Dielectric properties of Ba(Ti1 − xZrx)O3 solid solutions

This paper reports the structural and dielectric properties of Ba(Ti_1 − xZr_x)O₃ (x = 0-0.3) ceramics. Single-phase solid solutions of the samples were determined by X-ray diffraction. Microscopic observation by scanning electron microscope revealed dense, single-phase microstructure with large grains (20-60 μm). The evolution of dielectric behavior from a sharp ferroelectric peak (for x ≤ 0.08) to a round dielectric peak (for 0.15 ≤ x ≤ 0.25) with pinched phase transitions and successively to a ferroelectric relaxor (for x = 0.3) was observed with increasing Zr concentration. Compared with pure BaTiO₃, broaden dielectric peaks with high dielectric constant of 25,000-40,000 and reasonably low loss (tanδ: 0.01-0.06) in the Ba(Ti_1 − xZr_x)O₃ ceramics have been observed, indicating great application potential as a dielectric material.     

Crystal structure and ferroelectric properties of Ca(Cu3−xMx)Ti4O12 (M = Fe and Ni) ceramics

M-substituted Ca(Cu_3−xM_x)Ti₄O₁₂ (CCMTO) ceramics, where M = Fe and Ni, were synthesized and the influence of M substitutions for Cu on the crystal structure and ferroelectric properties of CCMTO ceramics were investigated in this study. From the variations in the lattice parameters of CCMTO ceramics, the solubility limit of Ni substitution for Cu in CaCu_3−xNi_xTi₄O₁₂ (CCNTO) ceramics was x = 0.2, whereas that of CaCu_3−xFe_xTi₄O₁₂ (CCFTO) ceramics was x = 0.05. The crystal structural analysis of CCMTO ceramics revealed that the single phase of CCMTO ceramics belongs to the I23 non-centrosymmetric space group of I23; as a result, the P_r and E_c values of CCFTO ceramics at x = 0.05 were 1.8 μC/cm² and 40 kV/cm, respectively. The ferroelectric behavior of CCMTO ceramics by the M substitutions for Cu may be related to the displacement of a Ti⁴⁺ cation in the TiO₆ octahedra and tilting of the Ti–O–Ti angle because of the non-centrosymmetric space group.     

Effect of the Mn ion on electrical and magnetic properties of orthorhombic perovskite-type Ca(Mn1−xTix)O3−δ

Orthorhombic perovskite-type Ca(Mn_1−xTi_x)O_3−δ (0 ≤ x ≤ 0.7) was synthesized at 1173 K for 12 h in a flow of oxygen from a precursor gel prepared using citric acid and ethylene glycol. The Mn³⁺ ion was generated by substituting a Ti⁴⁺ ion in CaMnO₃. The average particle size was 100-300 nm and did not depend on x. The lattice constants and the (Mn, Ti)-O distance increased linearly with increasing x. The variation in global instability index (GII) indicated that the instability of the structure increases monotonically with increasing x. Ca(Mn_1−xTi_x)O_3−δ was an n-type semiconductor that had its minimum values of electrical resistivity (ρ) and activation energy (E_a) at x = 0.1. Ca(Mn_1−xTi_x)O_3−δ (x = 0 and 0.1) exhibited a weak ferromagnetic behavior. The variation in μ_eff indicated that the spin state of the Mn³⁺ ion changes from low to high at x = 0.1, then reverts to low in the range of 0.2 ≤ x ≤ 0.7. The variations in ρ and E_a are explained by the number of electrons according to the change in the spin state of the Mn³⁺ ion.     

Role of structural changes in dielectric,ferroelectric properties of Sr2KxNa1−xNb5O15 lead-free ceramics

Lead-free Sr₂K_xNa_1−xNb₅O₁₅ (0.00 ≤ x ≤ 0.20) piezoelectric ceramics were prepared by two-step solid state reaction method. Pure tungsten bronze structure could be obtained in all ceramics and K substitution could accelerate the phase formation at lower temperatures. The lattice constant calculation indicated expansion of the unit cell and reduced distortion of the crystal structure with K substitution due to the bigger ionic size of K⁺ (1.64 Å) compared to that of Na⁺ (1.39 Å). Electrical properties of Sr₂K_xNa_1−xNb₅O₁₅ ceramics greatly depended on the K content. Curie temperature T_c shifted downward, whereas the maximum dielectric constant ?_m and the degree of diffusion phase transition all increased initially and then decreased as K content increased, indicating that proper amount of K substitution with x between 0.05 and 0.10 could enhance the dielectric properties. All the ceramics showed an intermediate relaxor-like behavior between normal and ideal relaxor ferroelectrics according to the modified Curie–Weiss law. With increasing K content, the remnant polarization (P_r) decreased gradually and the coercive field (E_c) decreased initially and then increased. But normal ferroelectric hysteresis loops could be observed in all compositions. Besides, the underlying mechanism for variations of the electrical properties due to K substitution was explained in this work.     

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

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

Microstructure and martensitic transformation of Ti49Ni51 − xHfx high temperature shape memory alloys

In present work, the microstructure and martensitic transformation of Ti₄₉Ni_51 − xHf_x (x = 3-15) alloys were studied. The microstructure of Ti₄₉Ni_51 − xHf_x alloys consists of B19′ martensite and (Ti,Hf)₂Ni phase at room temperature. The martensitic transformation behavior is characterized by a single-stage transformation. With increasing Hf content, the transformation temperature increases from 75 to 279 °C resulting from the reduced valence electron concentration, indicating that the replacement of Hf for Ni is effective in increasing the transformation temperatures. The results suggest that the Ti₄₉Ni_51 − xHf_x shape memory alloy is one of potential candidates for high temperature applications.     

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

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

Structure, dielectric and ferroelectric anisotropy of Sr2−xCaxBi4Ti5O18 ceramics

Sr_2−xCa_xBi₄Ti₅O₁₈(x = 0, 0.05) powders synthesized by solid state route were uniaxially pressed and sintered at 1225 °C for 2 h. The obtained dense ceramics exhibited crystallographic anisotropy with a dominant c axis parallel to the uniaxial pressing direction which was quantified in terms of the Lotgering factor. Microstructure anisotropy of both compositions (x = 0, 0.05) consisted of plate like grains exhibiting their larger surfaces mostly perpendicular to the uniaxial pressing direction. Dielectric and ferroelectric properties of Sr_2−xCa_xBi₄Ti₅O₁₈ ceramics were measured under an electric field (E) applied parallel and perpendicularly to uniaxial pressing direction. The obtained dielectric ?_R(T) and polarization (P-E) curves depended strongly on E direction thus denoting a significant effect from microstructure and crystallographic texture. Sr_2−xCa_xBi₄Ti₅O₁₈ properties were also significantly affected by Ca content (x): Curie temperature increased from 280 °C (x = 0) to 310 °C (x = 0.05) while ?_R and remnant polarization decreased for x = 0.05. The present results are discussed within the framework of the processing and crystal structure-properties relationships of Aurivillius oxides ceramics.     

Modified tunable dielectric properties by addition of MgO on BaZr0.25Ti0.75O3 ceramics

Phase composition, microstructure and tunable dielectric properties of (1 − x)BaZr_0.25Ti_0.75O₃-xMgO (BZTM) composite ceramics fabricated by solid-state reaction were investigated. It was found Mg not only existed in the matrix as MgO, there was also trace amount of Mg²⁺ ions dissolved in the BZT grains, which led to Curie temperature of the BZTM composites ceramics shifting to below −100 °C. Dielectric permittivity of the BZTM composite ceramics was reduced from thousands to hundreds by manipulating the content of MgO. Johnson's phenomenological equation based on Devonshire's theory was used to describe the nonlinear dielectric permittivity of the ceramics with increasing applied DC field. With increasing content of MgO, anharmonic constant α_(T) increased monotonously. Dielectric permittivity was 672, while dielectric tunability was as high as 30.0% at 30 kV/cm and dielectric loss was around 0.0016 for the 0.6BaZr_0.25Ti_0.75O₃-0.4MgO sample at 10 kHz and room temperature.     

Correlation of crystal structure and microwave dielectric properties for Zn(Ti1−xSnx)Nb2O8 ceramics

The correlation of crystal structure and microwave dielectric properties for Zn(Ti_1−xSn_x)Nb₂O₈ ceramics were investigated. The Zn(Ti_1−xSn_x)Nb₂O₈ ceramics contained ZnTiNb₂O₈ and an unknown Columbite-type phase. The columbite structure phase with increasing degree of ordering led to decrease of dielectric constant, increase of Qf and τ_f. The ZnTiNb₂O₈ with decreasing cation valence led to increase of τ_f. The typical values were: ? = 30.88, Qf = 43,500 GHz, τ_f = −54.32 × 10⁻⁶/ °C.     

Low loss Sr1−xCaxLa4Ti5O17 microwave dielectric ceramics

Microwave dielectric ceramics in the Sr_1−xCa_xLa₄Ti₅O₁₇ (0 ≤ x ≤ 1) composition series were prepared through a solid state mixed oxide route. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1450-1580 °C. Theoretical density and molar volume decreased due to the substitution of Ca²⁺ for Sr²⁺ which was associated with a decrease in the dielectric constant (?_r) and temperature coefficient of resonant frequency (τ_f) but an increase in quality factor, Qf_o. Optimum properties were achieved for Sr_0.4Ca_0.6La₄Ti₅O₁₇ which exhibited, ?_r ∼ 53.7, Qf_o ∼ 11,532 GHz and τ_f ∼ −1.4 ppm/°C.     

Defect-dipole-induced two important macroscopic effects: The dielectric relaxation and the ferroelectric aging in hybrid-doped (Ba,Ca)TiO3 ceramics

To observe the dielectric relaxor behavior and the ferroelectric aging effect, the structural and electrical properties of (Ba_0.90Ca_0.10)(Ti_1−xCa_x)O_3−x (BCT-C) ceramics prepared using a conventional dry route were investigated. With increased concentration of Ca on the B-site in BCT-C ceramics, the tetragonal phase is decreased while the multiphases with the cubic pervoskite structure as a major constituent is increased and remained predominant in the BCT-C ceramics with x > 0.03. The increased amount of Ca on the B-site causes the high temperature phase transition to shift to the low temperature and results in an increase in the degree of diffusion and relaxation of the BCT-C ceramics. The observed dielectric relaxation behavior may be understood by a defect-dipole formed random electric field induced domain state. The aging effect controlled by the migration of mobile oxygen vacancies is rarely observed in aged BCT-C ceramics while it can be markedly observed in Bi-doped BCT ceramics. Based on the microscopic mechanism of the aging effect, the possible reasons for the aging effect are given.     

Effect of Pb(Fe1/2Nb1/2)O3 modification on dielectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbZr0.52Ti0.48O3 ceramics

10 mol% Pb(Fe_1/2Nb_1/2)O₃ (PFN) modified Pb(Mg_1/3Nb_2/3)O₃-PbZr_0.52Ti_0.48O₃ (PMN-PZT) relaxor ferroelectric ceramics with compositions of (0.9 − x)PMN-0.1PFN-xPZT (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared. X-ray diffraction investigations indicated that as-prepared ceramics were of pure perovskite phase and the sample with composition of x = 0.8 was close to morphotropic phase boundary (MPB) between rhombohedral and tetragonal phase. Dielectric properties of the as-prepared ceramics were measured, and the Curie temperature (T_c) increased sharply with increasing PZT content and could be higher than 300 °C around morphotropic phase boundary (MPB) area. At 1 kHz, the sample with composition of x = 0.1 had the largest room temperature dielectric constant ?_r = 3519 and maximum dielectric constant ?_m = 20,475 at T_m, while the sample with composition of x = 0.3 possessed the maximum dielectric relaxor factor of γ = 1.94. The largest d₃₃ = 318 pC/N could be obtained from as-prepared ceramics at x = 0.9. The maximum remnant polarization (P_r = 28.3 μC/cm²) was obtained from as-prepared ceramics at x = 0.4.     

Investigations on structural evolution and dielectric characteristics of high performance Bi-based dielectrics

A new system of (Bi_1.5Zn_1−x/3Ti_xNb_1.5−2x/3)O₇ (0 ≤x ≤ 1.5) ceramics have been successfully developed and the dielectric properties have been systematically studied. The results showed the formation of temperature compensation dielectrics over the wide range of Ti concentrations. The incorporation of Ti⁴⁺ into the bismuth zinc niobate ceramics induce the decrease of lattice constant linear while remaining cubic pyrochlore phase. The IR spectra confirm the formation of pyrochlore structure and give information about the distribution of ions between the A and B sites. It has been found that the effect of Ti substitution on dielectric properties of sintered ceramics intensifies with a higher x. The system exhibits the novel high permittivity and low dielectric loss: the permittivity values (?_r) saturate at 160-210, and loss values remain at low values (∼1 × 10⁻⁴). The temperature dependence of permittivity is strongly dependent with the compositions. Dielectric relaxation phenomena have been observed during low temperature. New high frequency and MW materials, differed by Ti content, with temperature compensation and controllable dielectric constant of 150-210 have been developed.     

Microstructural evolution and dielectric properties of Cu-deficient and Cu-excess CaCu3Ti4O12 ceramics

The microstructural evolution and dielectric properties of CaCu_3−xTi₄O_12−x (3 − x = 2.8-3.05) ceramics were investigated. Normal grain growth behavior was observed at Cu/Ca ≤ 2.9, while abnormal grain growth was observed at Cu/Ca ≥ 2.95. A CuO-rich intergranular liquid phase at Cu/Ca ≥ 2.95 and angular grain morphology were the main reasons for abnormal grain growth. However, the abundant intergranular liquid at Cu/Ca = 3.05 significantly affected the relative dielectric permittivity and dielectric loss. The CuO composition is the key parameter that determines the microstructure and dielectric properties of CCTO ceramics.     

Composition dependence of optical constants in ferroelectric Ba(Ti1 − x,Nix)O3 thin films by optical transmittance technique

Ba(Ti_1 − x,Ni_x)O₃ ferroelectric thin films with perovskite structure are prepared on fused quartz substrates by a sol-gel process. Optical transmittance measurements indicate that Ni-doping has an obvious effect on the energy band structure of BaTiO₃. It has been found that the refractive index n, extinction coefficient k, and band gap energy E_g of the films are functions of the film composition. The E_g of Ba(Ti_1 − x,Ni_x)O₃ decreases approximately linearly as the Ni content increases, which is attributed to the decline of conduction band energy level with increasing the Ni content. On the other hand, n and k both increase linearly with increasing the Ni content because of the increase of packing density. These results indicate that thin films might have potential applications in BaTiO₃-based thin-film optical devices.     

Synthesis, characterization, and dielectric properties of Ba(Ti1−xSnx)O3 nanopowders and ceramics

We prepared Ba(Ti_1−xSn_x)O₃ powders and ceramics by means of the sol-gel process, with dibutyltin dilaurate as the Sn precursor. The samples were characterized by means of Fourier-transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy, and also determined the dielectric properties of the ceramics. The powders synthesized by means of the sol-gel process had a grain size on the nanometer scale, with the grains mainly composed of a cubic BaTiO₃ phase. Sn can disperse into BaTiO₃ more uniformly in the sol-gel technique using dibutyltin dilaurate as the Sn precursor. With increasing Sn concentration, the grain size of the Ba(Ti_1-xSn_x)O₃ ceramics increased and the maximum dielectric constant (?_max) first increased and then decreased. At a Sn concentration of 5 mol%, ?_max reached its maximum value (19,235).     

Different microstructure and dielectric properties of Ba1−xCaxTiO3 ceramics and pulsed-laser-ablated films

A comparative study of the microstructure and dielectric properties between Ba_1−xCa_xTiO₃ (BCT) ceramics and films were performed in the whole Ca concentration range of x = 0-1. The ceramics were prepared by conventional solid-state reaction technique and the films by the method of pulsed-laser deposition. X-ray diffraction (XRD) study of the BCT ceramics exhibited a pure tetragonal phase for x = 0-0.25, a tetragonal-orthorhombic diphase for x = 0.25-0.85 and a pure orthorhombic phase for x = 0.90-1.00. And the dielectric phase transition temperature from tetragonal to cubic was marginally affected by the Ca doping into BaTiO₃. However, BCT films deposited on Pt/Si/SiO₂/Si substrates showed a different microstructure and dielectric properties. Tetragonal-orthorhombic diphase was not found in the BCT films for x = 0.25-0.85, and a large decrease of the Curie point and diffuse phase transition were observed in the BCT films. Based on the compositional analysis, such phenomena were ascribed to the occupancy of some Ca²⁺ to the Ti⁴⁺ sites in the BCT films.     

Novel transparent conducting oxide: Anatase Ti1−xNbxO2

Single-crystalline Ti_1−xNb_xO₂ (x = 0.2) films of 40 nm thickness were deposited on SrTiO₃ (100) substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction measurement confirmed epitaxial growth of anatase (001) film. The resistivity of Ti_1−xNb_xO₂ films with x ≥ 0.03 is 2-3 × 10^− 4 Ω cm at room temperature. The carrier density of Ti_1−xNb_xO₂, which is almost proportional to the Nb concentration, can be controlled in a range of 1 × 10¹⁹ to 2 × 10²¹ cm^− 3. Optical measurements revealed that internal transmittance in the visible and near-infrared region for films with x = 0.03 was more than 97%. These results demonstrate that the presently developed anatase Ti_1−xNb_xO₂ is one of the promising candidates for the practical TCOs.     

Effect of Bi and Ti substitutions for Na and Nb on ferroelectric properties of oriented (Bi4.5+xNa0.5−x)(Ti2xNb2−2x)WO15 compounds

(Bi_4.5+xNa_0.5−x)(Ti_2xNb_2−2x)WO₁₅ (BNTNW) compounds were synthesized and their ferroelectric properties were characterized. The X-ray powder diffraction patterns of the compounds revealed that they have a single phase over the whole composition range. The linear variations of the lattice parameters with composition indicate the formation of solid solutions, resulting in a reduction in the orthorhombicity of the compounds. The remnant polarization of the BNTNW decreased from 8.5 to 5.1 μC/cm² with increasing x, which may be related to the orthorhombicity of the compounds. By using hot forging, an oriented BNTNW compound at x = 0 was obtained. Strong reflections from (0 0 l) were observed for sample // in which the measurement direction is parallel and the orientation factor of such sample was approximately 0.72. A remarkable increase in the remnant polarization (P_r) of the compound was observed for the sample ⊥ in which the direction of applied pressure is perpendicular to the measurement direction; the highest P_r value was 18 μC/cm².