FP-LAPW study of energy bands and optical properties of the filled skutterudite $$\hbox {CeRu}_{4}\hbox {As}_{12}$$ with spin–orbit coupling

The density functional theory (DFT)-based fully relativistic version of the full-potential linearized augmented plane wave method with spin–orbit coupling (SOC) has been used to study the electronic and optical properties of the filled skutterudite \(\hbox {CeRu}_{4}\hbox {As}_{12}\). The exchange and correlation potential has been treated with the local density approximation (LDA). The analysis of the density of states and energy bands in the vicinity of the Fermi energy level suggests the semiconducting nature of the material with narrow indirect energy band gap of 0.11 eV; however, the gap value increases to 0.17 eV for without SOC calculation. Additionally, the modified Becke–Johnson (mBJ) potential has been utilized along with the LDA approach to estimate the precise value of the energy band gap of the material. The mBJ treatment enhances the energy band gap to ?0.2 eV. In order to understand the structural and mechanical properties of the sample material, the elastic constants are also estimated at ambient conditions. The analysis of the elastic constants suggests the brittle nature of the material whose stiffness is comparable with that of \(\hbox {CeOs}_{4}\hbox {Sb}_{12}\) and the covalent contribution is expected in the bonding. The optical response of the material has been studied from the energy bands, which reflects the metallic behavior of the material in the infrared region of frequency radiation and turns to act as opaque material with superluminal behavior at ultraviolet frequency radiation. The inclusion of the hybrid functional in the calculation suggests the metallic nature of the material.     

Computational study of transport properties of graphene upon adsorption of an amino acid: importance of including –$$\hbox {NH}_{2}$$ and –COOH groups

The effects of histidine and its imidazole ring adsorption on the electronic transport properties of graphene were investigated by first-principles calculations within a combination of density functional theory and non-equilibrium Greens functions. Firstly, we report adsorption energies, adsorption distances, and equilibrium geometrical configurations with no bias voltage applied. Secondly, we model a device for the transport properties study: a central scattering region consisting of a finite graphene sheet with the adsorbed molecule sandwiched between semi-infinite source (left) and drain (right) graphene electrode regions. The electronic density, electrical current, and electronic transmission were calculated as a function of an applied bias voltage. Studying the adsorption of the two systems, i.e., the histidine and its imidazole ring, allowed us to evaluate the importance of including the carboxyl (–COOH) and amine (–\(\hbox {NH}_{2}\)) groups. We found that the histidine and the imidazole ring affects differently the electronic transport through the graphene sheet, posing the possibility of graphene-based sensors with an interesting sensibility and specificity.     

Series and parallel resistance effects on the C–V and G–V characteristics of $$\mathrm{Al}/\mathrm{SiO}_{2}$$/Si structure

This paper investigates the electrical behavior of the C–V and G–V characteristics of \(\mathrm{Al}/\mathrm{SiO}_{2}/\mathrm{Si}\) structure. The modeling of capacitance and conductance has been developed from complex admittance treatment applied to the proposed equivalent circuit. Poisson transport equations have been used to determine the charge density, surface potential, total capacitance, and flatband and threshold voltages as a function of the gate voltage, frequency (\(\omega )\), and series \(({R}_{\mathrm{s}})\) and parallel \(({R}_{\mathrm{p}})\) resistances. Results showed a frequency dispersion of C–V and G–V curves in both accumulation and inversion regimes. With increasing frequency, the accumulation capacitance is decreased, whereas the conductance is strongly increased. The shape, dispersion, and degradation of C–V and G–V characteristics are more influenced when parallel and series resistances \((\mathrm{R}_{\mathrm{s}}\), \(\mathrm{R}_{\mathrm{p}})\) are dependent to substrate doping density. The variation of \(\mathrm{R}_{\mathrm{s}}\) and \(\mathrm{R}_{\mathrm{p}}\) values led to a reduction of flatband voltage from ?1.40 to ?1.26 V and increase of the threshold voltage negatively from ?0.28 to ?0.74 V. A good agreement has been observed between simulated and measured C–V and G–V curves obtained at high frequency.     

Single-breath-hold abdominal $${T}_{1}$$ mapping using 3D Cartesian Look-Locker with spatiotemporal sparsity constraints

Objective

Our aim was to develop and validate a 3D Cartesian Look-Locker \({T}_{1}\) mapping technique that achieves high accuracy and whole-liver coverage within a single breath-hold.

Materials and methods

The proposed method combines sparse Cartesian sampling based on a spatiotemporally incoherent Poisson pattern and k-space segmentation, dedicated for high-temporal-resolution imaging. This combination allows capturing tissue with short relaxation times with volumetric coverage. A joint reconstruction of the 3D + inversion time (TI) data via compressed sensing exploits the spatiotemporal sparsity and ensures consistent quality for the subsequent multistep \({T}_{1}\) mapping. Data from the National Institute of Standards and Technology (NIST) phantom and 11 volunteers, along with reference 2D Look-Locker acquisitions, are used for validation. 2D and 3D methods are compared based on \({T}_{1}\) values in different abdominal tissues at 1.5 and 3 T.

Results

\({T}_{1}\) maps obtained from the proposed 3D method compare favorably with those from the 2D reference and additionally allow for reformatting or volumetric analysis. Excellent agreement is shown in phantom [bias\(_{3{\mathrm{T}}}\) < 2%, bias\(_{1.5{\mathrm{T}}}\) < 5% for (120; 2000) ms] and volunteer data (3D and 2D deviation < 4% for liver, muscle, and spleen) for clinically acceptable scan (20 s) and reconstruction times (< 4 min).

Conclusion

Whole-liver \({T}_{1}\) mapping with high accuracy and precision is feasible in one breath-hold using spatiotemporally incoherent, sparse 3D Cartesian sampling.

     

Improved device performance in a CNTFET using La$$_{}$$O$$_{3}$$3 high-$$\kappa $$κ dielectrics

The scaling of MOSFETs is an important and effective way for achieving high performance and low power consumption. One of the bottlenecks for scaling is the physical gate oxide thickness. This paper presents and evaluates a new method for scaling carbon nanotube field-effect transistors (CNTFETs) using \(\hbox {La}_{2}\hbox {O}_{3}\) as a new gate dielectric, which has excellent electrical properties. The proposed CNTFET is simulated using HSPICE. Some of the main digital and analog parameters such as current ratio, subthreshold swing (SS), transconductance, and intrinsic gain have been studied. The simulation results show that the proposed CNTFET outperforms present CNTFETs in terms of current ratio, transconductance, and intrinsic gain.     

Structure and dielectric properties of Bi5−x La x Nb3O15 ceramics

Bi_5?x La _x Nb₃O₁₅ (x?=?0–?1.25) ceramics prepared by conventional solid-state reaction were studied using X-ray diffraction (XRD), electron probe microanalysis (EPMA) and dielectric spectroscopy techniques. The XRD analysis indicated single phase solid solution of Bi_5?x La _x Nb₃O₁₅ is formed for x?≤?1.25. EPMA showed good densification and homogeneous microstructures for the ceramics. With increasing x, the dielectric constant decreases monotonously and can vary from 258 to 158 at 300 kHz. The frequency dependence of dielectric constants indicated these ceramics are promising candidates for high frequency applications.     

Synthesis, electrical and thermal properties of Bi4V2−xZrxO11 (x = 0.0, 0.02, 0.06 and 0.10) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xZr_xO₁₁ (x?=?0.0, 0.02, 0.06 and 0.10) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been checked by X-ray diffraction method. The dielectric constant, dielectric loss and ac conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its ac conductivity increases with the increase of temperature. The dc conductivity of all the materials has been measured as a function of temperature from room temperature to 673 K and its activation energy was calculated using the relation σ?=?σ_oexp (?Ea/kT). The Modulated Differential Scanning Calorimetry (MDSC) has been used to investigate the effect of substitution on the heat capacity and heat flow of the compounds. The results are discussed in detail.     

Structure and microwave dielectric properties of Sm(2−x)/3Li x TiO3

The structural evolution, and microwave dielectric properties of ceramics (x = 0.0 ≤ x ≤ 0.5) were investigated in this work. X-ray diffraction (XRD) results show that samples with x > 0.3 exhibit a single perovskite phase. Impurity phases of Sm₂Ti₂O₇ and TiO₂ appear and their amount increases with the decrease of x when x ≤ 0.3. TEM observation indicates that the A-site is ordered in x = 0.5, but not in x = 0.3). The dielectric constant decreases with the increase of x for 0.1 ≤ x ≤ 0.4 and then increases with further increase in x up to x = 0.5. The Q×f value decreases with the decrease of x due to the increased occurrence of Sm₂T₂O₇ secondary phase, defects and twinning boundaries. The temperature coefficient of resonant frequency is negative and its absolute value decreases greatly with the decrease of x value.     

Thermoelectric properties of Ca3Co4−xMnxO9+δ with x = 0.00, 0.05, 0.10, and 0.15

Ca₃Co_4?xMn_xO_9+δ (x?=?0.00, 0.05, 0.10, and 0.15) sample were prepared by conventional solid state synthesis. The thermoelectric properties were measured at 15 K–300 K. The XRD results revealed that all the samples are single phase. The thermopower of all the samples was positive, indicating that the predominant carriers were holes over the entire temperature range. Both the electric resistivity and the thermopower increased with increasing Mn content. Ca₃Co_3.95Mn_0.05O_9+δ had the highest power factor of 3.40 μW cm^?1 K^?2 at 163 K, representing an improvement of about 187 % compared to undoped Ca₃Co₄O_9+δ. These results suggested that there is scope for improving the thermoelectric characteristics via partial substitution of Mn for Co.     

Thermoelectric properties of rare earth doped Ca3-xRExCo4O9 (RE = Dy,Er, Gd,and Tb; x = 0, 0.01, 0.03, and 0.05)

Ca_3-xRE_xCo₄O₉ thermoelectric ceramics with different rare earth (RE = Dy, Er, Gd, and Tb) substitution for Ca have been successfully produced by the classical solid state method. All these rare earths in small proportions produce the same effects on the thermoelectric phase, reflected on a similar and significant decrease of the electrical resistivity, compared with the undoped samples. The Seebeck coefficient slightly decreases with all the studied substitutions while the power factor values appreciably increase at high temperatures for small amounts (0.01) of doping elements. Further doping produces the decrease of power factor which indicates that the optimal doping level has been determined to be 0.01 for all the tested rare earths which produces, approximately, the same improvement, around 20 % of the power factor obtained in the undoped samples at 800 °C.     

Low-temperature sintering and dielectric properties of the Bi(Nb1−x Ta x )O4 system

Low-temperature sintering and dielectric properties of the Bi(Nb_1?x Ta _x )O₄ (x?=?0.1, 0.3, and 0.5) system was investigated as a function of the zinc borosilicate (ZBS) glass content with a view to applying this system to LTCC technology. The addition of 7 wt% ZBS glass ensured a successful sintering below 900°C. The complete solid solution of Bi(Nb, Ta)O₄ with an orthorhombic structure was formed and the high temperature form of Bi(Nb, Ta)O₄ with a triclinic structure was not observed. The second phase of Bi₂SiO₅ was observed for all compositions. The non-relative liquid phase sintering (NLPS) occurred and the one-stage sintering was conducted. The Q?×?f values were improved by the addition of Ta. Bi(Nb_0.7Ta_0.3)O₄ with 7 wt% ZBS glass sintered at 900°C demonstrated 35.8 in the dielectric constant (? _r), 2,200 GHz in the quality factor (Q?×?f ₀), and ?48 ppm/°C in the temperature coefficient of resonant frequency (τ _f).     

Dielectric and pyroelectric properties of (1 − x)PST-xPZT ferroelectric ceramics

Pb(Sc_1/2Ta_1/2)O₃ (PST) ceramics were investigated greatly in the world for their unique pyroelectric, ferroelectric and dielectric properties and comprehensive applications on uncooled focal plane arrays, infrared detectors and other electronic devices. However, the PST ceramics doped with other perovskite ferroelectrics showed more excellent electrical and electronic properties. In this paper, (1???x)PST-xPZT(PSTZT) ferroelectric ceramics were prepared by conventional solid state process. The experiment results demonstrated that the PSTZT ceramics had pure perovskite phase. The temperature dependence of permittivity of PSTZT ceramics was investigated in detail, which indicated that PSTZT was not a complete diffusive phase transition ferroelectric ceramics. At room temperature, the pyroelectric coefficient of PSTZT (x?=?0.1) ceramics was about 15*10^?8C/(cm² K).     

分数,百分数;w,φ,x

从事材料研究离不开材料配方,配方即是各组分元素（例如Ｎｄ２Ｆｅ１４Ｂ合金中的Ｎｄ、Ｆｅ和Ｂ）或化合物（例如ＭｎＺｎ铁氧体中的ＭｎＯ、ＺｎＯ和Ｆｅ２Ｏ３）在整个材料中所占比例。而这比例通常是按各元素或化合物的质量（以前称为重量）、体积、物质的量或原子数...     

Dielectric and piezoelectric properties of sodium lithium niobate Na1−x Li x NbO3 lead free ferroelectric ceramics

High density sodium lithium niobate lead free ceramics near the morphtropic phase boundary [Na _x Li_1?x NbO₃, (LNN), x?=?0.12] were prepared by the solid state reaction method. XRD patterns showed that the lattice structures were changed after polarization. The temperature dependence of the dielectric constant and dielectric loss, pyroelectric coefficient and DSC curves of LNN ceramics showed that there exist three phase transitions from room temperature up to the Curie temperature. The hysteresis loop and piezoelectric properties were measured and discussed.     

Investigation of dielectric and relaxor ferroelectric properties in Ba(Zr x Ti1−x )O3 ceramics

Barium zirconate titanate Ba(Zr _x Ti_1?x )O₃ (BZT x?=?0.1, 0.15, 0.2, 0.25) ceramics doped with Nb₂O₅ have been prepared by a traditional solid phase reaction. The temperature dependence of dielectric permittivity has been investigated. The results show that the phase transition temperature T _c is depressed and the diffuse phase transition behavior is enhanced with increasing Zr content. The Cole–Cole plot has been discussed and the cause of the deviation has been analyzed. The temperature dependence of inverse dielectric constants was investigated. A modified Curie–Weiss law can be used to describe the diffuseness of a phase transition, and diffusion factor increases with the Zr content.     

Crystal Growth and High Temperature Piezoelectricity of La3Ta0.5Ga5.5 − x Al x O14 Crystals

For the application of high temperature piezoelectric devices, Al^{3 +} substituted La₃Ta_0.5Ga_5.5O₁₄ (LTG) crystals with chemical formula of La₃Ta_0.5Ga_{5.5 – x}Al_xO₁₄ (LTGA) were synthesized and grown by -PD (Micro-pulling-down) and Czochralski technique. LTGA compound has been shown to exhibit congruent melting in a wide compositional range without destabilization of the melt during growth, while distribution coefficient of the substituted Al^{3 +} ion was close to unity. LTGA crystals have shown preferable effects for temperature stability on piezoelectric properties in the range from R.T (room temperature) to 500_C.     

Preparation and Properties of Bi4 − x Nd x Ti3O12 Thin Films by Chemical Solution Deposition

Neodymium-modified Bi₄Ti₃O₁₂, (Bi, Nd)₄Ti₃O₁₂ (BNT) ferroelectric thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates using metal-organic precursor solutions by the chemical solution deposition method. The BNT precursor films crystallized into the Bi layered perovskite Bi₄Ti₃O₁₂ (BIT) as a single-phase above 600C. The synthesized BNT films revealed a random orientation having a strong 117 reflection, whereas non-substituted BIT thin films exhibited a random orientation with strong 00l diffractions. Among Bi_{4 – x}Nd_xTi₃O₁₂ [x = 0.0, 0.5, 0.75, 1.0] thin films, Bi_3.25Nd_0.75Ti₃O₁₂ thin films showed a well-saturated P-E hysteresis loop with the highest P_r (22 C/cm²) and a low E_c (69 kV/cm) at an applied voltage of 5 V. The Nd-substitution with the optimum amount for the Bi site in the BIT structure was effective not only for promoting the 117 preferred orientation but also for improving the microstructure and ferroelectric properties of the resultant films.     

Chemical Solution Deposition of Epitaxial La1−x (Ca, Sr) x MnO3 Thin Films

We report on the epitaxial growth of magnetoresistive La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ thin films by chemical solution deposition. Thin films were prepared by spin-coating of single-crystal LaAlO₃ (100) substrates with precursor solutions of different concentrations and crystallized at 850°C. The structure of the thin film was found to be influenced by the concentration of the spin-coating solution. The thin film structure and epitaxy was clearly improved by reducing the concentration of the precursor solution. All thin films displayed excellent electrical properties such as a low resistivity and very high metal-insulator transition temperatures T _MI .     

Past, present and future of fuel cells

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