Classical Solid State Research Articles

Charge analysis in (RE)CrO4 scheelites by combined Raman spectroscopy and computer simulations

The quest for structure-property relationships in scheelite-type (RE)CrO4 compounds (where RE is a rare earth element) is a difficult task due to the number of exceptions found in RE empirical trends and the uncommon Cr(V) oxidation state. In this work, we experimentally and computationally analyse how the stretching vibrational frequencies ν1(Ag) and ν3(Eg) associated with the [CrO4] tetrahedral units evolve in the (RE)CrO4 crystal family (RE ​= ​Nd, Gd, Dy, Ho, and Lu). Since previously reported Cr–O distances and volume changes along with the RE series are not sufficiently accurate to explain the monotonic decrease observed for the ν1(Ag) and ν3(Eg) frequencies, a deeper analysis was performed involving the well-known fact that the bond strength (force constant) decreases as the interatomic distance increases. Our results demonstrates that structural and spectroscopic parameters can be reconciled with classical solid state chemistry ideas when charge effects are considered. This analysis provides a new method for predicting chromium oxidation states from Raman spectroscopy that can be generalised to the study of other crystal families.

Nanoscale microstructures and novel hydrogen storage performance of as cast V47Fe11Ti30Cr10RE2 (RE = La, Ce, Y, Sc) medium entropy alloys

As classical BCC structure solid state hydrogen storage materials, vanadium-based solid solution alloys occupied a prominent position in the field of hydrogen storage materials due to their significant advantages such as the ability to absorb and desorb hydrogen with high capacity under moderate conditions. In this paper, RE-containing medium entropy BCC solid solution alloys were designed. The microstructure, phase composition and hydrogen storage properties of the medium entropy alloys were systematically studied. Microstructural analysis showed that nanoscale crystals were found in as-cast medium entropy alloys obtained by arc melting followed by natural cooling inside the furnace. This is different from the vanadium-based alloys that are often regarded as traditional coarse-grained alloys in the past decades. The V 47 Fe 11 Ti 30 Cr 10 RE 2 alloys can be fully activated by one cycle of hydrogen ab/de-sorption after pretreatment. The kinetic test shows that the time required for the as-cast RE-containing medium entropy alloys hydrogen uptake to 90% saturation is less than 100 s at room temperature. The alloys exhibit very excellent hydrogen absorption kinetic properties than reported alloys takes at least about 300 s. This is due to the fact that the present alloys are composed of nanocrystals with numerous interfaces and grain boundaries, and these defects can act as good channels for the diffusion of hydrogen atoms. The V 47 Fe 11 Ti 30 Cr 10 Y 2 alloy exhibits a maximum capacity of 3.41 wt% at 295 K. The thermodynamics of hydrogen ab/de-sorption and the hydrogen desorption under non-isothermal conditions were also studied in detail. • Nanoscale crystals were found in as cast RE-containing medium entropy BCC solid solution alloys prepared by arc melting. • The alloys have numerous interfaces and grain boundaries. • The time required for the alloys hydrogen uptake to 90% saturation is less than 100 s.

CVD Yöntemi ile Karbon Katkılanmış Bor Kullanılarak Üretilen MgB2 Süperiletkeninin Yapısal ve Manyetiksel Özelliklerine Sıcaklık Etkisinin İncelenmesi

Carbon, which is known to play a improvement role on the superconductivity properties of MgB2, was doped into MgB2 by CVD (chemical vapor deposition) method, and the change of structural and magnetic properties observed in MgB2 in relation to the change of sintering temperature was investigated. In this context, in the sample preparation step, amorphous nano boron powders with carbon added by chemical vapor deposition method were mixed with magnesium powders at certain mass ratios and sintered at four different temperatures (700-800-900-1000 0C) with the classical solid state reaction method and converted into carbon-added MgB2 samples. SEM photographs of amorphous nano-boron powders with carbon added were taken and subjected to elemental analysis. The structural and magnetic properties of the samples obtained were examined. X-ray diffraction graph, magnetization values and Magnetic Field-Magnetic Moment (M-H) graphs of the samples obtained by XRD method and the critical current density values with Bean Method were found and Magnetic Field-Critical Current Density (Jc-H) graph was created. It was determined that, in all the samples obtained, the MgB2 superconductor structure was formed and the carbon structures included in the structure caused changes in the lattice parameters due to the ion radius difference, that fracture occurred in the magnetization curve of the sample prepared by sintered at 1000 0C due to the intense impurities caused by the phase transitions due to the high temperature, in samples prepared at low temperatures, and that magnetization curves that could not expand sufficiently were observed, flux jumping occurs in the magnetization curve and this also affected the critical current density. In addition, the change in the critical current density value from 7.0×10^3 A/cm2 to 2.8×10^4 A/cm2 showed that the reaction temperature was an effective parameter on the experimental results. As a result of the examinations, when compared between the 4 different sintering temperature values used, it was found that the sintering temperature of 900 0C was the temperature at which the best physical results were obtained in MgB2.

Development of Melilite-Type Oxide Ion Conductors.

Lowering the operating temperature of solid oxide fuel cells (SOFCs) requires high performance oxide ion conductor electrolytes. Recently tetrahedra-based structures have been attracting considerable attention for oxide ion conductor development, among which the layered tetrahedral network melilite structure appears particularly interesting owing to its remarkable capability to accommodate and transport interstitial oxide ions, compared with isolated tetrahedral anion structures. Stabilization and migration mechanisms of interstitial oxide ions in melilites have been systematically investigated using local structural relaxation from both electrostatic Coulomb interaction and chemical bonding aspects based on atomic and electronic structures respectively using experimental and theoretical approaches. These reveal cationic size and chemical bonding effects on stabilization and migration mechanisms of interstitial oxide ions. Lately, full crystallization from glass, an innovative synthesis method, was employed to produce new metastable melilite oxide ion conductors which are inaccessible using classic solid state reaction owing to cationic size effect. Finally, the thermal and chemical stability at low temperature and the high oxide ion conductivity of the best melilite oxide ion conductors based on LaSrGa3 O7 are likely to provide real possibilities of applications of melilite-type electrolytes in SOFCs and other related devices.

A new color-adjustable self-emitting in SrGa2Ge2O8 substituted by Eu3+, energy transfer and the determination of luminescence center

To explore a new color-adjustable self-emitting in SrGa2Ge2O8:Eu phosphors, a series of experiments and characterization were carried out in this paper. Through a classic solid state method, we successfully synthesized the SrGa2-yGe2-zO8:xEu (0 ≤ x, y, z ≦ 0.2) phosphors. The resulting SrGa2-yGe2-zO8:xEu (0 ≤ x, y, z ≦ 0.2) phosphors had been structurally characterized by X-ray Powder Diffraction Refinements (XRD) and Energy Disperse Spectrometer (EDS). In the present study, it was found that under the excitation of 277 nm, by changing the concentration of doped europium ions, a series of color changes from cyan to white are obtained in SrGa2Ge2O8. The energy transfer from the host to the Eu ions occurs. And the energy transfer ability from the host to Eu3+ were shown to be induced when aluminum was substituted to the nominal composition. The bond energy calculation result shows that the doped Sr2+, Ga3+, Ge4+ ions are substituted by Eu3+, Al3+ and Si4+, respectively, which is consistent with the XRD Rietveld refinement analysis. Also, the EDS analysis shows that atomic ratio is 10:19:20 for Sr/Ga/Ge in SrGa2Ge2O8, which is consistent with the XRD result. Diffuse reflection (DR) spectra and electronic structure display the energy band gap is 4.49 and 3.487eV, respectively. Excited by the 260 nm light, it presents a broad band peaks from 350 to 650 nm with the peak at 441 nm. When Al3+/Si4+ ions are doped in it, the red-shift of the matrix and the photoluminescence improvement of SrGa2Ge2O8: Eu can be found.

Dimension-reconfigurable bubble film nanochannel for wetting based sensing

Dimensions and surface properties are the predominant factors for the applications of nanofluidic devices. Here we use a thin liquid film as a nanochannel by inserting a gas bubble in a glass capillary, a technique we name bubble-based film nanofluidics. The height of the film nanochannel can be regulated by the Debye length and wettability, while the length independently changed by applied pressure. The film nanochannel behaves functionally identically to classical solid state nanochannels, as ion concentration polarizations. Furthermore, the film nanochannels can be used for label-free immunosensing, by principle of wettability change at the solid interface. The optimal sensitivity for the biotin-streptavidin reaction is two orders of magnitude higher than for the solid state nanochannel, suitable for a full range of electrolyte concentrations. We believe that the film nanochannel represents a class of nanofluidic devices that is of interest for fundamental studies and also can be widely applied, due to its reconfigurable dimensions, low cost, ease of fabrication and multiphase interfaces.

Effect of Rubidium Substitution on the Physical and Superconducting Properties of Textured High-Tc BSCCO Samples

In this research, the effects of rubidium (Rb) substitution on the microstructural, physical, and superconducting properties of Bi2Sr2Ca1-xRbxCu2O8 + y with x = 0.0, 0.025, 0.05, 0.075, 0.10, and 0.125 superconductor have, in detail, been studied. For this purpose, samples were prepared through the classical solid state reaction route, followed by directional grown using the laser floating zone technique and annealing. XRD measurements showed that all samples are composed of Bi-2212 phase as the dominant one, together with less amount of secondary phases. The crystal symmetries of samples were determined as pseudo tetragonal. SEM-EDX confirmed that Bi-2212 phase is the major one, with minor amounts of Bi2 + x(Sr,Ca)2O6 + d, (Sr,Ca)CuO2, CuO2, and CaO secondary phases. In magnetization versus temperature measurements, very sharp diamagnetic transition is observed. The critical onset temperatures, TC, for all samples are obtained around 90 K. From M-H measurement, it has been found that all samples have very large loop areas. By using the data from M-H measurements in the Bean model, the intragranular critical field, JC, has been determined. It has been found that the x = 0.05Rb sample shows the highest superconducting properties and the largest JC values (2.2 105 A/cm2 at 10 K). Moreover, the maximum pinning force, FPmax, at this temperature has also been obtained in x = 0.05Rb sample (8.5 108 Oe A/cm2).

Kinetic pathways of ordering and phase separation using classical solid state models within the steepest-entropy-ascent quantum thermodynamic framework

The kinetics of ordering and concurrent ordering and phase separation are analyzed with an equation of motion initially developed to account for dissipative processes in quantum systems. A reduced-order energy eigenstructure, or pseudo-eigenstructure, is constructed from a static concentration wave method to describe the configuration-dependent energy in a binary alloy. This pseudo-eigenstructure is used in conjunction with an equation of motion that follows steepest entropy ascent to calculate the kinetic path that leads to ordering and phase separation in a series of hypothetical alloys. By adjusting the thermodynamic solution parameters, it is demonstrated that the model can predict: (a) the stable equilibrium state, (b) the unique thermodynamic path and kinetics of continuous or discontinuous ordering, and (c) the kinetics of concurrent processes involving simultaneous ordering and phase separation.

Plasma optics in the context of high intensity lasers

The use of plasmas provides a way to overcome the low damage threshold of classical solid-state based optical materials, which is the main limitation encountered in producing and manipulating intense and energetic laser pulses. Plasmas can directly amplify or alter the characteristics of ultra-short laser pulses via the three-wave coupling equations for parametric processes. The strong-coupling regime of Brillouin scattering (sc-SBS) is of particular interest: recent progress in this domain is presented here. This includes the role of the global phase in the spatio-temporal evolution of the three-wave coupled equations for backscattering that allows a description of the coupling dynamics and the various stages of amplification from the initial growth to the so-called self-similar regime. The understanding of the phase evolution allows control of the directionality of the energy transfer via the phase relation between the pulses. A scheme that exploits this coupling in order to use the plasma as a wave plate is also suggested.

High performance solid electrolyte-based NO2 sensor based on Co3V2O8 derived from metal-organic framework

In this paper, a well-performing solid electrolyte-based NO2 sensor was initially assembled by using Co3V2O8 derived from Co-V-MOF as sensitive electrode material and La10Si5.5Al0.5O26.75 as solid electrolyte. The sensor displayed excellent sensing behaviors towards NO2 by comparison with the sensor using Co3V2O8 fabricated from classical solid state method as electrode material at 575 °C. The sensor exhibited good response-recovery characteristics to different NO2 concentrations, with a sensitivity of 78.2 mV/decade in the NO2 concentration range of 50–500 ppm. The sensor also showed good repeatability, strong anti-interference ability to CH4, CO2, O2, NO and CO, as well as good long-term stability for 30 test days at 575 °C. In addition, the sensor had a low cross-sensitivity to water vapor in the relative humidity of 20%–98% at 575 °C. The good sensing behaviors could be attributed to the synergistic effect of highly disperse Co/V catalysis sites from Co-V-MOF as well as the larger three-phase boundary of Co3V2O8/ La10Si5.5Al0.5O26.75/NO2. The sensing mechanism of the sensor was investigated and it followed the mixed-potential model.

Understanding the open circuit voltage in organic solar cells on the basis of a donor-acceptor abrupt (p-n++) heterojunction

By using electrical characterization and classical solid state semiconductor device theory, we demonstrate that the open circuit voltage (Voc) in organic solar cells based on non-intentional doped semiconductors is fundamentally limited by the built-in potential (Vbi) originated at a donor-acceptor abrupt (p-n++) heterojunction in case of selective contacts. Our analysis is validated using P3HT:PCBM devices fabricated in our research group. We also demonstrate that such a result can be generalized using data already reported in literature for fullerene-based solar cells. Finally, we show that the dependence of Voc on the device contacts can be understood in terms of the potential barriers formed by the Fermi level alignment of semiconductors at the heterojunction and at the Schottky junctions.

Structure, Optical, and Photocatalytic Properties of Oxynitride Solid Solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N Prepared from Soft‐Chemistry Precursors

Three perovskite oxynitride solid solutions Ca1–xSrxNbO2N, CaNb1–xTaxO2N, and SrNb1–xTaxO2N were prepared by low temperature ammonolysis of soft‐chemistry precursors. In particular, we present for the first time a way to synthesize the substitution series Ca1–xSrxNbO2N, which cannot be prepared by ammonolysis of classical solid state precursors. All samples were phase‐pure and exhibit bandgaps in the visible light range that can be tailored by substitutions both of the A‐ and B‐type cations. Rietveld analysis was applied to determine cell parameters and crystal structures. In the case of Ca1–xSrxNbO2N a structural change from orthorhombic to tetragonal was found. After loading with CoOx the photocatalytic activities in the solution‐based methyl orange degradation were investigated and for SrNb1–xTaxO2N a considerable activity was found.

Synthesis and Electrical Characterization of Lead-Free Electronic Material: Bi(Co2/3Nb1/3)O3

A lead-free electronic compound with chemical composition Bi(Co2/3Nb1/3)O3 has been synthesized via classical solid state reaction based ceramic technology. The structure of the compound as well as the frequency and temperature field dependent resistive, conductive and dielectric properties of the specimen have been examined. The room temperature X-ray diffraction analysis exhibits the formation of the sample in orthorhombic crystal symmetry. The observed dielectric constant and tangent loss characteristics substantiate the prepared compound as a dielectric. The impedance spectra confirms the presence of negative temperature coefficient of resistance behaviour, grain and grain boundary effect in the fabricated compound. The compound modulus spectrum shows that the temperature dependent conductivity relaxation phenomenon is of non-exponential-type. The illustrated important characteristics props up the material for different device applications.

Effects of Prilling Process on the Microstructures and Electrical Properties of Lanthanum Chromite Ceramics

Lanthanum chromite(LaCrO3) with different amounts of PVB solution were synthesized by classical solid state reaction. We have studied the effects of different amounts of PVB solution( 0 mL, 1 mL, 2 mL, 3 mL) during prilling process on the microstructures and electrical properties of LaCrO3. The scanning electron microscopes, relative densities and resistivities of samples suggest: (1) the sinterability of LaCrO3is optimal among samples when adding 1 mL PVB solution to LaCrO3powder during prilling process. (2) sample with 1 mL PVB solution has the highest resistivity, while other counterparts’ resistivities have no distinct correspondence with the amount of PVB solution.

Effect of alkaline earth dopant on density, mechanical, and electrical properties of Cu0.97AE0.03CrO2 (AE = Mg, Ca, Sr, and Ba) delafossite oxide

CuCrO2 and Cu0.97AE0.03CrO2 (AE = Mg, Ca, Sr, and Ba) polycrystalline materials have been prepared through the classical solid state route. CuCrO2 is the major phase in all cases, with larger grain sizes when the alkaline earth dopant is larger. Doping also promotes the formation of secondary phases, which appear in the grain boundaries in the Ca, Sr, and Ba doped samples. Density has been drastically improved through doping, reflected in lower electrical resistivities and higher mechanical properties than the measured in undoped samples. In spite of a relatively high decrease of Seebeck coefficient, all doped samples reached higher power factor values than the undoped ones in the whole measured temperature range. The highest power factor has been reached in Mg doped samples, 0.32 mW/K2 m at 800 °C, which is among the highest obtained so far in randomly oriented polycrystalline CuCrO2 materials.

Mechanochemical synthesis of PbF2 by high energy ball milling

Lead(II)-fluoride was successfully prepared by high energy ball milling and for comparison by classical thermal solid state chemical reaction. The influence of different starting materials, fluorinating agents and synthesis methods on the formation of the orthorhombic α-phase and the cubic β-phase was investigated. XRD analysis provided insight of which phase was formed under varying synthesis conditions. 19F and 207Pb MAS NMR measurements delivered an even further insight into the local structures. Additional simulations of the 19F spectra were performed to identify the 19F-207Pb coupling constants of the four-fold coordinated fluorine sites in both phases.

Using a Battery to Synthesize New Vanadium Oxides

AbstractSodium electrochemical deintercalation in a battery was used as a route to synthesize new vanadium oxides. Sodium layered oxides were used as positive electrode materials in batteries and sodium was electrochemically deintercalated up to a precise composition resulting in the discovery of a new phase Na1/2VO2. As for many vanadium oxides, this compound presents a magnetic transition, slightly above room temperature, around 325 K, as well as a structural transition involving displacements of vanadium ions. The discovery of this new vanadium oxide and the study of its unique electronic properties have only been possible because the battery permits the synthesis of this new phase at room temperature. This shows that many more new systems could be explored using electrochemical (de)intercalation in a battery and new materials that would be impossible to synthesize by classical solid state reaction could be obtained.

Preparation of high performance Bi2Sr2Co1.8Ox thermoelectric materials from nanosized precursors

ABSTRACTBi2Sr2Co1.8Ox thermoelectric (TE) materials were prepared by three different synthesis methods producing nanosized precursors: coprecipitation (with ammonium carbonate or oxalic acid) and attrition milling, which were compared with those obtained by the classical solid state method. Microstructure has shown that precursors produced by coprecipitation and attrition milling methods produced nanometric precursors much smaller than the typical sizes produced by the solid state route. The TE properties are in agreement with the microstructural features, leading to lower resistivity in all the samples, compared with the solid state ones, while Seebeck coefficient is practically unchanged in all cases. As a consequence, maximum power factor values of around four times higher than those obtained in the classical solid state method have been determined. Moreover, the highest power factor value at 650°C is higher than the best results obtained in as-grown textured materials produced by the laser floating zone technique.

Microstructural evolution and solid state dewetting of epitaxial Al thin films on sapphire (α-Al2O3)

Solid state dewetting can be used for targeted patterning, but also causes degradation or failure of thin film devices. In this work the temperature-induced changes of a tetracrystalline model system with inhibited surface diffusion are studied. This is accomplished by growing Al thin films by molecular beam epitaxy on single crystalline (0001) oriented sapphire substrates. The as-deposited Al films form two orientation relationships (OR I and OR II) both subdivided in two twin-related growth variants leading to a tetracrystalline microstructure. Two processes evolve during annealing at 600 °C. Grain growth and texture evolution towards OR II occur in addition to the formation of drum-like voids in the Al film covered by a thin membrane. The surface oxide suppresses Al surface diffusion and in contrast to classical solid state dewetting interface and grain boundary diffusion dominate. High energy grain boundaries were identified as initial points of the void formation.

Effect of precursors on the microstructure and electrical properties of Bi2Ba2Co2O x

Bi2Ba2Co2O x thermoelectric materials have been prepared through three different synthesis methods. The corresponding precursors were obtained from a coprecipitation method using oxalic acid, attrition milling, and classical solid state method (used as reference). Microstructural studies of precursors have shown that the ones produced by coprecipitation and attrition milling led to smaller grain sizes than the ones obtained through ball milling. Infrared spectroscopy has demonstrated that a thermal treatment at 450 °C totally decomposes the metallic oxalates, producing a mixture of Bi and Co oxides, and Ba carbonate, the same average composition of the other precursors. After sintering procedure, it has been determined that the small grain size precursors produce high-density samples, reflected in a decrease of electrical resistivity without significant modification of the Seebeck coefficient. As a consequence, power factor values are more than two times higher than the measured in samples prepared by the classical solid state method. Moreover, the highest power factor values are in the order of the best reported in textured materials, demonstrating the critical role of precursors in the final properties of these materials.