Intralayer Distance Research Articles

Understanding Graphitic Carbon Nitride as Photocatalyst: A Case Study on Thermal Engineering of Physical and Chemical Features

Rationalizing material features according to the adopted synthetic strategy, aiming then to tune them on demand, is among the most relevant purposes of investigation in materials science. Herein, the systematic analysis of the dependence of graphitic carbon nitride (g‐C3N4) physical characteristics on the decomposition temperature of urea, rationalizing the impact of synthetic temperature on several characteristics of the materials (degree of N–H condensation, carbon vs nitrogen content, structural parameters, photoluminescence lifetime, surface area, pores volume), is discussed. g‐C3N4 nanostructures are fabricated by thermal decomposition of urea at different temperatures under ambient atmosphere, obtaining an almost ideal stoichiometry (C/N = 0.72) when setting the temperature at 600 °C. The samples show structural, textural, compositional, and optical differences directly depending on the fabrication temperature: specific surface area, pore volume and size, intralayer distance, and speed of radiative recombination of photogenerated charges are proportionally enhanced by increasing the synthesis temperature. The role played by all the physicochemical features of the prepared samples in promoting the catalytic degradation of Rhodamine B is investigated, highlighting their synergistic role in enhancing the catalytic efficiency. Significant differences in the dye degradation are recorded when using either UV or solar simulated light, demonstrating that Rhodamine B photosensitization rules the process.

Two new barium phosphides predicted by first-principles evolutionary algorithm

Two stable barium phosphides, Ba2P and BaP, are predicted by an evolutionary algorithm and first-principles calculations. Ba2P is a layered structure and isostructural to rhombohedral anti-CdCl2. The interlayer distance between Ba–P–Ba layers is larger than the intralayer distance of the Ba–P–Ba layers. BaP adopts a body-centered orthorhombic structure composed of P dumbbells. Rhombohedral Ba2P is metallic, whereas body-centered orthorhombic BaP is a semiconductor that exhibits a band gap of 0.345 eV; the dynamical stabilities of these two compounds were confirmed by phonon calculations and analysis. These findings should encourage further experimental study of the Ba–P system.

Experimental and theoretical revelation of a unique band topology in Sb[formula omitted]Te[formula omitted] topological insulator by substitution of Cu—A high pressure study

TI Sb1.9Cu0.1Te3 is an ideal platform for investigating such semiconducting to metal transition under extreme conditions. The unusual softening of two newly M1, M2 phonon modes combined with the sudden collapse in bond length, angle of succession, intralayer distance and the direct observation of band gap closure from theoretical density functional theory calculation validates a unique metal transition. To the best of our knowledge, the metallic transition pressure in the present observation is the lowest amongst the A2B3 TI family of compounds. This distinctive transition is stimulated by the p-d hybridization which is the concomitant effect of Cu and applied pressure. We also establish structural and vibrational anomalies from pressure induced angle dispersive synchrotron x-ray diffraction and Raman spectra of the bulk that signify changes in electronic topology of the Fermi surface. Our experimental observations on bulk corroborates an ETT (∼2.5 GPa) and 3 structural transitions in the present system.

Bright, noniridescent structural coloration from clay mineral nanosheet suspensions.

Structural colors originate by constructive interference following reflection and scattering of light from nanostructures with periodicity comparable to visible light wavelengths. Bright and noniridescent structural colorations are highly desirable. Here, we demonstrate that bright noniridescence structural coloration can be easily and rapidly achieved from suspended two-dimensional nanosheets of a clay mineral. We show that brightness is enormously improved by using double clay nanosheets, thus optimizing the clay refractive index that otherwise hampers structural coloration from such systems. Intralayer distances, and thus the structural colors, can be precisely and reproducibly controlled by clay concentration and ionic strength independently, and noniridescence is readily and effortlessly obtained in this system. Embedding such clay-designed nanosheets in recyclable solid matrices could provide tunable vivid coloration and mechanical strength and stability at the same time, thus opening a previously unknown venue for sustainable structural coloration.

Synthesis and anisotropic magnetism in quantum spin liquid candidates AYbSe2 (A = K and Rb)

The quantum spin liquid (QSL) state in rare-earth triangular lattices has attracted much attention recently due to its potential application in quantum computing and communication. Here, we report the single-crystal growth synthesis, crystal structure characterizations, and magnetic properties of AYbSe2 (A = K and Rb) compounds. The x-ray diffraction analysis shows that AYbSe2 (A = K and Rb) crystallizes in a trigonal space group, R-3m (No. 166) with Z = 3. AYbSe2 possesses a two-dimensional (2D) Yb–Se–Yb layered structure formed by edged-shared YbSe6 octahedra. The magnetic properties are highly anisotropic for both title compounds, and no long-range order is found down to 0.4 K, revealing the possible QSL ground state in these compounds. The isothermal magnetization exhibits a one-third magnetization plateau when the magnetic fields are applied in the ab-plane. Heat capacity is performed along both ab-plane and c axis and features the characteristic dome for triangular magnetic lattice compounds as a function of magnetic fields. Due to the change in the interlayer and intralayer distance of Yb3+, the dome shifts to low fields from KYbSe2 to RbYbSe2. All these results indicate that the AYbSe2 family presents unique frustrated magnetism close to the possible QSL and noncollinear spin states.

A New Family of Disorder-Free Rare-Earth-Based Kagome Lattice Magnets: Structure and Magnetic Characterizations of RE3BWO9 (RE = Pr, Nd, Gd-Ho) Boratotungstates.

Exploration of rare-earth (RE)-based Kagomé lattice magnets with spin-orbital entangled jeff = 1/2 moments will provide a new platform for investigating the exotic magnetic phases. Here, we report a new family of RE3BWO9 (RE = Pr,Nd,Gd-Ho) boratotungstates with magnetic RE3+ ions arranged on Kagomé lattice and perform its structure and magnetic characterizations. These serial compounds crystallize in a hexagonal coordinated structure with space group P63 (no. 173), where magnetic RE3+ ions have distorted Kagomé lattice connections within the ab plane and stacked in an AB-type fashion along the c axis. The interlayer RE-RE separation is comparable with that of the intralayer distance, forming 3-dimensional (3D) exchange coupled magnetic framework of RE3+ ions. The magnetic susceptibility data of RE3BWO9 (RE = Pr, Nd, Gd-Ho) reveal dominant antiferromagnetic interactions between magnetic RE3+ ions, but without visible magnetic ordering down to 2 K. The magnetization analyses for different RE3+ ions show diverse anisotropic behaviors, making RE3BWO9 as an appealing Kagomé-lattice antiferromagnet to explore exotic magnetic phases.

Enhanced photocatalytic performance and stability of 1T MoS2 transformed from 2H MoS2 via Li intercalation

Abstract Molybdenum disulfide is a competitive photocatalyst in organic pollutant degradation. 1T MoS2 was prepared by Li intercalation from hydrothermal synthesized 2H phase MoS2. The 1T MoS2 presents a lager intralayer distance of 12.0 A compared to that of 6.5 A in 2H MoS2. A stability of the prepared 1T phase was studied and a complete transformation of 1T to 2H was reached at 120 °C. The addition of nano-Au particle reduce the interlayered interaction in the MoS2 lattice. Both 1T@2H-MoS2 and 1T@2H-MoS2/Au present high decomposition rate of MB under visible light. 1T@2H-MoS2/Au presents a 90.4% decomposition of the modeling compound MB in 20 min compared to 25.2% MB conversion catalyzed by 2H-MoS2 under the same conditions.

Origin of the monolayer Raman signature in hexagonal boron nitride: a first-principles analysis

Monolayers of hexagonal boron nitride (h-BN) can in principle be identified by a Raman signature, consisting of an upshift in the frequency of the E2g vibrational mode with respect to the bulk value, but the origin of this shift (intrinsic or support-induced) is still debated. Herein we use density functional theory calculations to investigate whether there is an intrinsic Raman shift in the h-BN monolayer in comparison with the bulk. There is universal agreement among all tested functionals in predicting the magnitude of the frequency shift upon a variation in the in-plane cell parameter. It is clear that a small in-plane contraction can explain the Raman peak upshift from bulk to monolayer. However, we show that the larger in-plane parameter in the bulk (compared to the monolayer) results from non-local correlation effects, which cannot be accounted for by local functionals or those with empirical dispersion corrections. Using a non-local-correlation functional, we then investigate the effect of finite temperatures on the Raman signature. We demonstrate that bulk h-BN thermally expands in the direction perpendicular to the layers, while the intralayer distances slightly contract, in agreement with observed experimental behavior. Interestingly, the difference in in-plane cell parameter between bulk and monolayer decreases with temperature, and becomes very small at room temperature. We conclude that the different thermal expansion of bulk and monolayer partially ‘erases’ the intrinsic Raman signature, accounting for its small magnitude in recent experiments on suspended samples.

The effect of pressure and temperature on the magnetic and magnetocaloric properties of an MnNi0.9Ge1.1 alloy

The magnetic and magnetocaloric properties of a self-doped MnNiGe alloy of nominal composition MnNi0.9Ge1.1 have been investigated in ambient as well as in high pressure conditions. It orders ferromagnetically below around 225 K and undergoes first order martensitic phase transition (MPT) to an antiferromagnetic (AFM) martensite phase below 147 K. This self-doping results in a significant decrease in the lattice volume and hence the Mn–Mn intra-layer distance which induces ferromagnetism (FM) in otherwise AFM alloys. MPT affects this FM ordering and the alloy becomes predominantly AFM in nature below the structural transition temperature. The observed values of the magnetocaloric effects (MCE) are reasonably large at the magnetic (−5.5 J kg−1 K−1 for magnetic field changing from 0 to 50 kOe around 210 K) and structural (8.3 J kg−1 K−1 for magnetic field changing from 0 to 50 kOe around 136 K) transition temperatures in ambient condition. MCE is found to decrease with increasing external hydrostatic pressure (P) at MPT region, whilst this external P has vanishingly small effect on MCE around the magnetic transition temperature.

Superfluidity in density imbalanced bilayers of dipolar fermions

We study the zero temperature phase diagram of an imbalanced bilayer of dipolar fermions. We consider perpendicularly aligned identical dipoles in two layers and investigate the effect of population imbalance on the ground state phase at different layer spacings and average densities. The attractive part of the interlayer interaction could lead to the BEC-BCS crossover and the Fermi surface mismatch between two layers results in interesting uniform and nonuniform superfluid phases, which we have investigated here using the BCS mean-field theory together with the superfluid-mass density criterion. The density imbalance reduces the pairing gap. At low densities, where the system is on the BEC side of the crossover, this reduction is quite smooth while a dense system rapidly becomes normal at intermediate density polarizations. Stable homogeneous superfluidity is predicted to appear on the phase diagram when the dipolar length exceeds both the layer spacing and the average intralayer distance between dipoles, a regime which should be readily accessible experimentally. This homogeneous superfluid phase becomes unstable at intermediate densities and layer spacings. We have also examined that these uniform and inhomogeneous superfluid phases survive when the effects of intralayer screenings are also incorporated in the formalism.

Carbon Dioxide Transport in Carbon Nanopores

In the present study atomistic simulations are employed for investigating the CO2 transport properties through pores that are of slit, cylindrical and scroll configuration. We aim to investigate any possible differences in the adsorption process among the three different geometries focusing on the adsorption type that occurs along with pore filling and pore emptying mechanisms. Carbon-slit pores are of widths between 0.8 and 2.0 nm. The simulated Single-Walled Carbon Nanotubes (SWNTs) are of 1.08 and 2.17 nm ((8,8) and (16,16) respectively) while for the Carbon Nanoscrolls (CNSs) the inner diameter corresponds to a (6,6) SWNT with an intralayer distance of 0.4 to 1.0nm.

Enhanced carbon dioxide adsorption through carbon nanoscrolls

Over the last few years, significant efforts have been devoted to exploring the capabilities of carbon based structures for gas separation and filtration. In the present study the layering behavior of carbon dioxide transported through carbon nanoscrolls is examined through molecular dynamics simulations. The layering arrangements are investigated for carbon nanoscrolls with intralayer distances spanning from 4.2 to 8.3 Å at temperature of 300 K and pressures ranging from 5 to 20 bars. Characteristic layering structures are developed around the internal and external surfaces of the nanoscroll for all the examined cases. It is shown that the number of layers, their relative strength, and the starting point of bifurcation phenomena vary as a function of the nanoscrolls' intralayer distance, scroll's core radius, CO2 density, and gas structure interactions. It is also shown that the number of carbon dioxide molecules adsorbed per scroll's carbon particles is a function of the scroll's surface-to-volume ratio and is maximized under certain structural configurations.

Magnetic structures and phase transitions in PrMn2−xFexGe2

The magnetic properties and magnetic structures of PrMn2−xFexGe2 compounds (space group I4/mmm) have been investigated using magnetic, F57e Mössbauer effect (x=1.0,1.3,1.6), and neutron diffraction measurements (x=0.4,0.6,0.8,1.3) over the temperature range of 3–410 K. This has enabled the existing magnetic phase diagram for PrMn2−xFexGe2 to be extended from Fe concentration x=0–1 to the full range x=0–2 in terms of concentration and dMn–Mn, the intralayer distance. Analysis of the Mössbauer spectra (4.5–300 K) using a model which takes nearest-neighbor environments into account confirms the nonmagnetic nature of Fe atoms in these compounds, and leads to hyperfine parameters which deviate around the magnetic transition temperatures derived from the magnetic and neutron investigations while also enabling the Debye temperatures of PrMn2−xFexGe2 (x=0.4–1.6) to be determined. The experimental values for TCinter are found to decrease rapidly with increasing Fe concentration in the range x=0.0–0.6 compared with calculated TCinter values due to pressure (and therefore geometric) effects only. This behavior demonstrates that electronic effects and replacement of the magnetic Mn atoms with nonmagnetic Fe atoms contribute to the overall magnetic behavior of PrMn2−xFexGe2 compounds. Compared with intralayer Mn–Mn interactions, the interlayer Mn–Mn interactions play the major role in the anomalous thermal expansion observed at magnetic transition in these layered systems, with the interlayer Mn–Mn interactions governing the significant magnetovolume effects.

Magnetic phase transitions and giant magnetoresistance in La1−xSmxMn2Si2 (0≤x≤1)

The magnetic properties of La1−xSmxMn2Si2 (0≤x≤1) quasi-ternary layered intermetallic compounds have been studied by magnetic measurements. Based on the results of magnetic measurements, the x–T magnetic phase diagram of the compounds was defined. The concentration-dependent change in the magnetic state of the Mn sublattice in the compounds correlates with an unusual dependence of the type of interlayer Mn–Mn magnetic ordering on the intralayer Mn–Mn distance in the RMn2X2-type compounds. The compounds La1−xSmxMn2Si2 with x=0.25, 0.27 exhibit SmMn2Ge2-like magnetic behavior and giant magnetoresistance (−ΔR/R≈27%) at the field-induced antiferro-ferromagnetic metamagnetic phase transitions. The field-induced metamagnetic transitions were described in a model taking into account a strong Mn anisotropy, exchange magnetostriction and a strong dependence of the interlayer Mn–Mn exchange interactions on the Mn–Mn intralayer distance in the compounds.

High-pressure x-ray-absorption study of GaSe

The III-VI layered semiconductor InSe has been studied by high-pressure single crystal x-ray absorption spectroscopy up to a maximum pressure of 14 GPa. The In-Se distance has been measured in both the low- pressure layered phase and the high-pressure NaCl phase. The bond compressibility in the layered phase is lower than the ``a'' crystallographic parameter compressibility, which implies an increase of the angle between the In-Se bond and the layer plane. Under plausible hypothesis, a description of the evolution of the whole structure with pressure is given. In particular, the intralayer distance is observed to increase with increasing pressure. A plausible precursor defect and a simple mechanism for the transition are also presented. The conclusions can be readily translated to other III-VI layered semiconductors.

Transition metal–tin ordering in SrPtSn, SrAuSn and BaAuSn and 119Sn Mössbauer spectroscopy of CaPdSn, CaPtSn and SrAuSn

Abstract Pure samples of CaPdSn, CaPtSn, SrPtSn, SrAuSn and BaAuSn can be prepared by reacting the elements in glassy carbon crucibles or in sealed tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. The stannides have been investigated by X-ray diffraction on powders. Single crystal data yielded: TiNiSi type, Pnma , a =764.16(7), b =470.74(4), c =799.64(7) pm, wR 2 =0.0622, 469 F 2 values, 20 variables for SrPtSn, and CaCuGe type, Pnma , a =2341.4(3), b =481.80(5), c =826.7(1) pm, wR 2 =0.1368, 1136 F 2 values, 56 variables for SrAuSn. The platinum (gold) and tin atoms form two-dimensional layers of puckered Pt 3 Sn 3 and Au 3 Sn 3 hexagons with short PtSn (276 and 278 pm) and AuSn (279–286 pm) intralayer distances. These condensed two-dimensionally infinite nets are interconnected to each other via PtSn contacts (279 pm) in SrPtSn. In SrAuSn very weak interlayer AuSn (312 pm) and AuAu (340 pm) contacts occur, but stronger SnSn (304 pm) interactions. The SrAuSn structure is a superstructure of SrPtSn resulting from an isomorphic transition of index 3 from Pnma to Pnma . The KHg 2 type subcell of BaAuSn was determined from Guinier powder data: Imma , a =493.5(1), b =817.2(1), c =844.5(1) pm. 119 Sn Mossbauer spectra of TiNiSi type CaPdSn and CaPtSn show a single signal at 77 K at isomer shifts of δ =1.964(5) and 1.857(4) mm s −1 , respectively, subject to quadrupole splitting of ΔE Q =0.94(3) and 0.89(1) mm s −1 . SrAuSn shows two superimposed signals in a ratio of 2:1 at 77 K: δ 1 =2.03(5), δ 2 =2.12(5) mm s −1 , ΔE Q1 =0.9(1) and ΔE Q2 =0.6(2) mm s −1 .

Irreversible amorphization of tetragonal two-dimensional polymeric C 60 under high pressure

The pressure dependence of the cell parameters of tetragonal two-dimensional polymeric C 60 has been determined by angle-dispersive, X-ray diffraction in a diamond anvil cell. The compression of the c parameter, the interlayer distance, is typical of a weak Van der Waals interaction, whereas the compression of the a parameter indicates strong covalent interactions. Amorphization was observed to occur gradually between 10 and 29 GPa when inter- and intra-layer distances become similar. No transition to another crystalline phase was observed up to 41 GPa or on decompression.

Platinum–germanium ordering in UPtGe

The non-centrosymmetric structure of UPtGe was investigated by X-ray diffraction on both powders and single crystals: EuAuGe type, Imm2, a=432.86(5), b=718.81(8), c=751.66(9) pm, wR2=0.0738 for 399 F2 values and 22 variables. The platinum and germanium atoms form two-dimensional layers of puckered Pt3Ge3 hexagons with short PtGe intralayer distances of 252 and 253 pm. These condensed two-dimensionally infinite nets are interconnected to each other via weak PtPt contacts with bond distances of 300 pm. The two crystallographically independent uranium atoms are situated above and below the six-membered platinum–germanium rings. The U1 atoms have six closer germanium neighbors while the U2 atoms have six closer platinum neighbors. The group–subgroup relation with the KHg2 type structure is presented.

Unconventional magnetic and transport properties in Gd 1− xLa xMn 2Ge 2 with two-dimensional arrangement of Mn atoms

In this paper, we present our recent experimental results of magnetic and transport properties of Gd 1− x La x Mn 2Ge 2 intermetallic compounds with the ThCr 2Si 2-type layered structure. The results obtained indicate that, in GdMn 2Ge 2, a first-order transition from a collinear antiferromagnetic to a collinear ferrimagnetic state appears with decreasing temperature at T t3, below the Néel temperature T N. In Gd 1− x La x Mn 2Ge 2 compounds with x=0.05 and 0.075, after ordering ferrimagnetically at T t1, two kinds of first-order transitions from a canted ferrimagnetic to a non-collinear antiferromagnetic state and from a non-collinear antiferromagnetic to a reentrant canted ferrimagnetic state occur at T t2 and T t3. In Gd 0.925La 0.075Mn 2Ge 2, a field-induced metamagnetic transition from non-collinear antiferromagnetism to canted ferrimagnetism occurs at relatively low fields, accompanied by fractal like multi-step transitions, the so called “devil's stair-case”. Furthermore, a negative giant magnetoresistance (GMR) effect (Δ ρ/ ρ∼15%) was observed at the field-induced metamagnetic transition. The mechanism of this negative GMR was clarified by comprehensive measurements of the resistivity on single crystals Gd 0.925La 0.075Mn 2Ge 2 and TbMn 2Ge 2. With further increasing x, only canted ferrimagnetism appears with a compensation temperature for 0.10< x<0.40, whereas no compensation behavior appears for x>0.50. The phase diagram obtained indicates that the overall magnetism is controlled by the Mn–Mn intralayer distance in the tetragonal c-plane, reflecting the two-dimensional arrangement of Mn atoms.

High-pressure x-ray absorption study of GaTe including polarization

The evolution of the local structure in GaTe under pressure is studied by x-ray absorption spectroscopy experiments at the Ga K-edge (10.368 keV) on oriented single crystals. Taking advantage of the linearly polarized character of synchrotron radiation, the pressure evolution of both the Ga-Te and the in-plane Ga-Ga bond lengths could be determined, in spite of the small amplitude of the latter. Our measurements show that both distances are much less compressible than what could be inferred from the bulk compressibility, which evidences a strong variation of Ga-Ga-Te and Te-Ga-Te angles under pressure. The Te-Te intralayer distance perpendicular to the layers is observed to increase with increasing pressure. In the high-pressure NaCl phase, no anisotropy of the x-ray absorption fine structure spectrum is detected and local and bulk compressibilities coincide. With the help of microphotographic measurements the main source of instability of the layer structure is attributed to the tilt of the Ga-Ga bond with respect to the layer plane.