Bond Contraction Research Articles

Cretaceous/Palaeogene boundary transition induced lattice defects in illite and kaolinite associated with the Um-Sohryngkew river section, Meghalaya, India

Cetaceous-Palaeogene Boundary (KPB) transition records restricted to a unique, continuous, late Maastrichtian-early Danian, shallow marine Um Sohryngkew river succession (bearing planktonic foraminifers' CF4 to P1a biozones) have not been studied in detail. Earlier studies sub-divided it into lower, middle and upper parts, defined by the dominance of illite> illite/smectite; illite>kaolinite> montmorillonite and kaolinite > montmorillonite assemblages, respectively. However, limited studies were carried out on the KPB transition events, particularly for those reproduced in the illite (C2/m) and kaolinite (P1) lattice structures. Thus, illite and kaolinite cell parameters and interatomic distances have been studied to understand KPB transition events. For this purpose, layer-wise clay (0.2–2 μm) separates were analyzed by X-ray diffraction method and subjected to Rietveld refinement. Obtained data show substantial expansion in the c-axis of the kaolinite grains associated with the shaly marlite (P0 biozone) layer. Also, b- and c- axes of the kaolinite associated with the yellowish brown (CF3 biozone) layer indicate expansion and contraction, respectively. Moreover, Al–O bond in the kaolinite reflects contraction. Obtained cell parametric data and interatomic distances when plotted across the stratigraphic succession show notable contraction along b- and c- axes of the illite associated with the yellowish brown and shaly marlite layers of the CF3 and P0 biozones, respectively. The illite containing 26 atoms, linked to 38 and 34 bonds present in the intensely weathered lower and middle parts of the CF4 biozone, respectively. The illite in the moderately weathered upper part of the CF4 – CF1 biozones bearing 32 atoms and 44 bonds, represent Si–K and Al–K bond distortions together with the loss of Si4+ and K+. The coprolite-bearing shaly marlite layer (between the CF1 and P0 biozones) shows drastic changes in the illite structure, containing 48 atoms and 44 bonds, characterized by K–O, Si–K and Al–O bond contractions along with the retention of K+ and Al3+. Moreover, Al–O, Si–K, Al–K and Al–Al bonds connected strongly due to reinforcement of Al ions. A very low degree of alteration is noticed in case of preceding yellowish brown (CF3 biozone) layer. Owing to the weakening of the Al–O and Si–O bonds in the intensely weathered illite lattices of this layer show distortion as well as Al3+ and Si4+ losses, suggest incidence of thermal high. Sudden degeneration of illite lattices noticed in the shaly marlite layer is also marked with the planktonic foraminifers’ extinction, signifying biostratigraphic boundary. Thus, contraction in the c- axis as well as notable decrease in the bond lengths of illite (in this layer) is linked to KPB transition which includes major tectonic events, sea level changes and global-climatic changes caused environmental stress in the sea shelf. The substantial distortion in the illite lattices of the biozone CF2 corresponds to the most vigorous second phase of the Deccan volcanic eruption that occurred during 65.4–65.2 Ma.

Stress induced modification of electronic band structure and enhanced optical emission in 1-D GaN nanostructures

1-dimensional GaN nanowires (NW) and nanorods (NR) grown using catalyst assisted Chemical Vapour Deposition are investigated for their structural and optical properties, and their electronic band structure. X-ray Diffraction (XRD) studies reveal that biaxial strain increases with aspect ratio, which is corroborated by Raman studies wherein phonon related confinement effects are observed for NR due to the crystal strain. Photoluminescence studies show 3 and 6 times enhancement in the intensity of band edge emission of NW and NR, respectively, signifying the presence of a large number of band tail states. A small red shift in NW (3.43 eV) and large red-shift in NR (3.28eV) is reported, which are attributed to the change in the band gap and band structure of these morphologies. Valence band studies by X-ray Photoelectron Spectroscopy reveal the presence of band tail states for NR and surface bond contraction for NW. The effect of crystal strain on the electronic band structure on optical properties of 1-D GaN nanostructures with different aspect ratios is elucidated.

The strain effects in 2D hybrid organic-inorganic perovskite microplates: bandgap, anisotropy and stability.

Strain engineering provides an efficient strategy to modulate the fundamental properties of semiconducting structures for use in functional electronic and optoelectronic devices. Here, we report on how the strain affects the bandgap, optical anisotropy and stability of two-dimensional (2D) perovskite (BA)2(MA)n-1PbnI3n+1 (n = 1-3) microplates, using photoluminescence spectroscopy. Upon applying external strain, the bandgap decreases at a rate of -5.60/-2.74/-1.38 meV per % for n = 1, 2, and 3 2D perovskites, respectively. This change of the bandgap can be ascribed to the distortion of the octahedra (Pb-I bond contraction) in 2D perovskites, supported by a study on emission anisotropy, which increases with the increase of strain. In addition, the external strain can significantly deteriorate the stability of 2D perovskites due to the strain induced distortion which would make the penetration of moisture and oxygen into the perovskite microplates easier, resulting in much faster degradation rates. Our findings not only provide insights into the design and optimization of functional devices, but also provide a new approach to improve the stability of 2D perovskite based devices.

The BOLS-NEP theory reconciling the attributes of undercoordinated adatoms, defects, surfaces and nanostructures

This article describes a theory unifying the unusual performance of the undercoordinated adatoms, point defects, terrace edges, surfaces, and nanostructures of various shapes. The ideas of bond order-length-strength correlation and the associated nonbonding electron polarization (BOLS-NEP) feature that bonds between undercoordinated atoms contract spontaneously. Bond contraction raises the local density of charge and energy. Bond strength gain deepens the interatomic potential well to trap the core and bonding electrons deeply. In turn, the locally and densely entrapped electrons polarize those partially occupying the valence band and above pertaining to the lower-coordinated atoms. The BOLS-NEP theory reconciles the unusual behaviors of undercoordinated systems and the size dependency of nanostructures in their lattice oscillating dynamics, mechanical strength, thermal stability, photon emissivity, chemical reactivity, dielectric permeability, associated with generation of polarized Dirac fermions, serving as carriers for extraordinary catalysis, hydrophobicity, fluidity, lubricity, as well as monolayer high-T C superconductivity and topological insulator conductivity. • Atomic undercoordination shortens the local bonds and modifies the electron occupancy. • Nanocrystals prefer a core-shelled structure with a skin of two atomic layers thick. • Atomic cohesive energy dictates the thermal stability and the critical energy for phase transition. • Competition between energy density and cohesive energy transforms the Hall-Petch relationship. • Polarization dictates the catalysis, hydrophobicity, and monolayer high-T c superconductivity.

Optical Behaviors of a Microsized Single-Crystal MAPbI3 Plate under High Pressure

The correlation between the crystal structure and the optoelectrical property of methylammonium lead iodide (MAPbI3) is investigated by measuring the optical absorption and the photoluminescence spectra of a microsized single-crystal MAPbI3 plate (MSCMP) up to 20.43 GPa with confocal μ-spectroscopy. The pressure-induced phase transitions of an MSCMP are identified by the absorption edges of the absorption spectrum and the fluorescence peaks of the PL spectrum. A tetragonal–cubic phase transition is confirmed under a pressure within the range of 0.23 to 0.46 GPa. The optical property of the cubic phase is dominated by the competition between Pb–I bond contraction and PbI6 octahedron tilt up to 2.72 GPa. Furthermore, the MAPbI3 plate experiences an isostructural cubic phase transition with a unique optical behavior below 3.90 GPa. Little amount of nonradiative high-pressure phase presents a radiative emission mixed with a radiative low-pressure phase, which originates from the diffusion and recombination of...

Influence of electronic structure parameters on the electrical transport and magnetic properties of Y2−xBixIr2O7 pyrochlore iridates

We report the systematic study of structural, magnetic, and electrical transport properties of Y2−xBixIr2O7 (x=0.0, 0.1, 0.2, and 0.3) pyrochlore iridates. Chemical doping enhances electrical conductivity and antiferromagnetic correlation substantially. The replacement of a nonmagnetic Y3+ ion with nonmagnetic Bi3+ in Y2Ir2O7 tends to reduce the octahedral distortion, thus enhancing the antiferromagnetic correlation. Raman spectroscopy shows that the Ir–O bond contracts slightly, and the R–O′ bond turns longer as disorder and phononic oscillation are reduced by Bi doping, leading to wider t2g bands, which enhances the electrical conductivity. Additionally, the enhancement in electrical conductivity and antiferromagnetic correlation with Bi3+ doping is attributed to the hybridization between the Y3+(4p)/Bi3+(6s/6p) orbital with the Ir4+(5d) orbital as a result of enhancement in the Ir–O–Ir bond angle and contraction in the Ir–O bond length.

Unexpected Solute Occupancy and Anisotropic Polarizability in Lewis Basic Solutions.

Density functional computation revealed that in YOH solvation (Y = Li, Na, and K), the Y+ cation locates eccentrically at the interstitial hollow site to form the Y+·4H2O unit, and the hydroxyl adds an excessive electron lone pair ":" to form a OH-·H2O unit where the hydroxide stays in the the center. The surrounding four oriented H2O neighbors interact with the Y+ through Y+ ↔ H+ repulsion and Y+:O2- attraction, causing the Y+ eccentric dislocation by some 0.80 Å. The ":" turns one O:H-O bond into the O: ⇔ :O super hydrogen bond by altering H2O·4H2O into HO-·4H2O. The repulsive Y+ ↔ H+ enlarges its separation and the attractive Y+:O shortens itself, showing the anisotropic polarization of the Y+ cation. The anisotropic Y+ polarizability, O: ⇔ :O compressibility, and the H-O bond contraction of the solute OH- distorts the solute bonding network and disperses the O:H-O segmental phonon frequencies, as confirmed spectroscopically.

Anionic Effects on Metal Pair of Se-Doped Nickel Diphosphide for Hydrogen Evolution Reaction

The actual chemical environment of metal phosphides or chalcogenides during hydrogen evolution reaction (HER) has been debated. In this work, pyrite-phase NiP2, Se-doped NiP2, and NiSe2 were investigated by means of in situ and ex situ characterizations to dynamically study the transformation during electrocatalysis. We found that doping with selenide would generate more vacancies to facilitate the activation on water molecule, in which hydroxide poisoning on active site would be suppressed by the presence of selenide. Furthermore, the radial distance of Ni–Ni pair can serve as a descriptor to identify the mechanism of HER. For NiP2 and Se-doped NiP2, the radial distance of the metal (Ni–Ni) pair during HER is identical to the as-prepared one, implying that the HER active site is on a single metal site with a Heyrovsky step. A drastic bond contraction of Ni–Ni pair on NiSe2 indicates dual-site activation correlated with a chemical desorption of Tafel step. The role of anion effects and metal sites are com...

Actinide Contraction in Oxygen-Containing An(VI) Compounds

The actinide contraction effect in the structures of 55 crystals containing $$\rm{AnO}_2^{2+}$$ dioxocations (An = U, Np, Pu, Am) and belonging to 18 series of isostructural An(VI) compounds was analyzed using Voronoi-Dirichlet (VD) polyhedra. Analysis shows that the actinide contraction, as a rule, is accompanied by a regular decrease in the radii of the spherical domains (Rsd) of the volume equal to that of the VD polyhedra of the An(VI) atoms in the crystal structures. In the series U-Np-Pu, such contraction is accompanied by a regular increase in the second moment of inertia (G3) of the VD polyhedra, suggesting a decrease in the extent of their sphericity (due to stronger flattening of the coordination polyhedron in the form of bipyramid), whereas in going from Pu to Am the extent of sphericity of the VD polyhedron increases instead of decreasing. The results obtained confirm the viewpoint that the contraction and localization of the 5f shell start specifically from Am. The lack of correlation between the actinide contraction and relative strength of An-O bonds in the series U-Np-Pu-Am is noted.

Molecular Hydration of Carbonic Acid: Ab Initio Quantum Chemical and Density Functional Theory Investigation.

Molecular hydration of carbonic acid (H2CO3) is investigated in terms of bonding patterns in H2CO3···(H2O) n [ n = 1-4] hydrogen-bonded clusters within ab initio quantum chemical and density functional theory (DFT) frameworks. Successive addition of water molecules to H2CO3···H2O entails elongation of O-H (hydroxyl) bond as well as contraction of specific intermolecular hydrogen bonds signifying hydration of carbonic acid; these structural features get markedly enhanced under the continuum solvation framework. A comparison between the structurally similar clusters H2CO3···(H2O) n and HCOOH···(H2O) n [ n = 1-3] brings out the structural stability of the former. The present investigation in conjunction with the binding energy behavior of approaching water molecule(s) should serve as a precursor for pathways exploring aqueous dissociation of H2CO3 for larger clusters, as well as development of force-field potentials for acid dissociation process.

Unraveling the multiscale damping properties of two-dimensional layered MXene

MXene has emerged as an exciting two-dimensional nanomaterial because of its interesting multifunctional properties. In this paper, the authors report the multiscale damping behaviors of pure MAX and MXene. Dynamic loading of a multilayer MXene assembly shows an appreciable loss tangent (tan δ), indicating the energy-dissipation ability of the material. The tan δ value of MXene is recorded to be as high as 0·37, which is about a 200% improvement over that of pure MAX. It is hypothesized that there are multiscale energy-loss mechanisms active in the material. While intralayer bond contraction operates in individual MXene sheets, interlayer compression and sliding/shearing mechanisms are active between the stacked layers. The presence of functional groups, van der Waals interactions and a low coefficient of friction between the MXene sheets provide MXene with an extraordinary energy-dissipation ability. Damping behavior is highly stable in MXene for as high as 50 000 cycles, making it extremely promising for advanced applications requiring superior impact resistance, stability against noise and ability to damp mechanical vibrations.

Alloyed Tetranuclear Metal Chains of Pd4-n Ptn (n=0-3) Scaffolded by a New Linear Tetraphosphine Containing a PNP Bridge.

A new linear tetraphosphine containing a PNP phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan), was synthesized and utilized to support a series of Pd/Pt mixed metal tetranuclear chains, [Pd4-n Ptn (μ-rac-dpmppan)2 (XylNC)2 ](PF6 )2 (XylNC=xylyl isocyanide; n=0: Pd4 (1), 1: PtPd3 (2), 2: PtPd2 Pt (3), 2: Pt2 Pd2 (4), 3: Pt2 PdPt (5)), in which the number and positions of additional Pt atoms were successfully controlled depending on the respective synthetic procedures using transformations from 1 to 3 through 2 and from 4 to 5 by redox-coupled exchange reactions. The 31 P{1 H} NMR and ESI mass spectra and X-ray diffraction analyses revealed almost identical tetranuclear structures, with slight contraction of metal-metal bonds according to incorporation of Pt atoms. The electronic absorption spectra of 1-5 exhibited characteristic bands at 635-510 nm with an energy propensity depending on the number and positions of Pt centres, which were assigned to HOMO (dσ*σσ*) to LUMO (dσ*σ*σ*) transition by theoretical calculations. The present results demonstrated that the electronic structures of Pd/Pt mixed-metal tetranuclear complexes are finely tuned as orbital-overlapping alloyed metal chains by atomically precise Pt incorporation in the Pd4 chain.

X-ray absorption spectroscopy study of the electronic structure and local coordination of 1st row transition metal-promoted Chevrel-phase sulfides

The electronic structures of S and Mo as well as the local coordination of Mo are investigated as a function of metal promotion Chevrel-phase (CP) sulfides. We observe the effect of metal promoter-induced electron donation into the stoichiometric range MxMo6S8 (M = Fe, Ni, Cu; x = 0–2) through analysis of X-ray absorption near-edge structure regions. We further observe the effect of this promotion on the bonding environment of Mo6 metal centers through extended X-ray absorption fine structure analysis. We monitor expansion and contraction of Mo6 octahedra with and without metal promotion, as has been predicted by Hückel molecular orbital theory. We further observe a marked tunability in the electronic structure of sulfur upon charge transfer between promoting species and Mo6S8 units. Average Mo6 octahedron Mo–Mo bond contraction from 2.76 Å to as short as 2.69 Å was observed upon incorporation of metal promoters, while intercluster separation displays a pronounced increase for promoter-host lattices compared to un-promoted Mo6S8. To corroborate spectroscopically observed phenomena, we performed computational analyses of spin-polarized densities of state for the CP materials investigated herein, where a detectable increase in sulfur-based frontier orbital population is observed in accordance with experimentally validated orbital filling.

Structure investigation of InGaZn1-xCuxO4 (x = 0−1) and magnetic property of InGaCuO4

A series of layered compounds InGaZn1-xCuxO4 (x = 0−1) were prepared by sol-gel method for the first time and characterized by powder X-ray diffraction (PXRD). All these solid solutions adopt LnFe2O4-type structure and crystallize in R-3m. With an increase of Cu2+-content in InGaZn1-xCuxO4, the lattice showed an anisotropic change with a linear shrinkage and expansion of c- and a-axis, respectively. Rietveld refinements against PXRD data revealed that Cu2+/Zn2+ and In3+ cations reside in the (Cu/Zn)O5-based trigonal bipyramids (TBP) double layers and octahedral layers, respectively. And the anisotropic structure change stems from the dramatic contraction of M-Oapical bonds and slight expansion of M-Obasal bonds for the (Cu/Zn)O5 trigonal bipyramids, due to the Jahn-Teller active Cu2+ (d9) and smaller cationic size of Cu2+ (r = 0.65 Å) compared to Zn2+ (r = 0.68 Å).

Blue-Shifted Hydrogen Bonding in the Gas Phase CH/D3CN···HCCl3 Complexes.

Blue-shifting H-bonded complexes between CHCl3 and CH/D3CN have been identified by Fourier transform infrared spectroscopy in the gas phase at room temperature. The change in FTIR peak intensity of the mixture of the two components as a function of temperature and composition provides the basis for identification of the H-bonded band in the infrared spectrum. On complex formation with CH3CN and CD3CN, the C-H stretching frequency of CHCl3 shifts to the blue by +8.7 and +8.6 cm-1, respectively. The molecular electrostatic potential calculation at the MP2/6-311++G** level has been used to arrive at the geometry of the complex. It has been reported in the literature that CHCl3 and CH/D3CN form red-shifting H-bonded complex in Ar matrix. The red shifting has been verified by doing ab initio calculations in the presence of Ar atoms, which has been attributed to the matrix effect at low temperature. The interaction of Ar with CH3CN makes the CH3CN more basic and as a result it becomes better hydrogen bond acceptor and causes red shift. The potential energy scans and NBO analysis of the Cl3CH···NCCH3 complex have been compared with those of F3CH···NCCH3 and Cl3CH···NH3 complexes. The change in electron density of the CHCl3 as a function of C-H···N distance shows that the approach of CH3CN to CHCl3 induces a shift in electron density from the H atom to the Cl atoms of CHCl3 which leads to C-H bond contraction and blue shifting of C-H stretching frequency. However, in the complex Cl3CH···NH3, where frequency shift to the red is reported, charge transfer and electrostatic interaction dominate.

Phonon abundance-stiffness-lifetime transition from the mode of heavy water to its confinement and hydration

A combination of the spatially- and temporally-resolved phonon spectroscopies has enabled calibration of hydrogen bond transition from the vibration mode of heavy water to the core-shell structured nanodroplets and to the ionic hydration shells of salt solutions in terms of phonon abundance-lifetime-stiffness. It is uncovered that charge injection by salt solvation and skin formation by molecular undercoordination (often called confinement) share the same supersolidity characterized by HO (DO as a probe) bond contraction, O:H nonbond elongation, and polarization. Such a process of bond transition stems the solution viscosity, surface stress, and slowing down of the molecular dynamics and diffusivity. The nanodroplet skin reflection further hinders phonon energy dissipation associated with longer DO phonon lifetime.

Geometrically Compelled Disilene with λ4-Coordinate SiII Atoms.

The first hypercoordinated disilene with the longest Si═Si distance (2.623(1) Å) reported to date, the 5,6-bis(amidinato silylenyl)acenaphtene (amidinato = PhC(NtBu)2) (1), is presented. It results from a spatially compelled double dative interaction between the two singlet silylene moieties, due to their close proximity. The dynamic behavior of the Si═Si bond contraction and elongation in 1 predicted by quantum chemical calculations could be confirmed experimentally by variable temperature NMR spectroscopy. Compound 1 exhibits an ambivalent reactivity, reacting as disilene with ethylene, diphenylacetylene and benzophenone to give [2+2] cycloaddition products, but as bis(silylene) toward Ni(cod)2 (cod = cycloocta-1,4-diene) to form the corresponding bis(silylene)Ni0(η4-cod) complex.

Pressure-Induced Emission Enhancement, Band-Gap Narrowing, and Metallization of Halide Perovskite Cs3 Bi2 I9.

Low-toxicity, air-stable bismuth-based perovskite materials are attractive substitutes for lead halide perovskites in photovoltaic and optoelectronic devices. The structural, optical, and electrical property changes of zero-dimensional perovskite Cs3 Bi2 I9 resulting from lattice compression is presented. An emission enhancement under mild pressure is attributed to the increase in exciton binding energy. Unprecedented band gap narrowing originated from Bi-I bond contraction, and the decrease in bridging Bi-I-Bi angle enhances metal halide orbital overlap, thereby breaking through the Shockley-Queisser limit under relatively low pressure. Pressure-induced structural evolutions correlate well with changes in optical properties, and the changes are reversible upon decompression. Considerable resistance reduction implies a semiconductor-to-conductor transition at ca. 28 GPa, and the final confirmed metallic character by electrical experiments indicates a wholly new electronic property.

Quantum-Chemical Analysis of the Electron Transfer in the MgTiF6+12MgCl2 Molten System By Frontier Molecular Orbital Method

Investigation of the electrochemical charge transfer mechanism in molten salts containing transition metal complexes is a challenging task. Such studies could be facilitated by analysis of the corresponding model systems by quantum-chemical methods. However, in practice, a direct search for the transition state in such systems requires enormous computational time. In this work, we suggest to use an approach that allows us to qualitatively characterize possible variants of electron transfer and, thus, to sharply narrow the search for the transition state. We mean the use of the frontier molecular orbital method. The method is traditionally employed to evaluate the reactivity of species. However, when applied to electrochemical systems, the method can also provide extremely useful information on whether a certain electron transfer mechanisms is possible or impossible In this work, we were interested in the state of the complex TiF6 2- near the cathode surface. For this reason, on one side of the molten system, a flat boundary layer consisting of 17 chlorine and magnesium ions was formed. In general, the boundary ions of chlorine and magnesium are not in the same plane. The mutual displacement of these ions was determined from the computation in the model system C96H24+7MgCl2, where C96H24 is a flat carbon cluster simulating the surface of the cathode; hydrogen atoms close the broken bonds of carbon atoms to prevent artifacts. After optimization of this system, the chlorine anions shifted by 0.3 Å relative to the magnesium cations (Δd) in the direction opposite to the surface of the carbon cluster. The direction of this displacement corresponds to the effect of the electric field on the chlorine anions. Thus, the equilibrium shift Δd is 0.3 Å. The model system MgTiF6+12MgCl2 with such shift value will be considered referent. A systematic study of the influence of the Δd value and the length of Ti-F bonds (Δr) on the lowest unoccupied molecular orbital (LUMO) character showed the following: 1) the group of lower free MOs, the main contribution to which gives the TiF6 2- complex, is destabilized with increasing of Ti-F bond contraction; 2) when the shift Δd increases, this MO group is also destabilized and simultaneously free MOs belonging to the boundary ions become more stable. In particular, when the Ti-F bonds are compressed on Δr = 0.05 Å, the critical value of the shift Δd is 0.6 Å. That is, at Δd ≥ 0.6 Å and Δr = 0.05 Å, LUMO is delocalized between the complex and the bridge cation. At excessively large values of Δd and Δr, LUMO is completely localized on the boundary ions, but this is undesirable. The combination of the parameters Δd = 0.6, 0.7 Å and Δr = 0.05 Å is optimal. At these values, LUMO is delocalized between the complex and the bridge cation and the activation energy (~18 kJ mol-1) is close to the experimental value (21±4 kJ mol-1). An increase in the parameter Δr leads to a rapid increase in the activation energy, a contraction value of 0.05 Å is optimal. An equally important characteristic is the highest occupied molecular orbital (HOMO) type of the structure after electron transfer (ET). Theoretically, there may exist three main types of HOMO for our structures (after ET): 1) HOMO is completely localized on the boundary ions; 2) HOMO is delocalized between the boundary ions and the complex; 3) HOMO is completely localized on the complex. In the first case, probability of electron capture by the complex is very small. After diffusion of the complex into the depth of the melt, electron remains on the boundary ions and then returns to the cathode. In the second case, there is a significant probability of ET to the complex through the bridge cation. In the latter case, the probability of electron capture by the complex is close to 100%, if the complex is in contact with the surface of the electrode.

Pressure-Induced Structural Evolution and Optical Properties of Metal-Halide Perovskite CsPbCl3

Metal-halide perovskites have emerged as the most promising semiconductor materials for advanced photovoltaic and optoelectronic applications. Herein, we comprehensively investigate the optical response and structural evolution of metal-halide perovskite CsPbCl3 (ABX3) upon compression. Band gap realized a pronounced narrowing under mild pressure followed by a sharp increase, which could be ascribed to Pb–Cl bond contraction and inorganic framework distortion, respectively. The transformation of the crystal structure is confirmed and analyzed through in situ high-pressure X-ray diffraction and Raman experiments, consistent with the evolution of optical properties. Combining with the first-principles calculations, we understand the electronic band structure changes and phase transition mechanism, which are ascribed to severe PbCl6 octahedral titling and twisting. Our results demonstrate that the high-pressure technique can be used as a practical tool to modify the optical properties of metal-halide perovsk...