Influence of lanthanum and niobium doping on the relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The lead–barium–zirconate–titanate (PBZT) ceramics of composition (Ba/Zr/Ti: 25/70/30) exhibit classical relaxor ferroelectric behaviour similar to other complex lead perovskites such as lead–lanthanum–zirconate–titanate or lead–magnesium–niobiate. Influence of Nb or La admixture on grain structure, dielectric and pyroelectric properties was showed earlier. The effect of simultaneously lanthanum and niobium modified PBZT 25/70/30 ceramics on properties have been studied and compared with earlier results. The influence of the additives on the values of characteristic parameters describing the relaxor behaviour of the studied ceramics (ε^′_max, T_m, T_f, T_B) was determined.     

The influence of axial pressure on relaxor properties of BaBi2Nb2O9 ceramics

On the basis of our studies it results that dielectric properties of BaBi₂Nb₂O₉ ceramics are sensitive to axial pressure applied. The pressure causes an increase of dispersion in the real part of dielectric permittivity ?′(T,f) and a rise in the temperature T_m at which the maximum in ?′(T,f) dependence occurs. The applied pressure induces in the ?′(T) dependence an additional step-like anomaly, which appears at the temperature T_A < T_m. The applied pressure shifts both T_m and T_A at the same rate, i.e. dT_A/dX = dT_m/dX = +14 °C/kbar at high axial pressure range, above the threshold pressure X_thresh. The Vogel–Fulcher relationship is employed to determine the axial pressure influence on relaxor properties of BBN ceramics. The simulated order parameter q takes non-zero values below Burn‘s temperature T_B, where the polar clusters appear on cooling. For pressures higher than 0.8 kbar, the T_B changes at the rate dT_B/dX = −200 °C/kbar. The decrease in the difference between Burn's T_B and the freezing T_f temperatures induced by the applied axial pressure is observed. This could be ascribed to the narrowing of temperature range of relaxor behavior.     

Temperature induced dielectric polarization evolution in polycrystalline Pb(Cd1/3Nb2/3)O3

The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometric and dielectric measurements performed for the same polycrystalline Pb(Cd_1/3Nb_2/3)O₃ (PCN) sample are presented. These results reveal the complex character of polycrystalline PCN dielectric properties; in particular, no structural phase transition (PT) was observed. The thermal expansion coefficient indicates glass-like behaviour of PCN. The frequency and temperature dependencies of complex dielectric permittivity were measured and analyzed in terms of diffused/relaxor transition of the ferroelectric polarization. Temperature induced evolution of the relative dielectric permittivity was found to involve two processes. Dielectric permittivity changes, originating from thermally induced evolution of thermal equilibrium of interactions between main structural lattice and two sub-lattices present in the sample were interpreted in terms of thermal evolution of polar cluster sizes in the region of relaxor/glass-like transition.     

Relaxor behavior in (Ba1−3x/2Bix)(ZryTi1−y)O3 ceramics

New ferroelectric ceramics Bi-BZT of ABO₃ perovskite type were synthesized in the (Ba_1−3x/2Bi_x)(Zr_yTi_1−y)O₃ system by solid state reaction route. The effect of the substitution of barium by bismuth in the A cationic site on structural and dielectric properties was investigated. The dielectric constant was studied in the temperature range from 20 K to 320 K at frequencies ranging from 0.2 to 100 kHz. A clear relaxor behavior was observed for samples with x ≥ 0.075 and y = 0.1. In this case the value of the relaxation parameter γ ≈ 2 estimated from the linear fit of the modified Curie–Weiss law, indicates the relaxor nature of the Bi-BZT ceramics. The dielectric relaxation rate follows Vogel–Fulcher relation with an activation energy of 0.26 eV and 0.27 eV, an attempt frequency f₀ = 3.4 × 10¹² Hz and 5.7 × 10¹² Hz and a static freezing temperature T_VF = 98 K and 94 K respectively for x = 0.075 and x = 0.1.     

Structure and dielectric behavior of (1-x)Pb(Sc1/2Ta1/2)O3-xPb(In1/2Nb1/2)O3 solid solution

A solid solution system of (1-x)Pb(Sc_1/2Ta_1/2)O₃-xPb(In_1/2Nb_1/2)O₃ (x = 0.2, 0.4, 0.6, and 0.8) was synthesized by conventional solid-state reaction technique. The optimum sintering temperatures of ceramics with x = 0.2, 0.4, 0.6, and 0.8 were 1400?°C, 1400?°C, 1300?°C, and 1200?°C, respectively. At these temperatures, the densest samples and the maximum dielectric constant were obtained. With increasing x, the percentage of pyrochlore phase increased, indicating a decrease in the solubility of solid solution. For x = 0.2, with the sintering temperature increasing, the ordering degree decreased while the dielectric constant increased. For x = 0.6 and 0.8, at the highest sintering temperature, the most pyrochlore phase appeared and the minimum dielectric constant was obtained. In addition, the relaxor characteristics of solid solution ceramics were systematically investigated. It was found that the dielectric maximum decreased and the temperature at dielectric maximum shifted to higher temperature with x increasing. All compositions exhibited the second-order phase transition due to the analysis of dielectric behaviors on heating and cooling. Interestingly, the difference in dielectric maximum between heating and cooling became larger with PIN content increasing. The diffuseness exponents of all compositions were calculated to be in the range of 1.53–1.66, suggesting the typical relaxor. The polarization-electric field (P-E) hysteresis loops of all solid solutions showed the shapes of slim loop. Meanwhile, the coercive field and remnant polarization of all compositions were analyzed in detail.     

Effect of hot pressing on processing and properties of BBN ceramics

BBN (BaBi₂Nb₂O₉) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators.     

Effect of Nb doping on the relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

Strong influence of niobium admixture added to the lead–barium–zirconate–titanate ceramics of a chosen composition Ba/Zr/Ti 25/70/30 on grain structure, dielectric, and pyroelectric properties was confirmed. The Nb-modified ceramics exhibit classical relaxor ferroelectric behaviour similar to other complex lead perovskites such as lead–lanthanum–zirconate–titanate-type ceramics. Additional anomalies in ɛ′(T) curves in low frequency range were observed in the paraelectric phase for undoped ceramics. These anomalies and some disturbances in regularities typical for the relaxor ferroelectric behaviour in the vicinity of diffuse ferroelectric–paraelectric phase transition in undoped PBZT ceramics are eliminated by the Nb admixture. An attempt at a quantitative explanation is presented in the paper.     

Dielectric properties of CuO-doped La2.98/3Ba0.01(Mg0.5Sn0.5)O3 ceramics at microwave frequency

The microwave dielectric properties of La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics prepared by the conventional solid-state method were investigated for application in mobile communication. A 100 °C reduction of the sintering temperature was obtained by using CuO as a sintering aid. A dielectric constant of 20.0, a quality factor (Q × f) of 50,100 GHz and a temperature coefficient of resonant frequency τ_f of −78.3 ppm/°C were obtained when La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics with 0.25 wt.% CuO were sintered at 1500 °C for 4 h.     

Effect of BaTiO3 addition on the microstructure and relaxor ferroelectric properties of Sr0.7Ba0.3Nb2O6 ceramics

A conventional solid-state reaction was used to synthesize (1-x) Sr_0.7Ba_0.3Nb₂O₆–xBaTiO₃ (0.00≤x≤0.10) ceramics. The phase structure, microstructure, and dielectric and relaxor ferroelectric properties of these ceramics were investigated. Tungsten bronze structure can be observed in ceramics, and addition of BaTiO₃ can make the grain size decrease and the porosity increase. The dielectric characteristics show diffuse phase transition phenomena for all samples, which were demonstrated by a linear fit of the modified Curie-Weiss law with γ varying between 1.54 and 1.88. As the BaTiO₃ content increases, the transition temperature (T_C) decreases gradually and has a minimum value of 37.53 °C at composition x=0.06, and the maximum dielectric constant (ε_max) increases gradually from 66 to 3309 and subsequently decreases to 1625 at x=0.10. In addition, the relaxor ferroelectric properties of these ceramics at x=0.8 are consistent with the Volgel-Fulcher relationship; polarization versus electric field (P-E) loops were measured at a different temperature.     

The influence of sintering aids for Nd(Mg0.5Ti0.5)O3 microwave dielectric ceramics properties

The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg_0.5Ti_0.5)O₃ ceramics were investigated systematically. B₂O₃, Bi₂O₃, and V₂O₅ were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg_0.5Ti_0.5)O₃ ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg_0.5Ti_0.5)O₃ microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (_r) value of 26.2, a quality factor (Q × f) value of 61,307 (at 9.63 GHz), and τ_f value of −45.5 ppm/°C. NdVO₄ secondary phase was observed at 10 mol% V₂O₅ addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg_0.5Ti_0.5)O₃ incorporated with 10 mol% B₂O₃ with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important.     

Fabrication and characterization of (Pb(Mg1/3Nb2/3)O3, Pb(Yb1/2Nb1/2)O3, PbTiO3) ternary system ceramics

New ternary compositions in the Pb(Mg_1/3Nb_2/3)O₃-Pb(Yb_1/2Nb_1/2)O₃–PbTiO₃ (PMN-PYbN-PT) system were prepared using 0.5Pb(Yb_1/2Nb_1/2)O₃-0.5PbTiO₃ (PYbNT) and (1-x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (x = 0.26; PMNT26 or x = 0.325; PMNT32.5) powders synthesized via the columbite method. Dense (≥ 96% of theoretical density) ceramics with PMN/PYbN mole ratios of 25/75 (R-25), 50/50 (R-50) and 75/25 (R-75T and R-75R) were fabricated by reactive sintering at 1000 °C for 4 h. Therefore, incorporation of PYbNT to PMNT successfully decreased sintering temperature of PMNT from 1200 °C-1250 °C to 1000 °C. Samples with higher density and perovskite ratio together with lower weight loss possessed higher dielectric and piezoelectric values in each composition. The R-75 samples had remanent polarization (P_r) values of 34-36 μC/cm² and piezoelectric charge coefficient (d₃₃) of 560 pC/N. The sharp phase transition PMNT as a function of temperature became broader or more diffuse with increasing PYbNT content. However, PYbNT addition to PMNT increased Curie temperature (T_c) from 183 °C (for PMNT32.5) to 220-242 °C (for R-75T and R-75R) to 336 °C (for R-25). Therefore, these ternary compositions can be tailored for various high temperature applications due to the relatively higher T_c with enhanced piezoelectric and dielectric properties as compared to PMNT.     

Dielectric and ferroelectric properties of Ba(ZrxTi1−x)O3 ceramics

It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO₃-based system. In this study, barium zirconate titanate Ba(Zr_xTi_1−x)O₃ (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO₃-based compositions caused a decrease in Curie temperature (T_c). At T_c, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm² and 30 μC/cm², respectively.     

Study of relaxor behavior in a lead-free (Na0.5Bi0.5)TiO3-SrTiO3-BaTiO3 ternary solid solution system

In this work, single phase lead-free (0.8-x)(Na_0.5Bi_0.5)TiO₃−0.2SrTiO₃-xBaTiO₃ (NBT-ST-BT) ceramics were prepared by conventional solid state reaction method. The effect of BT on the structure and on the dielectric and ferroelectric properties of NBT-ST-BT were investigated. A structural transformation from pseudo-cubic to tetragonal along with possible phase coexistence was witnessed as the BT content was increased. A diffuse phase transition with considerable frequency dispersion in the dielectric response and slim P-E loops evidenced strong relaxor behavior for the ternary system at higher compositions of BT. An analysis of the frequency dependent T_m according to V-F and Power law indicated substantial interaction between the polar nano-regions and relatively broad distribution of freezing temperatures. The study of the dielectric constant at much higher and lower temperatures than T_m in the range of Burn's temperature (T_B) to freezing temperature (T_f) to provide useful information about the growth rate of polar nano-regions and their interactions for a better understanding of the relaxor behavior exhibited by the present ternary system.     

Effect of Bi2O3 additives on sintering and microwave dielectric behavior of La(Mg0.5Ti0.5)O3 ceramics

Bi₂O₃ was selected as liquid phase sintering aid to lower the sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics. The sintering temperature of La(Mg_0.5Ti_0.5)O₃ ceramics is generally high, about 1600 °C. However, the sintering temperature was significantly lowered about 275 °C from 1600 °C to 1325 °C by incorporating in 15 mol% Bi₂O₃ and revealed the optimum microwave dielectric properties of dielectric constant (?_r) value of 40.1, a quality factor (Q × f) value of 60,231 GHz, and the temperature coefficient (τ_f) value of 70.1 ppm/°C. During all addition ranges, the relative dielectric constants (?_r) were different and ranged from 32.0 to 41.9, the quality factors (Q × f) were distributed in the range of 928–60,231 GHz, and the temperature coefficient (τ_f) varies from 0.3 ppm/°C to 70.3 ppm/°C. Noticeably, a nearly zero τ_f can be found for doping 5 mol% Bi₂O₃ sintering at 1325 °C. It implies that nearly zero τ_f can be achieved by appropriately adjusting the amount of Bi₂O₃ additions and sintering temperature for La(Mg_0.5Ti_0.5)O₃ ceramics.     

Effects of Al2O3 addition on the microstructure and microwave dielectric properties of Ba4Nd9.33Ti18O54 ceramics

Ba₄Nd_9.33Ti₁₈O₅₄·x wt%Al₂O₃ (BNT-A) ceramics (x=0, 0.5, 1.0, 1.5, 2.0, 2.5) were prepared by the conventional solid state reaction. The effects of Al₂O₃ on the microstructure and microwave dielectric properties of Ba₄Nd_9.33Ti₁₈O₅₄ (BNT) ceramics were investigated. X-ray diffraction and backscatter electronic images showed that the Al₂O₃ additive gave rise to a second phase BaAl₂Ti₅O₁₄ (BAT). The formation mechanism and grain growth of the BAT phase were first discussed. Dielectric property test revealed that the Al₂O₃ additive had improved the dielectric properties of the BNT ceramics: increased the Q×f value from 8270 to 12,180 GHz and decreased the τ_f value from 53.4 to 11.2 ppm/°C. A BNT-A ceramic with excellent dielectric properties: ε_r=70.2, Q×f=12,180 GHz, τ_f=20 ppm/°C was obtained with 2.0 wt% Al₂O₃ added after sintering at 1320 °C for 4 h.     

Fabrication and electrical properties of Pb(Co1/3Nb2/3)O3 ceramics

Pb(Co_1/3Nb_2/3)O₃ (PCN) ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb₂O₆) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. From X-ray diffraction analysis, the optimum sintering temperature for the high purity PCN phase was found at approximately 1050 and 1100 °C. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it is also observed that at very high temperature the density began to decrease. PCN ceramic sintered at 1050 °C has small grain size with variation in grain shape. There is insignificant change of dielectric properties with sintering temperature. The P–E hysteresis loops observed at −70 °C are of slim-loop type with small remanent polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics.     

Enhanced ferroelectric properties in (Ba1−xCax)(Ti0.94Sn0.06)O3 lead-free ceramics

Lead-free (Ba_1−xCa_x)(Ti_0.94Sn_0.06)O₃ (BCST) (x = 0.01-0.04) ceramics were prepared using a solid-state reaction technique. The effects of Ca content on the phase structure and electrical properties of the BCST ceramics were investigated. High piezoelectric coefficient of d₃₃ = 440 pC/N, planar electromechanical coupling factor of k_p = 45% and dielectric constant ?_r = 6900 were obtained for the samples at x = 0.03. At room temperature, a polymorphic phase transition (PPT) from orthorhombic phase to tetragonal phase was identified in the composition range of 0.02 < x < 0.04.     

Processing and properties of Pb(Mg1/3Nb2/3)O3–PbTiO3-based ceramics

Ceramic compositions of a combination between lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃, and lead titanate, PbTiO₃, were fabricated using the Mg₄Nb₂O₉ precursor technique. Their electrical properties with respect to temperature and frequency were examined and the effect of sintering conditions on phase formation, densification, microstructure and electrical properties of the ceramics were examined. It has been found that optimisation of sintering conditions can lead to a highly dense and pyrochlore-free PMN–PT ceramics. The gradual decrease of the physical properties of the sintered ceramics was related to the gradual decrease of density and inhomogeneous microstructure. The results also revealed that for the lower concentration of lead titanate, a relaxor behaviour is noticed with a high electrostrictive effect, which was almost hysteretic free. However, higher amount of lead titanate led to a normal ferroelectric behaviour.     

Dielectric and impedance spectroscopy of Sr(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Sr(Bi_0.5Nb_0.5)O₃ was prepared using a high-temperature solid-state reaction technique. Preliminary X-rays diffraction studies exhibit the formation of a single-phase compound in the orthorhombic crystal system. The study of microstructure of gold-coated pellet by scanning electron microscopy (SEM) shows well-defined and homogeneous distribution of grains on the surface of the sample. Detailed studies of dielectric parameters (i.e., ε_r and tan δ) of the compound as a function of temperature at selected frequencies reveal that the values of these parameters are almost independent of temperature. Studies of impedance and related parameters exhibit that these electrical properties of the material are strongly dependent on temperature, and bear a good correlation with the microstructure of the material. The decrease in value of bulk resistance on increasing temperature suggests the existence of negative temperature co-efficient of resistance (NTCR) in the material. Studies of electric modulus show the presence of hopping conduction mechanism in the material with non-exponential-type of relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius- and NTCR- types of behaviors of the material. The ac conductivity spectrum provides a typical-signature of an ionic conducting system, and is found to obey Jonscher′s universal power law.     

La-, K- and Nb-doped 0.90(Bi0.5Na0.5TiO3)–0.10PbTiO3

Lanthanum, Potassium and Niobium have been selected as cation dopants to modify the relaxor characteristics of 0.90(Bi_0.5Na_0.5TiO₃)–0.10PbTiO₃. The experimental results show that La lowers the phase transition temperatures and decreases the grain size. In contrast, the grain size of K-doped composition tends to increase. Furthermore, the maximum of dielectric permittivity and the Curie temperature increase as compared to those of La-doped material. La can improve the broadness of dielectric permittivity of 0.90(Bi_0.5Na_0.5TiO₃)–0.10PbTiO₃. However, Nb is a better promising dopant for enhancing the relaxor behavior for this composition.