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.     

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.     

Synthesis and crystal structure of Ba3Si4C2

SiC powder prepared by the Na flux method at 1023 K for 24 h and Ba were used as starting materials for synthesis of tribarium tetrasilicide acetylenide, Ba₃Si₄C₂. Single crystals of the compound were obtained by heating the starting materials with Na at 1123 K for 1 h and by cooling to 573 K at a cooling rate of −5.5 K/h. The single crystal X-ray diffraction peaks were indexed with tetragonal cell dimensions of a = 8.7693(4) and c = 12.3885(6) Å, space group I4/mcm (No.140). Ba₃Si₄C₂ has the Ba₃Ge₄C₂ type structure which can be described as a cluster-replacement derivative of perovskite (CaTiO₃), and contains isolated anion groups of slightly compressed [Si₄]⁴⁻ tetrahedra and [C₂]²⁻ dumbbells. The electrical conductivity measured for a not well-sintered polycrystalline sample was 2.6 × 10⁻²–7 × 10⁻³ S cm⁻¹ in the temperature range of 370–600 K and slightly increased with increasing temperature. The Seebeck coefficient showed negative values of around −200 to −300 μV K⁻¹.     

Spontaneous magnetostriction of R2Fe13.6Si3.4 (R = U, Lu)

The thermal expansion of U₂Fe_13.6Si_3.4 and Lu₂Fe_13.6Si_3.4 has been measured by X-ray powder diffraction. Both compounds exhibit a large spontaneous magnetostriction. In the ground state, the volume effect 11.2 × 10⁻³ in U₂Fe_13.6Si_3.4 consists of almost equal contributions from the Fe–Fe and U–Fe exchange interactions (6 × 10⁻³ and 5 × 10⁻³, respectively). In Lu₂Fe_13.6Si_3.4, the volume effect is 8.9 × 10⁻³.     

Improved high-Q microwave dielectric resonator using ZnO-doped La(Co1/2Ti1/2)O3 ceramics

The microwave dielectric properties and the microstructures of ZnO-doped La(Co_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. Doped with ZnO (up to 0.75 wt%) can effectively promote the densification of La(Co_1/2Ti_1/2)O₃ ceramics with low sintering temperature. At 1320 °C, La(Co_1/2Ti_1/2)O₃ ceramics with 0.75 wt% ZnO addition possesses a dielectric constant (_r) of 30.2, a Q × f value of 73,000 GHz (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −35 ppm/°C.     

Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 × 10² exp(−39500/RT)% for the former alloy and c_s = 4.19 × 10² exp(−40200/RT)% for the latter, where R is in J mol⁻¹ K⁻¹ (8.314 J mol⁻¹ K⁻¹) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. Appropriate diffusion coefficients vary from 0.16 × 10⁻⁹ to 2.02 × 10⁻⁹ m² s⁻¹. With both alloys, the Ni₃Sn₄ intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni₃Sn₄ layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.     

Thermo-physical and thermal cycling properties of plasma-sprayed BaLa2Ti3O10 coating as potential thermal barrier materials

Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa₂Ti₃O₁₀ (BLT) was produced by solid-state reaction of BaCO₃, TiO₂ and La₂O₃ at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10^− 5–12.5 × 10^− 6 K^− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications.     

Synthesis and crystal structure of a new calcium borate, CaB6O10

A new calcium borate, CaB₆O₁₀, has been prepared by solid-state reactions at temperature below 750 °C. The single-crystal X-ray structural analysis showed that CaB₆O₁₀ crystallizes in the monoclinic space group P2₁/c with a = 9.799(1) Å, b = 8.705(1) Å, c = 9.067(1) Å, β = 116.65(1)°, Z = 4. It represents a new structure type in which two [B₃O₇]⁵⁻ triborate groups are bridged by one oxygen atom to form a [B₆O₁₃]⁸⁻ group that is further condensed into a 3D network, with the shorthand notation 6: ∞³[2 × (3:2Δ + T)]. The 3D network affords intersecting open channels running parallel to three crystallographically axis directions, where Ca²⁺ cations reside. The IR spectrum further confirms the presence of both BO₃ and BO₄ groups.     

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.     

Preparation and characteristic of spherical Li3V2(PO4)3

Spherical Li₃V₂(PO₄)₃ was synthesized by using N₂H₄ as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li₃V₂(PO₄)₃ has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li₃V₂(PO₄)₃ were 123 mAh g⁻¹ in the voltage range of 3.0–4.3 V and 132 mAh g⁻¹ in the voltage range of 3.0–4.8 V.     

Role of titanium valence states in optical and electronic features of PbO–Sb2O3–B2O3:TiO2 glass alloys

PbO–Sb₂O₃–B₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.5 mol.%) were synthesized. The samples are characterized by X-ray diffraction, scanning electron microscopy and DSC techniques. A variety of properties, i.e. optical absorption, photoluminescence, infrared, ESR spectra, magnetic susceptibility, photo-induced birefringence (PIB) and dielectric properties (constant ′, loss tan δ, a.c. conductivity σ_ac over a wide range of frequency and temperature) of these glass–ceramics have been explored. The analysis of these results indicated that Ti ion surrounding ligands play principal role in the observed PIB and the sample crystallized with 0.8 mol.% of TiO₂ is the most suitable for the applications in non-linear optical devices.     

New dielectric material system of La(Mg1/2Ti1/2)O3–Ca0.6La0.8/3TiO3 for microwave applications

The microstructure and microwave dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics system with ZnO additions (0.5 wt.%) investigated by the conventional solid-state route have been studied. Doping with ZnO (0.5 wt.%) can effectively promote the densification and the dielectric properties of xLa(Mg_1/2Ti_1/2)O₃–(1 − x)Ca_0.6La_0.8/3TiO₃ ceramics. 0.6La(Mg_1/2Ti_1/2)O₃–0.4Ca_0.6La_0.8/3TiO₃ ceramics with 0.5 wt.% ZnO addition possess a dielectric constant (_r) of 43.6, a Q × f value of 48,000 (at 8 GHz) and a temperature coefficient of resonant frequency (τ_f) of −1 ppm/°C sintering at 1475 °C. As the content of La(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 62,900 (GHz) for x = 0.8 is achieved at the sintering temperature 1475 °C. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance.     

Subsolidus phase relations in the system ZnO–P2O5–MoO3

The subsolidus phase relations of the ternary system ZnO–P₂O₅–MoO₃ were investigated by means of X-ray diffraction (XRD). Seven binary compounds and eight 3-phase regions were determined, and no ternary compound was found in this system. The phase diagram of pseudo-binary system Zn₃(PO₄)₂–Zn₃Mo₂O₉ was also constructed through XRD and differential thermal analysis (DTA) methods, and the result reveals this system is eutectic system. The eutectic temperature is 904 °C and the corresponding component is 30% Zn₃Mo₂O₉ and 70% Zn₃(PO₄)₂.     

Preparation of polyaniline–titanium dioxide hybrid materials in supercritical CO2

Polyaniline–titanium dioxide (PANI–TiO₂) hybrid materials were synthesized in supercritical CO₂ using two different methods. In the first method, separately synthesized TiO₂ particles were mixed with aniline to perform polymerization in supercritical CO₂. The second method included the preparation of aniline–TiO₂ hybrids through a sol–gel reaction of titanium isopropoxide in the presence of aniline. Further polymerization of aniline–TiO₂ hybrids in supercritical CO₂ produced PANI–TiO₂ hybrid particles. The final products showed the intrusion of PANI into the internal structure of TiO₂. The PANI–TiO₂ hybrid materials were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), electrical conductivity (EC), Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) measurements. PANI–TiO₂ nano-composites synthesized with the first method showed a relatively low electrical conductivity of 3.78 × 10⁻² S/cm at 20 °C. TGA suggested that the particles contained 40.6% TiO₂ by mass and showed a strong interaction at the interface of TiO₂ and PANI. The electrical conductivity of the hybrid particles produced using the second method increased to 7.75 × 10⁻² S/cm and the TGA results showed 34.4% TiO₂ by mass. Through SEM and TEM analyses it was confirmed that the PANI has been interpenetrated into the three-dimensional network of the TiO₂ when the second method was used.     

Phase relations and flux research for zinc oxide crystal growth in the ZnO–K2O–P2O5 system

The subsolidus phase relations of the ternary system ZnO–K₂O–P₂O₅ were investigated by means of X-ray diffraction (XRD). There are 7 binary compounds, 6 ternary compounds and 20 three-phase regions in this system. The phase diagram of the pseudo-binary system KZn₄(PO₄)₃–ZnO was also investigated by means of XRD and differential thermal analysis (DTA) methods. KZn₄(PO₄)₃–ZnO is a eutectic system with eutectic temperature about 952 °C and eutectic point at about 2 mol% ZnO. Only narrow composition range in the KZn₄(PO₄)₃–ZnO system is suitable for the growth of ZnO crystals.     

Thermodynamic studies on LaFeO3(s)

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO₃(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:

H°(T)−H°(298.15 K)(J mol⁻¹)(±1.2%)=−36887.27+103.53 T(K)+25.997×10⁻³T²(K)+11.055×10⁵/T(K).

The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:

C_p,m°(T)(JK⁻¹mol⁻¹)=103.53+51.994×10⁻³T(K)−11.055×10⁵/T²(K).

From the measured e.m.f. of the cell, (−)Pt/(LaFeO₃(s)+La₂O₃(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant Δ_fG_m°(T) values from the literature, the Δ_fG_m°(LaFeO₃, s, T) was calculated, and is given as:

Δ_fG_m°(LaFeO₃, s, T)(kJmol⁻¹)(±0.72)=−1319.2+0.2317T(K).

The calculated Δ_fH_m°(LaFeO₃, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJ mol⁻¹ and 128.9 J K⁻¹ mol⁻¹, respectively.     

Structure and electrochemical performance of FeF3/V2O5 composite cathode material for lithium-ion battery

Orthorhombic structure FeF₃ was synthesized by a liquid-phase method using FeCl₃, NaOH and HF solution as starting materials, and the FeF₃/V₂O₅ composites were prepared by milling the mixture of as-prepared FeF₃ and the conductive V₂O₅ powder. The properties of FeF₃/V₂O₅ composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge/discharge and cyclic voltammetry measurements. Results showed that the FeF₃/V₂O₅ composites can be used as cathode material for lithium-ion battery. Electrochemical measurements in a voltage range of 2.0–4.5 V reveal that the addition of conductive V₂O₅ improves significantly the electrochemical performance of FeF₃, and the FeF₃/V₂O₅ composite prepared by milling for 3 h exhibits high discharge capacity and good cycle performance, and its discharge capacity maintains about 209 mAh g⁻¹ at 0.1 C (23.7 mA g⁻¹) after 30 cycles.     

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.     

Raman and infrared study of 100 MeV swift Ag heavy ion irradiation effects in CaSO4·2H2O single crystals

The modifications of calcium sulphate (CaSO₄·2H₂O) single crystals are investigated by means of Raman and Fourier transform infrared spectroscopy (FT-IR) using 100 MeV Ag⁸⁺ ions in the fluence range 1 × 10¹¹ to 5 × 10¹³ ions/cm². It is observed that the intensities of the Raman modes decrease with increase in ion fluence. We determined damage cross-section (σ) for all the Raman active modes and found to be different for different Raman modes. Further, FT-IR studies have been carried out to confirm surface amorphisation for a fluence of 1 × 10¹³ ions/cm². It is observed that the absorption peaks at 1132–1156 cm⁻¹ corresponds to ν₃(SO₄²⁻) mode. The decrease in Raman peaks intensity with ion fluence is attributed to degradation of ν₃(SO₄²⁻) modes present on the surface of the sample.     

Determination of the crystallization kinetic parameters of Ge22.5Te77.5 glass using model-free and model-fitting methods

Differential scanning calorimetry (DSC) technique was used to study the kinetics of amorphous to crystalline transformation for Ge_22.5Te_77.5 glass. The kinetic parameters of glassy Ge_22.5Te_77.5 under non-isothermal conditions are analyzed by the model-free and model-fitting approaches from a series of experiments at different constant heating rates (1–50 K/min). A strong heating rate dependence of the activation energy of crystallization was observed. The analysis of the present data shows that the activation energy of crystallization is not constant but varies with the degree of crystallization and hence with temperature. The crystallization mechanisms examined using the local Avrami exponents indicate that one mechanism (two-dimensional growth) is responsible for the crystallization process for heating rates 1–30 K/min and two mechanisms (one- and two-dimensional growth) are working simultaneously during the amorphous–crystalline transformation of the Ge_22.5Te_77.5 glass for a heating rate 50 K/min. The reaction model that may describe crystallization process of the Ge_22.5Te_77.5 glass is Avrami–Erofeev model (g(α) = [−ln(1 − α)]^1/n) with n = 2 for the heating range 1–30 K/min and n = 1.5 at a heating rate 50 K/min for the whole range of conversion crystallization fraction (α = 0.05–0.95). A good agreement between the experimental and the reconstructed (α − T) curves has been achieved. The transformation from amorphous to crystalline phase in glassy Ge_22.5Te_77.5 demonstrates complex multi-step involving several processes.