine (TFP), n = 1, m = 1: L = 1,1'-bis(diphenylphosphino)ferrocene, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,5-bis(diphenylphosphino)pentane; n = 1, m = 2 or 3: L = 1,6-bis(diphenylphosphino)hexane) in the addition homoand copolymerization of norbornene (NB) and its derivatives have been studied. These complexes can be activated with the Lewis-acids (BF₃ ∙ OEt2 or AlCl3). The productivity of the [Pd(Cp)(PPh3)2][BF₄]/BF₃ ∙ OEt2 catalyst system in the polymerization of norbornene is up to 188800 molNB molPd⁻¹. The homopolymerization of 5-methoxycarbonylnorbornene and copolymerization of NB with 5-methoxycarbonylnorbornene or 5-phenylnorbornene were studied in the presence of BF₃ ∙ OEt2 and [Pd(Cp)(L)2][BF₄] (L = PPh3 or TFP). A hypothesis for the catalyst’s formation via the intramolecular rearrangement of the η5-Cp ligand into the η1-Cp form upon interaction with a Lewis acid is suggested. The structure of the [Pd(Cp)(TFP)2]BF₄ (I) was determined by X-ray diffraction. In the crystal structure of I, the palladium coordination sphere is characterized by a slight distortion of the square planar geometry of the central atom, and the cyclopentadiyl fragment is in an eclipsed conformation. Based on the XRD data, the steric hindrance of the TFP ligand was estimated (the cone angle is 149°).

Electrocatalytic facets of a newly designed cobalt(III) complex towards sustainable hydrogen evolution

A hybrid cobalt complex (C7H10ON)[Co(L)2].CH3OH (Co-complex) bearing an organic cation and anionic cobalt complex has been designed, synthesized, and structurally characterized. The tridentate chelator, 2-((2-hydroxybenzylidene)amino)-4-methylphenol (H2L), was prepared by the condensation reaction between salicylaldehyde and 4-methyl-2-amino phenol. Crystal structure analysis reveals a slight distortion in the octahedral coordination geometry of the cobalt(III) centre. This complex was evaluated in the hydrogen evolution reaction (HER) using a glassy carbon working electrode in acetonitrile (ACN), using tBu4NClO4 as the supporting electrolyte. The catalyst exhibited heightened catalytic activity when acetic acid was introduced, leading to a significant elevation in the catalytic wave at −1.6 V (V vs. Ag wire). The most pronounced activity was observed by adding 15 mM acetic acid, with a turnover number (TON) of 10.1. The catalyst’s durability was confirmed through controlled potential electrolysis (CPE) at −1.6 V for 2 h, displaying a steady current for the initial 20 min, followed by a gradual increase over the subsequent 2 h. A negligible amount of deposited metallic cobalt on the surface of the glassy carbon electrode through a ligand dissociation was evident during the electrocatalytic studies, as ensured by X-ray Photoelectron Spectroscopy (XPS) analysis. Further, the presence of ligand-centric reduction wave in the complex signifies the synergistic effect of the M−L cooperation and offers a plausible ECEC mechanistic route for the release of molecular hydrogen.

Biases in hand perception are driven by somatosensory computations, not a distorted hand model

To sense and interact with objects in the environment, we effortlessly configure our fingertips at desired locations. It is therefore reasonable to assume that the underlying control mechanisms rely on accurate knowledge about the structure and spatial dimensions of our hand and fingers. This intuition, however, is challenged by years of research showing drastic biases in the perception of finger geometry.1,2,3,4,5 This perceptual bias has been taken as evidence that the brain's internal representation of the body's geometry is distorted,6 leading to an apparent paradox regarding the skillfulness of our actions.7 Here, we propose an alternative explanation of the biases in hand perception-they are the result of the Bayesian integration of noisy, but unbiased, somatosensory signals about finger geometry and posture. To address this hypothesis, we combined Bayesian reverse engineering with behavioral experimentation on joint and fingertip localization of the index finger. We modeled the Bayesian integration either in sensory or in space-based coordinates, showing that the latter model variant led to biases in finger perception despite accurate representation of finger length. Behavioral measures of joint and fingertip localization responses showed similar biases, which were well fitted by the space-based, but not the sensory-based, model variant. The space-based model variant also outperformed a distorted hand model with built-in geometric biases. In total, our results suggest that perceptual distortions of finger geometry do not reflect a distorted hand model but originate from near-optimal Bayesian inference on somatosensory signals.

Charge Carrier Formation following Energy Gap Law in Photo-Activated Organic Materials for Efficient Solar Cells

The charge carrier formation and transport in the pristine polymers as well as in the polymer–fullerene blend is still a hot topic of discussion for the scientific community. In the present work, the carrier generation in some prominent organic molecules has been studied through ultrafast transient absorption spectroscopy. The identification of the exciton and polaron lifetimes of these polymers has led to device performance-related understanding. In the Energy Gap Law, the slope of the linear fit gradient (γ) of lifetimes vs. bandgap are subjected to the geometrical rearrangements experienced by the polymers during the non-radiative decay from the excited state to the ground state. The value of gradient (γ) for excitons and polarons is found to be −1.1 eV−1 and 1.14 eV−1, respectively. It suggests that the exciton decay to the ground state is likely to involve a high distortion in polymer equilibrium geometry. This observation supports the basis of Stokes shift found in the conjugated polymers due to the high disorder. It provides the possible reasons for the substantial variation in the exciton lifetime. As the bandgap becomes larger, exciton decay rate tends to reduce due to the weak attraction between the holes in the HUMO and electron in the LUMO. The precise inverse action is observed for the polymer–fullerene blend, as the decay of polaron tends to increase as the bandgap of polymer increases.

Structural aspects of Pt(η3-X1N1X2)(PL) (X1,2 = O, C, or Se) and Pt(η3-N1N2X1)(PL) (X1 = C, S, or Se) derivatives

Abstract This article covers 26 Pt(ii) complexes of compositions Pt(η3-X1N1X2)(PL) (X1,2 = O, C, or Se) and Pt(η3-N1N2X1)(PL) (X1 = C, S, or Se). These complexes crystallized in two crystal classes: monoclinic (14 examples) and triclinic (12 examples). The heterotridentate ligand with monodentate PL builds up a distorted square-planar geometry around each Pt(ii) atom. Each heterotridentate ligand Pt(η3-X1N1X2)(PL) creates two metallocyclic rings with a common N1 atom of the O1C2N1C3O2, O1C3N1C3O2, O1C2NN1C3O2, C1C2N1C2C2, and Se1C2N1NC2Se2 types. In Pt(η3-N1N2X1)(PL) complexes, the tridentate ligand with a common N2 atom forms the following types of metallocyclic rings: N1C2N2C2C1, N1C2N2NCS1, and N1CNN2NCSe1. The total mean values of τ4 for respective complexes as it grows in the sequence: 0.056 (Pt(η3-O1N1O2)(PL)) < 0.091 (Pt(η3-Se1N1Se2)(PL)) < 0.161 (Pt(η3-N1N2S1)(PL)) < 0.174 (Pt(η3-N1N2Se1)(PL)) < 0.188 (Pt(η3-C1N1C2)(PL)) < 0.211 (Pt(η3-N1N2C1)(PL)). The distortion of the square-planar geometry increases in the given sequences. The structural data (Pt–L, L–Pt–L) are analyzed and discussed with attention to the distortion of a square-planar geometry about the Pt(ii) atoms as well as of trans-influence.

Insight into the Structure and Redox Chemistry of [Carbonatotetraamminecobalt(III)] Permanganate and Its Monohydrate as Co-Mn-Oxide Catalyst Precursors of the Fischer-Tropsch Synthesis

[Carbonatotetraamminecobalt(III)] permanganate monohydrate was synthesized first in the metathesis reaction of [Co(NH3)4CO3]NO3 and NaMnO4 in aqueous solution. Its thermal dehydration at 100 °C resulted in phase-pure [Co(NH3)4CO3]MnO4 (compound 1). Compounds 1 and 2 (i.e., the hydrated form) were studied with IR, far-IR, and low-temperature Raman spectroscopies, and their vibrational modes were assigned. The lattice parameters were determined by powder X-ray diffraction (PXRD) and single crystal X-ray diffraction (SXRD) methods for the triclinic and orthorhombic compounds 1 and 2, respectively. The detailed structure of compound 2 was determined, and the role of hydrogen bonds in the structural motifs was clarified. UV studies on compounds 1 and 2 showed the distortion of the octahedral geometry of the complex cation during dehydration because of the partial loss of the hydrogen bonds between the crystal water and the ligands of the complex cation. The thermal decomposition consists of a solid phase quasi-intramolecular redox reaction between the ammonia ligands and permanganate anions with the formation of ammonia oxidation products (H2O, NO, N2O, and CO2). The solid phase reaction product is amorphous cobalt manganese oxide containing ammonium, carbonate (and nitrate) anions. The temperature-controlled thermal decomposition of compound 2 in toluene at 110 °C showed that one of the decomposition intermediates is ammonium nitrate. The decomposition intermediates are transformed into Co1.5Mn1.5O4 spinel with MnCo2O4 structure upon further heating. Solid compound 2 gave the spinel at 500 °C both in an inert and air atmosphere, whereas the sample pre-treated in toluene at 110 °C without and with the removal of ammonium nitrate by aqueous washing, gave the spinel already at 300 and 400 °C, respectively. The molten NH4NO3 is a medium to start spinel crystallization, but its decomposition stops further crystal growth of the spinel phase. By this procedure, the particle size of the spinel product as low as ~4.0 nm could be achieved for the treatments at 300 and 400 °C, and it increased only to 5.7 nm at 500 °C. The nano-sized mixed cobalt manganese oxides are potential candidates as Fischer-Tropsch catalysts.

Analysis of the causes determining dimensional and geometrical errors in 316L and 17-4PH stainless steel parts fabricated by metal binder jetting

This work aims at investigating the causes affecting the dimensional and geometrical accuracy of holes in metal binder jetting stainless steel parts. Parallelepiped samples with a through hole were produced using AISI 316L and 17-4PH powders, differing for diameter (3, 4, 5 mm), and position of the axes with respect to the building plane (6, 9, 12 mm distance). Dimensions and geometrical characteristics were measured at green and sintered state by a coordinate measuring machine, determining the dimensional change and the geometrical characteristics. As expected, the shrinkage of linear dimensions is anisotropic; moreover, change in volume and sintered density are significantly affected by the position in the printing chamber. Higher shrinkage was measured along building direction (Z) – 18.5 ÷ 19.5%, than in the building plane – 16.5 ÷ 17.5%, and slightly higher shrinkage – 0.5 ÷ 0.8% was measured along powder spreading direction (X) than binder injection direction (Y). A variation up to 3% in relative density of sintered parts depending on the position in the building plane was observed in 316L. The dimensional change of diameters generally confirmed the shrinkage predicted by the model previously developed—difference between real and expected dimensional changes lower than 3%, except for three geometries (4 ÷ 6%). The cylindricity form error of sintered parts was strongly underestimated by the prediction model (up to 0.15 mm), but underestimation was considerably reduced (generally lower than 0.05 mm) adding the cylindricity form error due to printing. Dimensional and geometrical accuracy of holes are strongly affected by shape distortion of the parallelepiped geometry, in turn due to layer shifting and inhomogeneous green density during printing, and to the effect of frictional forces with trays during sintering. Gravity load effect was also observed on the holes closest to the building plane. Future work will improve the reliability of the prediction model implementing the results of the present work.

PCQD‐AR: Subjective quality assessment of compressed point clouds with head‐mounted augmented reality

AbstractThis letter fully studies the coloured point cloud quality assessment in augmented reality (AR) environment through subjective test. Firstly, a point cloud dataset, named point cloud quality dataset‐AR, including ten reference point clouds and their 90 distorted versions is presented, which were generated using the reference software of video‐based point cloud compression across various combinations of geometry and texture quantization parameters. Then, the impact of geometry and texture distortions on perceived quality of point clouds in AR environment was discussed in detail. Moreover, the performance of existing objective point cloud quality assessment metrics on the proposed dataset is evaluated. The subjective dataset including the values of mean opinion score were released to public.