Contrasting microwave dielectric properties of zircon-structured AEuV2O8 (A = Bi,La) ceramics

Two zircon-structured ceramics AEuV₂O₈ (A = Bi, La) were prepared with optimal sintering temperatures of 900 °C and 1375 °C, respectively. They exhibited sharp contrast performances with medium ε_r ～ 28.7 ± 0.1, Q × f ～ 14,000 ± 300 GHz, and large positive τ_f ～ 75.7 ± 2.0 ppm/°C for BiEuV₂O₈, whereas low ε_r ～ 10.4 ± 0.1 Q × f ～ 25,100 ± 300 GHz, and negative τ_f ～ ? 40.7 ± 2.0 ppm/°C for LaEuV₂O₈. The rattling effect at the A-site was more dominant in determining microwave dielectric properties than that of compressed V⁵⁺ at the B-site. It resulted in the higher ε_r, lower Q × f and τ_ε, and larger τ_f of BiEuV₂O₈ than those of LaEuV₂O₈. Besides, their Q × f was related with the relative density, bond valence and FWHM of the B_1 g Raman mode.     

Relationship between bond characteristics and microwave dielectric properties of REVO4 (RE = Yb,Ho) ceramics

Two novel low-ε_r REVO₄ (RE = Yb, Ho) microwave dielectric ceramics with the symmetry of the zircon structure, space group I4₁/amd, were prepared using the solid-state method. Dense REVO₄ (RE = Yb, Ho) ceramics sintered at 1200 °C and 1160 °C performed ε_r ～ 12.3 ± 0.1 and 13.3 ± 0.1, Q × f ～ 28,200 ± 300 GHz and 24,100 ± 300 GHz, τ_f ～ ?18.8 ± 0.5 ppm/°C and ?17.4 ± 0.5 ppm/°C, along with thermal expansion coefficient (α_L) of 9.0 ppm/°C and 8.1 ppm/°C, respectively. Bond valence results indicated that the slightly rattling RE³⁺ cations at the A-site and compressed V⁵⁺ at the B-site occurred in both ceramics. The positive deviations (Δε_r) of porosity corrected ε_r(Corr) from those calculated by the Clausius-Mosotti equation ε_r(C-M), 8.1% for YbVO₄ and 17.7% for HoVO₄, were observed, implying that the rattling effect of RE³⁺ in dodecahedral A-site were greater than those of compressed V⁵⁺ in tetrahedral B-site. Rattling effect also led REVO₄ (RE = Yb, Ho) to develop higher ε_r, and smaller τ_ε and τ_αm, then closer to zero τ_f values than other zircon-structured REVO₄ (RE = Ce, Nd, Sm, Eu) ceramics with large negative τ_f. The differences in sintering temperature and microwave dielectric performance of both ceramics were discussed using the packing fraction, full width at half maximum (FWHM) of Raman modes and Phillips-Van Vechten-Levine (P–V-L) theory.     

Photocatalytic degradation of acetic acid on spinel ferrites MFe2O4 (M = Mg,Zn, and Cd)

Spinel ferrites MFe₂O₄(M = Mg, Zn, and Cd) with Fe(III) in a d⁵ electron configuration were prepared via a conventional solid-state reaction. The amount of CO₂ generated by the photocatalytic degradation of acetic acid on these ferrites was measured under irradiation by a xenon lamp with a power of 300 W. Photocatalytic degradation was observed for all the compounds, and the results revealed that MgFe₂O₄ exhibited the highest degradation, i.e., 196 μmol/g/h. The degradation in the presence of MFe₂O₄(M = Mg, Zn, and Cd) increased with increasing heating condition.     

Influence of Sm and Cd co-substitutions on physical,magnetic, Mössbauer,electric, and dielectric properties of Co2X hexagonal ferrites in presence of a hematite phase

X-type samarium-cadmium co-substituted hexaferrite with compositions Ba_2-xSm_xCo₂Cd_yFe_28-yO₄₆ (0.00 ≤ x ≤ 0.08, and 0 ≤ y ≤ 0.4) were prepared at 1340 °C using a simple heat treatment technique. All heated samples were characterized using FTIR, XRD, SEM, VSM, M?ssbauer, and low-frequency dielectric measurements. XRD analysis of prepared samples shows the formation of X as a major phase along with hematite. The M_S value varied from 67.01 Am²/kg to 50.43 Am²/kg; whereas the H_c value changed from 2.95 kA/m to 6.17 kA/m, A high value of M_S (67.01 Am²/kg) is observed in the pure sample, and a very low value of H_c (2.95 kA/m) is observed for x = 0.06, y = 0.3 compositions, but Mr/Ms < 0.5 confirm the multi-domain nature of prepared hexaferrites. Hysteresis loops of all samples are narrow, and confirmed that formed samples belong to magnetically soft. Mössbauer spectra of the three samples (S1, S3, and S5) show the existence of doublets. Significantly low values of coercivity, retentivity, and loss tangent in Sm–Cd substituted samples signified those prepared materials can be used to design electromagnets, transformer cores, electric motors, and maybe a potential candidate for lossless low-frequency applications.     

Enhanced gyromagnetic properties of Cu-substituted LiZnTi ferrites for LTCC applications

In this work, we prepared a type of LiZnTiCu ferrite with a large grain size and enhanced magnetic properties at ～900 °C by substituting Cu²⁺ ions and doping LBSCA glass. Rietveld refinement of XRD patterns indicates that the Fe³⁺ ions in B sites are partially replaced by the Cu²⁺ ions, which causes the monotone increase of lattice constant. SEM results show that the interaction of CuO nanoparticles and LBSCA glass causes two changes in the grain growth of the LiZnTiCu ferrites. The grain growth is suppressed when the amount of CuO nanoparticles is less than a threshold value (x = 0.05 for 900 °C; x = 0.20 for 875 °C). However, when enough CuO nanoparticles are added, the ferrites possess a large and compact microstructure. The variation of magnetic hysteresis (M-H) loops confirms that M_s follows the Néel's collinear spinel model with the increasing number of CuO nanoparticles (x ≤ 0.25). Finally, a type of LiZnTiCu ferrite (x = 0.15) with uniform large grains (average size >10 μm) and good magnetic parameters (4πM_s = 3457.59 G, H_c = 224.4 A/m and B_s = 236.4 mT) is obtained at ～900 °C.     

Monodomain MgCuZn ferrite with equivalent permeability and permittivity for broad frequency band applications

In order for the miniaturization of a broadband antenna to be achieved, monodomain Mg_0.78Cu_0.2Zn_0.02Fe_1.96O_3.94 ferrites with various microstructures were prepared by conventional solid-state reaction method. The effect of microstructure on the magnetic and dielectric properties was studied. The results displayed that monodomain MgCuZn ferrite is a potential magneto-dielectric material for broad frequency band applications. In addition, grain size and porosity apparently influenced the permeability and permittivity spectra of the monodomain ferrite. Specifically, densely sintered MgCuZn ferrites with an average grain size of 1.41 µm displayed equivalent permeability and permittivity (such as μ' and ε'~13), as along with a low loss factor (such as tan δ_μ<0.02, tan δ_ε<0.005) in a fairly wide frequency range extending from 10 MHz to 100 MHz.     

Magnetic,magnetostrictive, and AC impedance properties of manganese substituted cobalt ferrites

In this study, we investigated the effects of substituting Mn³⁺ for some Fe³⁺ in spinel lattice on the structure, magnetic properties, magnetostriction behavior, and AC impedance characteristics of cobalt ferrites. The manganese substituted cobalt ferrites (Co–Mn ferrites), CoMn_xFe_2−xO₄, with x varied from 0 to 0.3 in 0.1 increments, were prepared by solid-state reaction. XRD examination confirmed that all sintered Co-based ferrites had a single-phase spinel structure. The average grain size, obtained from SEM micrographs, increased from 8.2 μm to 12.5 μm as the Mn content (x) increased from 0 to 0.3. Both the Curie temperature and coercivity of Co-based ferrites decreased with greater amounts of Mn, while the maximum magnetization (at H=6 kOe) of Mn-substituted cobalt ferrites was larger than that of the pure Co-ferrite. Magnetostrictive properties revealed that the pure Co-ferrite had the largest saturation magnetostriction (λ_S), about −167 ppm, and the CoMn_0.2Fe_1.8O₄ sample exhibited the highest strain sensitivity (|dλ_⊥/dH|_m) of 2.23×10⁻⁹ A⁻¹m among all as-prepared Co-based ferrites. In addition, AC impedance spectra analysis revealed that the real part (Z′) of the complex impedance of Co–Mn ferrites was lower than that of pure Co-ferrite in the low frequency region, and the Co-based ferrites exhibited semiconductor-like behavior.     

Structural,electrical, optical and dielectric properties of yttrium substituted cadmium ferrites prepared by Co-Precipitation method

The yttrium substituted cadmium ferrites having composition Cd_1-xY_xFe₂O₄ (X = 0.00, 0.125, 0.250, 0.375, 0.500) were synthesized by the co-precipitation method and sintered at 1100 °C for 6 h. Structural, morphological, electrical, optical and dielectric characteristics were explored by XRD, SEM, EDS, FTIR, I–V two probes, UV–Vis and LCR techniques.XRD results confirmed the cubic structure of spinel ferrites. A decrease in lattice constants of the prepared samples was observed with the substitution of Y ions and was attributed to the difference in ionic radii of Y³⁺ (0.95 Å) and Cd²⁺ (0.97 Å) ions. Cationic distributions, ionic radii of both tetrahedral and octahedral sites, tolerance factor, oxygen positional parameters, bond lengths, interatomic distances, positional parameters and bond length angles were calculated from XRD data. The morphology of the prepared ferrites was studied using SEM and results ratified the XRD results. EDS confirmed the presence of all inserted elements in Cd_1-xY_xFe₂O₄ composition. DC resistivity and drift mobility of soft-ferrites were found to be increased from 1.047 × 10⁸–4.822 × 10¹⁰ Ω-cm and 5.87 × 10⁻¹² – 1.045 × 10⁻¹⁴ cm²V⁻¹s⁻¹, respectively, at 523 K with yttrium content confirming the behavior of semiconductor materials. The optical band gap energy calculated from the UV–Vis pattern of the Cd_1-xY_xFe₂O₄ system was decreased from 3.6011 to 2.8153 eV. DC resistivity and optical band gaps exposed inverse relation. FTIR results revealed lower and upper-frequency absorption bands in the ranges of 419.31–417.01 cm⁻¹ and 540.95–565.70 cm⁻¹, respectively. Dielectric constant and dielectric losses were in decreasing order, while ac conductivity revealed rising behavior with increasing frequency. Results showed the potential of yttrium doped Cd nanoferrites for applications in high-frequency microwave absorbing devices.     

Frequency, temperature and In dependent electrical conduction in NiFe2O4 powder

A series of polycrystalline spinel ferrites with the composition NiIn_xFe_2-xO₄ (0 ≤ x ≤ 0.3) were prepared by the solid state reaction to study the effect of In³⁺ ions substitution on their dc electrical resistivity and dielectric properties. The dc resistivity has been investigated as a function of temperature and composition. The indium ion increases the dc resistivity and activation energy of the system. A study of the dielectric properties of these mixed ferrites, as a function of composition, frequency and temperature, has been undertaken. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) all decreases with frequency as well as with the composition. The dielectric constant (ε′) and dielectric loss tangent (tanδ) were increases with increasing temperature. AC conductivity increases with increase in applied frequency. The dielectric behavior of the present samples is attributed to the Maxwell-Wagner type interfacial polarization. The conduction mechanism in these ferrites is due to electron hopping between Fe²⁺ and Fe³⁺ ions on adjacent octahedral sites.     

Structure,far-infrared reflectance spectra,and microwave dielectric properties of Ba2MGa11O20 (M = Bi,La) ceramics

Ba₂MGa₁₁O₂₀ (M = Bi, La; called BBG and BLG, respectively) ceramics with monoclinic space group I2/m were prepared through a solid-state reaction method. BBG ceramic sintered at 1150 °C for 6 h has the best microwave dielectric properties with low ε_r = 10.68, Q × f = 41,756 GHz, and negative τ_f = ?61.3 ppm/°C. BLG ceramic sintered at 1440 °C for 6 h exhibits ε_r = 13.94, Q × f = 45,592 GHz, and near-zero τ_f = ?16.3 ppm/°C. The large deviation between ε_r and ε_th was ascribed to the “rattling” effect of the cations and the existence of lone pair ions of Bi³⁺. The difference in Q × f of the two ceramics was discussed in terms of packing fraction, and the τ_f of BLG was closer to zero than that of BBG due to the smaller τ_ε value. Their intrinsic dielectric properties were analyzed through far-infrared reflectivity spectroscopy.     

Synthesis,structural and microwave absorption properties of Cr-doped zinc lanthanum nanoferrites Zn1-xCrxLa0.1Fe1.9O4 (x=0.09, 0.18, 0.27 and 0.36)

Cr-doped zinc-lanthanum nanoferrites Zn_1-xCr_xLa_0.1Fe_1.9O₄ (x = 0.09, 0.18, 0.27, and 0.36) were successfully synthesized using sonochemical reactors. Effect of powder production parameters were extensively studied and powder characterization was performed. Existence of cubic spinel structures in the prepared nanoferrites with the average crystallite size ranging from 35 to 51 nm was confirmed by X-ray diffraction studies. An electrochemical impedance analyzer was used to measure the dielectric constant (ε′), loss tangent (tan δ), and complex dielectric constant (ε") with respect to frequency and composition ratio. Maxwell–Wagner polarization and hopping mechanism were calculated to distinguish the variations in ε′, tan δ, and ε". The Nyquist impedance plots for nanoferrites revealed the pseudocapacitance as well as resistive behavior. Vibrating sample magnetometer studies reveled the ferromagnetic behavior of nanoferrites. Substantially increased saturation magnetization and decreased coercivity were noted with respect to increased Cr²⁺ ions in the prepared nanoferrites. It was found that the addition of chromium in Zn_1-xCr_xLa_0.1Fe_1.9O₄ nanoferrites enhances the optical, electrical, and magnetic properties of the nanoferrites.     

Enhanced Curie temperature and superior temperature stability by site selected doping in BCZT based lead-free ceramics

In this work, Bi³⁺ doped Ba_0.98-3x/2Bi_xCa_0.02Zr_0.02Ti_0.976Cu_0.008O₃ [0 ≤ x ≤ 0.03] lead free ceramics, to be employed for structural, dielectric and ferroelectric studies, have been synthesized via conventional solid state reaction method. Rietveld refinement of the X-ray diffraction (XRD) data evidences the existence of a pure perovskite phase with tetragonal symmetry for all ceramics. The Scanning Electron Microscopy (SEM) reveals that the grain size, which is 16.14 μm for x = 0 reduced to 2.11 μm for x = 0.03. Dielectric studies demonstrate excellent dielectric behavior with high Curie temperature (T_C ～159 °C), high dielectric constant (ε_r ～834, ε_max ～ 3146), and a low dielectric loss (tanδ ～ 0.019), for an optimum value of x = 0.02. The analysis of temperature coefficient of the dielectric permittivity indicates the applicability of these materials in multilayer ceramic capacitors. Impedance studies, conducted to understand the underlying physical mechanisms, are found to be in good agreement with the results of structural and dielectric studies. Furthermore, the ferroelectric measurement confirms the ferroelectric nature for all samples with an energy storage efficiency (η) of ～42% for x = 0.02 composition.     

A novel BaMg1.98Zn0.02V2O8 ceramic with low dielectric loss and good temperature stability for low temperature co-fired ceramic technology

In this paper, a series of BaMg_2-xZn_xV₂O₈ (0.02 ≤ x ≤ 0.08) ceramic has been obtained by ionic substitution at the Mg-site of BaMg₂V₂O₈ ceramics through the conventional solid-state reaction method. The relationship between the surface morphology and the microwave properties of ceramic samples was analyzed intensively. The results showed that the substitution of Mg²⁺ by an appropriate amount of Zn²⁺ can promote their densification, lower their sintering temperature, and reduce the dielectric loss of BaMg₂V₂O₈ ceramics significantly. The BaMg_1.98Zn_0.02V₂O₈ ceramic exhibits microwave dielectric properties as ε_r ～13.4, Q × f ～ 178,760 GHz, τ_f ～ -14.9 ppm/°C at the optimum sintering temperature (940 °C). This indicates that the ceramic prepared in this work, which combines low dielectric loss, good temperature stability, and low-temperature sintering ability, can be an ideal microwave dielectric material for low-temperature co-firing technology.     

Study of electrical transport properties of Eu+3substituted MnZn-ferrites synthesized by co-precipitation technique

Eu substituted MnZn-ferrites with nominal composition Mn_0.78Zn_0.22Eu_x Fe_(2?x)O₄ (x=0.0, 0.02, 0.04, 0.06, 0.08 and 0.10) were prepared by co-precipitation technique. The effect of Europium substitution on electrical transport properties of Mn–Zn ferrites is reported. XRD analysis reveals fcc phase in all the samples along with few traces of second phase. The lattice constant shows decreasing trend with the substitution of Eu due to partial solubility of Eu-ions in the lattice. Room temperature resistivity both at 10 and 20 V shows on average an increasing trend. This increase in resistivity is attributed to the unavailability of Fe⁺³ ions in the lattice due to Eu-substitution. The dc resistivity decreases with temperature for all the samples at 10 V and 20 V indicating the semiconducting behavior of these samples. Room temperature dc resistivity and activation energies show similar trend both at 10 V and 20 V indicating that the samples with high resistivity have high activation energies and vice versa. The dielectric constant (ε′), complex dielectric constant (ε″) and loss tangent of these samples decreased with the increase of Eu-concentration, following the Maxwell–Weigner model.     

Prospects of non-linear optical behaviour of PZT/ZnO heterostructures

PZT and ZnO heterostructures were fabricated by using the sol-gel spin-coating method on two different substrates, viz., ITO-coated glass and Corning glass. UV–Vis spectroscopy of these heterostructures showed 80% transparency in the visible region of the electromagnetic spectrum, which is desirable for optical device applications. Tauc's relation was used to calculate the energy bandgap, which was found to be blue shifted to 3.96 eV in the case of the heterostructure on ITO-coated glass and 3.9 eV for that on Corning glass, indicating a difference of ΔE = 0.06 eV due to the change in substrate. The refractive index (n), extinction coefficient (k), and the real and imaginary parts of the dielectric constant (ε₁ and ε₂) of the heterostructures were estimated. The second order non-linear refractive index (n₂) and the third order non-linear optical susceptibility (χ⁽³⁾) were determined by generalized Miller's rule in the photon energy range of 0.5–6.5 eV by using the UV–Vis spectroscopic data. The respective values of χ⁽¹⁾ and χ⁽³⁾ values were found to be in the range 0.10–0.45 and 3.88 × 10⁻¹³–6.0 × 10⁻¹². The optical and structural studies established that the nanocrystalline PZT-ZnO heterostructure on ITO-coated glass was more optically transparent and had better non-linear properties as compared to that on the corning glass substrate. These properties are advantageous for optoelectronic device applications.     

Characterization and low-temperature sintering of Ni0.5Zn0.5Fe2O4 nano-powders prepared by refluxing method

The as-prepared Ni_0.5Zn_0.5Fe₂O₄ powders fabricated directly from the solution of metal nitrates by the refluxing method were testified by the analysis of XRD, TEM, SAED and HRTEM. XRD pattern indicated that obtained Ni_0.5Zn_0.5Fe₂O₄ powders were single phase with spinel structure, TEM analysis showed that the powders with cubic shape were uniform in particle size of about 10-20 nm. Ceramics prepared by the as-synthesized Ni_0.5Zn_0.5Fe₂O₄ powders sintered at various temperatures between 950 °C and 1150 °C for 2 h were observed by SEM technique, which indicated that the Ni_0.5Zn_0.5Fe₂O₄ ferrites can almost be sintered to theoretic density at 1100 °C for 2 h, lower by at least about 200 °C compared with those ferrites prepared by the conventional oxide method. The relative magnetic loss tanδ/μ_i of the ceramic samples sintered at the temperature 1050 °C was measured to be of the order of 10^− 4-10^− 5 in the frequency range from 1 MHz to 10 MHz, and the threshold frequency of the ferrites was 77.2 MHz.     

Effect of SiC interphase on the mechanical,high-temperature dielectric and high-temperature microwave absorption properties of the SiCf/SiC/Mu composites

In this study, SiC interphase was prepared via a precursor infiltration-pyrolysis process, and effects of dipping concentrations on the mechanical, high-temperature dielectric and microwave absorption properties of the SiC_f/SiC/Mu composites had been investigated. Results indicated that different dipping concentrations influenced ultimate interfacial morphology. The SiC interphase prepared with 5 wt% PCS/xylene solution was smooth and homogeneous, and no bridging between the fiber monofilament could be observed. At the same time, SiC interphase prepared with 5 wt% PCS/xylene solution had significantly improved mechanical properties of the composite. In particular, the flexural strength of the composite prepared with 5 wt% PCS/xylene solution reached 281 MPa. Both ε′ and ε′′ of the SiC_f/SiC/Mu composites were enhanced after preparing SiC interphase at room temperature. The SiC_f/SiC/Mu composite prepared with 5 wt% PCS/xylene solution showed the maximum dielectric loss value of 0.38 at 10 GHz. Under the dual action of polarization mechanism and conductance loss, both ε′ and ε′′ of the SiC_f/SiC/Mu composites enhanced as the temperature increased. At 700 °C, the corresponding bandwidth (RL ≤ ?5 dB) of SiC_f/SiC/Mu composites prepared with 5 wt% PCS/xylene solution can reach 3.3 GHz at 2.6 mm. The SiC_f/SiC/Mu composite with SiC interphase prepared with 5 wt% PCS/xylene solution is expected to be an excellent structural-functional material.     

Effect of calcination temperature on optical,magnetic and dielectric properties of Sol-Gel synthesized Ni0.2Mg0.8-xZnxFe2O4 (x = 0.0–0.8)

The Ni_0.2Mg_0.8-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6 & 0.8) nanomaterials were prepared via sol-gel technique. These samples were calcined at three different temperatures (T) such as 400, 450 and 500 °C/5 h. Furthermore, the X-ray diffraction (XRD) patterns of all the calcined samples revealed the single phase cubic spinel structure. The lattice constants (a = b = c) were noticed to be increasing with increase of ‘x’. The grain shape, size and distribution of x = 0.0–0.8 contents were analyzed using field emission electron microscope (FESEM). The x = 0.2 content provided higher optical band gap energy (E_g) value than the remaining contents. Furthermore, the magnetization versus magnetic field (M − H) curves indicated the superparamagnetic nature of x = 0.0–0.8 contents. The high saturation magnetization (M_s) was noticed for x = 0.4 and 0.6 contents. In addition, the distribution of cations like Ni⁺², Mg⁺², Zn⁺², Fe⁺³ and Fe⁺² was performed between the tetrahedral (A) and octahedral (B) sites. The frequency dependence of dielectric constant (ε′), dielectric loss (ε") and ac-electrical conductivity (σ_ac) was investigated as a function of composition. Moreover, the temperature variation of ε′ showed the decreasing trend of dielectric transition temperature (T_e) with increase of ‘x’. The high ε′ of 163.1 (at 1 MHz) was noticed at x = 0.2 content calcined at 500 °C. Using the power law fit applied to the log σ_ac-log ω plots, the dc-electrical conductivity (σ_dc) and exponent (n) parameters were calculated.     

Effects of Ni2+ concentration on the composition,structure, magnetic properties,and DC-bias superposition characteristics of NiCuZn ferrites

Ni_xCu_0.2Zn_yFe_1.98O₄ (x = 0.16, 0.26, 0.35, 0.43, 0.50; y = 0.8?x) ferrites were prepared via solid-state reaction. The influence of Ni²⁺ concentration on ferrites composition, microstructure, magnetic properties and DC-bias superposition characteristics was studied by XRD, SEM, XPS, and VSM. Then, the effect of magnetic properties on the DC-bias superposition characteristics was analyzed. The results showed that the ferrites sintered at 900 °C for 3 h were all in pure spinel phase with an average grain size of 7.5 μm and a relative density of about 5.15 g cm^?3. With the increase in Ni²⁺ concentration, the saturation magnetization (M_s) and coercivity (H_c) of ferrites increased, but the magnetocrystalline anisotropy constant (K₁) first increased and then decreased. And the M_s, H_c, and K₁ of the specimen with x = 0.43 were 63.62 emu·g^?1, 27.36 Oe, and 1813.17 Oe·emu·g^?1, respectively. In particular, the specimen of x = 0.50 achieved the best DC superposition characteristics, where the H_70% was about 220 A m^?1. The incremental permeability of the specimens decreased rapidly at a bias magnetic field <400 A m^?1. The variation mainly originated from the domain wall displacement, and the rate of decrease was influenced by both M_s and K₁. At a bias magnetic field ≥400 A m^?1, the incremental permeability of the specimens decreased slowly, mainly because the number of domain walls decreased until disappearing, and the specimens tended to become a single domain structure. And the rate of decrease of incremental permeability was mainly affected by K₁.     

Densification,microwave dielectric properties and rattling effect of LiYbO2 ceramics with low εr and anomalous positive τf

LiYbO₂ ceramic with tetragonal structure formed only by [LiO₆] and [YbO₆] octahedra, exhibited a ε_r of 13.3 ± 0.2, Q × f of 24,700 ± 500 GHz and an abnormal positive τ_f of + 38.6 ± 3.0 ppm/°C as sintered at 1100 °C with low relative density of 88 %. Dense ceramic with relative density of 95.1 % was obtained with the addition of 1 wt% LiF when sintered at 1080 °C, exhibiting enhanced microwave dielectric properties of ε_r = 14.3 ± 0.2, Q × f = 41,200 ± 500 GHz, τ_f = +56.5 ± 3.0 ppm/°C and α_L = 8.5 × 10^?6/K. The large positive discrepancy as much as + 45.1 % between measured ε_r with porosity correction and calculated ε_r(C-M) using Clausius?Mossotti relations might be due to the rattling effect of Li⁺, which also led to the positive τ_f.