Magnetic phase diagram of CrTe1−xSbx (0.0≤x≤1.0)

Measurements of the high field magnetization of CrTe_1−xSb_x (0.0≤x≤1.0) were carried out at 4.2 K in pulsed magnetic fields up to 300 kOe. The temperature dependence of the magnetization of CrTe_1−xSb_x was measured in the temperature range from 4.2 K to 800 K. The magnetic phase diagram of CrTe_1−xSb_x (0.0≤x≤1.0) was determined, which is similar to the typical one for the mixed crystals of the layered antiferromagnetic and ferromagnetic compounds proposed by de Gennes.     

Self-propagating high-temperature synthesis with post-heat treatment of La1−xSrxFeO3 (x = 0–1) perovskite as catalyst for soot combustion

La_1−xSr_xFeO₃ (x = 0–1) perovskite, Sr-substituted LaFeO₃, was prepared by Self-propagating high-temperature synthesis (SHS) and its catalytic activity for soot combustion was experimentally examined in comparison with that of a conventional Pt/Al₂O₃ catalyst. The products were also characterized by XRD, FE-SEM, and BET specific surface area. The XRD analysis revealed that all the products had a perovskite phase as the major compound, together with intermediate phases with higher x values (x = 0.7–1). The BET specific surface area of the products increased with x. Moreover, the catalytic activity for soot combustion also increased with x, wherein the BET specific surface area appeared an appropriate index for explaining the observed activity. The sample with x = 0.8 exhibited the highest activity for soot combustion among all the SHS products. The soot combustion temperature of this product was as much as 100 °C lower than that of non-catalytic soot combustion. In other words, it had the same activity as that at only 20 °C higher, in comparison to conventional Pt/Al₂O₃ catalyst. More significantly, average apparent activation energy of sample with x = 0.8 calculated by Friedman method using TG/DTA was approximately 15 kJ/mol lower than that of Pt/Al₂O₃ catalyst. This result suggested that La_1−xSr_xFeO₃ has the possibility to be an alternative catalyst to Pt/Al₂O₃ catalyst.     

Investigation of the microwave dielectric properties of Ca1−xMgxLa4Ti5O17 ceramics for application in coplanar patch antenna

In this paper, the dielectric properties of Ca_1−xMg_xLa₄Ti₅O₁₇ ceramics at microwave frequency have been studied. The diffraction peaks of Ca_(1−x)Mg_xLa₄Ti₅O₁₇ ceramics nearly unchanged with x increasing from 0 to 0.03. Similar X-ray diffraction peaks of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic were observed at different sintering temperatures. A maximum density of 5.3 g/cm³ can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. A maximum dielectric constant (_r) and quality factor (Q × f) of Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h are 56.3 and 12,300 GHz (at 6.4 GHz), respectively. A near-zero temperature coefficient of resonant frequency (τ_f) of −9.6 ppm/°C can be obtained for Ca_0.99Mg_0.01La₄Ti₅O₁₇ ceramic sintered at 1500 °C for 4 h. The measurement results for the aperture-coupled coplanar patch antenna at 2.5 GHz are presented. With this technique, a 3.33% bandwidth (return loss <−10 dB) with a center frequency at approximately 2.5 GHz has been successfully achieved.     

dc-Magnetic susceptibility and EPR studies of vapour phase grown Cd1−xCoxTe crystals

Cd_1−xCo_xTe crystals (x = 0.001, 0.003, 0.005, 0.007 and 0.009) were grown by vapour phase technique. The grown diluted magnetic semiconducting (DMS) crystals were subjected to magnetization and dc-magnetic susceptibilities at room temperature. EPR spectra were recorded at 20 K for samples of all compositions. EPR spectra exhibited a broad resonance band around g  5.43. All the studies indicated the paramagnetic nature of the samples.     

Photoluminescence of CdxZn1−xO films grown on sapphire substrate by PLD technique

In this paper, the structural and optical properties of Cd_xZn_1−xO films were studied. The films were deposited by pulse laser deposition (PLD). The Cd concentration was changed in the range from x = 0 to 0.2. The structure of the films was characterized by an atom force microscope (AFM) and X-ray diffraction (XRD). The optical band gap of the films was measured by using transmission and photoluminescence (PL) spectra. The exciton recombination dynamics was investigated by means of the time-resolved photoluminescence (TRPL) spectra of the films at 77 K.     

Thermoelectric properties of hot-pressed Zn4Sb3−xTex

A series of samples have been fabricated through vacuum melting method followed by hot-pressing for Zn₄Sb_3−xTe_x (x = 0.02–0.08), XRD patterns indicated that all the samples were single-phased β-Zn₄Sb₃. Electrical conductivity and Seebeck coefficient were evaluated in the temperature range of 300–700 K, showing p-type conduction. The thermoelectric figure of merit (ZT) was increased with the increase of Te content. ZT values of 0.8 and 1.0 were obtained at 673 K for Zn_4.08Sb₃ and Zn₄Sb_2.92Te_0.08, respectively.     

The magnetic phase diagram of DyFe12−xMox (1.00≤x≤3.00)

The magnetocrystalline anisotropy and magnetic structure of DyFe_12−xMo_x (1.00≤x≤3.00) have been investigated in detail by X-ray diffraction, thermomagnetic analysis, AC magnetic susceptibility, singular point detection technique and angular-magnetization measurement. A magnetic phase diagram of DyFe_12−xMo_x (1.00≤x≤3.00) has been proposed. At room temperature, all DyFe_12−xMo_x compounds exhibit uniaxial anisotropy. At low temperature, a spin reorientation transition of axis-to-cone was observed for DyFe_12−xMo_x compounds with low Mo concentration, x<2.00. The spin reorientation temperature decreases with increasing Mo concentration. For DyFe_12−xMo_x compounds with high Mo concentration, magnetohistory effects were observed below 48 K.     

Investigation on the structures and electrochemical performances of La0.75−xZrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.2) electrode alloys prepared by melt spinning

In order to improve the electrochemical cycle stability of the La–Mg–Ni system A₂B₇-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La_0.75−xZr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (x = 0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni₃ and LaNi₅ as well as a residual phase LaNi₂. The substitution of Zr for La leads to an obvious increase of the LaNi₅ phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤ 0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate.     

Hydrogenation of CaLi2−xMgx (0 ≤ x ≤ 2) with C14 Laves phase structure

CaLi_2−xMg_x (0 ≤ x ≤ 2) which has the C14-type Laves phase structure has been successfully synthesized and hydrogenated. The C14-type Laves phase structure was kept after hydrogenation of CaLi_2−xMg_x (x = 0.2, 0.5, 1). After hydrogenation of CaLi₂ and CaMg₂, the Laves phase disappeared. The CaH₂ and LiH phases were formed from CaLi₂ and the CaH₂ and Mg phases from CaMg₂, respectively. CaLi_2−xMg_x (0 < x < 2) ternary alloys formed stable hydride phases with the C14-type Laves phase structure in contrast to CaLi₂ and CaMg₂ binary alloys.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Morphology, optical and magnetic properties of Zn1−xNixO nanorod arrays fabricated by hydrothermal method

Zn_1−xNi_xO (x = 0, 0.05, and 0.1) nanorod arrays were prepared by hydrothermal method. Morphology and structure analysis indicate that the nanorods have single-crystalline wurtzite structure, and no metallic Ni or NiO phase exists. Room temperature ferromagnetism (RTFM) was observed in the Zn_0.9Ni_0.1O nanorods. In addtion, photoluminescence spectra of Zn_1−xNi_xO (x = 0, 0.05, 0.1 and 0.2) samples exhibit near band edge UV emissions and orange-red emissions. And the orange-red emission is confirmed to have originated from the interstitial oxygen defects.     

The role of valence electron concentration in the cohesive properties of YBxN1−x, YCxN1−x and YNxO1−x compounds

The mechanical properties are not yet understood at basic levels. Previous works shows that the greatest hardness for rock-salt structures (such as TiC_xN_1−x) is attained for a valence electron concentration (VEC) of 4.2 electrons per atom. The present work is aimed to explore this concept for yttrium-based compounds. By means of first principles calculations we did a systematical investigation where nitrogen in YN (VEC = 4) was supplanted by either of B, C or O to reduce or increase its VEC, forming YB_xN_1−x, YC_xN_1−x and YN_1−xO_x ternary compounds. We have calculated the cohesive energy (E_O), cell volume (V_O), bulk modulus (B_O) and density of states (DoS) as a function of VEC. The Fermi level (E_f,) is shifted toward the valence band by substituting B or C in YN, and toward the conduction band by means of O. It is concluded that the optimal position for E_f (maximum B_O) is linked to the saturation of electronic states with e_g-symmetry. At this point the excess of electrons provided by O starts filling antibonding states with t_2g-symmetry. That is, B_O increases monotonically as a function of VEC until VEC  4.1, after that point B_O decrease.     

Thermoelectric performance of Mg2−xCaxSi compounds

Thermoelectric materials Mg_2−xCa_xSi (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1) compounds have been prepared by vacuum melting followed by hot-pressing. Effects of the substitution of Ca for Mg on phase structures and the thermoelectric properties of the hot-pressed compounds were investigated. It was found that the alloying of Ca in Mg₂Si based compounds increases the electrical conductivity and decreases the Seebeck coefficient of the compounds, due to the electronegativity difference between Ca and Mg. The dimensionless figures of merit of Mg₂Si and Mg_1.99Ca_0.01Si reach, respectively, 0.41 and 0.34 at 660 K.     

Thermoelectric properties of Sn1−x−yTiySbxO2 ceramics

Thermoelectric properties of Sn_1−x−yTi_y Sb_xO₂ ceramics were investigated in detail. The addition of Sb into SnO₂ matrix increased the electric conductivity, σ. The increase in the σ value should be caused by the increase in the carrier concentration. The Seebeck coefficients of all the samples were negative, which means that these samples have n-type conduction. The samples of this study have porous structure. The maximum Z value of all the samples measured in this study was 2.4 × 10⁻⁵ K⁻¹.     

Transport anisotropy and pseudo-gap state in oxygen deficient ReBa2Cu3O7−δ (Re = Y, Ho) single crystals

The temperature dependence of the transport anisotropy of ReBa₂Cu₃O_7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δ_c increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa₂Cu₃O_7−δ, the temperature dependence of the anisotropy of the resistivity ρ_c/ρ_ab(T) for the HoBa₂Cu₃O_7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity.     

Phase stability and electronic structures of YbAl3−xMx (M = Mg, Cu, Zn, In and Sn) studied by first-principles calculations

YbAl₃ is a potential thermoelectric (TE) material to be used in TE power generator utilizing waste heat sources. This work systematically investigated the alloying behavior of M in YbAl_3−xM_x (M = Mg, Cu, Zn, In and Sn) and their electronic structures by first-principles calculations. The solubility of alloying elements M and phase stability of YbAl_3−xM_x were studied by analyzing the elastic constants, formation and cohesive energies. The results show that Mg, In and Sn are the effective alloying elements for preparing YbAl_3−xM_x solid solutions, which are helpful for improving TE properties of YbAl₃.     

Fabrication and study on Ni1−xFexO-YSZ anodes for intermediate temperature anode-supported solid oxide fuel cells

Bimetal oxides Ni_1−xFe_xO (x = 0.01, 0.04, 0.08, 0.1, 0.15, 0.2, 0.4, 0.5) were synthesized and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) based on yttria-stabilized zirconia (YSZ) film electrolyte. A single cell consisted of Ni_1−xFe_xO-YSZ anode, YSZ electrolyte film, LSM–YSZ composite cathode was prepared and tested at the temperature from 600 °C to 850 °C with humidified hydrogen (75 ml min⁻¹) as fuel and ambient air as oxidant. It was found that the cell with Ni_0.9Fe_0.1O-YSZ anode showed the highest power density, 1.238 W cm⁻² at 850 °C, among the cells with different anode composition. The promising performance of Ni_1−xFe_xO as anode suggests that bimetal anodes are worth studied for SOFCs in future.     

Structural, magnetic and electrical transport properties for a series of La1−xSrxFe1−xMnxO3 (0.3 ≤ x ≤ 0.7) compounds

The structural, electrical transport and magnetic properties have been studied for compounds: La_1−xSr_xFe_1−xMn_xO₃ (0.3 ≤ x ≤ 0.7). The lattice parameter, a, first decreases with x, and followed by an increase when Sr²⁺ and Mn⁴⁺ was continuously doped. The cell parameters, b and c, slightly decrease with coupled substitution of Sr²⁺ for La³⁺ and Mn⁴⁺ for Fe³⁺. In the paramagnetic temperature range, formation of magnetic clusters is suggested; the sizes of clusters decrease with x up to 0.5, following that they increase sharply with continuing doping. The electrical behaviors of all specimens demonstrate insulators and the electrical resistivity increases with content of Mn⁴⁺ and Sr²⁺ ions doped. A variable range hopping model is suitable to describe electrical transport process for the compounds at low temperature. At high temperature the electrical transport process can be described by bipolaron model for all compounds.     

Substrates effect on Zn1−xMnxO thin films grown by RF magnetron sputtering

In this paper, we have presented the surface effect of the substrates on Mn doped ZnO (Zn_1−xMn_xO) thin films grown on Si(1 0 0) and sapphire [i.e. Al₂O₃(0 0 0 1)] by RF magnetron sputtering. These grown films have been characterized by X-ray diffraction (XRD), photoluminescence (PL) and vibrating sample magnetometer (VSM) to know its structural, optical and magnetic properties. All these properties have been found to be strongly influenced by the substrate surface on which the films have been deposited. The XRD results show that the Mn doped ZnO films deposited on Si(1 0 0) exhibit a polycrystalline nature whereas the films on sapphire substrate have only (0 0 2) preferential orientations indicating that the films are single crystalline. The studies of room temperature PL spectra reveal that the Zn_1−xMn_xO/Si(1 0 0) system is under severe compressive strain while the strain is almost relaxed in Zn_1−xMn_xO/Al₂O₃(0 0 0 1) system. It has been observed from VSM studies that Zn_1−xMn_xO/Al₂O₃(0 0 0 1) system shows ferromagnetic nature while the paramagnetic behaviour observed in Zn_1−xMn_xO/Si(1 0 0) system.     

Composition-controlled synthesis, structure and magnetic properties of ternary FexCoyNi100−x−y alloys attached on carbon nanotubes

Fe_xCo_yNi_100−x−y alloy nanoparticles with controllable compositions attached on the surface of carbon nanotubes (CNTs) were synthesized using an easy two-step route including adsorption and reduction processes. The nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The effect of the alloy composition on microstructure and magnetic properties of ternary FeCoNi alloys attached on carbon nanotubes have been studied. During the nominal composition range (x = 21, 24, 33, 37, 46 and y = 60, 46, 48, 48, 35), Fe_xCo_yNi_100−x−y alloy nanoparticles attached on CNTs are quasi-spherical, fcc–bcc dual phase, and the coercivity (H_c) and saturation magnetization (M_s) vary with the alloy composition. The H_c of Fe_xCo_yNi_100−x−y alloy nanoparticles attached on CNTs decreases and M_s increases with increasing Fe content. These demonstrate that the two-step route is promising for fabricating alloy nanoparticles attached on CNTs for magnetic storage and ultra high-density magnetic recording applications.