Effects of Co2O3 concentration on high Q-factor NiCuZn ferrites for 13.56 MHz radio identification communication

Co₂O₃-doped NiCuZn ferrites with a high (group A) or low (group B) permeability were prepared using the conventional ceramic method to obtain high Q-factor NiCuZn ferrites for a 13.56 MHz near-field-communication (NFC) system. The XRD patterns of samples from both groups exhibited single spinel phase. Permeability monotonously decreased with increasing Co₂O₃ content, whereas sintering density and saturation magnetic flux density (Bs) slightly changed with Co₂O₃ content. The permeability of 0.45 wt% Co₂O₃-doped ferrite (A_0.45) was similar to that of 0.10 wt% Co₂O₃-doped ferrite (B_0.10). However, the former sample presented a considerably higher Q-factor than the latter sample. The former sample also presented enhanced stability variation of Q-factor with frequency, which indicated an improved electromagnetic shielding function for the NFC system. The mechanisms involved were also elucidated.     

Cd-substituted NiZnCo ferrite with high dielectric constant and low coercivity for high-frequency electronic devices

This work investigated the effect of replacing Zn²⁺ ions with Cd²⁺ ions on the microstructure and electromagnetic properties of NiZnCo ferrites. The studies show that the Cd²⁺ ions substituted for Zn²⁺ ions at the A sites (tetrahedral sites) of the ferrite lattice. The large ionic radius of the Cd²⁺ ions can cause lattice distortion. Concurrently, the low melting point of CdO can effectively reduce the sintering temperature of NiZnCo ferrite, thereby significantly changing the magnetoelectric properties of NiZnCo ferrite. These changes are mainly manifested as the decrease in the saturation magnetization (Ms) from 66.6 to 58.5 emu/g and the increase in coercivity (Hc) from 31.2 to 34.8 Oe. The dielectric constant increases considerably, dielectric loss tanδ gradually decreases from 4.71 to 0.83 at 10 kHz, and DC resistivity ρ decreases considerably from 8.0 × 10⁴ to 1.61 × 10⁴ Ω m. Therefore, the substitution of Cd²⁺ ions in NiZnCo ferrite provides excellent electrical and magnetic properties, which provide a reference for the development of high-frequency miniaturized electronic equipment.     

Enhanced electromagnetic properties of low-temperature sintered NiCuZn ferrites by doping with Bi2O3

NiCuZn ferrite is a material suitable for low-temperature co-fired ceramic (LTCC) technology due to its high permeability and relatively low sintering temperature. The main research questions regarding NiCuZn ferrites are focused on reducing the sintering temperature of the NiCuZn ferrites to achieve compatibility with the Ag electrodes and improve their electromagnetic properties. In this study, the electromagnetic properties of NiCuZn (Ni_0.29Cu_0.14Zn_0.60Fe_1.94O_3.94) ferrites were enhanced by doping with Bi₂O₃, resulting in a reduction of the sintering temperature to 925 °C. The findings show that a suitable concentration of Bi₂O₃ doping could promote the growth of grains and result in NiCuZn ferrites with denser microstructures sintered at a low temperature. Furthermore, adding 0.30 wt% Bi₂O₃ to NiCuZn ferrite enhances its electromagnetic properties, such as a high real part of permeability (～937.6 @ 1 MHz), high saturation magnetization (～60.353 emu/g), low coercivity (～0.265 kA/m), and excellent dielectric constant (～14.71 @ 1 MHz). In addition, the chemically compatible Ag electrodes suggest that the NiCuZn +0.30 wt% Bi₂O₃ ceramics may be acceptable for LTCC technology.     

Effects of Bi2O3–CaCu3Ti4O12 composite additives on micromorphology,static magnetic properties,and FMR linewidth ΔH of NCZ ferrites

NiCuZn (NCZ) ferrites have been widely used in non-reciprocal microwave/millimeter ferrite devices, such as circulators. With the development of microwave/millimeter devices and components to high frequency, miniaturization, and lightweight applications, NCZ ferrites have needed to satisfy the essential requirements of high saturation magnetization 4πM_s, low coercivity H_c, and low ferromagnetic resonance (FMR) linewidth ΔH. Herein, 0.1 wt% Bi₂O₃ and 0.0–3.5 wt% CaCu₃Ti₄O₁₂ (CCTO) composite additives were introduced to NCZ ferrites, the influence of Bi₂O₃–CCTO composite additives on micromorphology, static magnetic properties, and FMR linewidth ΔH of NCZ ferrites have been demonstrated in detail. The results show that increasing the CCTO amounts in NCZ ferrites, saturation magnetization 4πM_s monotonically decreases from 5484Gs to 4819Gs, and both coercive force H_c and FMR linewidth ΔH first decreases and then increases with minimums of 31A/m and 147Oe, respectively. In addition, the theory of spin-wave narrowing and the law of approach to saturation have been adopted for the separation calculation of FMR linewidth ΔH to the crystalline anisotropy linewidth ΔH_a and porosity induced linewidth ΔH_p. The sample with 0.1 wt% Bi₂O₃ and 1.5 wt% CCTO possesses high saturation magnetization 4πM_s (5321Gs), remanence B_r (200 mT), low coercivity H_c (31A/m), and low FMR linewidth ΔH (147Oe). The state-of-the-art NCZ ferrites with outstanding performances manifest significant applied potency for microwave/millimeter devices and components in phase array radar systems.     

Nb5+ ion substitution assisted the magnetic and gyromagnetic properties of NiCuZn ferrite for high frequency LTCC devices

Nowadays, developing nickle zinc ferrites with excellent magnetic and gyromagnetic properties are of great importance for solving the matching problem of 5G communication system. However, much is discussed about soft magnetic properties, but little is reported gyromagnetic properties that is critical for microwave device applications. Herein, Nb⁵⁺ ions substituted Ni_0.29Cu_0.18Zn_0.53Nb_xFe_2-xO₄ (x = 0.00-0.05), possessing high saturation magnetization, approriate initial permeability, high cut-off frequency and low ferromagnetic resonance linewidth (@9.55 GHz), were synthesized by low-temperature firing (900 °C). The phase structure and morphology evolutions were studied in detail. The results of morphology observations revealed that Nb⁵⁺ substitution has significant role in determining produce compact and uniform microstructures of NiCuZn ferrites via suppress the grain growth, which further corresponding enhance the magnetic and gyromagnetic properties. As a result, a uniform and compact grain size can be obtained, corresponding to the change of magnetic and gyromagenetic properties have different trends. Enhanced magnetic and gyromagnetic performance including high initial permeability (μ' = 203 @1 MHz), saturation magnetization (4πM_s = 3966 Gauss) and low ferromagnetic resonance linewidth (ΔH = 203 Oe) of the NiCuZn ferrites is achieved though adjusting Nb⁵⁺ ions substitution. More importantly, this work not only for low temperature co-fired ceramic (LTCC) technology but also for high frequency and microwave frequency devices including phase shifter and radars.     

Effect of Bi2O3 contents on magnetic and electromagnetic properties of LiZnMn ferrite ceramics

Soft LiZnMn ferrites with low coercive force values and small grain sizes were developed by the solution combustion synthesis and low temperature sintering technique for microwave applications at a high frequencies. Bismuth oxide was used as an additive to lower the sintering temperature. The examination covered the influence of Bi₂O₃ on the crystal structure, microstructure, primary magnetic and dielectric characteristics of lithium-zinc-manganese ferrites. The most promising sample designed for using in microwave devices was produced by sintering at 1075 ℃ temperature for 8 h with added 1.5 wt% Bi₂O₃. These production conditions have yielded 2.98 µm average grain size in a ceramic product, the density is 4.84 cu cm/g, and the coercive force, residual induction, and saturation induction are 58 A/m, 2078.4 G, and 3439.1 G, respectively. In addition, this sample demonstrates a high initial magnetic permeability (μ_i = 168), Curie temperature (T_c = 437.5 ℃), high values of the dielectric loss tangent (tan δ_? = 6.32?10^?3), ferromagnetic resonance line width (ΔH = 280 Oe) and the resonance line of spin waves (ΔH_k = 1.87 Oe). Further increase in the bismuth oxide content allows observing a change in the ceramics microstructure, accompanied by a deterioration in the magnetic and electromagnetic characteristics. Here, the discussion covers the mechanism of change in the functional properties of lithium-zinc-manganese ferrites produced in the conditions of solution combustion with added bismuth oxide. Thus, synthesizing of initial pre-ceramic powder by glycine-nitrate combustion and subsequent low-temperature sintering with added bismuth oxide is a novel efficient technique of producing advanced soft high-frequency LiZnMn ferrites.     

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti1-xNbx)O3 solid solutions by Rietveld refinement and Raman spectra

Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were prepared by the conventional solid-state reaction method. The phase composition, sintering characteristics, microstructure and dielectric properties of Ti⁴⁺ replacement by Nb⁵⁺ in the formed solid solution Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics were systematically studied. The structural variations and influence of Nb⁵⁺ doping in Mg(Ti_1-xNb_x)O₃ were also systematically investigated by X-ray diffraction and Raman spectroscopy, respectively. X-ray diffraction and its Rietveld refinement results confirmed that Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics crystallised into an ilmenite-type with R-3 (148) space group. The replacement of the low valence Ti⁴⁺ by the high valence Nb⁵⁺ can improve the dielectric properties of Mg(Ti_1-xNb_x)O₃ (x = 0–0.09). This paper also studied the different sintering temperatures for Mg(Ti_1-xNb_x)O₃ (x = 0–0.09) ceramics. The obtained results proved that 1350 °C is the best sintering temperature. The permittivity and Q × f initially increased and then decreased mainly due to the effects of porosity caused by the sintering temperature and the doping amount of Nb₂O₅, respectively. Furthermore, the increased Q × f is correlated to the increase in Ti–O bond strength as confirmed by Raman spectroscopy, and the electrons generated by the oxygen vacancies will be compensated by Nb⁵⁺ to a certain extent to suppress Ti⁴⁺ to Ti³⁺, which was confirmed by XPS. The increase in τ_f from ?47 ppm/°C to ?40.1 ppm/°C is due to the increment in cell polarisability. Another reason for the increased τ_f is the reduction in the distortion degree of the [TiO₆] octahedral, which was also confirmed by Raman spectroscopy. Mg(Ti_0.95Nb_0.05)O₃ ceramics sintered at 1350 °C for 2 h possessed excellent microwave dielectric properties of ε_r = 18.12, Q × f = 163618 GHz and τ_f = ?40.1 ppm/°C.     

Triple-doping of (Ga1/2Nb1/2)xTi1-xO2 ceramics with Al3+ for enhanced giant dielectric response with simultaneous decrease in dielectric loss

An acceptor-donor co-doped (Ga_1/2Nb_1/2)_0.1Ti_0.9O₂ ceramic is triple-doped with Al³⁺, followed by sintering at 1450 °C for 5 h to obtain (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics with improved giant dielectric properties. Homogeneous dispersion of all dopants inside the grains, along with the partially segregated dispersion of the Ga³⁺ dopant along the grain boundaries, is observed. The (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics exhibit high dielectric permittivities (ε′～4.2–5.1 × 10⁴) and low loss tangents (tanδ～0.007–0.010), as well as a low-temperature coefficients (<±15%) between ? 60 and 200 °C. At 1 kHz, tanδ is significantly reduced by ～4.4 times, while ε′ is increased by ～3.5 times, which is attributed to the higher Al³⁺/Ga³⁺ ratio. The value of tanδ at 200 °C is as low as 0.04. The significantly improved dielectric properties are explained based on internal and surface barrier-layer capacitor effects, which are primarily produced by the Ga³⁺ and Al³⁺ dopants, respectively, whereas the semiconducting grains are attributed to Nb⁵⁺ doping ions.     

Structural,magnetic and electrical properties of K0.5Na0.5NbO3 doped NiZnCo ferrite for high frequency device

Ni_0.6Zn_0.4Co_0.2Fe_1.8O₄ ferrites doped with x wt.% K_0.5Na_0.5NbO₃ (0.00≤x≤1.00) were successfully prepared by solid-state reaction method. The lattice parameters a decreased and the diffraction peak of (311) shifted to higher angle with the increase of K_0.5Na_0.5NbO₃ (KNN) content. The grain size D initially increased to 3.12 μm (x = 0.50) and then reduced to 2.66 μm (x=1.00). The study also showed the addition of KNN effectively improved magnetic and electrical properties of NiZnCo ferrites. The saturation magnetization Ms decreased from 60.59 to 46.11 emu/g and the coercivity Hc overall showed a decreasing trend from 84.64–67.00 Oe. The dielectric constant ε´ of prepared samples increased when x≤0.75, then decreased when x>0.75, and all prepared samples had low loss tangent tanδ at high frequency. In addition, all samples exhibited high resistivity ρ and activation energy E_ρ.     

Enhancement in magnetic permeability of Ni-Co-Zn ferrites using CuO doping for RF and microwave devices

Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni_0.4Co_0.25Zn_0.35Fe₂O₄ ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ’ of 4-10) and relatively low magnetic loss tangent ( of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.     

Chemical interpretation,enhanced ferroelectric property and dielectric breakdown strength of CuO-added Sr2Nb2O7 ceramics

The structural interpretation and electrical properties of perovskite layer structured (PLS) Sr₂Nb₂O₇-xwt%CuO ceramics prepared by solid-state reaction method are investigated. The chemical interpretation of enhanced piezoelectricity is confirmed to be attributed to the rotation and/or distortion of oxygen octahedron caused by possible Cu²⁺ substitution at the A-site of Sr₂Nb₂O₇ by XRD refinement and variable-temperature Raman spectra. Sr₂Nb₂O₇-xwt%CuO (x?=?0.3, 0.5 and 0.7) ceramics shows enhanced ferroelectric properties with a larger P_r of ～4.1?μC/cm² and a smaller E_c of ～63.1?kV/cm. This study further explains the cations in A-site play a major structural role in the polarization process for PLS system. It was found that dielectric breakdown strength increases up to 258.8?kV/cm and then decreases gradually with the increase of CuO content. Impedance spectroscopy indicated that CuO addition could be helpful in increasing the grain boundary resistance then dielectric breakdown strength.     

The Cobalt Zinc Spinel Ferrite Nanofiber: Lightweight and Efficient Microwave Absorber

To solve the heavy mass problem of the traditional spinel ferrite using as the microwave absorber, the Co_xZn_(1?x)Fe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) ferrite nanofibres were synthesized by electrospinning method. The phase composition, morphology, and electromagnetic properties were analyzed. The results showed that all the as‐prepared Co_xZn_(1?x)Fe₂O₄ ferrites exhibited the homogeneous nanofibrous shape. The saturation magnetization and coercivity were enhanced by tuning the Co²⁺ content. The electromagnetic loss analysis indicated that the Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber performed the strongest microwave attenuation ability. The microwave absorbing coating containing 15 wt% of Co_0.6Zn_0.4Fe₂O₄ ferrite nanofiber showed the reflection loss less than ?10 dB in the whole X‐band and 80% of the Ku‐band frequencies. Meanwhile, the surface density was only 2.4 Kg/m².     

Effects of Bi2O3-Nb2O5 additives on microstructure and magnetic properties of low-temperature-fired NiCuZn ferrite ceramics

NiCuZn ferrite with superior magnetic performance is vital ceramic material in multilayer chip inductors (MLCI) applications. In this study, low-temperature-sintered Ni_0.22Cu_0.2Zn_0.58Fe₂O₄ ferrite ceramic doped with 1.0?wt% Bi₂O₃-x?wt% Nb₂O₅ (where x?=?0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) was synthesized via solid-state reaction method. Effects of Bi₂O₃-Nb₂O₅ additives on microstructures and magnetic properties of NiCuZn ferrite ceramics sintered at 900?°C were systematically investigated. Results indicate that an appropriate amount of Bi₂O₃-Nb₂O₅ composite additives can significantly promote grain growth and densification of NiCuZn ferrite ceramics when sintered at low temperatures. Specifically, samples doped with 1.0?wt% Bi₂O₃ and 0.4?wt% Nb₂O₅ additives exhibited excellent initial permeability (~ 410 @ 1?MHz), high cutoff frequency (~ 10?MHz), high saturation magnetization (~ 54.92?emu/g), and low coercive force (~ 20.32?Oe). These observations indicate that NiCuZn ferrite ceramics doped with appropriate amounts of Bi₂O₃-Nb₂O₅ additives are great candidate materials for MLCI applications.     

Effects of Mn-Addition on the Microstructure and Ferroelectric Properties of High-Temperature CaBi2Nb2O9 Ceramics

High temperature ferroelectric ceramics CaBi₂Nb₂O₉ + x wt% MnCO₃ (CBNO-x) are prepared by conventional sintering method. The microstructures and ferroelectric properties are studied. The Mn-added CBNO-based ceramics have a single Aurivillius phase structure. Nearly isotropic grains are obtained and the grains become larger with the increase of MnCO₃ addition. The Curie temperature T _c decreases slightly with the increase of MnCO₃ addition. The relative dielectric constant, dielectric loss, and the P–E hysteresis loop measurements indicate that Mn ions creates “soft” and “hard” doping effects simultaneously. Superior polarization performance (2P _r of 3.0 μC/cm² and 2E _c of 40.2 kV/cm) is obtained for the CaBi₂Nb₂O₉-0.375 wt% MnCO₃ ceramics.     

High-performance inductive couplers based on novel Ce3+ and Co2+ ions co-doped Ni-Zn ferrites

High-performance inductive couplers require Ni-Zn ferrites of high saturation magnetization, Curie temperature, permeability and application frequency. However, for inductive couplers some of these properties run against each other in one ferrite. To balance these requirements, in this work, novel Ni-Zn ferrite ceramics co-doped by Ce³⁺ and Co²⁺ ions with chemical formula Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ (x = 0–0.06) were designed and fabricated by a molten salt method. For the acquired ferrites, both Ce³⁺ and Co²⁺ ions could come into the lattices. The initially doped Co²⁺ ions would cause a slightly decreased grain size and dramatically reduced the specimen densification, but the further added Ce³⁺ ions could effectively inhibit the density reduction, while the grain size continues to dwindle. The additional Ce³⁺ ions would generate a foreign CeO₂ phase in the acquired specimens. The sole doping of Co²⁺ ions would aggrandize the saturation magnetization of ferrites, but the introduction of Ce³⁺ ions would cause its decrease. However, with an appropriate doping level, the Ce³⁺ and Co²⁺ ions co-doped ferrites could preserve a relatively high saturation magnetization, while the Curie temperature and cut-off frequency of the ferrites are dramatically augmented, although the permeability would be somewhat reduced. The as-acquired ferrites were simulated to apply in inductive couplers, revealing that the devices manufactured by the Ni_0.4Zn_0.5Co_0.1Ce_xFe_2-xO₄ ferrites had significantly high maximum operating frequency, compared with that of the one manufactured by pure Ni_0.5Zn_0.5Fe₂O₄ ferrite.     

Effect of Bi-substitution on the microstructure and electromagnetic properties of YCaZrVIG with low sintering temperature

Bi substituted YCaZrVIG ferrites, Y_2.3−xBi_xCa_0.7Zr_0.3V_0.2Fe_4.42O₁₂ (x=0.1, 0.25, 0.4, 0.5, 0.75) ferrites were prepared by conventional oxide method. The addition of Bi₂O₃ promoted the sintering performance and lowered the sintering temperature from 1420–1230 °C. However, it also resulted in the formation of minor second phases and the decrease of grain size. With the increase of Bi concentration, the dielectric constant increases linearly and then remains unchanged. The dielectric loss decreased firstly and then increased. The saturation magnetization (4πM_s) almost retained unchanged as the Bi concentration increased except for the sample with 0.75. The coercivity (H_c) decreased firstly and reached the minimum of 1.32 Oe at 0.25, and then rose when x>0.25, which was related to the facility of magnetic domain wall motion and magnetic moment reverse. Moderate addition of Bi also can increase the remanence (B_r) by improving sintering process. Additionally, we got the optimum electromagnetic properties in the samples with x=0.25 at 1230 °C: RD>97%, ε_r=15.7, tan δ_e=2.48×10⁻⁴, H_c=1.32Oe, 4πM_S=1663 Gs, B_r=583.91 Gs.     

High-temperature thermoelectric properties of polycrystalline CaMn1-xNbxO3-δ

The structural and thermoelectric (TE) properties of polycrystalline CaMn_1-xNb_xO_3-δ (0.025?≤?x?≤?0.25) were studied with X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and electrical transport measurements, with an emphasis placed on the Nb⁵⁺ content. The CaMn_1-xNb_xO_3-δ crystallized in an orthorhombic perovskite structure of the Pnma space group. The density and grain size of the CaMn_1-xNb_xO_3-δ samples gradually decreased when Nb⁵⁺ ions substituted Mn⁴⁺ ions. The CaMn_0.95Nb_0.05O_3-δ sample contained charge-ordered domains, stacking faults, and micro-twins. The substitution of Nb⁵⁺ for Mn⁴⁺ up to x?=?0.15 led to an increase in electrical conductivity, mainly due to an increased electron concentration. The CaMn_1-xNb_xO_3-δ samples with low Nb⁵⁺ contents (0.025?≤?x?≤?0.15) showed metallic behavior, whereas those with high Nb⁵⁺ contents (0.2?≤?x?≤?0.25) showed semiconducting behavior. The Nb⁵⁺ substitution lowered the absolute value of the Seebeck coefficient for the CaMn_1-xNb_xO_3-δ samples due to an increased electron concentration. The largest power factor (1.19?×?10^?4 W?m^?1 K^?2) was obtained for CaMn_0.95Nb_0.05O_3-δ at 800?°C. The partial substitution of Nb⁵⁺ for Mn⁴⁺ in CaMnO_3-δ proved to be highly effective for improving high-temperature TE properties.     

Large piezoelectric coefficient with enhanced thermal stability in Nb5+-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe³⁺, Nb⁵⁺ and Bi³⁺ cations in BCZT ceramics respectively. The results indicate that only Nb⁵⁺-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb⁵⁺ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating.     

Preparation,characterization, and giant dielectric permittivity of (Y3+ and Nb5+) co–doped TiO2 ceramics

The microstructure and giant dielectric properties of Y³⁺ and Nb⁵⁺ co–doped TiO₂ ceramics prepared via a chemical combustion method are investigated. A main rutile–TiO₂ phase and dense ceramic microstructure are obtained in (Y_0.5Nb_0.5)_xTi_1-xO₂ (x = 0.025 and 0.05) ceramics. Nb dopant ions are homogeneously dispersed in the microstructure, while a second phase of Y₂O₃ particles is detected. The existence of Y³⁺, Nb⁵⁺, Ti⁴⁺ and Ti³⁺ as well as oxygen vacancies is confirmed by X–ray photoelectron spectroscopy and X–ray absorption near edge structure analysis. The sintered ceramics exhibit very high dielectric permittivity values of 10⁴–10⁵ in the frequency range of 40–10⁶ Hz. A low loss tangent value of ≈0.08 is obtained at 40 Hz. (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics can exhibit non–Ohmic behavior. Using impedance spectroscopy analysis, the giant dielectric properties of (Y_0.5Nb_0.5)_xTi_1-xO₂ ceramics are confirmed to be primarily caused by interfacial polarization.     

Microstructure and enhanced magnetic properties of low-temperature sintered LiZnTiMn ferrite ceramics with Bi2O3-Al2O3 additive

Bi₂O₃ and Al₂O₃ were proven to separately have an impact on grain growth of LiZn ferrite ceramics. In this study, we synthesized LiZnTiMn ferrite ceramics under low temperature (<920 °C) using rationally designed formula of Bi₂O₃-Al₂O₃ as sintering agents. Microstructures, densities, and ferromagnetic performances were systematically investigated. Results show that appropriate amount of Bi₂O₃-Al₂O₃ leads to successful sintering of LiZnTiMn ferrites even below 900 °C. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) results show that spinel structure ferrite ceramics were obtained and that the addition of Bi₂O₃-Al₂O₃ accelerated solid-state reaction. Corresponding ferromagnetic properties, including saturation induction (B_s), remanence square ratio, coercivity (H_c), ferromagnetic resonance linewidth (ΔH), and M_s, were also investigated. At 920 °C, with addition amount of x=1 wt%, we obtain excellent performance: B_s=306 mT, B_r/B_s=0.849, H_c=2.34Oe, and ΔH=275 Oe. Results indicate that Bi₂O₃-Al₂O₃ is promising sintering agent for low-temperature sintering of LiZnTiMn ferrite ceramics.