C-axis Lattice Parameter Research Articles

Bismuth chalcogenide topological insulators crystals grown by the optical floating zone technique

In this paper, two procedures for the growth of both binary and ternary single crystals of bismuth chalcogenides by optical floating zone technique are described. Detailed characterization has been carried out on a series of samples, i.e. Bi2SexTe3-x, with x = 0 and 0.9, and Bi2-xSbxSe3, with x = 0 and 0.15, to isolate high quality single crystals, essential for an accurate study of the physical properties of the materials. Systematic compositional and structural analysis on the samples grown by the two different procedures have been compared to infer the optimal growth parameters to obtain the largest possible single crystals. The c-axis lattice parameter of Bi1.85Sb0.15Se3 is reported here for the first time.

Suppression of superconductivity by Sb-substitution into CeOBiS2 single crystals

Sb-substituted CeOBiS2 single crystals with 0.2–1.0 mm size have been successfully grown using CsCl/KCl flux. Sb substitution strongly suppressed the superconductivity in CeOBiS2, and the substitution of more than approximately 4 at% in Bi-site disappeared the superconductivity at a measurement range of above 0.36 K. Furthermore, the drastic change of c-axis lattice parameter was observed in a neighborhood to Sb substitution amount, which maybe suggests the structural transition in CeOBiS2. The Ce valence state of the obtained single crystals was evaluated. However, the established correlations between Ce valence state and superconductivity could not be revealed.

A Kinetic Indicator of Ultrafast Nickel-Rich Layered Oxide Cathodes

Elucidating high-rate cycling-induced nonequilibrium electrode reactions is crucial for developing extreme fast charging (XFC) batteries. Herein, we unveiled the distinct rate capabilities of a series of Ni-rich layered oxide (NRLO) cathodes by quantitatively establishing their dynamic structure–kinetics relationships. Contrary to conventional views, we discovered electrode kinetic properties obtained ex-situ near equilibrium states failed to assess the effective rate capability of NRLOs at ultrafast C rates. Further, the kinetic phase heterogeneity, characterized by the dynamic separations in in-situ X-ray diffraction patterns and deviations in NRLO c-axis lattice parameters, exclusively correlated with the capacity reduction under XFC and became an effective indicator of the NRLO rate capability. Enhancing the cycling temperature boosted the rate capability of studied NRLOs by ∼10%, which was further verified to mitigate the kinetic phase heterogeneity during XFC. Overall, this study lays the groundwork for tuning the kinetic phase heterogeneity of electrodes to develop ultrafast batteries.

Preparation (HgBa2Ca2Cu2.85La0.15O8+δ) compound and Study of the impact of partial substitution of mercury with (In2O3)on the structural characteristics

In the current work, we focused on the impact of Indium oxide partial substitution at the (Hg) site on the structural characteristics of the (HgBa2Ca2Cu2.85La0.15O8+δ) compound with (0,0.05,0.1,0.15,0.2 and 0.25). Samples were prepared by the (SSR) method. The combined powder was crushed with a pressure of 7 tons per square centimeter to create a disc with a thickness of (0.2 cm) and a diameter of (1.5 cm). The samples sintered for 24 hours at a rate that was changed from ambient temperature to 820 °C. For the samples which were doped with (In=0.05) in comparison to other samples, the highest value of the c-axis lattice parameter and a pseudo-tetragonal structure were discovered using (XRD) analysis. It was discovered that altering the In concentrations in all of the results of our sample changes the volume fraction VPh(1223), mass density dm, and c/a. It was also determined that the change in lattice parameters, degree of crystallinity, crystal size, and strain (in different ways) resulted from a change in the indium oxide concentrations for all samples.

Effect of Residual Oxygen Concentration on the Lattice Parameters of Aluminum Nitride Powder Prepared via Carbothermal Reduction Nitridation Reaction.

Residual oxygen in wurtzite-type aluminum nitride (AlN) crystal, which significantly affects phonon transport and crystal growth, is crucial to thermal conductivity and the crystal quality of AlN ceramics. In this study, the effect of residual oxygen on the lattice of AlN was examined for as-synthesized and sintered samples. By controlling reaction time in the carbothermal reduction nitridation (CRN) procedure, AlN powder was successfully synthesized, and the amount of residual oxygen was systematically controlled. The evolution of lattice parameters of AlN with respect to oxygen conc. was carefully investigated via X-ray diffraction analysis. With increasing amounts of residual oxygen in the as-synthesized AlN, lattice expansion in the ab plane was induced without a significant change in the c-axis lattice parameter. The lattice expansion in the ab plane owing to the residual oxygen was also confirmed with high-resolution transmission electron microscopy, in contrast to the invariant lattice parameter of the sintered AlN phase. Micro-strain values from XRD peak broadening confirm that stress, induced by residual oxygen, expands the AlN lattice. In this work, the lattice expansion of AlN with increasing residual oxygen was elucidated via X-ray diffraction and HR-TEM, which is useful to estimate and control the lattice oxygen in AlN ceramics.

Magneto-Elastic Coupling in a Sinusoidal Modulated Magnet Cr2GaN

We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr2GaN. A magnetic phase transition is identified at T ≈ 170 K, whereas no trace of structural transition is observed down to 6 K. Combining Rietveld refinement with irreducible representations, the spin configuration of Cr ions in Cr2GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector k = (0.365, 0.365, 0). Upon warming up to the paramagnetic state, the magnetic order parameter closely resembles to the temperature dependence of c-axis lattice parameter, suggesting strong magneto-elastic coupling in this compound. Therefore, Cr2GaN provides a potential platform for exploration of magnetically tuned properties such as magnetoelectric, magnetostrictive and magnetocaloric effects, as well as their applications.

Growth and characterization of Bi2Sr2Ca1–x Y x Cu2O8+δ single-crystal whiskers

Substitution of Y for Ca in the Bi2Sr2CaCu2O8+δ (Bi-2212) system is known to effectively change the hole carrier density. In this paper, we report the growth and characterization of Y-substituted Bi-2212 whisker crystals. The evaluated Y content in the whiskers increased as we increased the nominal Y-ratio in the Bi–Sr–Ca–Y–Cu–Te precursor. The X-ray diffraction patterns of whiskers aligned on a glass plate only showed (00l) Bragg peaks of the Bi-2212 phase, indicating that the grown whiskers are single crystalline. The c-axis lattice parameter showed a monotonic decrease with Y-substitution. The resistivity of Y-substituted whiskers showed a systematic decrease in superconducting transition temperature and an increase in normal resistivity, suggesting that the hole carrier density was controlled via Y-substitution. Based on these results, we propose that Bi-2212 with various carrier concentrations can be easily obtained by growing Y-substituted whiskers. Furthermore, such whiskers with controlled T c might be useful for microelectronic applications such as terahertz oscillators.

Effects of phosphorus doping on the physical properties of axion insulator candidate EuIn2As2

We report an investigation on the single crystal growth, magnetic and transport properties of EuIn2(As1−x P x )2 (0 ≤ x ≤ 1). The physical properties of axion insulator candidate EuIn2As2 can be effectively tuned by P-doping. With increasing x, the c-axis lattice parameter decreases linearly, the magnetic transition temperature gradually increases and ferromagnetic interactions are enhanced. This is similar to the previously reported high pressure effect on EuIn2As2. For x = 0.40, a spin glass state at T g = 10 K emerges together with the observations of a butter-fly shaped magnetic hysteresis and slow magnetic behavior. Besides, magnetic transition has great influence on the charge carriers in this system and negative colossal magnetoresistance is observed for all P-doped samples. Our findings suggest that EuIn2(As1−x P x )2 is a promising material playground for exploring novel topological states.

Effects of Sn substitution in SrRuO3 epitaxial films

Epitaxial SrRu1−xSnxO3 (0 ≤ x ≤ 1) thin films were deposited on SrTiO3 (001) substrates by sequential two-target synthesis using pulsed laser deposition to achieve stable phases in this family of quaternary perovskites. The SrRu1−xSnxO3 films exhibit a good crystalline quality, a sharp interface between film and substrate, and an atomically smooth surface. A gradual expansion of the c-axis lattice parameter was observed with Sn doping serving as a means to tune chemical pressure and magnetism. With an increase in Sn doping, the resistivity of the film increased, and the ferromagnetism decreased. These results illustrate use of lattice engineering, e.g., tuning of c-axis lattice parameter with chemical doping, to control electronic and magnetic properties of epitaxial thin films for applications in oxide electronics.

Reduced coercive field in epitaxial thin film of ferroelectric wurtzite Al0.7Sc0.3N

Epitaxial ferroelectric wurtzite films exhibiting clear polarization-electric field hysteresis behavior are presented. The coercive field of this epitaxial Al0.7Sc0.3N film on the W/c-sapphire substrate is 0.4 ± 0.3 MV cm−1 (8%) smaller than that of a conventional fiber textured film on a Pt/TiOx/SiO2/Si substrate, attributed to the 0.01 ± 0.007 Å smaller c-axis lattice parameter in the epitaxial film. The strain and decrease in the coercive field most likely originate from epitaxial strain rather than the mismatch in the thermal coefficient of expansion. These results provide insight for further coercive field reduction of wurtzite ferroelectrics using epitaxial mismatch strain.

Nominal Effect of Mg Intercalation on the Superconducting Properties of 2H-NbSe2.

2H-NbSe2 is a phonon-mediated, Fermi-surface topology-dependent multiband superconductor with an incommensurate charge-density wave (CDW) that coexists at a local level with superconductivity. Usually, the intercalation in 2H-NbSe2 enriches the CDW, enhances the c-axis lattice parameter, and distorts the Fermi surface, which result in a decrease in the superconducting transition temperature (Tc). The rate of decrease of Tc depends on the electronic structure, size, valence, magnetic nature, and electronegativity of the intercalating species. Herein, we report an unusual effect of Mg intercalation on the superconductivity of 2H-MgxNbSe2 (x = 0.0, 0.02, 0.06, 0.08, 0.10, and 0.12) synthesized by a high-temperature solid-state reaction method. Unlike other s- and p-block elements/species as intercalants (Rb, Sn, Ga, and Al) that have a sharp detrimental effect on the Tc of 2H-NbSe2 within 1-5% of intercalation, Mg is found to be an exception. Upon Mg intercalation up to x = 0.06, no remarkable changes in Tc as compared to the parent 2H-NbSe2 (Tc ∼ 6.7 K) are observed, and further intercalation results in a small decrease in Tc (for x = 0.12, Tc = 6.2 K). From heat-capacity measurements, it is inferred that superconducting Mg-intercalated 2H-NbSe2 exhibits strong electron-phonon coupling. Electronic structure calculations on two s-block element intercalated compounds of formula M0.125NbSe2 (M = Mg, Rb) show that Rb s-, p-, and d-states completely overlap with the Nb d states, while the Mg s states lie in a low-energy region as compared to Nb d states, indicating a weak interaction between the intercalant and the Nb sublattice in Mg0.125NbSe2 as compared to Rb0.125NbSe2. These results suggest that the electronic states of the Nb network in 2H-NbSe2 are least altered with Mg intercalation, which could be one of the reasons for the minimal effect on the Tc with intercalation.

Growth of High-Performance 4-5μm Thick Film REBCO Tapes Doped With Hafnium Using Advanced MOCVD

Advanced metal organic chemical vapor deposition technique (A-MOCVD) was used to grow 4-5 μm thick REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (REBCO, RE = rare earth) films, doped with 5% and 15% Hf. Thick REBCO films doped with 5% Hf exhibit self-field critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) over 1.8 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K and 3 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 65 K, 1.5 T. Increasing the Hf content to 15% resulted in J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> above 9 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 20 K, 9 T. The effect of (Ba+Hf)/Cu content in Hf-added (5 and 15 mol.%) REBCO films on the critical current density at 77 K, 0 T, c-axis lattice parameter and out-of- plane texture has been studied. In addition to growth of thick film REBCO tapes with superior performance, the A-MOCVD reactor has been used to quadruple the precursor-to-film conversion efficiency above 45%. This achievement has a first order impact in lowering the cost of REBCO tapes made by A-MOCVD.

Effect of Magnesium Doping to Reduce the Charge Reservoir Layer in Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) Superconductors

The charge reservoir layer plays a crucial role in the charge transfer mechanism in high-temperature superconductors. The effect of reducing the thickness of the Cu0.5Tl0.5Ba2O4−δ charge reservoir by replacing Ba with Mg atom in Cu0.5Tl0.5-1223 crystal has been studied. Cu0.5Tl0.5(Ba2−xMgx)Ca2Cu3Oy (x = 0, 0.15, 0.25, 0.35) superconductor samples were synthesized by a two-step solid-state reaction method. The as-grown samples showed orthorhombic crystal structure in which the c-axis lattice parameter and unit cell volume were systematically suppressed with increasing incorporation of Mg into the final compound, thereby resulting in suppression of the charge reservoir. The room-temperature resistivity increased with the Mg doping content, while the Tc and Tc-onset values decreased according to both resistivity and alternating-current (AC) susceptibility measurements. Fourier-transform infrared (FTIR) absorption measurements revealed three phonon modes related to vibrations of Tl–OA–Cu(2), Cu(1)–OA–Cu(2), and CuO2 planar oxygen atoms at around 420 cm−1, 480 cm−1 to 540 cm−1, and 580 cm−1, respectively. The apical oxygen mode of Tl–OA–Cu(2) type was hardened whereas the position of the latter two modes remained unchanged with increasing Mg doping in the final compound. Excess conductivity analyses showed a significant decrease in the onset temperature for Cooper pair formation (T*2D−SW). The coherence along the c-axis ξc(0), the interlayer coupling J, and the Fermi velocity vF of superconducting carriers increased with increasing Mg doping at Ba sites. These result suggest that the transfer mechanism of charge carriers from the Cu0.5Tl0.5Ba2O4−δ charge reservoir layer to the conducting CuO2 planes became more efficient, as evidenced by the increased coherence length ξc(0) and Fermi velocity vF of the carriers. However, the suppression of parameters such as Bc0(T), Bc1(T), Jc0(0), and τφ indicates that the density of pinning centers was suppressed with increasing Mg doping in the final compound.

Matching conflicting oxidation conditions and strain accommodation in perovskite epitaxial thin-film ferroelectric varactors

Perovskite oxide materials of the general chemical formula ABO3 are a rich playground for epitaxial stacks of different functional layers for novel device applications. In the example of a tunable metal–insulator–metal ferroelectric varactor (tunable capacitor) made from the highest conducting perovskite SrMoO3 as an electrode and the tunable dielectric Ba0.5Sr0.5TiO3 (BST), we show how the extremely conflicting oxidation potentials can be conciliated in a fully functional heterostructure. Controlling the growth kinetics by the substrate temperature, oxygen pressure, and oxidation time, the formation of the non-conducting Mo6+ states can be effectively suppressed and the BST cation stoichiometry can be tuned. The cumulative impact of the cation nonstoichiometry, epitaxial strain, and oxygen deficiency in the BST films leads to the expansion of their c-axis lattice parameter via the formation of point defects. The dielectric permittivity of 440, the high tunability of 3.5, and the quality factor of 50 are achieved for the varactors at the frequency of 1 GHz. It turns out that the varactor performance is anti-correlated to the tetragonal lattice distortion of BST, which itself is interrelated to the oxidation conditions. The mechanism of the leakage current through oxygen deficient BST layers of the varactors is analyzed within the combined scenarios of the space-charge limited current and Poole–Frenkel field-assisted emission from traps. The achieved high capacitance per unit area of 0.04 pF/μm2 and moderate leakage currents of 0.025 μA/pF make these varactors suitable for applications in microwave microelectronic devices.

Investigating the Formation of MoSe2 and TiSe2 Films from Artificially Layered Precursors.

The reaction of ultrathin layers of Mo and Ti with Se was investigated, and significantly different reaction pathways were found. However, in both systems postdeposition annealing results in smooth dichalcogenide films with specific thicknesses determined by the precursor. X-ray diffraction (XRD) patterns of as-deposited Mo|Se films around a 1:2 ratio of Mo to Se contain weak, broad reflections from small and isolated MoSe2 crystallites that nucleated during deposition and a sharper intensity maximum resulting from the composition modulation created from the alternating deposition of Mo and Se layers. In contrast, as-deposited Ti|Se films around a 1:2 ratio of Ti to Se contain narrow and intense 00l reflections from TiSe2 crystallites and do not contain a Bragg reflection from the sequence of deposited Ti|Se layers. The as-deposited TiSe2 crystallites have a larger c-axis lattice parameter than was previously reported for TiSe2, however, which suggests a poor vertical interlayer registry and/or high defect densities including interstitial atoms. In-plane XRD patterns show the nucleation of both TiSe2 and Ti2Se during deposition, with the Ti2Se at the substrate. For both systems, annealing the precursors decreases the peak width and increases the intensity of reflections from crystalline TiSe2 and MoSe2. Optimized films consist of a single phase after the annealing and show clear Laue oscillations in the specular XRD patterns, which can only occur if a majority of the diffracting crystallites in the film consist of the same number of unit cells. The highest quality films was obtained when an excess of ∼10% Se was deposited in the precursor, which presumably acts as a flux to facilitate diffusion of metal atoms to crystallite growth fronts and compensates for Se loss to the open system during annealing.

Effects of 800 MeV Xe Irradiation on 2H-NbSe2 Single Crystals

Effects of artificial defects on 2H-NbSe2 single crystals introduced by 800 MeV Xe irradiation with a dose equivalent matching field B Φ up to 8 T were studied. The bulk magnetization measurements performed by a commercial SQUID magnetometer reveal strong enhancement of critical current density in NbSe2 after introducing defects by 800 MeV Xe irradiation. T c is found to be robust against the 800 MeV Xe irradiation, while c-axis lattice parameter shows an obvious increase with increasing B Φ.

Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa2Cu3O7 Films.

Epitaxial films of high critical temperature () cuprate superconductors preserve their transport properties even when their thickness is reduced to a few nanometers. However, when approaching the single crystalline unit cell (u.c.) of thickness, decreases and eventually, superconductivity is lost. Strain originating from the mismatch with the substrate, electronic reconstruction at the interface and alteration of the chemical composition and of doping can be the cause of such changes. Here, we use resonant inelastic x-ray scattering at the Cu edge to study the crystal field and spin excitations of NdBaCuO ultrathin films grown on SrTiO, comparing 1, 2 and 80 u.c.-thick samples. We find that even at extremely low thicknesses, the strength of the in-plane superexchange interaction is mostly preserved, with just a slight decrease in the 1 u.c. with respect to the 80 u.c.-thick sample. We also observe spectroscopic signatures for a decrease of the hole-doping at low thickness, consistent with the expansion of the c-axis lattice parameter and oxygen deficiency in the chains of the first unit cell, determined by high-resolution transmission microscopy and x-ray diffraction.

Pulsed laser deposited transparent and conductive V-doped ZnO thin films

ZnO and vanadium-doped ZnO (0.7–4.1 at.%) thin films were deposited onto corning glass substrates by the pulsed laser deposition technique using a KrF excimer laser (λ = 248 nm). The films were deposited at 500 °C under an oxygen pressure of 1 Pa with a laser fluence of 2 J/cm2. The structural, morphological, optical and electrical properties as a function of the dopant atomic concentration were investigated by means of X-ray diffraction, Scanning Electron Microscopy, spectrophotometry, conductivity and Hall measurements. All the doped and undoped films show a preferential orientation along the c-axis with a deterioration at higher doping levels (>4 at. %). Besides, as the doping amount increases the in-plane stress leads to an increase of the c-axis lattice parameter. The films are transparent within the wavelength range 400–1200 nm. The electrical resistivity of the films drops from 8.2 10−3 to 1.3 10−3 Ω cm with an increase in the dopant concentration up to 0.9 at. % and then rises as the dopant level is increased further.

Possible lattice and charge order in CuxBi2Te2Se

Metal intercalation into layered topological insulator materials such as the binary chalcogenide Bi2X3 (X = Te or Se) has yielded novel two-dimensional (2D) electron-gas physics, phase transitions to superconductivity, as well as interesting magnetic ground states. Of recent interest is the intercalation-driven interplay between lattice distortions, density wave ordering, and the emergence of new phenomena in the vicinity of instabilities induced by intercalation. Here, we examine the effects of Cu-intercalation on the ternary chalcogenide Bi2Te2Se. We report the discovery, in Cu0.3Bi2Te2Se, of a periodic lattice distortion (PLD) at room temperature, together with a charge density wave (CDW) transition around Td = 220 K. We also report, for the first time, a complete study of the CuxBi2Te2Se system, and the effect of Cu-intercalation on crystal structure, phonon structure, and electronic properties for 0.0 ≤ x ≤ 0.5. Our electron diffraction studies reveal strong Bragg spots at reciprocal lattice positions forbidden by ABC stacking, possibly resulting from stacking faults, or a superlattice. The c-axis lattice parameter varies monotonically with x for 0 < x < 0.2, but drops precipitously for higher x. Similarly, Raman phonon modes and soften monotonically for 0 < x < 0.2 but harden sharply for x > 0.2. This indicates that Cu likely intercalates up to x ∼ 0.2, followed by partial site-substitutions at higher values. The resulting strain makes the 0.2 ≤ x ≤ 0.3 region susceptible to instabilities and distortions. Our results point toward the presence of an incommensurate CDW above Td = 220 K. This work strengthens prevalent thought that intercalation contributes significantly to instabilities in the lattice and charge degrees of freedom in layered chalcogenides. Further work is required to uncover additional density wave transitions, and possible ground states such as superconductivity.

Aluminum Ion Implantation in MgB2 Thin Films

Superconducting magnesium diboride is a possible candidate for replacing Nb in superconducting radio frequency (SRF) cavities because of its higher T c and potentially higher breakdown field. However, the existence of two energy gaps, the σ gap at 7.2 eV and the π gap at 2.2 eV, could impact the RF properties of MgB 2 . It has been shown that chemical doping and disorder can increase the interband scattering, thus modifying the two gaps. In this work, we performed Al ion implantation in MgB 2 thin films to introduce Al doping in the films. The Al ion implanted films showed decreases in transition temperature, from 40.4 K in the pristine films to non-superconducting above the dose of 2 × 10 14 atoms/cm 2 . An expansion in the c-axis lattice parameter with increasing dose was also observed. These results suggest that the degradation of superconductivity in the Al ion implanted films is mainly due to the ion beam damage rather than Al doping.