Difference In Lattice Parameters Research Articles

Studies on Doping Concentration Variations in 4H-SiC Substrates Using X-ray Contour Mapping

Highly doped 4H-SiC will show a significant lattice parameter difference with respect to the undoped material. We have applied the recently developed monochromatic contour mapping technique for 4H-SiC crystals to a 4H-SiC wafer crystal characterized by nitrogen doping concentration variation across the whole sample surface using the synchrotron monochromatic X-ray beam. Strain maps of 0008 and -2203 planes were derived by deconvoluting the lattice parameter variations from the lattice tilt. Analysis reveals markedly different strain values within and out of the basal plane indicating the strain induced by nitrogen doping is anisotropic in the 4H-SiC hexagonal crystal structure. The highest strain calculated along growth direction [0001] and along [1-100] on the closed packed basal plane is up to -4x10-4 and -2.7x10-3 respectively. Using an anisotropic elasticity model by separating the whole bulk crystal into numerous identical rectangular prism units, the measured strain was related to the doping concentration and the calculated highest nitrogen level inside wafer crystal was determined to be 1.5x1020cm-3. This is in agreement with observation of double Shockley stacking faults in the highly doped region that are predicted to nucleate at nitrogen levels above 2x1019 cm-3.

Theoretical Evaluation of Possibility to Control Nucleation and Growth of Heteroepitaxial Carbon Films by Applied Fields

On the basis of the literature review, comparison of physical and chemical properties of materials and calculations, it was showed that the copper, saturated with hydrogen, is an appropriate substrate material<br />for heteroepitaxial growth of diamond films. The atomic hydrogen in tetrapores of copper crystalline lattice will be the crystallisation centre of carbon. Herewith the difference in lattice cell parameters between<br />the substrate and the growing diamond film is considerably reduced, i.e. epitaxial growth of crystal is possible. Besides, the disposition of tetrapores on the copper surface (111) and, respectively, of atomic hydrogen located in them, creates conditions for preferential formation of tetragonal bonds of carbon. The estimations have shown that it is possible to create conditions for preferential oriented growth of diamond films through changing the magnitude and configuration of applied fields.

Magnetic Properties of (Nia-Znb)X Cu1-X Ferrite Nanoparticle Fabricated by Sol-Gel Process

Abstract In future, more mobile devices with different frequencies will be used at the same time. Therefore, it is expected that the trouble caused by wave interference between devices will be further intensified. In order to prevent this trouble, investigation of selective frequency transmission or absorption material is required. In this paper, magnetic properties of nickel-zinc-copper ferrite nano powder was researched as wave absorber. (Nia-Znb)xCu1-xFe2O4(NZCF) nanoparticles were fabricated by the sol-gel method. The influence of copper substitution on lattice parameter change was analyzed by X-ray diffraction (XRD), particle size was analyzed by scanning electron microscopy (SEM), and Magnetic properties analyzed by vibrating sample magnetometer (VSM). The NZCF and Nickel-zinc ferrite (NZF) lattice parameter difference was 0.028 Å and particle size was calculated as 30 nm with the XRD peak. The VSM results of (Ni0.3-Zn0.3)0.6Cu1-0.6Fe2O4 annealed sample at 700°C for 3hous were 58.5 emu/g (Ms), 22.8 Oe (Hc). It was the most suitable magnetic properties for wave absorber in this investigation.

Interdiffusion Processes in High-Coercivity RF-Sputtered Alnico Thin Films on Si Substrates

Alnico V thin film samples with the thickness of 100 nm were prepared by radio-frequency sputtering on Si substrates with and without a SiO2 layer. Heat treatment of the as-deposited thin films in above ambient pressure in an Ar atmosphere at a temperature range of 600–900°C, followed by quenching and/or slow cooling, leads to higher coercivity values compared to bulk Alnico magnets. Annealing at 800°C followed by quenching results in the highest coercivity reported here of 1.8 kOe. The formation of several triangular-shaped features along the interface between the substrate and the film were observed. A high-resolution transmission electron microscope analysis showed these to be formed via interdiffusion of Fe, Co and Ni atoms into the Si substrate. These features show a large difference in lattice parameters compared with the magnetically soft bulk Fe-Co-Si alloys, and a heterogeneous or layered magnetic ion distribution inside these features could be the origin of the high coercivity observed in the heat-treated films.

Crossover from localized to itinerant states in hydrocarbon Mott insulators.

Crossover from an itinerant state to an isolated electronic state in electron-doped polycyclic aromatic hydrocarbon (PAH) was studied for the two smallest zigzag-type molecules of naphthalene (NN) and anthracene (AN) by focusing on their 1 : 1 stoichiometry, A1(NN) and A1(AN), with alkali metals (A = K and Rb). The competition between on-site Coulombic repulsion energy (U) and bandwidth (W) was argued in terms of their magnetic and electrical properties upon lattice expansion, when A varies from K, with a smaller ionic radius, to Rb, with a larger ionic radius. The temperature-dependence of magnetic susceptibility shows a pronounced hump associated with antiferromagnetic (AFM) interactions for Rb1(NN), being similar to those of K1(NN) and K1(AN) in the earlier report. On the other hand, Rb1(AN) intriguingly exhibits paramagnetic susceptibility, observed in a nearly localized electron system, being apart from an highly correlated Mott insulating state. Crystal structural analyses of the X-ray diffraction profiles show a small difference in lattice parameters of the ab plane among K1(NN), K1(AN), and Rb1(NN), whereas Rb1(AN) exhibits a significantly larger value than those of the others, being indicative of greatly modified interaction energies. The different magnetic properties observed in Rb1(AN) are interpreted from its modified intermolecular distance. The possibility of an emergent metallic state of K1(AN) under high pressure has also been described, referring to electrical transport measured under high pressure.

Modeling intrinsic residual stresses built-up during growth of nanostructured multilayer NbN/CrN coatings

Composition modulated NbN/CrN nanostructured multilayer coatings were deposited onto martensitic stainless steel. The coatings were obtained by cathodic arc process, in an industrial-size physical vapor deposition (CAPVD) chamber. The coatings reached 15μm thick, consisting of multilayers of different periodicities (4nm≤Λ≤20nm), which were achieved by varying the rotating speed of the samples in a 2-fold rotation table. The obtained coatings were characterized by High Resolution Transmission Electron Microscopy (HRTEM) and Selected Area Diffraction (SAD) in order to assess the crystal structure, epitaxy and degree of coherency of the NbN/CrN interface. The results showed that the coatings were formed by alternate individual layers of NbN and CrN separated by highly coherent interfaces, and revealed cross-contamination between the layers. Compositional variation measured across the multilayers, by Electron Energy Loss Spectroscopy (EELS) showed that the lower the coating periodicity (Ʌ), the greater is the cross-contamination in the NbN and CrN individual layers. A Finite Element Analysis (FEA) model was developed for assessing the intrinsic residual stresses due to differences of lattice parameters of the NbN and CrN structures, based on chemical composition gradients obtained from EELS measurements. The results show the build-up of stress gradients from the center of individual layers towards the interface, differently from other results published in literature. The smaller the periodicity the higher are the stress gradients developed near the NbN/CrN interfaces. The results are discussed based on the possible interaction of dislocations with stress fields developed near the NbN/CrN interfaces. The proposed model is consistent with former experimental results, which indicates that the smaller the periodicity, the greater is the coating hardness when periodicities range from 4nm to 20nm.

GaAs/Ge crystals grown on Si substrates patterned down to the micron scale

Monolithic integration of III-V compounds into high density Si integrated circuits is a key technological challenge for the next generation of optoelectronic devices. In this work, we report on the metal organic vapor phase epitaxy growth of strain-free GaAs crystals on Si substrates patterned down to the micron scale. The differences in thermal expansion coefficient and lattice parameter are adapted by a 2-μm-thick intermediate Ge layer grown by low-energy plasma enhanced chemical vapor deposition. The GaAs crystals evolve during growth towards a pyramidal shape, with lateral facets composed of {111} planes and an apex formed by {137} and (001) surfaces. The influence of the anisotropic GaAs growth kinetics on the final morphology is highlighted by means of scanning and transmission electron microscopy measurements. The effect of the Si pattern geometry, substrate orientation, and crystal aspect ratio on the GaAs structural properties was investigated by means of high resolution X-ray diffraction. The thermal strain relaxation process of GaAs crystals with different aspect ratio is discussed within the framework of linear elasticity theory by Finite Element Method simulations based on realistic geometries extracted from cross-sectional scanning electron microscopy images.

Current Status of the Quality of 4H-SiC Substrates and Epilayers for Power Device Applications

ABSTRACTInterfacial dislocations (IDs) and half-loop arrays (HLAs) present in the epilayers of 4H-SiC crystal are known to have a deleterious effect on device performance. Synchrotron X-ray Topography studies carried out on n-type 4H-SiC offcut wafers before and after epitaxial growth show that in many cases BPD segments in the substrate are responsible for creating IDs and HLAs during CVD growth. This paper reviews the behaviors of BPDs in the substrate during the epitaxial growth in different cases: (1) screw-oriented BPD segments intersecting the surface replicate directly through the interface during the epitaxial growth and take part in stress relaxation process by creating IDs and HLAs (Matthews-Blakeslee model [1] ); (2) non-screw oriented BPD half loop intersecting the surface glides towards and replicates through the interface, while the intersection points convert to threading edge dislocations (TEDs) and pin the half loop, leaving straight screw segments in the epilayer and then create IDs and HLAs; (3) edge oriented short BPD segments well below the surface get dragged towards the interface during epitaxial growth, leaving two long screw segments in their wake, some of which replicate through the interface and create IDs and HLAs. The driving force for the BPDs to glide toward the interface is thermal stress and driving force for the relaxation process to occur is the lattice parameter difference at growth temperature which results from the doping concentration difference between the substrate and epilayer.

The effect of silicon doping on the transformation of amorphous calcium phosphate to silicon-substituted α-tricalcium phosphate by heat treatment

In the present study, the effects of silicon dopant contents on the phase composition of silicon-substituted hydroxyapatite (Si-HA) powders were investigated. Si-HA as-prepared samples, with varying silicon (Si) dopant contents, were prepared by an aqueous precipitation method. The phase transformation of the as-prepared samples during sintering was also discussed. The analyses of the as-prepared powders confirmed the formation of well-crystallized Si-HA at low Si dopant concentrations (≤1.5wt% Si). Contrarily, silicon-substituted amorphous calcium phosphate (Si-ACP) and amorphous silica formed at high Si dopant concentrations (>1.5wt% Si). Upon sintering at 1000°C, Si-HA (≤1.5wt% Si) underwent no phase transformations, whereas Si-ACP (>1.5wt% Si) transformed to biphasic silicon-substituted α-tricalcium phosphate (Si-α-TCP) and HA (no additional phases such as β-TCP, silicocarnotite or CaO were detected). Rietveld refinement on X-ray diffraction patterns was conducted to determine the percentage contents of ACP and differences of lattice parameters between pure α-TCP and Si-α-TCP. X-ray photoelectron spectroscopy measurements suggested the formation of amorphous silica and decomposition of the Si-ACP to Si-α-TCP were correlated. The results confirmed that Si doping led to formation of Si-ACP, which primarily transformed to Si-α-TCP upon sintering. The current study highlights a possible account of recrystallization of Si-ACP directly to Si-α-TCP at low sintering temperatures.

Theoretical investigation of the magnetic and structural transitions of Ni-Co-Mn-Sn metamagnetic shape-memory alloys

The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of Ni2-xCoxMn1.60Sn0.40 (0 <= x <= 0.50) are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temperature (T-C) are in agreement with the available experimental data. The martensitic phase transformation (MPT) occurs for x < 0.43, where the austenite is in the ferromagnetic (FM) state whereas the martensite is in the antiferromagnetic (AFM) one at 0 K. The x dependence of the lattice parameter, elastic modulus, and energy difference between the FM austenite and the AFM martensite well accounts for the decrease of the MPT temperature (TM) with the Co addition. With increasing x, the increase of the magnetic excitation energy between the paramagnetic and FM austenite of these alloys is in line with the T-C similar to x. The Ni 3d as well as the Co 3d electronic states near the Fermi level are confirmed mainly dominating the phase stability of the studied alloys.

Lattice Parameters of Hexagonal and Cubic Boron Nitrides at High Temperature and High Pressure

The lattice parameters of hBN and cBN at a range of the synthetic temperature and pressure (1200∼2100K, 4.0∼8.0GPa) were calculated using ab initio density-functional theory. Lattice parameters a of hBN and cBN calculated by theoretical methods, were in good agreements with the experimental results, with the maximum relative difference being 2.50% and 1.53%, respectively. Meanwhile, the maximum relative difference of lattice parameters c of hBN in theoretical method was 7.53%, which was also reasonably consistent with the experimental results. It was found that the lattice parameters of hBN and cBN increased slowly with temperature, but decreased rapidly with pressure.

Impact of dislocations and defects on the relaxation behavior of InGaN/GaN multiple quantum wells grown on Si and sapphire substrates

We investigated the relaxation behavior of InGaN/GaN blue multiple quantum wells (MQWs) grown on Si (111) and sapphire (0001) substrates to determine how the threading dislocation density (TDD) in the underlying GaN layer, the thickness of the MQWs, and the growth substrate (Si or sapphire) affect the relaxation behavior of MQWs. The results demonstrate that the value of the in‐plane lattice parameter difference between MQWs and GaN (IPLDMQWs–GaN) is strongly dependent on the TDD in the underlying GaN layer. The thickness of the InGaN well layer has the greatest effect on the IPLDMQWs–GaN value of the blue MQW structure: a thin InGaN well layer with high In content is more effective than a thick InGaN well layer with low In content for obtaining high‐quality blue MQWs without misfit dislocations (MDs). Furthermore, MQWs grown on Si are likely to contain MDs and unlikely to form V‐defects, whereas the opposite tendency is true of MQWs grown on sapphire. Using threading dislocations, MDs, and V‐defects, we propose relaxation mechanisms for MQWs grown on Si (111) and sapphire (0001) substrates.

Enhancement of Ferroelectrics: Strain-engineered Ferroelectric Thin Films

E nhancement of F erroelectrics : S train - engineered F erroelectric T hin F ilms Hongling Lu B S J In 1920, Joseph Valasek discovered that the polarization of the compound known as Rochelle Salt could be reversed by application of an external electric field. In effect, he was the first to recognize ferroelectric properties in a crystal. Ferroelectric materials are generally defined as those whose spountaneous polarization can be reversed through the application of an external electric field (Scott, 2007). (Fig. 1) Figure 1: Perovskite oxides, of general formula ABO3 with a pseudocubic structure, where A and B are two different cations, furnish many interesting ferroelectrics. The B-type cation is octahedrally coordinated with oxygen. In the example shown, BaTiO3, it is the relative symmetry breaking displacement of the Ti atoms with respect to the O atoms which is responsible for the spontaneous polarization. BaTiO3 has three ferroelectric phases: tetragonal, orthorhombic and rhombohedral. (Oxides. (n.d.). Strain engineering is a strategy employed in exploring the special behavior of ferroelectric materials where a strained layer of ferroelectric epitaxially grown with respect to the crystalline substrate layer.(Eom et al., 2008) (Fig. 2) Figure 2: Before deposition, the structure is in an (a) unstrained state. When deposited on a substrate the energetic preference of the deposited atoms to follow the underlying substrate (epitaxy) can result in the film beginning in either (b) biaxial compression or (c) biaxial tension (Schlom, Chen, Fennie, Gopalan, Muller, Pan, Uecker, 2014) This process creates a strained state. Under this strained state, the properties of the ferroelectric film differ greatly compared to the bulk ferroelectric, in a way that makes it suitable for use in applications such as memory storage on microchips. Before strain engineering, researchers used chemical alloying or doping to manipulate the properties of bulk ferroelectrics. A typical 0.1% strain--stretching of material to a length 0.1% “Strain engineering is a strategy employed in exploring the special behavior of ferroelectric materials where a strained layer of ferroelectric epitaxially grown with respect to the crystalline substrate layer.” At first, ferroelectric devices were restricted to bulk materials, but in the 1980s, thin-film, a technology utilizing extremely thin layers of material, was developed. The focus of ferroelectric study has since moved from bulk properties to its thin-film properties, especially with the promise of using ferroelectric materials in computer microchips, a type of thin- film technology. Ferroelectric materials with spontaneous polarization due to the special arrangement of atoms in a lattice structure exhibit interesting pyroelectric and piezoelectric properties and have, therefore, attracted a lot of scientific attentions. greater than the original length--will cause bulk ferroic oxides to crack. Epitaxial strain has the advantage of resulting in a more durable and ideally disorder-free film. Strain field is the electric field that results from a strained lattice structure, and in strain engineering, differences in lattice parameters between the epitaxial film and the underlying substrate are what create the strain of the overall thin-film material. Past decades have seen a rapid progress in algorithms and calculations for analyzing thin-film ferroelectrics. Some of the methods include first principles calculations(determining electronic structure by solving Schrodinger’s equation), 3 • B erkeley S cientific J ournal • S ymmetry • F all 2015 • V olume 20 • I ssue 1

X-ray Topography Studies of Relaxation during the Homo-Epitaxy of 4H-SiC

ABSTRACTA review is presented of Synchrotron X-ray Topography and KOH etching studies carried out on n type 4H-SiC offcut substrates before and after homo-epitaxial growth to study defect replication and strain relaxation processes and identify the nucleation sources of both interfacial dislocations (IDs) and half-loop arrays (HLAs) which are known to have a deleterious effect on device performance. We show that these types of defects can nucleate during epilayer growth from: (1) short segments of edge oriented basal plane dislocations (BPDs) in the substrate which are drawn by glide into the epilayer; and (2) segments of half loops of BPD that are attached to the substrate surface prior to growth which also glide into the epilayer. It is shown that the initial motion of the short edge oriented BPD segments that are drawn from the substrate into the epilayer is caused by thermal stress resulting from radial temperature gradients experienced by the wafer whilst in the epi-chamber. This same stress also causes the initial glide of the surface half-loop into the epilayer and through the advancing epilayer surface. These mobile BPD segments provide screw oriented segments that pierce the advancing epilayer surface that initially replicate as the crystal grows. Once critical thickness is reached, according to the Mathews-Blakeslee model [1], these screw segments glide sideways under the action of the mismatch stress leaving IDs and HLAs in their wake. The origin of the mismatch stress is shown to be associated with lattice parameter differences at the growth temperature, arising from the differences in doping concentration between substrate and epilayer.

Thermal expansion of CaIrO3 post-perovskite determined by time-of-flight measurements

The thermal evolution of the CaIrO3 post-perovskite structure has been determined by neutron powder diffraction (time-of-flight) measurements in a wide temperature range, from 1.8K to 550K. The linear expansion is similar to that found in previous x-ray diffraction studies, being αb > αc > αa,. However, the difference in relative lattice parameters is less pronounced in the present case, suggesting a more isotropic evolution under temperature. Other structural differences found at low and high temperatures through several X-ray and neutron diffraction studies have been also analysed.

Tibia bone properties at different time course of ovariectomized rats.

BackgroundThe model of bilaterally ovariectomized rats mimics the accelerated bone loss observed in postmenopausal women due to estrogen deficiency. Although calcium is main mineral in bone, previous study in human showed there is hypermineralization and higher calcium level in hydroxyapatite crystal structure from osteoporosis patients. This study was aimed to investigate the effect of time course ovariectomized on tibia bone turn over markers, mineral elements, hydroxyapatite crystale, mesostructure, and histomorphometry.MethodsA total of 30 Wistar female rats were randomly assigned into three groups (n = 10 each): control group, ovariectomy group follow up for one month and two month. All animals procedures was according to Animal Ethics Guidelines and approval by ethic committee of the Medical Faculty, Lambung Mangkurat University which obtained prior the study. Expression of osteocalcin (OC) and C-telopeptyde collagen type I (CTX) was analyzed by ELISA method. Tibia bone mineral element was measured using X-Ray Fluorescence. Hydroxyapatite crystale structure was analyzed using X-Ray Diffracttion. Mesostructure was determined using Scanning Electron Microscope. Histomorphometry was analyzed using BoneJ software analyzer. ANOVA test was used to analyze the different level of serum bone turnover markers and bone mineral elements.ResultsSerum OC and CTX were significantly decrease in one month and two month after ovariectomized groups compared to sham-operated group (P < 0.05). The levels Ca, P, Fe, Cu, Zn, Ni, Ca/P, and Cu/Zn were not significantly different in all groups (P > 0.05). The structure of hydroxyapatite crystal in one month and two month after ovariectomized groups were different compared with sham-operated control group. Mesostructure of tibia bone after one and two month ovariectomized procedure significantly different than that in sham-operated rats. The level of trabecular volume were lower significantly on OVX-1 and OVX-2 groups compared with sham group (P < 0.05). The trabecular thickness and spacing were increase significantly on OVX-1 and OVX-2 groups compared with sham group (P < 0.05). The trabecular number were significantly decrease OVX-1 and OVX-2 groups than that sham group (P < 0.05).ConclusionWe found that two month after ovariectomized decrease serum osteocalcin but not change bone mineral elements in rats. Also, we found the difference of lattice parameter of hydroxyapatite crystale structure and trabecular properties which determined bone mesostructure.

Affect of Interactions between FM/AFM in La&lt;sub&gt;5/8&lt;/sub&gt;Ca&lt;sub&gt;3/8&lt;/sub&gt;Mn&lt;sub&gt;1-&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Co&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt; System on the Magnetic Properties

This paper studies changes in the relationship between magnetic properties of La5/8Ca3/8Mn1-xCoxO3 (x≤0.3) system and temperature and magnetic field. By the lattice structure of the sample when x=0.3 varies with temperature analysis that, related changes of lattice structure also occurred in the magnetic transition region. The difference of lattice parameter is increased, orthogonal O' phase substitute orthogonal O. We speculate that spin-state transitions may be appear in this interval. At low temperature of x=0.3 sample, the behavior of AFM sample should coexist with the CG, eg itinerant electron reduce, resistance increase and drastically reduce conductivity.

Development of Lithium Iron Phosphate Cathode Materialfor Super Long Life Lithium-Ion Battery

Introduction LiFePO4 (LFP) is a well known, low cost and a safe lithium ion cathode material. The charge and discharge process in LFP proceeds viatwo-phase reactions. This process produces particles in which two phases coexist with different lattice parameters. For phases which exhibit a large difference in lattice parameters, large stresses will occur in the interface plane between the phases.In the case of LFP, the volume change during charge and discharge is 7% and the difference of the interface plane (mismatch of bc plane) is 1.5%. These values are larger than other cathode materials and this causes micro-cracks inside the particles during the repeated charge and discharge process.In order to solve this problem, we have used first principles calculations to investigate the effect of various substitute elements into different atomic positions within LFP. These calculations indicate that certain compositions reduce the volume change and the mismatch of interface. Experiment Several compositions with a variety of substitutions onto the Li site, Fe site, the P site are calculated. The composition in which P was substituted by Si and Fe was substituted by Zr was the most promising optimal composition, Li (Fe1-xZrx) (P1-2xSi2x) O4. The calculated volume change ratio of this material was 3.2% at x = 0.125, which shows a very small value compared to 7% of the un-substituted LFP.Samples were synthesized by the following sol-gel method. First, iron nitrate (Fe (NO3) 3.6 H2O) was solved into alcohol, and then lithium acetate (LiCH3COO · 2H2O) was add to this solution. After lithium acetate are completely solved, then Zr and Si source was add to this solution. TEOS was used for Si source, and ZrCl4 was used for Zr source. After that, phosphoric acid (H3PO4) was added to this solution. After the adding of propylene oxide (PO), solution changes to solid gel immediately. The obtained gel was allowed to promote gelation by heating for 24 hours at 60 deg in a closed container. The obtained the dried gel was ground in a mortar, and calcined at 550 deg. under a nitrogen atmosphere. Results and discussion Structural analysis from x-ray diffraction data and subsequent Rietveld refinements show that the substituted materials were single phase with no impurities. The maximum substitution of Zr in Fe was found to be 12.5%.From the X-ray diffraction pattern of the sample after full-charging, the lattice constant was calculated. The variation of the volume change ratio and mismatch of bc plane for various substitution was shown in Fig.1. The volume change ratio was 6.5 % for the un-substituted LFP. The volume change ratio decrease with substitution, the volume change ratio of 3.7 % was achieved in 12.5% substituted samples. In addition, the bc plane ratio was also decrease with substitution, and reduced to about 0.4% in the replacement of 12.5%.Fig. 2 shows the cycle performance of two pouch cells that comprise of 1. A substituted LFP cathode / graphite anode and 2. An un-substituted LFP / graphite anode. For the un-substituted cathode cell, the capacity decreases with cycling. For the substituted LFP cell, the capacity degradation was only 15% after 10,000 cycles. These results show that the substituted cathode that has a low volume change during charge and discharge and this enhances the cell cycle life remarkably.

Iron isotope effect in the iron arsenide superconductor (Ca0.4Na0.6)Fe2As2

We report a new sample synthesis technique for polycrystalline (Ca1−xNax)Fe2As2 (0<x≤0.6) and measurements of an iron isotope effect in optimally doped (Ca0.4Na0.6)Fe2As2 with three types of iron isotopes (54Fe, natural Fe, and 57Fe). We synthesized isotope samples carefully not to give rise to a difference in the Na content x between different isotope samples, which becomes potentially a factor for an extrinsic difference in the superconducting transition temperature Tc between those samples. No significant difference in lattice parameters between those samples is shown by measurements of powder x-ray diffraction (XRD), implying that the Na content in samples is well-controlled. Our estimate of the iron isotope coefficient αFe defined by -d InTc/d lnMFe, where MFe is the iron isotope mass, is -0.19. These indicate that in (Ca0.4Na0.6)Fe2As2, the iron isotope coefficient becomes definitely negative. We discuss the implications of this fact, considering previous measurements of an iron isotope effect in different iron-based superconductors.

L-asparagine crystals with wide gap semiconductor features: Optical absorption measurements and density functional theory computations

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.