Sintering behaviors, magnetic and electric properties of Bi-Zn co-doped Co2Y ferrites

The Bi and Zn substitution effects on the sintering behaviors, magnetic and electric properties of hexagonal ferrites with a composition of 2(Ba_1−xBi_xO)·2(Zn_yCo_0.8−yCu_0.2O)·6(Fe_2−x/3Zn_x/3O₃) were investigated. The results showed that the addition of Bi and Zn can significantly promote Co₂Y densification. The Y phase may be triggered to decompose into M and spinel phases at high sintering temperatures (above 1050 °C) for samples with excess Bi (x = 0.2) substitution, which resulted in densification and magnetic properties degradation. Co₂Y ferrites with x = 0.1 and y = 0.4 sintered at 1050 °C show a relative density of 94%, a high initial permeability of 4.5, a quality factor (Q) of 50.     

Structural, optical and electromagnetic properties of Bi1−xHoxFeO3 multiferroic materials

Bi_1−xHo_xFeO₃ (x = 0.00, 0.05, 0.10, 0.15 and 0.20) polycrystalline ceramics were synthesized by a solid-state reaction and their structural, absorption, Raman scattering, impedance and magnetic properties were investigated. The substitution of rare earth Ho for Bi was found to decrease the impurity phase in BiFeO₃ ceramics. There appears an anomalous change in the lattice constants, optical band gap as well as the impedance spectroscopy and magnetization of samples at x = 0.10, suggesting a limit of dissolubility of Ho doped ions in BiFeO₃. Additionally, the Raman measurement performed for the lattice dynamics study of Bi_1−xHo_xFeO₃ samples reveals a band centered at around 1000-1300 cm⁻¹ which is associated with the resonant enhancement of two-phonon Raman scattering in the multiferroic Bi_1−xHo_xFeO₃ samples. Ho-doped BiFeO₃ also showed a ferromagnetic-like behavior with M_r = 1070 × 10⁻⁴ and M_s = 1.60 emu/g for optimum content x = 0.10, which is similar to the solid solution system of BiFeO₃.     

Growth and characterization of perovskite LaGaO3 crystals doped with Sr and Mn

Single crystals of LaGaO₃ doped with Sr and Mn (LSGMn) were grown by the Czochralski method from the melt with compositions: La_1−xSr_xGa_1−yMn_yO₃, x = y = 0.02; 0.05 and x = 0.05, y = 0.06. Single crystals with 20 mm diameter with convex crystal-melt interface were grown on LaGaO₃ oriented seed with pulling rate of 2 mm/h. Single crystals were dark and have strong tendency to spiral growth. This tendency was decreased with increasing the Mn content in comparison with Sr. Effective segregation coefficients for Sr and Mn in LaGaO₃ are lower than 1. Room-temperature structural measurements by X-ray powder diffraction showed perovskite structure with Pbnm space group for all measured samples. Orthorhombic b and c lattice parameters decrease, whereas a slightly increases with decreasing orthorhombic unit cell volume that is related to increased amount of Mn and Sr in the melt. Thermal analysis and Raman investigations showed that the temperature of the first order phase transitions temperature form orthorhombic to rhombohedral structure observed in pure LaGaO₃ at about 150 °C decreases to about 49 °C at the bottom part of crystal with x = y = 0.05 composition.     

Superconductors of SmFe1−xCoxAsO synthesized by mechanical alloying

The SmFe_1−xCo_xAsO (x = 0 − 0.25) superconductors were synthesized by mechanical alloying (MA) and rapid sintering method with Co atoms doped into FeAs layers to replace the Fe sites. The phase purity and superconducting properties of the samples were characterized by X-ray diffraction, electrical resistivity, magnetic susceptibility and Hall coefficient. All the samples belong to the tetragonal ZrCuSiAs structure type with the grain size in 1-3 μm. The superconducting critical temperature T_c of SmFe_0.9Co_0.1AsO was 12.5 K, and the structure/SDW transition was suppressed by Co doping. The negative Hall coefficient of SmFe_0.9Co_0.1AsO indicated the electron conduction in the sample. The charge carrier density is about 2 × 10²⁰ cm⁻³ at the temperature lower than 150 K, larger than that of SmFeAsO.     

Effects of Tl-filling into the voids and Rh substitution for Co on the thermoelectric properties of CoSb3

In order to enhance the thermoelectric (TE) properties of CoSb₃, we tried to reduce the lattice thermal conductivity (κ_lat) by filling Tl into the voids and substitution of Rh for Co. We prepared polycrystalline samples of Tl_x(Co_1−yRh_y)₄Sb₁₂ (x = 0, 0.05, 0.10, 0.15, 0.20 and y = 0.1, 0.2) and examined their TE properties from room temperature to 750 K. All the samples indicated negative values of the Seebeck coefficient (S). Both the electrical resistivity and the absolute values of the S decreased with increasing the Tl-filling ratio. The Tl-filling and Rh substitution reduced the κ_lat, due to the rattling and the alloy scattering effects. The minimum value of the κ_lat was 1.54 W m⁻¹ K⁻¹ at 550 K obtained for Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂. Tl_0.20(Co_0.8Rh_0.2)₄Sb₁₂ exhibited the best TE performance; the maximum value for the dimensionless figure of merit ZT was 0.58 at around 600 K.     

Structure, dielectric and electrical properties of cerium doped barium zirconium titanate ceramics

Rare-earth doped barium zirconium titanate (BZT) ceramics, Ba(Zr_0.25Ti_0.75)O₃ + xCeO₂, (x = 0-1.5 at%) were obtained by a solid state reaction route. Perovskite-like single-phase compounds were confirmed from X-ray diffraction data and the lattice parameters were refined by the Rietveld method. It is found that, integrating with the lattice parameters and the distortion of crystal lattice, there is an alternation of substitution preference of cerium ions for the host cations in perovskite lattice. Morphological analysis on sintered samples by scanning electron microscopy shows that the addition of rare-earth ions affects the growth of the grain and remarkably changes the grain morphology. The effect of rare-earth addition to BZT on dielectric and electrical properties is analyzed. High values of dielectric tunability are obtained for cerium doped BZT. Especially, the experimental results on the effect of the contents of rare-earth addition on the resistivity of BZT ceramics were investigated, demonstrating that the samples with x = 0.4 and x = 0.6 could be semiconducting in air atmosphere.     

Thermoelectric properties of n-type Ca1−xDyxMn1−yNbyO3−δ compounds (x = 0, 0.02, 0.1 and y = 0, 0.02) prepared by spray-drying method

We report the high temperature thermoelectric properties of Ca_1−xDy_xMn_1−yNb_yO_3−δ (x = 0, 0.02, 0.1 and y = 0, 0.02) synthesized by spray-drying method. A maximum power factor (PF) value of 2.65 μW K⁻² cm⁻¹ is obtained at 1100 K for CaMn_0.98Nb_0.02O_3−δ. This represents an improvement of about 75% with respect to undoped CaMnO_3−δ sample at the same temperature. We also provide a complete structural characterization of the samples.     

Structure and electrical properties of MnO2-doped Sr2−xCaxNaNb5O15 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics Sr_2−xCa_xNaNb₅O₁₅ + y wt% MnO₂have been prepared by the conventional solid state reaction method. Our results reveal that Ca²⁺and Mn ions have entered into the Sr₂NaNb₅O₁₅ lattices to form a solid solution with tungsten-bronze structure. The substitution of Ca²⁺ induces a decrease in piezoelectric coefficient d₃₃, electromechanical coupling factors k_p and k_t, while, the addition of Mn ions decreases the sintering temperature and effectively promotes the densification of the ceramics. The effect of substitution of Ca²⁺and Mn ions on the structure, electrical properties and diffused phase changing were investigated systematically. For the ceramic with x = 0.05 and y = 0.5, the piezoelectric, dielectric and ferroelectric properties become optimum, giving a piezoelectric coefficient d₃₃ = 190 pC/N, electromechanical coupling factors k_p = 13.4% and k_t = 36.5%, ?_r = 2123, loss tangent tan δ = 0.038, remanent polarization P_r = 4.76 μC/cm², coercive field E_c = 12.68 kV/cm, and Curie temperature T_c = 260 °C.     

Effects of Mn substitution on ferro- and piezoelectric properties of Bi0.86Sm0.14FeO3 thin films

The Bi_0.86Sm_0.14FeO₃ (BSFO) and Bi_0.86Sm_0.14Fe_1 − xMn_xO₃ (BSFMO) (x = 0.01, 0.03, 0.05) thin films were deposited on indium tin oxide/glass substrates via a metal organic deposition method. 1 at.% Mn doping leads to an evident reduction of the leakage current in BSFO film. More importantly, the Bi_0.86Sm_0.14Fe_0.99Mn_0.01O₃ film exhibits the lowest coercive field (E_c = 272 kV/cm), the largest remanent polarization (P_r = 53.6 μc/cm²) and the remanent out-of-plane piezoelectric coefficient (d₃₃ = 146 pm/V). However, further increase of Mn doping content results in the deterioration of the charge retaining capability and the piezoelectric properties of the films. The negative influence of high Mn doping contents was discussed based on the structure change and the contribution of irreversible movement of non-180° domain walls in the aged films.     

Role of Ce-Mn substitution on structural, electrical and magnetic properties of W-type strontium hexaferrites

W-type hexaferrites with nominal composition Sr_1−xCe_xCo₂Mn_yFe_16−yO₂₇ (x = 0.00, 0.02, 0.04, 0.06 & y = 0.0, 0.2, 0.4, 0.6) has been synthesized by the chemical co-precipitation method. The effect of substitution of Ce at Sr & Mn at Fe site on the structural, magnetic and electrical properties has been investigated. The XRD patterns confirm single W-type hexaferrite phase and various parameters such as lattice constants (a & c), cell volume (V), crystallite size (D), X-ray density (d_x), bulk density (d_b) and porosity (P) were calculated from XRD data. The crystallite size is found in the range of 22.5-30 nm and this size is small enough to obtained suitable signal-to-noise ratio in high density recording media. The magnetic properties such as saturation magnetization, remanence, squareness ratio and coercivity were calculated from hysteresis loops and were observed to increase with increase in Ce-Mn concentration up to a certain substitution level. The resistivity showed interesting behavior with temperature, showing metal-to-semiconductor transition temperature. The increase in saturation and remanence suggest that the synthesized materials can be used in the high density recording media.     

Calculation of band offsets in Cd1−xXxTe alloys, X = Zn, Mg, Hg and Mn and magnetic effects in CdMnTe

Due to the large variety of properties offered by the telluride binaries CdTe, ZnTe, MgTe, HgTe and MnTe as well as their mixed ternary alloys, an accurate knowledge of their electronic band parameters is crucial. These materials have been extensively studied but, some points bearing on several properties have never previously reported or are still not clear. In this paper, we report results on the conduction and valence band offsets of the pseudo-morphically strained Cd_1−xX_xTe layer on relaxed Cd_1−yX_yTe substrate, X = Zn, Hg, Mg and Mn. Based on the Van Der Walle model, calculations have been performed for the all range of material and substrate 0 ≤ x,y ≤ 1. These discontinuities have not yet calculated for X = Mg, Mn or Hg in the all range 0 ≤ x,y ≤ 1. For the CdMnTe diluted magnetic semiconductor which we focus more interest due to its considerable current interest for applications, calculations have been done without and with correction taking into account magnetic effect of magnesium ions Mn²⁺. It is found that the introduction of only a few percent of Mn into CdTe provides a unique opportunity to combine two important fields in physics, semiconductivity and magnetism. We can take advantage both of possibility of applications in solid-state lasers and exceptional magnetic properties offered by this magnetic diluted semiconductor.This study presents important quantities that are required to model quantum structures and offers a fast and inexpensive way to check device designs and processes.     

Comparison of dehydriding kinetics between pure LaNi5 and its substituted systems

The kinetic mechanisms of dehydriding reaction in La_0.8M_0.2Ni₅ and LaNi_4.5T_0.5 were comparatively investigated by the Chou model and the first order model, and the former was superior to the latter from the comparison of theoretical calculated results and experimental data. According to the characteristic time (t_c) in the Chou model, substituting La (t_c = 71.36 s) with Ce (t_c = 35.64 s), Nd (t_c = 30.82 s) and Pr (t_c = 28.86 s) increased the dehydriding reaction rate, but partial substitution of Ni (t_c = 71.36 s) with Co (t_c = 102.29 s), Fe (t_c = 116.70 s) and Cu (t_c = 120.62 s) decreased the hydrogen desorption reaction rate. The Chou model was also used to discuss the effect of different amount of Ni substituted with Fe and Co. The dehydriding reaction rates of La(Ni_1−xFe_x)₅ increased with x leveling from 0 to 0.20 but decreased with x increasing from 0.20 to 0.30, while that of LaNi_5−yCo_y decreased with increasing the amount of Co from 0 to 3.00. In addition, the Chou model was successfully applied to predicting the kinetic properties of LaNi_4.8Sn_0.2 at 40 °C and 60 °C, which exhibited an excellent agreement with the experimental data.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

Composition dependence of magnetic properties of directly quenched Nd-Fe-Ti-Zr-B bulk magnets

Magnetic properties, phase evolution, and microstructure of directly quenched Nd_yFe_97−y−zTi_3−xZr_xB_z (x = 0-3; y = 7-10; z = 14-19) bulk magnets of 0.9 mm in diameter have been investigated. Proper Zr substitution for Ti and appropriate Nd and B contents modify the magnetic phases constitution and refine the grain size from 200-250 nm to 50-100 nm. Consequently, the magnetic properties of the rods are enhanced remarkably from _iH_c = 6.2 kOe and (BH)_max = 5.6 MGOe for Zr-free rods to _iH_c = 6.7-13.5 kOe and (BH)_max = 6.7-8.2 MGOe for Zr-substituted Nd_yFe_97−y−zTi_3−xZr_xB_z rods (x = 0.5-2; y = 8-10; z = 14-16). The optimum magnetic properties of B_r = 6.6 kG, _iH_c = 9.6 kOe and (BH)_max = 8.2 MGOe were achieved for Nd_9.5Fe_72.5Ti_2.5Zr_0.5B₁₅ alloy.     

The Mn-doping effect on the charge ordering state of La1/3Sr2/3FeO3

The longitudinal ultrasonic velocity (V_l), as well as resistivity has been measured in single-phase polycrystalline La_1/3Sr_2/3Fe_1−xMn_xO₃ (x = 0, 0.025, 0.05) at a frequency of 10 MHz, from 20 K to 300 K. It is found that with increasing Mn-doping level, the resistivity increases and the charge ordering transition temperature T_CO shifts to lower temperature. For all samples, upon cooling down from 300 K, a substantial softening in V_l above T_CO and dramatic stiffening below T_CO are observed. This abnormal elastic softening above T_CO can be described well by the mean-field theory, which indicates that this feature is due to the electron-phonon coupling via the Jahn-Teller effect and this coupling is enhanced with the Mn doping. Below T_CO, another softening in V_l is observed for x = 0, and weakens with the increasing of Mn content. This character is attributed to the breathing-type distortion of Fe-O octahedron and suggests that the charge disproportionation (CD) transition is suppressed by the Mn substitution.     

Fabrication and properties of Ba(Zr1−xCex)0.9Y0.1O2.95/NaCl composite electrolyte materials

Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95/NaCl (x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr_1−xCe_x)_0.9Y_0.1O_2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10⁻² S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen.     

Hydrothermal synthesis of superconductors Ba1−xKxBiO3 and double perovskites Ba1−xKxBi1−yNayO3

Superconductors Ba_1−xK_xBiO₃ and body-centered double perovskites Ba_1−xK_xBi_1−yNa_yO₃ have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures T_C of Ba_1−xK_xBiO₃ decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level.     

Structural characterization of layered LiNi0.85−xMnxCo0.15O2 with x = 0, 0.1, 0.2 and 0.4 oxide electrodes for Li batteries

We report the synthesis of LiNi_0.85−xCo_0.15Mn_xO₂ positive electrode materials from Ni_0.85−xCo_0.15Mn_x(OH)₂ and Li₂CO₃. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi_0.85−xCo_0.15Mn_xO₂ materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi_0.85−xCo_0.15Mn_xO₂ compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and L_M-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn⁴⁺ with Ni²⁺ and Mn⁴⁺ with Li⁺.     

Coexistence of room temperature ferroelectricity and ferrimagnetism in multiferroic BiFeO3-Bi0.5Na0.5TiO3 solid solution

The structure, ferroelectric and magnetic properties of (1 − x)BiFeO₃-xBi_0.5Na_0.5TiO₃ (x = 0.37) solid solution fabricated by a sol-gel method have been investigated. X-ray diffraction and Raman spectroscopy measurements show a single-phase perovskite structure with no impurities identified. Compared with pure BiFeO₃, the coexistence of ferroelectricity and ferrimagnetism have been observed at room temperature for the solution with remnant polarization P_r = 1.41 μC/cm² and remnant magnetization M_r = 0.054 emu/g. Importantly, a magnetic transition from ferrimagnetic (FM) ordering to paramagnetic (PM) state is observed, with Curie temperature T_C ∼ 330 K, being explained in terms of the suppression of cycloid spin configuration by the structural distortion.     

Dielectric and ferroelectric properties and electric conductivity of sol-gel derived PBZT ceramics

(Pb_1−xBa_x)(Zr_1−yTi_y)O₃ (PBZT) is a solid solution in which ferroelectric, relaxor or antiferroelectric properties are observed depending on composition. The substitution of Ba²⁺ into A position of the perovskite structure leads to the decrease in phase transition temperature and it gradually leads to relaxor properties. The majority of papers describe PBZT obtained from oxides. We report the results of the investigation of the properties and phase transitions of (Pb_1−xBa_x)(Zr_0.65Ti_0.35)O₃ ceramics with x = 0.09, 0.25 and 0.35 obtained by the sol-gel method with final free sintering (FS) at 1573 K/4 h and by the hot pressing (HP) method at 1473 K/2 h/20 MPa. Unlike pure PZT, the properties of HP-PBZT samples obtained at lower (1473 K) temperature are a little inferior than FS samples. It is probably related to the fact that barium requires higher final sintering temperatures.We present the results of XRD and dielectric measurements vs. temperature for PBZT ceramics. On the basis of dielectric measurements a.c. conductivity and activation energies have been calculated. In agreement with earlier literature data, we note that with the increasing Ba content T_m decreases and the maximum of ?(T) is wider. However, we do not observe a shift of T_m with increasing frequency. The room P(E) hysteresis loops become more narrow and the polarization is smaller. The increase in dielectric losses with increasing temperature makes the measurement of hysteresis loops at low frequencies and high temperatures difficult.