Polycrystalline Samples Research Articles

Impact of carbon nanotubes on superconducting properties and ferromagnetism of indium-doped Bi-2212 superconductors: Critical current density enhancement

Carbon nanotubes (CNTs) was incorporated as artificial flux pinning centers within the In-Bi-2212 HTSC matrix. The research focused on polycrystalline samples with the composition (Bi1.8Pb0.2Sr1.9In0.1CaCu2O8)1-x/(CNT)x, where x varied from 0 to 0.01. XRD was employed to analyse phase formation, and lattice parameters. Magnetic measurements provided insights into the diamagnetic behaviour and highest obtained onset temperatures was (Tc = 77K) for x = 0 sample. the magnetic interactions examinations between the CNT additives and the superconducting matrix at 20 K was explored the relationships between microstructure, BSCCO phase content, magnetic hysteresis loops, calculated critical current densities, and flux densities across the samples. The experimental and theoretical results indicate that CNT incorporation significantly influences the superconducting properties of In-doped-Bi-2212, particularly its flux densities and pinning mechanisms. However, the study emphasizes the importance of carefully controlling CNT nanoparticle additions to optimize the balance between microstructural features and superconducting parameters in BSCCO HTSCs.

Sampling volumes in powder diffraction experiments

We present a simple analytical formalism based on the Lorentz-Scherrer equation and Bernoulli statistics for estimating the fraction of crystallites (and the associated uncertainty parameters) contributing to all finite Bragg peaks of a typical powder pattern obtained from a static polycrystalline sample. We test and validate this formalism using numerical simulations, and show that they can be applied to experiments using monochromatic or polychromatic (pink-beam) radiation. Our results show that enhancing the sampling efficiency of a given powder diffraction experiment for such samples requires optimizing the sum of the multiplicities of reflections included in the pattern along with the wavelength used in acquiring the pattern. Utilizing these equations in planning powder diffraction experiments for sampling efficiency is also discussed.

Structural, Magnetic, and Transport Properties of Ti(Fe,Re)2Sn Heusler Alloys

This study investigates polycrystalline samples of TiFe2−xRexSn (with x = {0, 0.02, 0.04, 0.06, 0.2}) synthesized using conventional arc-melting and spark plasma sintering. Structural and morphological analysis shows that low Re substitutions result in good phase purity with minor traces of secondary phases, while higher Re content leads to the segregation of additional phases. The magnetism and electrical resistivity of the samples are affected by inherent Fe–Ti atomic disorder, with the effects of secondary phases becoming more prominent in the samples with higher Re content. The Seebeck coefficient values increase only for TiFe1.98Re0.02Sn, while the power factor increases for x = {0, 0.02, 0.04}, reaching maximal values for x = 0.02 at ~ 300 K and x = 0.04 at ~ 325 K, i.e., (2.22 ± 0.2) × 10−4 Wm−1 K−2. The thermal conductivity of the samples increases with x, resulting in modest values of the figure of merit, with the maximum achieved for x = 0.02 at 325 K, i.e., 0.015 ± 0.002.

Atomic structure of different surface terminations of polycrystalline ZnPd

The intermetallic compound ZnPd has been found to have desirable characteristics as a catalyst for the steam reforming of methanol. The understanding of the surface structure of ZnPd is important to optimize its catalytic behavior. However, due to the lack of bulk single-crystal samples and the complexity of characterizing surface properties in the available polycrystalline samples using common experimental techniques, all previous surface science studies of this compound have been performed on surface alloy samples formed through thin-film deposition. In this study, we present findings on the chemical and atomic structure of the surfaces of bulk polycrystalline ZnPd studied by a variety of complementary experimental techniques, including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM), and microspot low-energy electron diffraction (μ-LEED). These experimental techniques, combined with density functional theory (DFT)-based thermodynamic calculations of surface free energy and detachment kinetics at the step edges, confirm that surfaces terminated by atomic layers composed of both Zn and Pd atoms are more stable than those terminated by only Zn or Pd layers. DFT calculations also demonstrate that the primary contribution to the tunneling current arises from Pd atoms, in agreement with the STM results. The formation of intermetallics at surfaces may contribute to the superior catalyst properties of ZnPd over Zn or Pd elemental counterparts. Published by the American Physical Society 2024

Single-crystal elastic moduli, anisotropy, and the B1–B2 phase transition of NaCl at high pressures

Pressure dependences of the highest and lowest possible longitudinal sound velocities in single crystals of the B1 and B2 phases of NaCl were extracted from examination of their polycrystalline samples using the technique of time-domain Brillouin scattering. Based on the data collected up to 41 GPa, we largely extended the pressure range where single-crystal elastic moduli, Cij(P), and elastic anisotropy of the two cubic phases are measured, especially the experimental data for the B2 phase formed upon the reconstructive phase transition. The B1 phase of NaCl exhibits strong and growing anisotropy with increasing pressure, while that of the B2 phase is much weaker. Comparing with the previous experimental Cij(P) of other compounds exhibiting or expected to exhibit the B1–B2 phase transition, such as CaO, MgO, and (Mg1−x, Fex)O, we concluded that the transition is initiated by the shear instability due to violation of the Born stability criterion [C44(P)–P] > 0 and predicted the presently-not-verified transition pressures for MgO and (Mg1−x, Fex)O.

Analysis of Thermoelectric Properties of Hot-deformed Bismuth Telluride Sintered Materials

Bismuth telluride (Bi2Te3)-based alloys are widely used for thermoelectric cooling and power generation at low temperatures, and they are the only commercially available materials for thermoelectric applications below 500 K. The rhombohedral unit cell with a large c/a lattice constant ratio consisting of - Te-Bi-Te-Bi-Te- stacked layers inevitably brings about a large anisotropy in transport properties, which is why texturing is very important in polycrystalline Bi2Te3</sub alloys for maximum performance. In this report, p and n-type polycrystalline Bi2Te3</sub alloys were synthesized and hot-deformed to investigate the effects of texturing on thermoelectric properties. Hot deformation (HD) induces the strong alignment of (001) orientations along the compression direction, and a remarkable increase in the orientation factor F of (001) orientations is observed after HD in both p and n-type materials. All of the hot-deformed polycrystalline samples showed increased electrical conductivity (σ), power factor (PF), and thermal conductivity (k) in the in-plane (IP) direction, and vice versa in the out-of-plane (OOP) direction, which makes the IP direction of the hot-deformed bodies more favorable for module fabrication in terms of power factor, for both p and n-type Bi2Te3</sub-based alloys. However, due to the different degree of anisotropy of k and σ, the figures of merit (zT) were maximized in the OOP direction in the p-type materials after HD, whereas the zTs of the n-type materials were higher in the IP direction. This occurs because the anisotropy factor of electron conduction is higher than that of hole conduction, which more than offsets the advantage of the smaller k in the c-direction of n-type Bi2Te3</sub. The maximum zT of 1.33 (OOP) and 0.90 (IP) were obtained after HD from the p and n-type Bi2Te3 alloys, respectively, which were 9.3% and 18.4% higher than those of as-sintered materials.

Bulk high-temperature superconductivity in pressurized tetragonal La2PrNi2O7.

The Ruddlesden-Popper (R-P) bilayer nickelate, La3Ni2O7, was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa (ref. 1). Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions2-4. Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction2,4,5. The presence of a new 1313 polymorph and competing R-P phases obscured proper identification of the phase for HTSC6-9. Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La2PrNi2O7 polycrystalline samples. We find that substitutions of Pr for La effectively inhibit the intergrowth of different R-P phases, resulting in a nearly pure bilayer structure. For La2PrNi2O7, pressure-induced orthorhombic to tetragonal structural transition takes place at Pc ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18-20 GPa reach and , which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates.

Temperature-dependent diffraction studies on the stannides Sr3Rh4Sn4, Sr3Ir4Sn4 and Sr2.43Eu0.57Ir4Sn4

Abstract The stannides Sr3Rh4Sn4 and Sr2.43Eu0.57Ir4Sn4 (Na3Pt4Ge4-type, space group I 4 ‾ $\overline{4}$ 3m) were synthesized by induction-melting of the elements in sealed tantalum tubes followed by an annealing sequence to increase the crystallinity. Their polycrystalline samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data. The basic building units are [Rh4Sn4] respectively [Ir4Sn4] stellae quadrangulae which condense to rigid three-dimensional networks. A striking crystal chemical feature of the Na3Pt4Ge4-type phases are pronounced anisotropic displacements of the divalent cations. Additional structure refinements of Sr3Rh4Sn4 and Sr2.43Eu0.57Ir4Sn4 and the previously reported stannide Sr3Ir4Sn4 at 90 K reveal less anisotropic behavior in going to lower temperatures.

KEARNS TEXTURE PARAMETERS AND PROPERTIES OF HEXAGONAL MONO- AND POLYCRYSTALS

Problem statement. Polycrystals' physical and mechanical properties are determined by the corresponding properties of single crystals (crystallites) that make up the polycrystal, and their distribution by orientation in the polycrystal (texture). In metals with a hexagonal structure, the use of Kearns texture parameters, which show the degree of coincidence of the hexagonal axis of crystallites with a given direction in a polycrystalline sample, allows determining the property of a polycrystal in this direction, if the properties of a single crystal in the direction of its hexagonal axis and the perpendicular direction are known. It is also possible to solve the inverse problem: determining the properties of a single crystal in the direction of its hexagonal axis and the perpendicular direction based on the properties of the polycrystal and the determined of the Kearns texture parameters. Materials and methods. Elastic and mechanical characteristics of hexagonal alloys based on titanium (Grade 1 and VT1-0) and magnesium (Mg − 10 % Li and ZE10) were studied after different types of deformation − rolling, alternating bending, and twist extrusion. The Kearns texture parameters were determined by the X-ray method based on the data of the construction of inverse pole figures (IPF) in the normal direction (ND) to the sheets plane and the rolling direction (RD). The results of the experiment. It is shown that the specified method allows to calculate the elastic and mechanical properties of the specified polycrystals after they undergo various types of deformation with an error of no more than 5−10 %, as well as to solve the inverse problem of calculating the properties of single crystals with an error of no more than 5 %. Conclusions. Using the parameters of the Cairns texture and the characteristics of single crystals of magnesium alloys ZE10, Mg 5 % Li, titanium Grade1 and VT1-0 made it possible to calculate the corresponding properties of polycrystals and their anisotropy. The use of Cairns texture parameters, experimental values of the modulus of elasticity, tensile strength and yield strength of polycrystalline sheets of the studied magnesium and titanium alloys made it possible to evaluate the characteristics. There are strong correlations between the values of the modulus of elasticity, the mechanical characteristics of the studied sheets of magnesium and titanium alloys, on the one hand, and the corresponding parameters of the Cairns texture, on the other hand.

Ternary gallide Zr7Pd7–xGa3+x (0 ≤ x ≤ 1.8): Synthesis, crystal and electronic structures

The new ternary compound Zr7Pd7-xGa3+x (0 ≤ x ≤ 1.8) was synthesized by arc melting the elements under argon and subsequent annealing the ingots at 870 K for 720 h. The polycrystalline samples were characterized by powder X-ray diffraction (XRD) and the crystal structure of the compound was determined from single crystal X-ray diffraction data. Zr7Pd7Ga3 crystallizes with a ternary version of the Zr7Ni10 type of structure exhibiting statistical mixtures of palladium and gallium atoms on three crystallographically independent nickel sites (oS68, Cmce, a = 12.997(3), b = 9.623(2), c = 9.630(2) Ǻ, Z = 4, R1 = 0.033, wR2 = 0.067 for 719 unique reflections with Io> 2σ(Io) and 48 refined parameters). The crystal structure of Zr7Pd7Ga3 is represented by a 3D Pd–Ga framework built of sinusoidal layers of Pd and Ga stacking along the b axis sandwiching the Zr atoms. The homogeneity range of the compound Zr7Pd7–xGa3+x has been refined from powder XRD and EDX data: 0 ≤ x ≤ 1.8; variation of the lattice parameters is the following: a = 13.0174(8)–12.904(3), b = 9.6306(8)–9.559(8), c = 9.6348(8)–9.700(5) Å. Electronic structure calculations have been performed for an idealized model Zr7Pd10 as well as a model compound Zr7Pd6.5Ga3.5 revealing that the Ga-free Zr7Pd10 is significantly destabilized by strong Pd–Pd anti-bonding interactions. Substitution of Pd by Ga reduces those, stabilizing Zr7(Pd,Ga)10 which features strong heteroatomic bonding between Zr and the Pd/Ga substructure, putting it into the class of polar intermetallics.

Ni4Nb1.8W0.1Ti0.1O9: Stabilization of the I-Type Ni4Nb2O9 Structure and First Magnetic Study of This Corundum-like Compound.

For the first time, we report on the structural and magnetic properties of a polycrystalline sample of Ni4Nb2O9 from I-type (Fdd2), obtained by the partial cosubstitution of Nb5+ by Ti4+ and W6+. The crystal structure is investigated by combining synchrotron X-ray, neutron, and electron diffraction at room temperature. This I-type structure is derived from the corundum-like Ni4Nb2O9 II-type (Pbcn) and is noncentrosymmetric and polar. The Ni-lattice is composed of the stacking of distorted honeycomb layers with double zigzag ribbons 60° disoriented from each other in two successive double layers. The connection between layers is ensured by the sharing of octahedra faces building (Nb,W,Ti)2O9, Ni2O9, and Ni3O12 units. This study shows how the disruption of the Nb2O6 units by smaller d0 cations impacts the structure, significantly modifying the Ni network and, thus, the magnetic properties. The latter were studied by dc- and ac-magnetic susceptibility, and the magnetic structure was solved by neutron powder diffraction. A ferrimagnetic behavior occurs below 68 K, followed by a re-entrant spin-glass-like behavior below ≈50 K.

Impact of Zn-Ion Doping on the Structural and Optical Properties of Cobalt Chromite System

The structural and optical properties of Zn-ion doped CoCr2O4 multiferroic materials were investigated in this work. We successfully synthesized Co[Formula: see text]ZnxCr2O4 ([Formula: see text], 0.2 and 0.4) polycrystalline samples using the conventional solid-state reaction route method. The XRD pattern confirmed the cubic spinel structure of the Zn-doped CoCr2O4 samples, with the Fd3m space group. The Williamson–Hall (W–H) and Debye–Scherrer techniques were employed to determine the crystalline size of the cobalt chromite system. The average crystalline sizes, calculated using the Debye–Scherrer formula, were found to be 35[Formula: see text]nm, 34[Formula: see text]nm and 32[Formula: see text]nm, for the CoCr2O4, Co[Formula: see text]Zn[Formula: see text]Cr2O4, and Co[Formula: see text]Zn[Formula: see text]Cr2O4 samples, respectively. These results show that the crystalline size calculated using the Debye–Scherrer formula decreased with an increase in Zn doping. We observed from the Raman spectra, the presence of three distinct bands at 188[Formula: see text]cm[Formula: see text] (F2g), 504[Formula: see text]cm[Formula: see text] (F2g), 662[Formula: see text]cm[Formula: see text] (A1g) and one weak band at 434[Formula: see text]cm[Formula: see text](Eg). These Raman bands are also present in the Zn-doped CoCr2O4 system, indicating structural stability even with doping. The energy band gap, calculated using the tauc plot, was determined as 3.15[Formula: see text]eV, 3.24[Formula: see text]eV and 3.27[Formula: see text]eV for CoCr2O4, Co[Formula: see text]Zn[Formula: see text]Cr2O4 and Co[Formula: see text]Zn[Formula: see text]Cr2O4 samples, respectively. The formation of the cobalt chromite spinel system was further confirmed by the FT-IR spectra.

A molecular dynamics study of the effect of initial pressure on the mechanical resilience of aluminum polycrystalline

Polycrystalline materials are essential in engineering due to their ability to withstand various forces, heat, and environmental conditions. The arrangement of atoms within these crystals significantly affects their mechanical properties. This study used molecular dynamics simulations to explore how initial pressure affects the mechanical resilience of aluminum polycrystals. Aluminum composite materials, known for their strength, flexibility, and environmental sustainability, are the focus of this investigation. We particularly investigated stress-strain reactions at 1, 2, and 3 bar initial pressures. Reduced free volume causes atomic migration to be hampered as pressure increases, therefore affecting mean square displacement and diffusion coefficient. The results show that ultimate strength and Young's modulus of the polycrystalline samples were 30 and 6.64 GPa at 1 bar pressure. Moreover, the results demonstrated a notable decrease in mechanical performance by increasing pressure; the ultimate strength and Young's modulus of the polycrystalline samples diminished to 5.66 GPa and 22.43 GPa, respectively, at 3 bar. Furthermore, the heat flux increased by rising initial pressure in the Al-polycrystalline sample due to the compression of material that reduced atomic distances. This improved atomic arrangement facilitated more efficient heat transfer. These insights are essential for engineering applications, as they establish a foundation for the production of aluminum components that maintain structural integrity in the face of extreme conditions.

Enhancement in power factor through rare-earth samarium doping in Cu2SnSe3 system

Cu2SnSe3 has drawn enough attention as a potential thermoelectric material due to its unique electronic and thermal properties. We present the impact of Sm doping on the Cu2SnSe3 system’s Sn site. The polycrystalline samples of Cu2Sn1-x Sm x Se3 (0 ≤ x ≤ 0.08) were prepared using the solid-state reaction technique followed by conventional sintering. The crystal structure was characterized using XRD and the results reveal that the samples have a diamond cubic structure with a space group of F4̄3m. Scanning Electron Microscopy (SEM) analysis indicates a uniform surface homogeneity within the sample. Furthermore, the introduction of Sm causes a reduction in porosity. The electrical transport characteristics were studied in the mid temperature range of 300–650 K. The Seebeck coefficient of all the samples were found to be positive within the temperature range under study, suggesting that holes constitute the majority charge carriers. This is also confirmed by the Hall measurements as the carrier concentration was positive for all the samples. The inclusion of Sm has led to a reduction of electrical resistivity and Seebeck coefficient and hence power factor of ~539 μW mK−2 for x = 0.08 at 630 K which is ten times greater as compared to x = 0 whose power factor is ~56 μW mK−2 at 630 K is achieved which makes it suitable for thermoelectric applications.

Structure and physical properties of a new telluride Mg1.2(1)In1.2(1)Si2Te6

A new Mg-containing disordered quaternary telluride Mg1.2(1)In1.2(1)Si2Te6 is prepared at 1223 K by direct fusion of elements. This mixed metal telluride adopts a trigonal (P3‾1m space group) structure having refined cell constants of a = b = 7.0603(3) Å and c = 7.1681(4) Å. Four unique crystallographic sites are filled in the structure: one disordered metal site (In1/Mg1), one partially filled Mg2, one Si1, and one Te1. Each metal ion (In and Mg) in the structure sits at the center of a distorted octahedron of Te1 atoms. Two Si atoms are involved in forming an ethane-like Si2Te6 unit with the help of a Si−Si bond. The local coordination environment around each Si atom can be described as a distorted tetrahedron comprising one Si1 and three Te1 atoms. A polycrystalline sample with the loaded composition of Mg1.2In1.2Si2Te6 shows an optical bandgap of 1.02(2) eV. The p-type semiconducting nature of the Mg1.2In1.2Si2Te6 sample was established from the positive values of the Seebeck coefficient (S) and resistivity studies. The complex structure of the Mg1.2In1.2Si2Te6 phase, which features heavy elements (In and Te), helps to achieve ultralow total thermal conductivity (ktot) of 0.33 W/mK at 773 K.

Phase-field simulations of ferro-electro-elasticity in model polycrystals with implications for phenomenological descriptions of bulk perovskite ceramics

We investigate the role of polycrystalline disorder on the effective ferro-electro-elastic behavior of perovskite ferroelectric ceramics under electro-mechanical loading. Assuming random initial grain orientations, we use high-resolution phase-field simulations and periodic homogenization of two-dimensional model polycrystals to study the evolution of the domain microstructure within and across grains as well as the resulting effective, macroscopic polarization and strain fields under loading. The number of randomly-oriented grains in simulations, at fixed grain size and fixed numerical resolution per grain, is used to control the polycrystalline disorder. Results indicate that, when the polycrystalline samples are sufficiently disordered (i.e., when sufficiently many randomly-oriented grains are considered), their effective electromechanical response under uniaxial compression is stable, and the concomitant polarization and deformation are always aligned with the mechanical load. Thus, the present study supports the viewpoint that polycrystalline disorder in bulk perovskite ceramics stabilizes the overall ferro-electro-elastic response despite the underlying nonconvex polarization energy landscape.

Two-gap superconducting states of LaRu[formula omitted]Si[formula omitted]

We synthesize high-quality LaRu3Si2 (Tc= 7.5 K) polycrystalline sample and report the superconducting gap anisotropy relative to the temperature dependence of μ0Hc2 and Cel/γTc below Tc. The μ0Hc2 satisfies T-linear dependence until it approaches a low temperature region (T≤0.25Tc), and this behavior may not agree with the WHH theory. Based on T-linear fitting, the μ0Hc2(0) is estimated to be 10.2 T. The Cel/γTc below Tc cannot be expressed by a simple exponential fit. It is considered that although a larger gap (2Δ1/kBTc=3.63) opens at 3 K ≤T≤Tc, low-lying quasiparticle excitations at T≤ 3 K are dominated by a smaller gap (2Δ2/kBTc=2.62). Our experimental results indicate the feasibility of a two-gap superconducting state of LaRu3Si2.

Microstructural investigation of Au ion-irradiated Eu-doped LaPO4 ceramics and single crystals

Ceramics and single crystals of LaPO4 monazite doped with Eu(III) were irradiated with 14 MeV Au5+ ions at three different fluences. Changes to crystallinity, local coordination environments, and topography were probed using grazing-incidence X-ray diffraction (GIXRD), vertical scanning interferometry (VSI), scanning electron microscopy (SEM), Raman, and luminescence spectroscopy. GIXRD data of the ceramics revealed fluence dependent amorphization. A similar level of amorphization was detected for samples irradiated with 5 × 1013 ions/cm2 and 1 × 1014 ions/cm2, whereas the sample irradiated with the highest fluence of 1 × 1015 ions/cm2 appeared slightly less amorphous. VSI showed clear swelling of entire grains at the highest ion fluence, while more localized damage to grain boundaries was detected for ceramic samples irradiated at the lowest fluence. Single crystal specimens showed no pronounced topography changes following irradiation. SEM images of the ceramic irradiated at the highest fluence showed topological features indicative of grain surface melting. Raman and luminescence data showed a different degree of disorder in polycrystalline vs. single crystal samples. While changes to PO4 vibrational modes were observed in the ceramics, changes were more subtle or not present in the single crystals. The opposite was observed when probing the local Ln-O environment using Eu(III) luminescence, where the larger changes in terms of an elongation of the Eu-O (or La-O) bond and an increasing relative disorder with increasing fluence were observed only for the single crystals. The dissimilar trends observed in irradiated single crystals and ceramics indicate that grain boundary chemistry likely plays a significant role in the radiation response.

Effect of calcination on the structural, morphological and optical properties of earth abundant Cu2FeSnS4 powders prepared by solid-state reaction

In this paper, we investigate the effect of calcination on the properties of Cu2FeSnS4 (CFTS) prepared by solid-state reaction. As fabricated, the polycrystalline sample was crushed and the powders was calcined at different temperatures (TC = 800, 900 and 1000 °C). A Rietveld analysis shows that the calcined powders have predominately the stannite phase with a nearly stoichiometric composition, with the presence of a small amount of SnS, supported by Raman scattering. Energy dispersive spectroscopy confirms the homogeneity of the CFTS materials. Moreover, the analysis of the surfaces of CFTS pellets using scanning electron microscopy showed a more compact and dense morphology as the calcination temperature increases, thus enhanced photosensitivity. From optical studies, we found that the bandgap energy decreases from 1.40 to 1.18 eV with increasing calcination temperature. Calcination can be a tool to engineer the optical band gap.

Substrate Charge Transfer Induced Ferromagnetism in MnSe/SrTiO3 Ultrathin Films.

The observation of superconductivity in MnSe at 12 GPa motivated us to investigate whether superconductivity could be induced in MnSe at ambient conditions. A strain-induced structural change in the ultrathin film could be one route to the emergence of superconductivity. In this report, we present the physical property of MnSe ultrathin films, which become tetragonal (stretched ab-plane and shortened c-axis) on a (001) SrTiO3 (STO) substrate, prepared by the pulsed laser deposition (PLD) method. The physical properties of the tetragonal MnSe ultrathin films exhibit very different characteristics from those of the thick films and polycrystalline samples. The tetragonal MnSe films show substantial conductivity enhancement, which could be associated with the presence of superparamagnetism. The optical absorption data indicate that the electron transition through the indirect bandgap to the conduction band is significantly enhanced in tetragonal MnSe. Furthermore, the X-ray Mn L-edge absorption results also reveal an increase in unoccupied state valance bands. This theoretical study suggests that charge transfer from the substrate plays an important role in conductivity enhancement and the emergence of a ferromagnetic order that leads to superparamagnetism.