Effect of B-site ion substitution on chemical bond characteristics and microwave dielectric properties of ZnWO4 ceramics

Herein, the influence of Mo⁶⁺ substitution on the crystal structure, microstructures, chemical bond characteristics, vibration characteristics and microwave dielectric properties of ZnMo_xW_1-xO₄(x = 0−0.12) ceramics prepared by a solid-state reaction were investigated. The results show that Mo⁶⁺ substitution does not produce secondary phase, the densification temperature decreases from 1100 to 925 ℃, and Q × f values increased from 19605 GHz (x = 0) to 61640 GHz (x = 0.06) at 925 ℃, which resulted from the packing fraction, U_tW-O and microstructures. Also, the τ_f values were optimized to −34 ppm/°C due to changes in the degree of structural order and stability of chemical bonds.Af_iW-O, molecular polarizability and porosity first led to an increase in permittivity and decrease thereafter. The ZnMo_0.06W_0.94O₄ ceramics sintered at 925℃ exhibited satisfactory properties (ε_r = 15.10, Q × f = 61,640 GHz, and τ_f = -34 ppm/°C), providing a potential candidate for microwave devices.     

Effect of La and Ni substitution on structure,dielectric and ferroelectric properties of BiFeO3 ceramics

In this communication, we present the results on Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples processed by solid-state reaction route in order to study crystalline and electronic structure, dielectric and ferroelectric properties. The best refinement was achieved by choosing rhombohedral structure (R3c) for BiFeO₃ and Bi_0.9La_0.1FeO₃ samples. Whereas, the XRD pattern of BiFe_0.95Ni_0.05O₃ and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ samples were refined by choosing rhombohedral (R3c) and cubic (I23) structure. Raman scattering measurement infers nine Raman active phonon modes for all the as prepared samples. The substitution of Ni ion at Fe-site in BiFeO₃ essentially changes the modes position i.e. all the modes are observed to shift to lower wave number. Dielectric constant (ε′) and dielectric loss (tan δ) as a function of frequency have been investigated and they decreases with increasing frequency of the applied alternating field and become constant at high frequencies. This feature is a characteristic of Maxwell Wagner type of interfacial polarization. The remnant polarization (P_r) for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.08, 0.11, 0.69 μC/cm², respectively and the value of coercive field for Bi_0.9La_0.1FeO_3, BiFe_0.95Ni_0.05O₃, and Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ are 0.53, 0.67, 0.68 kV/cm, respectively. X-ray absorption spectroscopy (XAS) experiments at Fe L₂,₃ and O K-edges are performed to investigate the electronic structure of well-characterized Bi_1−xLa_xFe_1−yNi_yO₃ (x=0.0, 0.1; y=0.0, 0.05) samples. The presence of reasonable ferroelectric polarization at room temperature in Bi_0.9La_0.1Fe_0.95Ni_0.05O₃ ceramics makes it suitable for technological applications.     

Effect of small amount of cobalt substitution on structure and microwave dielectric properties of barium magnesium niobate ceramics

We investigated effects of substituting cobalt for magnesium on microstructures and microwave dielectric properties of BaMg_1/3Nb_2/3O₃ ceramics. Nucleation and growth of 1:2 ordered domains dominate microstructural variations for Ba(Mg_1?xCo_x)_1/3Nb_2/3O₃ ceramics. Microstructures such as grains sizes and domain sizes significantly dominate variations of Q × f value. Less ordered domains are nucleated when substituting small amount of cobalt (x < 0.1). Accordingly, domains and grains significantly grow with increased cobalt substitution. The 1:2 ordering degree is subsequently increased, and Q × f achieves a maximum value at x = 0.05. Nevertheless, while cobalt substitution exceeds x = 0.1, more ordered nuclei occur and consequently affect the domain growth and the grain growth. The Q × f value remarkably decreases at x = 0.1, and varies due to different ordering degrees and compositions. The Q × f value of specimens at x = 0.05 becomes as high as 43,000, and is similar to that of specimens at x = 0.5.     

Effect of phase transition on the microwave dielectric properties of BiNbO4

BiNbO₄ specimens were transformed from the orthorhombic to triclinic phase at 1040 °C. The calculated intrinsic dielectric properties of the specimens were changed from K = 42, Qf = 15700 GHz in the orthorhombic phase to K = 30, Qf = 8900 GHz in the triclinic phase. The change of Qf value resulted from the increase of the dispersion parameter and modes for nonsymmetrical structure with the phase transition. TCF of the specimens decreased due to the increase of the octahedral distortion of BiNbO₄ with change from the orthorhombic to the triclinic phase. These results are due to the increase of bond valence of BiNbO₄ with the phase transition.     

Effect of Ce and La substitution on dielectric properties of bismuth titanate ceramics

Effect of Ce and La substitution on the microstructure and dielectric properties of bismuth titanate (BT) ceramics was investigated. Bismuth titanate ceramics (Bi_4−xA_xTi₃O₁₂) (A = Ce or La; x = 0, 0.5, 1) were processed by sintering of pressed pellets, prepared from nanopowder synthesized by the modified sol-gel method. Pure and La modified bismuth titanate ceramics have single Bi₄Ti₃O₁₂ phase of Aurivillius type, whereas a small amount of Bi₂Ti₂O₇ pyrochlore phase appears in Ce modified bismuth titanate ceramics. In the same time addition of La and Ce improved sinterability of BT ceramics. The results of the measurement of dielectric constant and loss tangent at different frequencies (100 Hz-1 MHz) as a function of temperature reveal that Ce modified ceramics has a diffuse phase transition. Temperature T_m, corresponding to the maximum value of the dielectric constant, is shifted to higher temperature and the maximum value of the dielectric constant is decreased with increasing frequency, which indicate that relaxor behavior is caused by Ce substitution.     

Effect of LMZBS glass on the microstructure and microwave dielectric properties of monocelsian ceramics

BaAl₂Si₂O₈–Li₂O–MgO–ZnO–B₂O₃–SiO₂ (BAS-LMZBS) glass ceramics were prepared through the solid-state route. The phase transformation, microstructure, bulk density and microwave dielectric properties of (1-x)BaAl₂Si₂O₈-xLMZBS(x = 0.1–0.4) the glass ceramics were examined. The effects of the LMZBS additive as a mineralizer on the hexagonal-to-monoclinic transformation were investigated by X-ray diffraction and scanning electron microscope. All of the hexagonal phases were converted into monoclinic phases when x = 0.1, and it was found that LMZBS glass affected the densification of the ceramic samples. Monocelsian was successfully prepared, and its sintering temperature was reduced from above 1400 °C–870 °C by adding LMZBS glass. Excellent microwave dielectric properties (ε_r = 7.31, Q × f = 48,926 GHz and τ_ƒ = −48 ppm/°C) were obtained at 870 °C. This sample shows great chemical compatibility with Ag electrodes and can be a promising candidate for practical applications of low-temperature, co-fired ceramics.     

Effect of Fe substitution on the piezoelectric,dielectric and ferroelectric properties of PNZST ceramics

Fe-doped (Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30)_0.52Ti_0.48]_0.98O₃ (PNZST) ceramics were prepared via conventional solid state reaction method, and the effect of Fe doping on their structural and electrical properties was investigated in detail. Results showed that Fe³⁺ cations could dissolve into readily the B-sites of perovskite structure for the PNZST ceramics with the less amount of Fe content (≤0.8 wt%), resulting in the full densification after sintered at 1300 °C. Meanwhile, Fe doping caused a structure transform from the tetragonal to the rhombohedral. The better electric properties for PNZST ceramic with 0.6 wt% Fe content were obtained, i.e. piezoelectric constant d₃₃=380 pC/N, electromechanical coupling factor k_p=0.57, mechanical quality factor Q_m=225, dielectric constant ε_r=1190, loss tangent tan δ=0.007 and curie temperature T_c=318 °C.     

Effect of Zn2+ substitution on the microwave dielectric properties of LiMgPO4 and the development of a new temperature stable glass free LTCC

The LiMg_(1?x)Zn_xPO₄ ceramics have been prepared by the solid state ceramic route. The LiMg_(1?x)Zn_xPO₄ ceramic retains the orthorhombic structure up to x = 0.2. The compositions with 0.3 ≤ x ≤ 0.8 exist as a mixture of orthorhombic and monoclinic phases. When Mg²⁺ is fully replaced with Zn²⁺ (x = 1.0) complete transition to monoclinic phase occurs. The ceramic with x = 0.1 (LiMg_0.9Zn_0.1PO₄) sintered at 925 °C exhibits low relative permittivity (?_r) of 6.7, high quality factor (Q_u × f) of 99,700 GHz with a temperature coefficient of resonant frequency (τ_f) of ?62 ppm/°C. The slightly large τ_f is adjusted nearly to zero with the addition of TiO₂. LiMg_0.9Zn_0.1PO₄–TiO₂ composite with 0.12 volume fraction TiO₂ sintered at 950 °C shows good microwave dielectric properties: ?_r = 10.1, Q_u × f = 52,900 GHz and τ_f = ?5 ppm/°C. The ceramic is found to be chemically compatible with silver.     

Effect of frequency and temperature on dielectric properties of polystyrene at microwave frequencies

Ambient dielectric measurements as functions of frequency in X-band microwave region have been made on solid samples of polystyrene. Effects of temperature (?120 to +160°C) at three different frequencies have also been studied. The measurement technique applied based on short-circuited waveguide method of Roberts and von Hippel modified by Dakin and Works for low loss and medium loss samples. Two different types of relaxations are identified originating from main chain motion, wagging, and rotational motions of pendent phenyl group. Intrinsic activation energy for polystyrene molecule, dipole moment per repeat unit, and the average apparent energy of a polystyrene molecule associated with its induced transient dipoles have also been calculated and the data so obtained are explained and compared with standard literature.     

Improved sintering and microwave dielectric properties of Li2CaSiO4 ceramic with magnesium atom substitution

The influence of Mg²⁺-ion substitution on the sintering and microwave dielectric properties of Li₂CaSiO₄ ceramic was investigated using the traditional solid-state reaction method and density functional theory. X-ray diffraction, scanning electron microscopy, Raman spectrometry, network analysis and simultaneous thermal analysis were used to characterise the macro properties. The replacement of Ca²⁺-ion with Mg²⁺-ion led to the transformation of dodecahedron into tetrahedron. In addition, the bond length and bond population related to the calcium site decreased. The atom vibration and microstructure characteristics were modified due to the lattice distortion. The densification temperature decreased from 1000 °C to 925 °C. The relative density increased from 70% to 80.5%. The dielectric properties were improved, that is, ε_r = 5.63, tanδ = 0.0019 at 8 GHz as 4% (molar ratio) Ca²⁺-ions were replaced by Mg²⁺-ions.     

Effect of La doping on microwave dielectric properties of translucent polycrystalline alumina ceramic

In this paper, the microstructure and microwave dielectric properties of translucent polycrystalline alumina (PCA) with different amounts of La₂O₃ (co-doped with 500 ppm MgO) were investigated. Compared with those doped only with 500 ppm MgO, the translucent PCA co-doped with 500 ppm La₂O₃ exhibited a higher Q×f value, which might be caused by the significantly larger ionic radius of La³⁺. As the La₂O₃ content was further increased, the presence of an increasing amount of impurities (LaAl₁₁O₁₈) would deteriorate the Q×f value significantly.     

Effect of Mg doping on microwave dielectric properties of translucent polycrystalline alumina ceramic

In this paper, the microstructure and microwave dielectric properties of translucent polycrystalline alumina (PCA) with various addition amounts of MgO were investigated. Translucent PCA was obtained by adding ～500–2000 ppm MgO. Compared with the undoped PCA, the translucent PCA doped with 500 ppm MgO showed a higher density and a much higher Q×f value. As the MgO content further increased, the dielectric constants (ε_r) of the translucent PCA samples showed no significant change, while the Q×f values decreased rapidly. The increased amount of impurities (MgO or spinel) was believed to be the main reason for the lower Q×f values.     

Effect of Ni2+ substitution on structural,magnetic, dielectric and optical properties of mixed spinel CoFe2O4 nanoparticles

Nanoparticles of Co_1−xNi_xFe₂O₄ with x=0.0, 0.10, 0.20, 0.30, 0.40 and 0.50 were synthesized by co-precipitation method. The structural analysis reveals the formation of single phase cubic spinel structure with a narrow size distribution between 13–17 nm. Transmission electron microscope images are in agreement with size of nanoparticles calculated from XRD. The field emission scanning electron microscope images confirmed the presence of nano-sized grains with porous morphology. The X-ray photoelectron spectroscopy analysis confirmed the presence of Fe²⁺ ions with Fe³⁺. Room temperature magnetic measurements showed the strong influence of Ni²⁺ doping on saturation magnetization and coercivity. The saturation magnetization decreases from 91 emu/gm to 44 emu/gm for x=0.0–0.50 samples. Lower magnetic moment of Ni²⁺ (2 µ_B) ions in comparison to that of Co²⁺ (3 µ_B) ions is responsible for this reduction. Similarly, overall coercivity decreased from 1010 Oe to 832 Oe for x=0.0–0.50 samples and depends on crystallite size. Cation distribution has been proposed from XRD analysis and magnetization data. Electron spin resonance spectra suggested the dominancy of superexchange interactions in Co_1−xNi_xFe₂O₄ samples. The optical analysis indicates that Co_1−xNi_xFe₂O₄ is an indirect band gap material and band gap increases with increasing Ni²⁺ concentration. Dispersion behavior with increasing frequency is observed for both dielectric constant and loss tangent. The conduction process predominantly takes place through grain boundary volume. Grain boundary resistance increases with Ni²⁺ ion concentration.     

Effect of yttrium (Y) substitution on the structure and dielectric properties of BaTiO3

As the rate of application of multilayer ceramic capacitors (MLCCs) in small electronic devices increases, the use of the raw material barium titanate (BaTiO₃) with a small particle size and excellent dielectric properties becomes needed. Due to the size effect, small-sized BaTiO₃ generally has a cubic phase structure with a low dielectric constant, which limits its use in MLCCs. We report the preparation of small cubic phase Y-doped BaTiO₃ (BYT) nanoparticles by a hydrothermal method and the preparation of highly dielectric tetragonal phase BYT ceramics based on this method. XRD and Raman analysis showed that the BYT nanoparticles are in substable cubic phases. The particle size of the BYT nanoparticles, measured by TEM, XRD, and BET, was approximately 35 nm. The dielectric properties of the BYT ceramics were tested by an impedance analyzer, and the dielectric constant of the BYT ceramics was 7547 when the Y³⁺ doping amount was 0.5 mol%. In addition, the substitution mechanism of Y³⁺ doping in BaTiO₃ crystals was proposed from XPS and EPR analysis. The results demonstrate for the first time that the 50 nm cubic phase BaTiO₃ powder can meet the needs of next-generation high-capacity MLCCs. This work provides a reference for small cubic phase BaTiO₃ as a dielectric material for high-capacity MLCCs.     

Effect of the raw materials on the properties of cordierite ceramics

Various compositions of cordierite charge that meet the requirements of the world's leading cordierite producers can be produced from domestic raw materials. The properties of cordierite are shown to depend on the charge composition at the same content of the main oxides and impurities. The effect of the temperature of preliminary calcination of the talc on the properties of the cordierite samples obtained in the process of one-stage sintering is studied.     

Effect of Ni substitution on the dielectric properties and lattice vibration of Ba(Mg1/3Ta2/3)O3

Far infrared reflectivity spectra for Ba(Mg_1/3,Ta_2/3)O₃ and Ba([Mg_1−xNi_x]_1/3,Ta_2/3)O₃ ceramics were measured and eigenfrequencies and damping constants of transverse optical modes were estimated in order to investigate the variations in the dielectric properties with Ni substitution. These ceramics were prepared by the conventional solid phase reaction method using high purity chemicals. The observed reflectivity spectra were fitted as a function of the vibration frequencies and the damping constants. The permittivity and Qf value decreased with Ni substitution. The decrease in permittivity is due to the decrease in the damping constant of 4th vibration mode of the oxygen layer vibration. The decrease in Qf value is due to the increase in the damping constant of 5th vibration mode of the oxygen layer vibration. It was inferred that the increase in the Qf value might be due to the substitution of the Ni ion for the Ta ion in the Ta layer in the BMT.     

Evanescent microwave probe study on dielectric properties of materials

A recently developed evanescent microwave probe (EMP) technique combined with systematically quantitative analyses is demonstrated. We use a three-dimensional (3D) finite element simulation to model the electromagnetic field inside the resonant cavity and inside the sample near the tip. We also proposed an analysis model for the sample's quality factor (Q), which is usually hindered by the conductor losses of the resonator. Measurement on various dielectric samples agrees very well with the theoretical model, demonstrating the validity of analyses for the EMP resonator and providing a possibility for dielectric imaging the surface of the samples with high resolution.     

Effect of ClH aromatic substitution on structural and dielectric properties of poly(p-xylylene)

A basic understanding of the structure–property relations and how they are influenced by the molecular architecture is imperative for the future development of polymer thin films in a large number of applications including those in the electronics industry. A new study has been illustrated in this work to demonstrate the effect of an aromatic Chlorine–Hydrogen substitution on the structural and dielectric properties of poly-para-xylylene (parylene N) ((–CH₂–C₆H₆–CH₂–)_n). X?Ray Diffraction (XRD) analysis reveals that the chlorination of the aromatic rings of poly-para-xylylene stabilize the crystalline structure of the materials (α–monoclinic), increases the d-spacing, decreases the crystallinity, and increases the value of the dielectric parameters. Furthermore, the permittivity is increased from 2.68 (PPX N) to 3.1 (PPX C) and the conductivity is increased by two order of magnitude at room temperature at frequency 1 KHz. Fourier Transformation Infrared Spectrometer (FTIR) and Energy Dispersion X-ray (EDX) analyses shows that the different as deposited parylene type are deprived of extrinsic polar bonds who can influenced on the dielectric properties. The increase of the dielectric properties and the changes of the morphologies structure are associated to the change in the intermolecular interaction due to the Cl_H aromatic substitution of poly-p-xylylene.     

Mineralogical and dielectric properties of mullite and cordierite ceramics produced using wastes

In this work technical ceramics containing industrial inorganic wastes was carried out. Ceramic formulations prepared with clay, magnesium oxide and residues of kaolin and alumina as raw materials, were formed in a disk-shaped specimens using the uniaxial pressing process and sintering at temperatures from 950°C to 1400°C. The mineralogical, physical and dielectric characteristics of the fired samples were investigated. The dielectric properties, the relative dielectric constant (ε_r) and the loss tangent (tan δ) were evaluated at frequencies of 0.1, 1, 10, and 100?kHz at room temperature. Mullite and cordierite were present as major phases at the highest temperatures. Relative dielectric constant values closest to that of mullite (ε_r = ~ 5 to ~ 6) and cordierite (ε_r =?~ 4 to ~ 6) at 1?kHz. On the other hand, the lowest dielectric losses (tan δ ~ 0.06 to ~ 0.04) were observed for the formulations containing the mullite major phase, and tan δ ~ 0.009 to ~ 0.003 for formulations that showed cordierite as main phase. It was verified that an increase in temperature promoted a reduction of porosity, a property that had a direct influence on the dielectric properties of the formulations. The materials obtained from the residues presented low dielectric constants and loss tangents, which make them suitable for use in electrical and electronic systems.     

Effects of Ni2+ substitution on the structure and dielectric properties of Bi1.5MgNb1.5O7 cubic pyrochlores

The dielectric properties of bismuth-based cubic pyrochlores strongly depend on the environment of the A-site ions, e.g. the Ni²⁺ ions doped into Bi_1.5MgNb_1.5O₇ (BMN) pyrochlores for tailoring dielectric properties. Both BMN and Bi_1.5NiNb_1.5O₇ (BNN) ceramics exhibit a cubic pyrochlore structure with preferential (222) planes. However, {442} reflections are observed in BNN pyrochlores, revealing an off-center displacement of A and O' ions. The dielectric constant of BNN pyrochlores is lower than that of BMN pyrochlores, besides BNN pyrochlores have a larger dielectric loss (0.002) than BMN pyrochlores (0.0007). Ni-doping results in a loose and flexible structure contributing positively to the dielectric tunability, besides creating a large amount of oxygen vacancies. The higher amount of oxygen vacancies increases the dielectric loss of BNN pyrochlores. However, BNN pyrochlores exhibit enhanced temperature stability, with a temperature coefficient of –57 ppm/^oC, which is significantly better than that of BMN pyrochlores (–362 ppm/^oC).