Influence of Zr doping on the dielectric properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Pure and Zr-substituted CaCu₃(Ti_1−x Zr _x )₄O₁₂ (x = 0, 0.01, 0.02, 0.03) ceramics were prepared by the Pechini method. X-ray powder diffraction analysis indicated the formation of single-phase compound, and all the diffraction peaks were completely indexed by the body-centered cubic perovskite-related structure. The effects of Zr⁴⁺ ion substituting partially Ti⁴⁺ ion on the dielectric properties were investigated in frequency range between 100 Hz and 1 GHz. The low frequency (f ≤ 10⁵ Hz) dielectric constant decreases with Zr substitution and the high frequency (f ≥ 10⁷ Hz) dielectric constant is unchanged. Interestingly, a low-frequency relaxation was observed at room temperature through Zr substitution. The observed dielectric properties in Zr-substituted samples were discussed using the internal barrier layer capacitor model. A corresponding equivalent circuit was adopted to explain the dielectric dispersion. The characteristic frequency of low-frequency relaxation rises due to the decrease of the resistivity of grain boundary with Zr substitution, which is likely responsible for the large low-frequency response at room temperature.     

Effects of Nd-substitution on microstructures and dielectric characteristics of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> ceramics

Ca_1−3x/2Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2) ceramics were prepared by a solid state reaction process, and single-phased structures were obtained for all the compositions. The dielectric characteristics of pure and Nd-substituted CaCu₃Ti₄O₁₂ ceramics were investigated together with the microstructures. The mixed-valent structures of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in the present ceramics were confirmed by X-ray photoelectron analysis. The dielectric relaxation in the low temperature range was examined in detail and the variation of dielectric constant and dielectric loss was attributed to the modification mixed-valent structures.     

Dielectric relaxations in SrTiO3 doped with La2O3 and MnO2 at low temperatures

In addition to the dielectric relaxation around 170 K in the cubic structure of Sr_1–3x/2La _x TiO₃, a similar relaxation was observed at about 70 K in the tetragonal structure with an activation energy in the range 0.13–0.16 eV which increases as x in Sr_1–3x/2La _x TiO₃ varies from 0.60–3.00 at%. This relaxation is explained by Skanavi's model and is discussed in terms of thermal motions of Ti⁴⁺ between potential minima produced by lattice distortions in the tetragonal structure. In order to provide a direct evidence for the suggestion that the dielectric relaxation around 170 K in the cubic is due to thermal motions of Ti⁴⁺, dielectric properties on manganese-doped specimens, Sr_1–3x/2La _x Mn _y Ti_1–y ),O₃ with x=1.40×10^–2 and y=0.1×10^–2, were investigated because Mn⁴⁺ substitutes for Ti⁴⁺. As well as the relaxation due to Ti⁴⁺, this specimen exhibits another peak due to Mn⁴⁺ with an activation energy somewhat smaller than that of Ti⁴⁺. The activation energies and the relative intensity of these relaxation processes are explained by the difference in ionic radii of Mn⁴⁺ and Ti⁴⁺ and the difference in formation energies of a strontium vacancy adjacent to Mn⁴⁺ and that to Ti⁴⁺, which were calculated theoretically using a shell model.     

Structure and properties of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 solid solution ceramics

The widely used piezoelectric Pb(Zr_1−x Ti _x )O₃ ceramics have been known to have Zr⁴⁺ and Ti⁴⁺ randomly distributed on the B-site lattice in the ABO₃ perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg_1/2W_1/2)O₃ − xPb(Zr_0.5Ti_0.5)O₃ (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg_1/2W_1/2)O₃ and the ferroelectric order in Pb(Zr_0.5Ti_0.5)O₃ leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, T _m, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties.     

Microstructure,dielectric, and energy storage performance of (Zn1/3Nb2/3)4+ complex-ion modified (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics

In this study, (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)_1-x(Zn_1/3Nb_2/3)_xO₃ ceramics were synthesized by conventional solid-phase methods, referred to as BCZT-xZN (x?=?0.0, 0.1, 0.2, 0.3, 0.4). The effects of adding different contents of (Zn_1/3Nb_2/3)⁴⁺ ion on the microstructure, dielectric and ferroelectric properties of BCZT ceramics were studied. Scanning electron microscopy (SEM) results showed that the average particle size of the samples was significantly reduced after the addition of (Zn_1/3Nb_2/3)⁴⁺ ion, and a second phase appeared when the addition amount was?≥?0.3. The dielectric properties show that with (Zn_1/3Nb_2/3)⁴⁺ ion replacing the B-site of BCZT ceramics, the dielectric constant decreases significantly and the Curie temperature decreases below room temperature. At the same time, we observed that the ceramic has good stability to temperature (-150 °C–200 °C) and frequency (10²–10⁶ Hz) changes. The addition of (Zn_1/3Nb_2/3)⁴⁺ ion can significantly reduce the residual polarization and improve the breakdown strength of ceramics. When x?=?0.3, The maximum energy storage density of ceramics is 0.994 J/cm³, which is about four times higher than that of pure BCZT ceramic (0.25 J/cm³). These findings fully demonstrate the great potential of BCZT ceramics in energy storage.

     

Influence of ZrO<Subscript>2</Subscript> addition on the structure,thermal stability,and dielectric properties of ZnTiO<Subscript>3</Subscript> ceramics

The zinc titanates doped with zirconium were synthesized by conventional solid-state reaction using metal oxides. X-ray diffractometry and differential scanning calorimetry analysis results indicated that the stable region of the hexagonal Zn(Zr _x Ti_1−x )O₃ phase extended to a high temperature (above 945 °C). The c/a value decreased as the Zr concentrations increased, which may be caused by the Zr⁴⁺ addition resulting in a shorter distance between the center ion and its nearest neighbors of the octahedron, and the bonding force between the B-site ion and oxygen ion of ABO₃ perovskite-like structure becoming stronger. The dielectric properties exhibited a significant dependence on the sintering temperatures and the amount of ZrO₂ addition. The dielectric constant decreased and Curie temperature (T _c) increased slightly with the increasing amounts of Zr ions. This is caused by the second phase of ZnZrO₃ which was deposited at the grain boundaries and inhibited the grain growth. Furthermore, diffuse phase transition with a maximum permittivity at a transition temperature that is close to room temperature in Zn(Zr _x Ti_1−x )O₃ was observed.     

Effects of Nb doping on microstructure and properties of Bi4Ti3?xNbxO12 thin films prepared by magnetron sputtering

Bi₄Ti_3−xNb_xO₁₂ ferroelectric thin films were fabricated on p-Si substrates by magnetron sputtering. The effects of Nb doping on microstructure and properties of Bi₄Ti_3−xNb_xO₁₂ films were investigated. Bi₄Ti_3−xNb_xO₁₂ films had the same structure as Bi₄Ti₃O₁₂ with smaller and more uniform grains. The dielectric and ferroelectric properties of Bi₄Ti_3−xNb_xO₁₂ films were improved by Nb doping. Bi₄Ti_3−xNb_xO₁₂ films have better dielectric and ferroelectric properties with P _r = 16.5 μC/cm², E _C < 100 kV/cm, ε _r > 290, low dielectric loss (<0.9%) and clockwise C–V curves with a memory window of 0.9 V when x = 0.03–0.045, while an excessive Nb doping would lead to bad dielectric and ferroelectric properties.     

Control of the structure,morphology and dielectric properties of bismuth titanate ceramics by praseodymium substitution using an intermediate fuel agent-assisted self-combustion synthesis

The volatilization of bismuth (Bi) species and bismuth oxide (Bi₂O₃) leads to the presence of the oxygen vacancies (V _O⁰⁰) and consequently restrains the properties of bismuth titanate (BIT; Bi₄Ti₃O₁₂). This report presents the incorporation of different atomic ratios of praseodymium ion (Pr³⁺: x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) into the BIT (Bi_4−x Pr _x Ti₃O₁₂) ceramics through an intermediate fuel agent-assisted self-combustion synthesis (IFSC). X-ray diffraction and Raman spectroscopy results revealed that some of bismuth ion (Bi³⁺) in the pseudo-perovskite layer containing Ti–O octahedra was substituted by Pr³⁺ ion. The substitution by ion with a smaller ionic radius caused the structure distortion and consequently resulted in the phase transformation from an orthorhombic symmetry to a tetragonal symmetry. Besides, it suppressed the volatilization of Bi and Bi₂O₃ and increased the stability of metal–oxygen octahedra in the BIT. These play a crucial role to control the crystal growth, as well as limit the V _O⁰⁰. Dense ceramic with a relative density up to 96.2% was obtained by incorporating Pr³⁺ with atomic ratio of 1.0. It exhibited high dielectric constant as 908.19 and low dissipation factor as 0.0011. The results address the possibility to control the structure, morphology and dielectric properties of BIT ceramic by incorporating Pr³⁺ ion through IFSC.     

Effect of Gd3+ substitution on dielectric properties of nano cobalt ferrite

CoGd_xFe_2 ? xO₄ (x = 0.0, 0.1, 0.3, 0.5) nano magnetic ferrite particles were synthesized by chemical co-precipitation method. The variation of dielectric parameters like dielectric constant, dielectric loss, capacitance and resistance for different Gd³⁺ compositions has been measured at room temperature for frequency dependence in the range of 100 Hz to 10 MHz using impedance analyzer. Results of measurements reveal strong dependence of dielectric parameters on frequency and Gd³⁺ ion content. Dielectric constant, dielectric loss, capacitance and resistance decrease with increasing frequency for all the CoGd_xFe_2 ? xO₄ compositions. Increase in Gd³⁺ ion composition in material, increases the values of dielectric constant, dielectric loss and capacitance while decreases the electrical resistance of nano-particles. A qualitative explanation is given for the composition and frequency dependence of dielectric parameters.     

Effect of CuO on the microstructure and electrical properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 piezoceramics

In this study, the effect of CuO content on the microstructure and electrical properties of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃ (BCZT) ceramics was systematically studied. The addition of CuO effectively results in an increase of grain sizes in BCZT ceramics. BCZT ceramics endure a lattice distortion due to the Cu²⁺ part substitution for the Ti⁴⁺ site, and a low-sintering temperature of BCTZ ceramics is induced by the addition of CuO. With increasing CuO content, the dielectric constant and the dielectric loss of BCTZ ceramics decrease, together with the decrease of the remanent polarization and the coercive field. Effects of sintering temperature and dwell time on the microstructure and electrical properties of BCZT ceramics with x = 0.5 mol% CuO were also studied, and an optimum sintering condition helps to further improve its electrical properties. BCZT ceramics with x = 0.5 mol% CuO possess optimum electrical properties: d ₃₃ ~ 403 pC/N and k _p ~ 44.6% when sintered at a low temperature of 1400 °C for 6 h. As a result, BCZT ceramics with a sintering aid of CuO are a promising candidate for the transducer and transformer applications.     

Effect of Zr+4 ion substitution on the structural, dielectric and electrical properties of Sr5LaTi3Nb7O30 ceramics

Polycrystalline Zr-modified Sr₅LaTi₃Nb₇O₃₀ compound was prepared by a high-temperature solid-state reaction technique. X-ray structural analysis confirmed the formation of compound in an orthorhombic system at room temperature. Detailed studies of the dielectric parameters (dielectric constant and tangent loss) as a function of frequency (1–100 kHz) at different temperature (150 to 650 K) were carried out. It was found that as Zr⁺⁴ concentration increases in Sr₅LaTi_{3 – x} ZrxNb₇O₃₀, the value of dielectric constant decreases. These compounds show ferroelectric-paraelectric phase transition of diffuse type at 283, 305 and 320 K for x = 0, 1 and 2 respectively. The transition temperature (T _c) shifts towards higher temperature and maximum dielectric constant value (_max) decreases with increasing Zr⁺⁴ concentration for x = 0 to x = 2. When Ti⁺⁴ cations were completely replaced by Zr⁺⁴ cations (i.e., Sr₅LaZr₃Nb₇O₃₀), the compound does not show any phase transition. Impedance-spectroscopic studies provided an insight into the electrical properties and understanding of relaxation behavior of the material. Measurement of electrical conductivity as a function of temperature suggests that the compounds have a negative temperature coefficient of resistivity (NTCR) with a typical semiconductor behavior.     

Microstructural and dielectric properties of donor doped (La3+) CaCu3Ti4O12 ceramics

The effect of La³⁺ doping on Ca²⁺ sites in CaCu₃Ti₄O₁₂ (CCTO) was examined. Polycrystalline samples in the chemical formula Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ with x = 0, 0.5, 1 were synthesized via the conventional solid state reaction route. X-ray powder diffraction analysis confirmed the formation of the monophasic compounds and indicated the structure to be remaining cubic with a small increase in lattice parameter with increase in La³⁺ doping. The dielectric and impedance characteristics of Ca_(1-x)La_(2/3)x Cu₃Ti₄O₁₂ were studied in the 100 Hz–10 MHz frequency range at various temperatures (100–475 K). A remarkable decrease in grain size from 50 μm to 3–5 μm was observed on La³⁺ substitution. The dielectric constant of CaCu₃Ti₄O₁₂ decreased drastically on La³⁺ doping. The frequency and temperature responses of dielectric constant of La³⁺ doped samples were found to be similar to that of CaCu₃Ti₄O₁₂. The effects of La³⁺ doping on the electrical properties of CaCu₃Ti₄O₁₂ were probed using impedance spectroscopy. The conducting properties of grain decreased while that of the grain boundary increased on La³⁺ doping, resulting in a decrease of the internal barrier layer effect. A decrease in grain boundary capacitance and stable grain response in La³⁺ doped CCTO ceramics were unambiguously established by modulus spectra studies.     

Incorporation of bismuth into Ba6− x R8+2/3x Ti18O54(R = Nd, Gd)

Microstructural investigations and microanalyses of a series of Ba_6–x R _8+2/3x Ti₁₈O₅₄ ceramics (R = Nd, Gd) revealed that the solid-solubility limit for the isovalent substitution of R ³⁺ by Bi³⁺ depends on the composition of the Ba_6–x R _8+2/3x Ti₁₈O₅₄ phase. For the Nd analogue the solid-solubility limit (y in Ba_6–x (Nd_1–y Bi _y )_8+2/3x Ti₁₈O₅₄) decreases with a decrease in x from y = 0.16 for x = 2.0 to y = 0.10 for x = 0.8. An even lower solid-solubility limit (y = 0.06) was found for the Ba_4.5(Gd_1–y Bi _y )₉Ti₁₈O₅₄ compound (x = 1.5). All substituted Nd compositions exhibit higher permittivities (93–99), lower temperature coefficients of permittivity (11–15 ppm/K) and higher dielectric losses (Q · f = 1300–5500 GHz) than the parent compositions. By exceeding the solid-solubility limit, abrupt changes in the microstructural and dielectric characteristics are induced.     

Phase, microstructure and microwave dielectric properties of Zr-doped SrLa4Ti5?xZrxO17

The effect of Zr⁺⁴ substitution for Ti⁺⁴ on the phase, microstructure and microwave dielectric properties of compositions in the SrLa₄Ti_5−xZr_xO₁₇ (0 ≤ x ≤ 0.1) series was investigated. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffractometer when sintered in the temperature range 1,450–1,580 °C for 4 h in air. The substitution of Zr⁺⁴ for Ti⁺⁴ enabled processing of highly dense ceramics with a decrease in temperature coefficient of resonant frequency (τ_f) from ~117 to 70 ppm/°C, dielectric constant (ε_r) from 60.8 to 57.3, with no significant effect on the quality factor. In the present study, optimum properties i.e. ε_r ~ 57.3, τ_f ~ 70 ppm/°C and quality factor (Q _u  × f _o ) ~ 9,841 GHz, were achieved for SrLa₄Ti_4.9Zr_0.1O₁₇. The trend of the results demonstrates that further studies with increased Zr⁺⁴ content are required to achieve ultra low loss SrLa₄Ti_5−xZr_xO₁₇ ceramics.     

Effects of Bi2O3 and Cr2Ti3O9 Co-doping on dielectric properties in BaTiO3-based ceramics

A microwave ceramic with general composition (1-x-y) BaTiO₃ + x Cr₂Ti₃O₉ + y Bi₂O₃ has been prepared by solid state synthesis at 1300-1400 °C. The phase composition, perovskite structural parameters and dielectric properties have been obtained by X-ray diffraction and dielectric measurements as a function of chemical composition and temperature. At low doping levels the formation of BaTiO₃-based solid solution has been found. The precipitation of BaCrO₃ has been detected at x = y = 2.0 mol%. A model of the incorporation of Cr³⁺ and Bi³⁺ ions into BaTiO₃-based crystal lattice has been proposed. Diffused phase transition in the temperature range 100-140 °C have been revealed by dielectric measurements for different ceramic composition. As high dielectric constant as 7311 and as low dielectric loss as 0.02 have been found for the composition of 0.98BaTiO₃-0.01Cr₂Ti₃O₉-0.01Bi₂O₃.     

Microwave dielectric and elastic properties of glass-added Ba6−3xR8+2xTi18O54 (x = 2/3)

Microwave dielectric properties of Ba_6−3xSm_8+2xTi₁₈O₅₄ (x = 2/3) [BST] ceramics with the addition of 0–3 wt.% of various glasses have been studied. It has been found that the addition of 0.5 wt.% of the glasses decreases the sintering temperature by about 150 °C. In general, addition of 0.5 wt.% of Zn, Mg and Pb-based glasses deteriorate the quality factor, whereas aluminum and barium borosilicates do not decrease it considerably. The quality factor and dielectric constant decrease with increasing amount of glass. The temperature coefficient of resonant frequency shifts towards positive or negative depending on the composition of the glass. A glass–ceramic composite with a dielectric constant 64, Q × f nearly 8500 GHz and near to zero τ_f could be obtained at a sintering temperature of 1175 °C when 3–4 wt.% Al₂O₃–B₂O₃–SiO₂ glass was added to BST ceramic. The Young's modulus decreases with increasing amount of glass, irrespective of the composition of glass.     

Microwave dielectric properties of (Ca0.8Sr0.2)(SnxTi1−x)O3 ceramics

In this paper, we study the behavior of the B-site behavior with the incorporation of Sn⁴⁺ ion in (Ca_0.8Sr_0.2)TiO₃ ceramics. An excess of Sn⁴⁺ resulted in the formation of a secondary phase of CaSnO₃ and SrSnO₃ affecting the microwave dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics. The dielectric properties of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics were improved because of the solid solution of Sn⁴⁺ substitution in the B-site. The temperature coefficient of resonant frequency (τ_f) of the (Ca_0.8Sr_0.2)(Sn_xTi_1?x)O₃ ceramics also improved with increasing Sn content.     

Relaxor behavior of (1 − x)BaTiO3–x(Bi3/4Na1/4)(Mg1/4Ti3/4)O3 (0.2 ≤ x ≤ 0.9) ferroelectric ceramic

The (1 − x)BaTiO₃–x(Bi_3/4Na_1/4)(Mg_1/4Ti_3/4)O₃ (0.2 ≤ x ≤ 0.9) ceramics were prepared by conventional solid-state reaction route. Their dielectric properties were found to follow a modified Curie–Weiss law and an empirical Lorenz-type relation in respective temperature regions. Their dielectric relaxation times fit well with the Vogel–Fulcher relation for x = 0.2, 0.3, and 0.4. For x = 0.5, 0.6, 0.7, and 0.8, however, the fitting curves of Vogel–Fulcher relation showed certain deviation from the experimental data. Based on the theoretical treatment of Landau–Ginsburg–Devonshire theory, an approximate treatment of the E-field dependence of the permittivity was adopted and found to describe well the field dependence of the permittivity for x = 0.3 at temperatures equal to and below T _m (temperature of maximum dielectric permittivity). A combined Langevin-type expression used in the present work appears to give a good account for the field dependence of the permittivity, assuming polar regions are of a statistical cluster size. For polar clusters of linear dimension L ~ 4–8 nm for instance, the fitted values of polarization are in the range of P ~ 6.2–9.8 μC/cm².     

Enrichment of piezoelectric properties in Nb5+doped (0.94) (Na0.5Bi0.5)TiO3–(0.06) BaTiO3 ceramics across morphotropic phase boundary region

Lead-free piezoelectric compounds (0.94)(Na_0.5Bi_0.5)TiO₃–(0.06) BaTiO₃ [NBBT (94/06)]?+?x wt.% Nb⁵⁺ (x?=?0%, 1%, 1.5%, 2%, and 2.5%) were synthesized by the solid-state reaction route and these powders were pelletized and sintered for dielectric and piezoelectric characterization. The phase coexistence Monoclinic (Cc)?+?Rhombohedral (R3c) was affirmed using X-ray Powder diffraction analysis. The structural properties like cell parameters and space group of the synthesized ceramics were investigated by the Rietveld refinement analysis. The surface morphology and grain size of the fractured ceramics were explored using SEM imaging technique. The dielectric properties for all the ratios of NBBT (94/06) ceramics were examined using LCR meter. The piezoelectric coefficients such as d₃₃ and g₃₃ of Nb-doped NBBT (94/06) ceramics were investigated. The saturation polarization (P_s) and remanent polarization (P_r) were exhibited from the P–E hysteresis loop analysis at room temperature. The appropriate addition of Nb⁵⁺ (x?=?1.5%) in NBBT (94/06) material demonstrates eminent dielectric constant and piezoelectric coefficient d₃₃ than other wt.% of Nb. The replacement of Ti⁴⁺ with higher radius cations Nb⁵⁺ in B-site of ABO₃ composes tilting of polar BO₆ octahedra resulting in rhombohedra distortion (RD) (90° ? α), in addition, the polarizability of ions and various valance states of B-site cations could be responsible for RD (90° ? α) ensuing relatively high dielectric constant and piezoelectricity.

     

Effect of Mg and Ti doping on the luminescence of Y2O2S:Eu

The Y₂O₂S:Eu³⁺,Mg²⁺,Ti^IV (x_Eu = 0.028, x_Mg = 0.086, x_Ti = 0.03) materials were prepared with the flux fusion method. According to X-ray powder diffraction, the materials had the hexagonal crystal structure. The emission of Y₂O₂S:Eu³⁺,Mg²⁺,Ti^IV was centered at 627 nm (λ_exc : 250 nm) due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The excitation spectra (λ_em : 627 nm) showed broad bands at 240 and 320 nm due to the O²⁻ → Eu³⁺ and S²⁻ → Eu³⁺ charge transfer transitions, respectively. The latter band can also overlap with the Ti → Eu³⁺ energy transfer. In the excitation spectra with synchrotron radiation, in addition to the O²⁻ → Eu³⁺ and S²⁻ → Eu³⁺ charge transfer transitions, excitation over the band gap was observed at 4.8 eV (258 nm). The red persistent luminescence due to the ⁵D₀ → ⁷F₂ emission from Eu³⁺ residing in the regular Y³⁺ site of the host was ca. 10 min with 1 min fluorescent lamp irradiation. In addition, a very broad band was observed at 600 nm probably due to the Ti³⁺ emission.