Crystallographic and dielectric aspects of Pb[(Mg,Zn)1/3Ta2/3]O3 system with 40 at.% Nb substitution

A total of 40 at.% Nb was substituted for Ta in the Pb[(Mg,Zn)_1/3Ta_2/3]O₃ system in order to enhance perovskite development. System powders were prepared by a B-site precursor method. Perovskite formation yields and lattice parameters of the pyrochlore/perovskite structures were determined from X-ray diffraction results. Weak-field low-frequency dielectric responses of the system ceramics were investigated as functions of temperature, composition, and frequency. Phase transition modes reflected in the dielectric constant spectra were further analyzed in terms of diffuseness parameters.     

Synthesis and dielectric/ferroelectric characteristics of Ta-modified PMN0.6·PZN0.2·PT0.2 ceramics

Ceramic powders of a [Pb(Mg_1/3Nb_2/3)O₃]_0.6·[Pb(Zn_1/3Nb_2/3)O₃]_0.2·[PbTiO₃]_0.2 system (with Nb replaced by Ta) were prepared via solid-state reaction routes. The structures developed in the B-site precursor and perovskite systems are discussed. Weak-field low-frequency dielectric characteristics as well as the polarization behavior of the perovskite ceramics are presented. The relaxation modes of the dielectric constant spectra are analyzed in terms of diffuseness parameters. A very high maximum dielectric constant of 37 900 (@1 kHz) was obtained when 1/4 of Nb was replaced by Ta. Internal microstructures of the sintered samples are also reported.     

Characterization and dielectric properties of Ba5NdZnM9O30 (M=Nb, Ta) ceramics

Ba₅NdZnM₉O₃₀ (M=Nb, Ta) ceramics were prepared by the conventional high temperature solid state reaction route. The sintered samples were characterized by X-ray diffraction and scanning electron microscopy methods. They belong to paraelectric phases of filled tetragonal tungsten bronze structure at room temperature and have high dielectric constants of 282 and 85, combined with low dielectric losses of 0.0048 and 0.0081 at 1 MHz for Nb- and Ta-based ceramics, respectively.     

Displacive disorder in three high-k bismuth oxide pyrochlores

We use time-of-flight neutron powder diffraction to examine static displacive disorder in three different pyrochlore A₂B₂O₆O′ compounds with Bi on the A site. The compounds (Bi_1.5Zn_0.5)(Nb_1.5Zn_0.5)O₆O′ (BZN), (Bi_1.5Zn_0.5)(Ta_1.5Zn_0.5)O₆O′ (BZT), and (Bi_1.5Zn_0.5)(Sb_1.5Zn_0.5)O₆O′ (BZS), are of interest – particularly BZN – for their high dielectric constants in the absence of any phase transition from the cubic high temperature phase. The local structures of the three compounds is characterized by displacive disorder from the ideal pyrochlore positions for both the A and O′ sites, with the precise nature of the disorder being quite similar. However the extent of displacive disorder is different, despite the B–O networks being nearly identical in the three compounds. The reported dielectric constants of the three compounds are related to the extent of local displacement, and BZN, with the largest extent of local atomic displacement of A and O′, is also reported to have the largest dielectric constant at 1 MHz. The dielectric constants are also related to the magnitudes of the thermal parameters of the different ions. The strongest correlation is found to involve the thermal parameter on the B site (Nb, Ta, or Sb).     

Microwave and photoluminesent characterizations of (Ca<Subscript>2</Subscript>Mg<Subscript>3</Subscript>)(X<Subscript>1.75</Subscript>Sb<Subscript>0.25</Subscript>)TiO<Subscript>12</Subscript> [X = Nb and Ta] ceramics

(Ca₂Mg₃)(X_1.75Sb_0.25)TiO₁₂ [X = Nb and Ta] ceramics are prepared through the conventional solid-state route. The samples are calcined at 1,100 and 1,180 °C, and are sintered at 1,250 and 1,375 °C. The substitution of Sb decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The microstructure of the sintered pellet is studied using scanning electron microscopy. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_uxf) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Sb substitution, thermal stability is achieved, with the increase in dielectric constant, without much change in the quality factor. The materials have intense emission lines in the wavelength region 500–700 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Preparation of Mg-modified Pb[Zn1/3(Ta0.4Nb0.6)2/3]O3 ceramics and dielectric characteristics

Mg (full composition range) and Nb (60 at %) were simultaneously substituted into Pb(Zn_1/3Ta_2/3)O₃, in an attempt to stabilize the perovskite structure. System powders were prepared using a B-site precursor method in order to enhance perovskite formation. The developed structures were examined by X-ray diffraction, from which perovskite phase yields as well as lattice parameters of the pyrochlore and perovskite were determined. Low-frequency dielectric responses of the ceramics were investigated. Phase transition modes (reflected in the dielectric constant spectra) were further analyzed in terms of diffuseness parameters.     

Structure and dielectric properties of Nd substituted Bi1.5MgNb1.5O7 ceramics

New pyrochlore ceramics Bi_(1.5?x)Nd _x MgNb_1.5O₇ with x = 0–0.6 were synthesized by doping Nd into the A site in the Bi_1.5MgNb_1.5O₇ pyrochlore. The Nd substituted Bi_1.5MgNb_1.5O₇ ceramics were prepared utilizing solid-state reaction and investigated by X-ray diffraction, scanning electron microscope and dielectric measurements. The crystal structure was characterized as single cubic pyrochlore phase for x ≤ 0.5 while the second phase appeared at x = 0.6. With increasing Nd content from 0 to 0.5, the lattice parameters decreased slightly and the average grain size pronouncedly reduced from ~7.5 to ~5.0 μm. The Nd incorporation resulted in attractive enhancement of the dielectric properties including the temperature coefficient of dielectric constant that was remarkably optimized with the lowest value of ?16 ppm/°C at x = 0.5. A good combination of low dielectric loss, superior temperature coefficient and high dielectric permittivity can be achieved for the composition of x = 0.5, which seems to be very appealing for the practical use in high-frequency multilayer ceramic capacitors.     

Relaxor phase evolution and temperature-insensitive large strain in B-site complex ions modified NBT-based lead-free ceramics

Lead-free Bi_0.495(Na_0.8K_0.2)_0.495Sr_0.01Ti_1?x (Fe_0.5Me_0.5) _x O₃ ceramics with x = 0?0.03/0.04 mol (Me = Nb, Sb and Ta, abbreviated as FN0.5–FN4, FS0.5–FS3 and FT0.5–FT3, respectively) were fabricated by a conventional solid-state reaction method. The effects of B-site complex ions content on relaxor phase evolution and electromechanical properties were systematically investigated. Results showed that the modification of FN, FS and FT complex ions can significantly reinforce the B-site compositional disorder, effectively destroy the long-range ferroelectric order and tune the ferroelectric–relaxor transition point (T _FR) to around room temperature. The relatively high strain performances (dynamic \(d_{{33}}^{*}\) values) of 567, 550 and 600 pm/V were obtained in FN2, FS1.5 and FT2 critical compositions, respectively. The large strain responses are closely associated with the reversible relaxor–ferroelectric phase transformation. Furthermore, the electrostrain of FT2 sample presents a temperature-insensitive characteristic with the variation less than 10% up to 120 °C. These findings indicate that the B-site complex ions modified NBT-based ceramics can be considered as promising candidates for lead-free electromechanical actuator applications.     

Dielectric behavior and Raman spectra of lanthanum-doped lead magnesium niobate ceramics

Lanthanum-doped lead magnesium niobate (PLMN) ceramics were fabricated by columbite route. The effects of La-addition on dielectric behavior and Raman spectra were investigated. The trivalent La³⁺-doping showed inhibiting effects on grain growth process. The average grain size decreased and pyrochlore phase was detected along with the perovskite phase above 2 mol% La-addition. Temperature dependence of permittivity measured at 1 kHz was investigated. Due to La³⁺-doping, the maximum of dielectric constant decreased and the temperature of the maximum permittivity moved to lower temperature. An oval-form hysteresis loop was observed on La-doped (3 mol%) lead magnesium niobate (PMN) sample, which revealed that La-doped PMN owned partially normal ferroelectric feature. Raman spectra showed a shift of the peak around 270 cm⁻¹, which identified a distortion of the center symmetric ordered structure and enforced B-site compositional fluctuation. The shift of A_1g mode (around 780 cm⁻¹) indicated that degree of chemical order at B-site increased and PLMN contained 1:1 B-site ordered nanoregion (clusters) with Fm-3m symmetry.     

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.     

Microstructure and properties of lead-free (Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>)TiO<Subscript>3 </Subscript>based piezoelectric ceramics doped with different cations

Different cations doped lead-free piezoelectric (Bi_1/2Na_1/2)TiO₃ ceramics with the general formula Na_0.4995Bi_0.4995Ba_0.001Ti_0.998M_0.002O₃ (M = Nb, Ta, and Sb) were fabricated. The effects of processing parameters and doping on phase content, microstructure, dielectric and piezoelectric properties of the materials were discussed. Experimental results show that Nb doped (Bi_1/2Na_1/2)TiO₃ exhibits superior polarization performance over the existing lead-free ceramics with a d₃₃ value of 122 pC/N obtained when poled at 60 kV/cm at room temperature. The best piezoelectric properties were achieved in (Bi_1/2Na_1/2)TiO₃ doped with Ta having a measured d₃₃ value of 164 pC/N for samples poled at 100 °C under the applied field of 50 kV/cm.     

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.     

Dielectric and photoluminesent properties of (Ca2Mg3-xPbx)A2(Ti0.75Zr0.25)O12 [x?=?0 & 0.25; A?=?Nb & Ta] microwave ceramics

(Ca₂Mg_3−xPb_x)A₂(Ti_0.75Zr_0.25)O₁₂ [x = 0 & 0.25; A = Nb & Ta] ceramics are prepared through the conventional solid-state route. The substitution of Zr decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_u x f) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Pb substitution in (Ca₂Mg₃)(Nb/Ta)₂(Ti_0.75Zr_0.25)O₁₂, thermal stability is achieved with the increase in dielectric constant and quality factor. The dielectric behavior at low frequency range 50 Hz–5 MHz is also studied. The microstructure of the sintered pellet is studied using scanning electron microscopy. The materials have intense emission lines in the wavelength region 590 nm to 750 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Nonlinear electrical characteristics and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 1.0 mol% Ca and different concentrations of Ta were obtained by sintering processing at 1450°C. The microstructures, nonlinear electrical behavior and dielectric properties of the ceramics were investigated. The samples have nonlinear coefficients of = 2.0–5.0 and ultrahigh relative dielectric constants which is up to 10⁵. Especially, the effects of Ta dopant on the nonlinear electrical characteristics and dielectric properties of the (Ca, Ta)-doped TiO₂ ceramics were studied in detail. When the concentration of Ta is 2.0 mol%, the sample exhibits the highest nonlinear coefficient and a comparatively lower dielectric constant. By analogy to a grain-boundary atomic defect model, the effects of Ta and the nonlinear electrical behavior of the TiO₂ system were explained.     

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.

     

Oxygen vacancy-related dielectric relaxation and electrical conductivity in La-doped Ba(Zr0.9Ti0.1)O3 ceramics

Ba_1?xLa_x (Zr_0.9Ti_0.1)_1?x/4O₃ (BLZT) ceramics with x = 0.02 (BLZT-1), 0.04 (BLZT-2), 0.06 (BLZT-3) and 0.08 (BLZT-4) were prepared by a solid-state reaction route. Crystal structure of the BLZT ceramics was determined using X-ray diffraction and Raman spectroscopy. While the ceramics for x ≤ 0.04 are pure phase with cubic perovskite structure, pyrochlore La₂Zr₂O₇ appears in the samples with x = 0.06 and 0.08. Dielectric properties as function of temperature and frequency showed more than one dielectric anomaly were found at high temperatures during heating but they weakened or disappeared during cooling. Both dielectric relaxation and electrical conductivity were taken into account in point defect mechanism. The double-ionized and short-range hopping of oxygen vacancy should be mainly responsible for the dielectric anomalies and conduction behavior. Activation energy of conductivity E _con is lower than half of the band gap E _g obtained by UV–Vis spectroscopy, which results from emergency of oxygen vacancies. In visible light region, the ceramics show a strong absorption with band gap of about 3.57 eV.     

On the feasibility of synthesizing complex perovskite ferroelectric ceramics via a B-site oxide mixing route

Several relaxor-based complex perovskite ferroelectric ceramics were synthesized by conventional solid-state reaction method via different routes, i.e., the B-site oxide mixing route, the straight calcination method and the columbite/wolframite precursor method. Structure analysis and physical properties measurements prove that the B-site oxide mixing route is efficient and feasible in the synthesizing of complex perovskite ferroelectrics since such a technique is superior in suppressing pyrochlore phases, stabilizing the perovskite structure, and improving the amount of perovskite phase as compared to the straight calcination method and the columbite/wolframite precursor method. The dielectric properties are improved correspondingly, namely exhibiting the largest value of dielectric maximum, the sharpest dielectric response peaks and the least frequency dispersion of dielectric properties in the ferroelectric ceramics prepared via the B-site oxide mixing route, which is considered as correlating with the amount of pyrochlore phases, ceramic density, grain size, and microstructure morphology of the ceramics synthesized.     

Role of B″ Ion (B″ = Nb, Ta) on perovskite development, lattice parameters and dielectric properties of (Ba,Pb)(Zn1/3B″2/3)O3 ceramics

Ceramic powders of Pb(Zn_1/3B_2/3)O₃ (where B is Nb or Ta ions) complex-perovskite compositions, with gradual replacements of Pb by Ba, were prepared by using a B-site precursor method. Phases developed in both systems were identified by X-ray diffraction and perovskite contents were evaluated as a function of the amount of Ba substitution. Variations of lattice parameters of the pyrochlore and perovskite structures with composition modifications are interpreted in terms of the 6- and 12-fold cation sizes. Weak-field dielectric properties of the two systems in the low-frequency range are compared.     

Effect of Sb5+ substitution on the dielectric properties of Ba3LiTa3Ti5O21 ceramics

The effects of substitution Sb for Ta on the sintering behavior and the microwave dielectric properties of Ba₃LiTa₃Ti₅O₂₁ ceramic were studied. Single-phase polycrystalline microwave dielectric ceramics Ba₃LiTa_3?x Sb _x Ti₅O₂₁(x = 0–3) were prepared by the solid-state reaction method. The sintering behavior and microwave dielectric properties of Ba₃LiTa_3?x Sb _x Ti₅O₂₁ ceramics were found to be affected by Sb substitution for Ta. With the increasing Sb content, the densified (>95 % of their theoretical X-ray density) temperatures of Ba₃LiTa_3?x Sb _x Ti₅O₂₁ ceramics increased from 1,160 to 1,220 °C, the dielectric constant (ε _r ) decreased from 55.5 to 27, and the Q × f value enhanced significantly from 18,480 to 29,400 GHz, with τ _f improving from 70 to ?25 ppm/°C. A near zero τ _f value could be obtained by carefully adjusting the Sb content.     

Giant dielectric permittivity of Ca and Sb-co-doped TiO2 ceramics

The continuous development of microelectronic devices with integrated functions has led to an increasing interest in the development of dielectric ceramics with high dielectric constant, low dielectric loss, good frequency, and temperature stability. In this work, (Ca, Sb)-co-doped TiO₂ (CSTO) ceramics were prepared by solid-phase reaction sintering method and their phase structure, microstructure, giant dielectric properties, and mechanism were systematically investigated. The results show that the secondary phase of CSTO ceramic samples appeared when x?≥?4%. The average grain size of CSTO ceramics decreased as the amount of doping increases, and all CSTO ceramics had giant dielectric constants. When the doping amount was x?=?4%, the CSTO ceramics obtained optimum dielectric properties, where ε′ = 2.6?×?10⁵ and tan δ?=?0.10. X-ray photoelectron spectroscopy (XPS) results showed that the giant dielectric origin was mainly due to the Sb⁵⁺ doping that generated electrons inside the material, Ca²⁺ doping that enhanced the generation of vacancies inside the material, and the defective dipole clusters produced that improved the dielectric properties of the CSTO ceramics. This work is critical for the development and deployment of new TiO₂-based giant dielectric ceramics.