New superconducting lead cuprate with 1201 structure, (Pb0.5B0.5) (SrLa)CuOz

New Pb-based superconducting cuprate with the 1201 structure has been synthesized in the (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z system. From X-ray powder diffraction study, the almost-single 1201 phase sample is found to be obtained at x = 1.0 and y = 0.5 for the nominal composition of (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z. The crystal structure has a tetragonal symmetry with the lattice parameters of a = 0.3779 nm and c = 0.8654 nm. The sample shows an onset of superconductivity at about 32 K as measured by the temperature dependence of the DC magnetic susceptibility.     

Structural and superconducting properties of Bi1.7Pb0.4Sr2 − xYbxCa1.1Cu2.1Oy system

The structural, electrical and superconducting properties of Bi_1.7Pb_0.4Sr_2 − xYb_xCa_1.1Cu_2.1O_y system has been studied for different Yb concentrations. The samples are prepared by solid state synthesis in the polycrystalline bulk form. Structural analysis by X-ray diffraction, microstructural examination by SEM and measurements of electrical and superconducting properties have been conducted to study the effects of Yb substitution at Sr site. The critical temperature (T_C) and critical current density (J_C) are found to increase drastically with Yb substitution. Maximum values of T_C and J_C are observed for x = 0.3 and x = 0.2 respectively. The increase in T_C and J_C is explained due to the substitution effect of Yb³⁺ in place of Sr²⁺ and consequent change in the hole concentration in the CuO₂ planes. Above the optimum levels T_C and J_C begin to reduce due to secondary phase formation. A metal-insulator transition originating from the change of carrier concentration is found to occur at higher doping level (x > 0.5).     

Structural, magnetic and dielectric properties of Bi5−xLaxTi3Co0.5Fe0.5O15 ceramics

The Bi_5−xLa_xTi₃Co_0.5Fe_0.5O₁₅ (0 ≤ x ≤ 0.4) ceramics were successfully synthesized by a modified Pechini process. The samples were characterized by X-ray diffraction and no impurity phase has been detected. The cell volume of the composites increases monotonously with the increase of La content, which indicates that La ions have been incorporated into the lattice of Bi₅Ti₃Co_0.5Fe_0.5O₁₅. The magnetic measurements show that La doping on Bi sites has enhanced the magnetization of Bi_5−xLa_xTi₃Co_0.5Fe_0.5O₁₅ (0 ≤ x ≤ 0.4). Both the dielectric constants and loss tangent of all the samples decrease on increasing frequency and then become almost constant at room temperature. The La doped Bi₅Ti₃Co_0.5Fe_0.5O₁₅ samples exhibit improved dielectric and ferroelectric properties, with higher dielectric constant enhanced remnant polarization and lower losses at room temperature.     

Structural and superconducting properties of neodymium added (Bi,Pb)2Sr2CaCu2Oy

The effects of neodymium (Nd) addition on the phase evolution, structural and superconducting properties of (Bi,Pb)₂Sr₂CaCu₂O_y [(Bi,Pb)-2212] prepared by solid state synthesis in bulk polycrystalline form were studied. The Nd content was varied from x = 0 to 0.5 on a general stoichiometry of Bi_1.7Pb_0.4Sr_2.0Ca_1.1Cu_2.1Nd_xO_y. The samples were characterized by differential thermal analysis (DTA), powder X-ray diffraction, scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis (EDX), resistance-temperature (R-T) measurements and superconductivity measurements at 64 K. It was found that the melting temperature of (Bi,Pb)-2212 slightly increases and the endotherm broadens due to the Nd-addition. The c-lattice parameter initially decreases and then increases with Nd addition. The critical temperature (T_C) and the critical current density (J_C) of the added samples are highly enhanced. The added sample shows a maximum onset critical temperature (T_C-onset) of 95.56 K (x = 0.3) and a maximum critical current density of 719 A/cm² at 64 K (x = 0.2) against 76.7 K and 100 A/cm², respectively, for the pure sample. The results show that the enhancement in superconducting properties are not due to any improvement in microstructure or grain growth, but due to a decrease in hole concentration as a result of Nd doping, which changes the system from ‘over-doped condition’ to ‘optimally doped condition’.     

Piezoelectric and dielectric properties of K0.5Na0.5NbO3-LiSbO3-BiScO3 lead-free piezoceramics

(1 − x) (0.95K_0.5Na_0.5NbO₃-0.05LiSbO₃)-xBiScO₃ lead-free piezoceramics have been fabricated by an ordinary pressure-less sintering process. The relationship between the BS content, phase structure, density, and piezoelectric properties and their temperature stability was discussed particularly. All compositions show a main perovskite structure, showing room-temperature symmetries of orthorhombic at x = 0, of tetragonal at 0.002 ≤ x ≤ 0.01. When 0.002 ≤ x ≤ 0.008, the ceramics have excellent electrical properties of d₃₃ = 265-305 pC/N, k_p = 45-54%, ?_r = 1346-1638, Curie temperature T_c = 315-370 °C and depolarizing temperature T_d = 315-365 °C, comparable to that of other KNN-based piezoceramics. The results indicate that the ceramics are promising lead-free piezoelectric materials.     

Rising Tc in Bi and Cu co-doped BaTiO3

The solid solution (Ba_1−2xBi_2x)(Cu_xTi_1− x)O₃ (0.0 < x ≤ 0.10) was prepared by conventional high temperature reaction. In the region of x ≤ 0.040 single phases of tetragonal perovskite-type compounds were obtained and the c-axis increased up to x = 0.015 and the maximum of the a/c ratio was 1.0123 at x = 0.010. In x > 0.040 a small amount of an unknown impurity phase appeared in addition to a tetragonal perovskite-type phase. The Curie temperature Tc increased to 140 °C at x = 0.010. Rising Tc was confirmed by temperature dependence of the dielectric constants and the endothermic peaks observed in DTA curves. This is the first example for rising Tc in the solid solution based on BaTiO₃ except for doping of Pb²⁺ ion.     

Enhanced thermoelectric properties of Mg2Si0.58Sn0.42 compounds by Bi doping

N-type Mg₂Si_0.58Sn_0.42 − xBi_x (0 ≤ x ≤ 0.015) compounds were prepared by melting the element metals in sealed tantalum tubes followed by hot pressing. The XRD results indicate that all samples are composites containing both major magnesium silicide solution phase and minor magnesium stannide solution phase. The Hall measurements show that the carrier concentrations and electrical conductivities increase with the increase of Bi doping amount. It was found that the intrinsic excitation shifts to high temperature due to Bi doping, which leads to the increase of the peak-temperatures of the Seebeck coefficient. The maximum dimensionless figure of merit is 0.65 at 700 K for the sample x = 0.015.     

Dielectric, ferroelectric and piezoelectric properties of Bi0.5Na0.5TiO3-(Ba0.7Ca0.3)TiO3 ceramics at morphotropic phase boundary composition

(1 − x)Bi_0.5Na_0.5TiO₃-x(Ba_0.7Ca_0.3)TiO₃ (BNT-xBCT, 0 ≤ x ≤ 0.15) solid solutions have been synthesized by a conventional solid state sintering method for obtaining a morphotropic phase boundary (MPB) with good piezoelectric properties. X-ray diffraction patterns reveal that a MPB of rhombohedral and tetragonal phases is formed at compositions 0.09 ≤ x ≤ 0.12. Addition of BCT into BNT greatly lowered coercive field E_c without degrading remanent polarization P_r. The specimen with x = 0.09 has the good piezoelectric properties: d₃₃ = 125 pC/N and k_p = 0.33. A modified Curie-Weiss law was used to fit the dielectric constant of BNT-xBCT ceramics, and a frequency dispersion was observed during the phase transitions from antiferroelectric to paraelectric in specimens with x exceeding 0.06.     

High temperature thermopower and electrical resistivity studies in the transparent conducting oxide Sn doped MgIn2O4

Sn doping in an n-type transparent conducting oxide MgIn₂O₄ is carried out and its effect on the high temperature transport properties viz. thermopower and electrical resistivity is studied. A solid solution exists in the composition window Mg_1+xIn_2−2xSn_xO₄ for 0 < x ≤ 0.4. The band gap as well as the transport properties increases with increasing Sn concentration. The high temperature resistivity properties indicate degenerate semiconducting behavior for all the compositions. The highest figure of merit obtained is 0.12 × 10⁻⁴ K⁻¹ for the parent compound at 600 K.     

Effects of BiAlO3 on structure and electrical properties of K0.5Na0.5NbO3-LiSbO3 lead-free piezoceramics

(1−x)(0.948 K_0.5Na_0.5NbO₃-0.052LiSbO₃)-xBiAlO₃ (KNNLS-xBA) lead-free piezoceramics were synthesized by conventional solid state reaction method. The compositional dependence of phase structure and electrical properties of the ceramics was systemically studied. XRD patterns revealed that all the ceramic samples possessed pure perovskite structure. In addition, polymorphic phase transition (PPT) for the ceramics with BA doping could not be observed in the measuring range from room temperature to 500 °C. Within the studied range of BA addition, the ceramics with x = 0.002 represented a relatively desirable balance between the degradation of the piezoelectric properties, improvement in temperature stability and mechanical quality factor. It was found that the KNNLS-0.002BA ceramics exhibited optimum overall properties (d₃₃ = 233 pC/N, k_p = 35%, tanδ = 0.047, P_r = 27.3 μC/cm², Q_m = 56 and T_c = 349 °C), suggesting that this material should be a promising lead-free piezoelectric candidate for piezoelectric applications.     

Structure and electrical properties of (1 − x)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3 ceramics near morphotropic phase boundary

The binary lead-free piezoelectric ceramics with the composition of (1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ were synthesized by conventional mixed-oxide method. The phase structure transformed from rhombohedral to tetragonal phase in the range of 0.16 ≤ x ≤ 0.20. The grain sizes varied with increasing the Bi_0.5K_0.5TiO₃ content. Electrical properties of ceramics are significantly influenced by the Bi_0.5K_0.5TiO₃ content. Two phase transitions at T_t (the temperature at which the phase transition from rhombohedral to tetragonal occurs) and T_c (the Curie temperature) were observed in all the ceramics. Adding Bi_0.5K_0.5TiO₃ content caused the variations of T_t and T_c. A diffuse character was proved by the linear fitting of the modified Curie-Weiss law. Besides, the ceramics with homogeneous microstructure and excellent electrical properties were obtained at x = 0.18 and sintered at 1170 °C. The piezoelectric constant d₃₃, the electromechanical coupling factor K_p and the dielectric constant ?_r reached 144 pC/N, 0.29 and 893, respectively. The dissipation factor tan δ was 0.037.     

Effect of yttrium doping on the dielectric properties of CaCu3Ti4O12 thin film produced by chemical solution deposition

Pure and yttrium substituted CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0, 0.02, 0.1) thin films were prepared on boron doped silica substrate employing chemical solution deposition, spin coating and rapid thermal annealing. The phase and microstructure of the sintered films were examined using X-ray diffraction and scanning electron microscopy. Dielectric properties of the films were measured at room temperature using electrochemical impedance spectroscopy. Highly ordered polycrystalline CCTO thin film with bimodal grain size distribution was achieved at a sintering temperature of 800 °C. Yttrium doping was found to have beneficial effects on the dielectric properties of CCTO thin film. Dielectric parameters obtained for a CaCu₃Ti_4 − xY_xO_{12 − x / 2} (x = 0.02) film at 1 KHz were k ∼ 2700 and tan δ ∼ 0.07.     

Fluorine-doped LiNi0.5Mn1.5O4 for 5 V cathode materials of lithium-ion battery

Fluorine-doped 5 V cathode materials LiNi_0.5Mn_1.5O_4−xF_x (0.05 ≤ x ≤ 0.2) have been prepared by sol-gel and post-annealing treatment method. The results from X-ray diffraction and scanning electron microscopy (SEM) indicate that the spinel structure changes little after fluorine doping, but the particle size varies with fluorine doping and the preparation conditions. The electrochemical measurements show that stable cycling performance can be obtained when the fluorine amount x is higher than 0.1, but the specific capacity is decreased and 4 V plateau capacity resulting from a conversion of Mn⁴⁺/Mn³⁺ remains. Moreover, influence of the particle size on the reversible capacity of the electrode, especially on the kinetic property, has been examined.     

Enhanced multiferroic properties and tunable magnetic behavior in multiferroic BiFeO3-Bi0.5Na0.5TiO3 solid solutions

A series of multiferroic (1−x)BiFeO₃−x(Bi_0.5Na_0.5)TiO₃ (BF-BNT) (x = 0 − 0.6) solid solution ceramics were prepared by a sol-gel method. The XRD results show that increasing BNT content induce a gradual phase transformation from rhombohedral to pseudocubic structure near x = 0.4. Compared with pure BiFeO₃, superior multiferroic properties are obtained for x = 0.3 with remnant polarization P_r = 1.49 μC/cm² and saturated magnetization M_s = 0.51 emu/g. Importantly, the paramagnetic (PM) to ferromagnetic (FM) transition is observed for the solutions, and the Curie temperature (T_C) can be tuned by varying the content of BNT. This observed FM ordering is discussed in terms of the possible existence of the long-range superexchange interaction of Fe³⁺-O-Ti-O-Fe³⁺ in the chemically ordered regions.     

Microwave dielectric properties of (Pb1−3x/2Lax)(Mg1/2W1/2)O3

La modified Pb(Mg_1/2W_1/2)O₃ were prepared by solid-state reaction process, and the sintering behavior, microstructure and microwave dielectric properties were investigated by X-ray powder diffraction (XRD), Raman scattering and HP network analyzer in this paper. A series of single phase perovskite type solid solutions with A-site vacancies (Pb_1−3x/2La_x(Mg_1/2W_1/2)O₃ (0 ≤ x ≤ 2/3)) were formed. The solid solution took cubic perovskite type structure (Fm3m) with random distribution of A-site vacancies when 0 < x < 0.5, and tetragonal or orthorhombic structure with the ordering of A-site vacancies when 0.5 ≤ x ≤ 2/3. The dielectric constant and temperature coefficient of resonant frequency decrease with increasing La content. Relatively good combination microwave dielectric properties were obtained for x = 0.56: ?_r = 28.7; Q × f = 18098; and τ_f = −5.8 ppm/°C.     

SmAlO3-modified (K0.5Na0.5)0.95Li0.05Sb0.05Nb0.95O3 lead-free ceramics with a wide sintering temperature range

Lead-free ceramics (1 − x)(K_0.5Na_0.5)_0.95Li_0.05Sb_0.05Nb_0.95O₃-xSmAlO₃ (KNLNS-xSA) were prepared by conventional sintering technique. The phase structure, dielectric and piezoelectric properties of the ceramics were investigated. All compositions show a main perovskite structure, exhibiting room-temperature symmetries of tetragonal at x ≤ 0.0075, of pseudo-cubic at x = 0.0100. The Curie temperature of KNLNS-xSA ceramics decreases with increasing SmAlO₃ content. Moreover, the addition of SmAlO₃ can effectively broaden the sintering temperature range of the ceramics. The KNLNS-xSA ceramic with x = 0.0050 has an excellent electrical behavior of piezoelectric coefficient d₃₃ = 226 pC/N, planar mode electromechanical coupling coefficient k_p = 38%, dielectric loss tan δ = 3.0%, mechanical quality factor Q_m = 60, and Curie temperature T_C = 327 °C, suggesting that this material could be a promising lead-free piezoelectric candidate for piezoelectric applications.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

Tantalum influence on physical properties of (K0.5Na0.5)(Nb1−xTax)O3 ceramics

Lead-free (K_0.5Na_0.5)(Nb_1−xTa_x)O₃ ceramics with x = 0.00-0.30 were prepared by the solid-state reaction technique. The effects of Ta on microstructure, crystallographic structure, phase transition and piezoelectric properties have been investigated. It has been shown that the substitution of Ta decreases Curie temperature T_C and orthorhombic-tetragonal phase transition temperature T_O-T, while increasing the rhombohedral-orthorhombic phase transition temperature T_R-O. In addition, piezoelectric activity is enhanced with the increase of Ta content. The ceramics with x = 0.30 have the high value of piezoelectric coefficient d₃₃ = 205 pC/N. Moreover, k_p shows little temperature dependence between −75° C and 75 °C, and d₃₃ exhibits very good thermal stability over the range from −196 °C to 75 °C in the aging test.     

Structural and transport properties of stoichiometric Mn-doped magnetite: Fe3−xMnxO4

The polycrystalline samples of Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50) were prepared by a solid-state route reaction method. X-ray diffraction pattern shows that Mn²⁺ doped magnetites are in single phase and possess cubic inverse spinel structure. The resistivity measurements (10 < T < 300 K) for x = 0.0 and 0.01 confirms the first order phase transition at the Verwey transition T_V = 123 K and 117 K, respectively. No first order phase transition was evidenced for Fe_3−xMn_xO₄ (0.10 ≤ x ≤ 0.50). Small polaron model has been used to fit the semiconducting resistivity behavior and the activation energy ?_a, for samples x = 0.10 and 0.50 is about 72.41 meV and 77.39 meV, respectively. The Raman spectra of Fe_3−xMn_xO₄ at room temperature reveal five phonons modes for Fe_3−xMn_xO₄ (0.01 ≤ x ≤ 0.50) as expected for the magnetite (Fe₃O₄). Increased Mn²⁺ doping at Fe site leads to a gradual changes in phonon modes. The Raman active mode for Fe_3−xMn_xO₄ (x = 0.50) at ≅641.5 cm⁻¹ is shifted as compared to parent Fe₃O₄ at ≅669.7 cm⁻¹, inferring that Mn⁺² ions are located mostly on the octahedral sites. The laser power is fixed to 5 mW causes the bands to broaden and to undergo a small shift to lower wave numbers as well as increase in the full width half maxima for A_1g phonon mode with the enhancement of Mn²⁺ doping. Mössbauer spectroscopy probes the site preference of the substitutions and their effect on the hyperfine magnetic fields confirms that Mn⁺² ions are located mostly on the octahedral sites of the Fe_3−xMn_xO₄ spinel structure.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.