Lattice Compression Research Articles

Reply to "Comment on 'Osmotic pressure of compressed lattice knots' ".

The free energy of a model of uniformly weighted lattice knots of length n and knot type K confined to a lattice cube of side length L-1 is given by F_{L}(ϕ)=-1/Vlogp_{n,L}(K), where V=L^{3} and where ϕ=n/V is the concentration of monomers of the lattice knot in the confining cube. The limiting free energy of the model is F_{∞}(ϕ)=lim_{L→∞}F_{L}(ϕ) and the limiting osmotic pressure of monomers leaving the lattice knot to become solvent molecules is defined by Π_{∞}(ϕ)=ϕ^{2}d/dϕ[F_{∞}(ϕ)/ϕ]. I show that, under very mild assumptions, the functions P_{L}(ϕ)=ϕ^{2}d/dϕ[F_{L}(ϕ)/ϕ]|_{n} and Π_{L}(ϕ)=ϕ^{2}d/dϕ[F_{L}(ϕ)/ϕ]|_{L} are finite-size approximations of Π_{∞}(ϕ).

Electrochemical Oxidation of Methanol and Ethanol at Rh@Pt and Ru@Pt Catalysts

The influence of the amount of Pt deposited onto Rh and Ru nanoparticles on the oxidation of methanol and ethanol has been compared in H2SO4(aq) at ambient temperature and in a proton exchange membrane (PEM) cell at 80 °C. In H2SO4(aq), Rh@Pt and Ru@Pt show similar enhancements in activities over Pt for both methanol and ethanol oxidation. However, differences in the optimum Pt coverage indicate that compression of the Pt lattice by Rh plays a dominate role, while ligand effects are more important for Ru@Pt. In the PEM cell, the Ru core enhanced activities significantly for both methanol and ethanol, while activities were suppressed by the Rh core. This may arise from dominance of ligand and/or bifunctional effects for the Ru@Pt catalyst at 80 °C. Data from the PEM cell showed that the stoichiometry for ethanol oxidation at Ru@Pt was higher than for Rh@Pt, indicating a higher selectivity for the complete oxidation to CO2.

Anomalous lattice compression in the hexagonal La2O3– A high pressure X-ray diffraction, Raman spectroscopy and first principle study

High pressure behavior of hexagonal rare earth sesquioxide La2O3 have been investigated using X-ray diffraction, Raman spectroscopy and first principle calculations. Though the hexagonal structure is stable up to 26.5 GPa, incompressibility along the a axis is visible above 9.7 GPa. Rietveld structure refinements in conjunction with the Stephans anisotropic strain broadening model revealed the onset of an atypical bond compression and modification in the relative intensities of the diffraction peaks at ∼5.6 GPa. A significant increase in the intensity of 100 reflection and a clear reduction in the intensity of 103 reflection above 5.6 GPa suggests that pressure induces sliding of the adjacent La–O layers in opposite directions rather than compressing along the a axis. Further, a negative correlation of in-plane strain with pressure above 5.6 GPa indicate the layer sliding is accompanied by a reduction of in-plane strain in the hexagonal structure. Raman studies show the lifting of the degeneracy of the two stretching modes, in-plane Eg and out of plane A1g, and the change of slope of ω vs. P curve for the two in-plane Eg modes at 3.6 GPa. First principle density functional theory calculation substantiates our experimental observations that the pressure induced anisotropic strain distribution is driving the system into low energy configurations. The Birch –Murnaghan equation of state fit to the experimental pressure-volume data yielded a bulk modulus value of B0 = 102(5) GPa with B′0 = 9.8(1.0) for P ≤ 9.7 GPa, in good agreement with the 114 GPa of density functional theory calculations.

Magnesium-rich nanoprecipitates in calcite: atomistic mechanisms responsible for toughening in Ophiocoma wendtii.

The brittlestar Ophiocoma wendtii is theorised to employ a technique already used in metallurgy in order to optimise the mechanical properties of calcitic microlenses within their skeletons. These microlenses contain arrays of Mg-rich nanoprecipitates, which are proposed to inhibit crack propagation through the compression of the local host lattice. Here, we employ classical molecular dynamics in order to study the effects of Mg-rich nanoprecipitates on lattice strain, stress distributions and crack propagation in calcite. Our quantitative results on lattice strain and stress induced on the host matrix are compatible with empirical estimates. Simulations of crack propagation demonstrate that the inclusion of a Mg-rich region results in an increase in stress required to fracture the crystal, as well as higher residual stress in the fractured crystal. This is the result of an inhomogeneous stress distribution causing a more disordered fracture, as well as deflections of the crack away from the lowest energy (10.4) surface. The results agree with the proposal that the compression of the host lattice inhibits propagation, and offer insight into other mechanisms through which the nanoprecipitates affect crack propagation.

Theoretical Studies of the Structural, Electronic and Magnetic Properties of the CoFeCeZ (Z = P, As and Sb) Quaternary Heusler Alloys

In this paper, we investigate the structural, electronic and magnetic properties of CoFeCrZ ([Formula: see text], As,Sb) quaternary Heusler alloy, using the first-principles full potential linear muffin-tin orbital (FP-LMTO) method within the spin gradient generalized approximation (GGA) for the exchange and correlation potential. Our results demonstrate that in ferromagnetic phase, the all alloys CoFeCrZ are stable in type-1 configuration and are half-metallic ferromagnets (HMF) with gaps of 0.99[Formula: see text]eV, 0.57[Formula: see text]eV and 0.70[Formula: see text]Ev, respectively. The obtained negative formation energy shows that CoFeCrZ alloys have strong structural stability. The calculated total magnetic moment, [Formula: see text] for all alloys exhibit Slater-Pauling rule, [Formula: see text]. At zero pressure, the three alloys shown 100% spin-polarization at Fermi–level [Formula: see text] with high Curie temperatures [Formula: see text]. Our calculation indicate also that the half-metallicity and high magnetic moment of CoFeCrP, CoFeCrAs and CoFeCrSb are robust against the lattice compression (up to 7.80%, 5.40% and 11%, respectively). On the basis of these results, it is suggested that the CoFeCrZ Heusler could be suitable for spintronics devices applications.

The free energy of compressed lattice knots

A compressed knotted ring polymer in a confining cavity is modelled by a knotted lattice polygon confined in a cube in . The GAS algorithm (Janse van Rensburg and Rechnitzer 2011 J. Knot Theol. Raman 20 1145–71) is used to sample lattice polygons of fixed knot type in a confining cube and to estimate the free energy of confined lattice knots. Lattice polygons of knot types the unknot, the trefoil knot, and the figure eight knot, are sampled and the free energies are estimated as functions of the concentration of monomers in the confining cube. The data show that the free energy is a function of knot type at low concentrations, and (mean-field) Flory–Huggins theory (Flory 1942 J. Chem. Phys. 10 51–61; Huggins 1942 J. Phys. Chem. 46 151–8) is used to model the free energy as a function of monomer concentration. The Flory interaction parameter of knotted lattice polygons in is also estimated.

First Adsorbed Water Layer and Its Wettability Transition under Compressive Lattice Strain

A molecular-level description of a near-surface water structure and a handy manipulation of its properties are relevant to a broad range of scientific and technological phenomena. Here, through a s...

Theoretical Insights on the High Pressure Behavior of Pentazolate Anion Complex [Co(H2O)4(N5)2]\xb74H2O

Periodic dispersion corrected density functional theory (DFT) calculations were carried out to examine the Hirshfeld surface, two dimensional (2D) fingerprint plots, crystal structure, molecular structure and density of state of all-nitrogen pentazolate anion complex [Co(H2O)4(N5)2]·4H2O under hydrostatic pressure from 0 to 20 GPa. The GGA/PW91-OBS method was applied in the present study. The intercontacts in [Co(H2O)4(N5)2]·4H2O were analyzed by Hirshfeld surfaces and 2D fingerprint plots. With ascending pressure, the lattice constants, compression rates, bond lengths, bond angles, and density of states change irregularly. Under 11.5, 13.0 and 15.8 GPa, covalent interaction competition is obvious between Co−N and Co−O bonds. It is possible to achieve orderly modification and regulation of the internal structure of [Co(H2O)4(N5)2]·4H2O by applied pressure. This is in accordance with the results from density of states analysis. The external compression causes the nonuniformity of electron density and the differential covalent interaction between pentazolate anion, coordinated water and atom Co. It is of great significance to interpret inter/intramolecular interaction and structural stability of [Co(H2O)4(N5)2]·4H2O and provide theoretical guidance for the design of metal complexes of all-nitrogen pentazolate anion.

Pressure variations of the 5f magnetism in UH3

Pressure variations of the Curie temperature of the 5f ferromagnet β-UH3 were studied using the Mo-alloyed hydride (UH3)0.82Mo0.18, which is stable in air and has very similar TC and magnetization per U atom. By means of ac magnetic susceptibility a linear decrease of TC was observed for pressures up to 3.2 GPa. The coefficient dTC/dp = −2.05 K/GPa gives dlnTC/dp = 1/T*dTC/dp ≈ −0.011 GPa−1. This value is smaller than expected for a 5f-band ferromagnet with relatively short U-U distances and suggests that UH3 may be more localized than expected. Among AnX compounds, similar dependence was found e.g. for US. Revisiting existing data on lattice elasticity for β-UH3, bulk modulus B ≈ 100 GPa can be assumed, leading to dlnTC/dlnV = 1.1. Experimental data are confronted with results of GGA + U electronic structure calculations. Plausible values of direct Coulomb U and Hund’s exchange J are deduced. The lattice compression was found to reduce predominantly the orbital moments.

Structural and electro-optical properties of electrospun Cu-Doped ZnO thin films

Pure and Cu-doped ZnO thin films (TFs) were synthesized on glass substrates via the electrospinning method, and the effects of Cu concentration on electro-optical and structural properties were investigated. The nanofibers (NFs) changed to cross-linked nanoparticles (NPs) via calcination at 400 °C. XRD results indicate that Cu2+ was successfully incorporated into the ZnO host to form a hexagonal wurtzite structure. The crystallography of Cu-doped ZnO (CZO) was systematically investigated; it was found that both c/a ratio and compressive lattice strain increased. The photoluminescence (PL) behavior of CZO TFs revealed that the excitonic and redshifted UV emissions were manipulated by Zni, Oi, VZn, OZn and VO defect states. Optical absorption measurements showed excellent transmission percentages (above 87%) in the visible light range. The optical band gap of ZnO TFs decreased from 3.3 eV to 3.2 eV after incorporation of Cu. The results of this study show that electrospun CZO TFs has immense potential for use in electro-optical applications.

Study of structural and surface morphological properties of Tb doped ZnO nanoparticles using XRD, XPS and fractal analysis

A systematic study was performed on Tb3+ doped ZnO nanoparticles of different mole-fraction using Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and X-ray Photoemission Spectroscopy (XPS) measurements. XRD studies confirm that all the samples are in wurtzite phase. XRD analysis suggests a compressive lattice strain as doping concentration increases. The strain generated in the doped samples is found to be more as compared to pure nanoparticle samples. XPS result indicates the presence of several oxygen species adsorbed on the surface. Furthermore, the effect of incorporation of Tb3+ ions into ZnO nanoparticles was explored using fractal analysis approach to extract the quantitative surface parameters. The fractal dimension is a scale invariant technique for representation and understanding of surface morphology of nanostructures. Fractal dimension provides a clear distinction between vertical and horizontal properties of the surfaces and their correlation. This technique could be very useful in selecting the suitable substrate for various technological applications. The lateral correlation length was estimated by auto-correlation function. While, the roughness exponent and fractal dimension were calculated from height-height correlation function. Moreover, this study reveals that the complexity of surface increases with doping. Moreover, as doping increases, the surface becomes more and more zagged as compared to pure samples.

The free energy of compressed lattice knots

Abstract IOP Publishing has withdrawn this article upon the author's request due to several issues with the mathematical content. The osmotic pressure of monomers in a knotted ring polymer in a confining cavity is modelled by a lattice polygon confined in a cube in ${\mathbb Z}^3$. These polygons can be knotted and are called lattice knots. In this paper the GAS algorithm \cite{JvRR11} is used to estimate the free energy of lattice knots of knot types the unknot, the trefoil knot, and the figure eight knot, as a function of the concentration of monomers in the confining cube. The data show that the free energy is a function of knot type at low concentrations, and (mean-field) Flory-Huggins theory \cite{Flory42,H42} is used to model the free energy as a function of monomer concentration. The Flory interaction parameter of lattice polygons in ${\mathbb Z}^3$ is also estimated. At critical values of the concentration the osmotic pressure may vanish, and these critical concentrations, suitably rescaled, is dependent on knot type.

Strain-Induced Increase of Dielectric Constant in EuO Thin Film

Recently, lattice dynamics of the highly strained Europium monoxide, as a promising candidate for strong ferroelectric-ferromagnet material, applied in the next-generation storage devices, attracted huge attention in the solid-state electronics. Here, the authors investigate the effect of tensile strain on dielectric properties of pulsed laser deposited EuO thin films from 10 to 200 K. A nearly 3% out-of-plane lattice compression is observed as the film thickness was reduced to ∼8 nm, which could originate from the lattice mismatch between film and a LaAlO3 substrate. The temperature and frequency dependence of capacitance and loss factor of the films reveals the dominant role of electronic and ionic polarization below 100 K. The interdigitated capacitor fabricated on strained film shows almost 50% increase of capacitance compared to the relaxed one, which corresponds to a considerable increase of dielectric constant induced by in-plane tensile strain. Softening of the in-plane polarized transverse optical (TO) phonon modes of EuO lattice due to tensile strain might have the major contribution to this behavior according to the Lyddane–Sachs–Teller relation.

Magnetic and structural properties of Fe-doped layered cobaltite TbBaCo1.91Fe0.09O5.5 at high pressures

The crystal and magnetic structures of the perovskite-like, oxygen deficient layered cobalt oxide TbBaCo1.91Fe0.09O5.5 have been studied by means of neutron diffraction at high pressures up to 6.2 GPa in the temperature range 5–300 K and X-ray diffraction at high pressures up to 30 GPa and ambient temperature. The structural anomalies in lattice compression at P = 20–25 GPa were revealed, which could be associated with the insulator-metal transition. At ambient pressure below TN = 300 K a formation of the complex magnetic structure on the Co/Fe sublattice, comprising the G-type antiferromagnetic (AFM) and ferromagnetic (FM) components, was observed. Below T ≈ 150 K the FM component vanished. At T = 5 K a presence of the long range AFM order on the Tb sublattice was also revealed. At high pressures, the FM component has become suppressed and the only G-type AFM order was found for the Co/Fe sublattice. The Néel temperature decreased noticeably down to 275 K at P = 6.2 GPa with a pressure coefficient dTN/dP = −4 K/GPa. The intrinsic mechanisms of the observed pressure-induced magnetic phenomena are discussed.

Influence of ionic liquids and concentration of red phosphorous on luminescent Cu3P nanocrystals

Highly crystalline, phase pure Cu3P nanocrystals (NCs) have been successfully synthesized using ionic liquid-assisted solvothermal method at relatively low temperature (200 °C). Herein, ionic liquids (ILs) are used as a structure directing/templating agent. Effect of ILs and precursor concentration on crystal phase, crystallite size, lattice strain, morphology and grain size of Cu3P NCs is studied. In the presence of IL, crystallite size and lattice strain significantly change with changing the concentration of red phosphorus. For example, smaller crystallite size (38.5 nm) and compressive lattice strain are obtained when 10 times of red phosphorous is used. However, bigger size (41.9 nm) and tensile lattice strains are obtained for the lower concentration of phosphorous (5 times). At higher phosphorus concentration, hexagonal shaped micro-crystals with prominent grain are observed. HRTEM images reveal that spherical-shaped particles on further agglomeration through Ostwald ripening process form hexagonal-shaped bigger microstructures. However, on doping the rare-earth ions (RE3+ = Ce3+/Tb3+) in the Cu3P NCs show the green luminescence (at 542 nm) which is attributed to the emission of Tb3+ ions. To the best of our knowledge, this is the first report on rare-earth doped Cu3P nanoparticles and shows promise on the luminescence aspect of Cu3P nanomaterials along with its already existing plasmonic and semiconducting properties.

Highly Efficient and Selective Oxidation of Ethanol to Acetaldehyde by a Hybrid Photocatalyst Consisting of SnO2 Nanorod and Rutile TiO2 with Heteroepitaxial Junction.

Single-crystal SnO2 nanorods were grown on rutile TiO2 with a heteroepitaxial relation of SnO2 {001}/TiO2 {001} (SnO2 -NR#TiO2 ) by a hydrothermal reaction. Resulting compressive lattice strain in the SnO2 -NR near the interface induces a continuous increase in the a-axis length extending over 60 nm to relax towards the [001] direction from the root to the tip. UV-light irradiation of the robust SnO2 -NR#TiO2 stably progresses the selective oxidation of ethanol to acetaldehyde with an external quantum yield of 25.6 % at excitation wavelength (λex )=365 nm under ambient temperature and pressure. Spectroscopic analyses and density functional theory simulation results suggested that the extremely high photocatalytic activity stems from the smooth interfacial electron transfer from TiO2 to SnO2 -NR through the high-quality junction and subsequent efficient charge separation due to the lattice strain-induced unidirectional potential gradient of the conduction band minimum in the SnO2 -NR.

High-Pressure Band-Gap Engineering and Metallization in the Perovskite Derivative Cs3 Sb2 I9.

Among photovoltaic materials, the antimony-based, perovskite-like structure Cs3 Sb2 I9 stands out owing to its low toxicity and air stability. Here, changes in the optoelectronic properties and crystal structure of the lead-free perovskite derivative Cs3 Sb2 I9 are reported, caused by pressure-induced lattice compression. At 20.0 GPa, Cs3 Sb2 I9 with a wide band gap (2.34 eV) successfully broke through the Shockley-Queisser limit (1.34 eV), accompanied by clear piezochromism from orange-yellow to opaque black. Additionally, Cs3 Sb2 I9 experienced completely reversible amorphization at 20.0 GPa. These optical changes could be attributed to atomic-orbital overlap enhancement caused by contraction of the Sb-I bond length and diminution of the Sb-I bond angle. In addition, Cs3 Sb2 I9 underwent a transition from semiconductor to conductor upon compression and obtained metallic properties at 44.3 GPa, indicating new electronic properties. The obtained results may further broaden the research prospects of halide perovskite materials in the field of photovoltaics.

Electrochemical stability and bio-mineralization capability of zinc substituted and elemental zinc reinforced calcium phosphate composite coatings synthesized through pulsed electro-deposition

Recent studies showed that zinc, as one of the essential element in the human body, is able to promote osteoblast proliferation and bone growth when present with calcium phosphate phases. In this study, zinc substituted and zinc reinforced calcium phosphate composites were prepared by electro chemical deposition from aqueous electrolyte bath. Nucleation rate and reaction time were varied to understand the relation between in-situ formation mechanism of various phases with the varying reaction kinematics and kinetics. The thin functional composite coatings were compared in terms of their surface morphology, lattice structure, surface elemental composition and related electrochemical corrosion resistance along with bio-mineralization capability under simulated body fluid (SBF). On a particular parameter of 10 mA/cm2 current density and 20% duty cycle, nano tubes enriched in elemental zinc; hopeite and calcium orthophosphate composite phases are formed. This unique microstructural morphology and composition make the coating surface 10 times more electrochemical corrosion resistant compared to all other coatings. A high amount of zinc substitution in calcium phosphate phases leads to the development of high compressive lattice strain, which in turn results in rapid dissolution of the coating under contact with SBF. During bio-mineralization, the zinc loading ratio is rapidly decreased for the initial 7 days through preferential dissolution and enrichment in calcium ions and subsequently stabilized at 60% from the initial 83% in nano tube structures. The effective adherence of osteoconduction product on the nano tube structure is achieved post 14 days. In summary, electrochemical deposition was found as an effective way to design various tailor-made/functionally graded zinc-calcium phosphate composite coatings based on specific requirements of biodegradability, biocompatibility and surface properties.

Osmotic pressure of compressed lattice knots

A numerical simulation shows that the osmotic pressure of compressed lattice knots is a function of knot type, and so of entanglements. The osmotic pressure for the unknot goes through a negative minimum at low concentrations, but in the case of nontrivial knot types 3_{1} and 4_{1} it is negative for low concentrations. At high concentrations the osmotic pressure is divergent, as predicted by Flory-Huggins theory. The numerical results show that each knot type has an equilibrium length where the osmotic pressure for monomers to migrate into and out of the lattice knot is zero. Moreover, the lattice unknot is found to have two equilibria, one unstable, and one stable, whereas the lattice knots of type 3_{1} and 4_{1} have one stable equilibrium each.

Growth temperature and relaxation of lattice strain in epitaxial Pt films exhibiting diffraction fringes

We fabricated Pt epitaxial films on SrTiO3(111) using a dc-sputtering method. The surface structure, the surface morphology, and the electrochemical properties are discussed. Reflection high-energy electron diffraction (RHEED) observation reveals that epitaxial films are obtained at substrate temperatures higher than 450 °C. The RHEED patterns exhibit clear streaks up to the 1st order Laue zone, which indicates the high crystallinity and the atomically smooth surface. Oscillation in the intensity of the X-ray diffraction pattern is observed near the Pt-111 peak. It is caused by multiple scattering, showing the perfection in the lattice plane stacking along the out-of-plane direction. Analysis using a dynamic theory of diffraction shows that the film is subjected to a compressive in-plane lattice strain. The in-plane lattice parameter decreases by approximately 0.3%. The oscillation amplitude decreases at 600 °C, which suggests that the lattice relaxation occurs caused by misfit dislocation.