Morphotropic phase boundary and electrical properties of lead-free bismuth sodium lanthanum titanate—barium titanate ceramics

The important properties of lead-free piezoelectric ceramics have been investigated from Bismuth Sodium Lanthanum Titanate and Barium Titanate system: (1 − y)(Bi_0.5Na_0.5)_{(1 − 1.5x)}La _x TiO₃(BNLT)—yBaTiO₃(BT) where x = 0.017 and y = 0 − 0.2, respectively. The morphotropic phase boundary (MPB) was found to be around y = 0.1 by the x-ray diffraction and dielectric measurement at various amount of BT. The temperature dependence of dielectric constant (ε _r ) at various value of y showed the diffuse phase transition exhibiting the relaxor type ferroelectrics. The degree of diffuseness increased at a high doping content of about y = 0.15 where the second phase transition (T₂) of the ferroelectric to antiferroelectric phase disappeared. Moreover, this sample had the maximum piezoelectric coefficient (d ₃₃) of about 112 pC/N with relatively low dielectric constant. The optimum sintering temperatures and the microstructures of the dense BNLT-BT ceramics were also examined.     

Structural and electrical properties of SrBi2VxNb2?xO9 ferroelectric ceramics: Effect of temperature and frequency

Aurivillius type bismuth layered materials have received a lot of attention because of their application in ferroelectric non-volatile random access memories. Among bismuth layer structured ferroelectric ceramics SrBi₂Ta₂O₉ (SBT)/SrBi₂Nb₂O₉ (SBN) are of great interest for researchers because of their fatigue resistance and less distorted structure. Recently vanadium substitution in SBN/SBT has shown interesting electric and dielectric properties. In the present work, processing conditions, microstructure and electrical studies of vanadium doped SBN ferroelectric ceramics have been performed. Samples of compositions SrBi₂V _x Nb_2-x O₉, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides / carbonates. The samples were calcined at 700 °C and sintered at 800 °C. X-ray diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68 ?) by smaller pentavalent vanadium ion (0.59 ?) at B site on the microstructure, Curie temperature, Dielectric constant, Dielectric loss and electrical conductivity have been investigated. Dielectric properties of SBVN have been investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. Curie temperature is observed to be maximum in x = 0.1 vanadium doped sample. Strong relaxor like dielectric relaxation at the transition temperatures have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature. The variation of conductivities in these samples is also reported.     

Tunable Dielectric Characteristics of 0.9Pb(Fe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)O<Subscript>3</Subscript>/0.1CaTiO<Subscript>3</Subscript>

Tunable dielectric characteristics of 0.9Pb(Fe_1/2Nb_1/2)O₃/0.1CaTiO₃ relaxor ferroelectric ceramics were investigated as the function of DC bias field and temperature. High tunability (more than 20%) was obtained in the present ceramics under a relatively weak DC bias field (1.4 kV/cm). The value of tunability changed from negative to positive with increasing DC field. For the simulation of the dielectric constant under DC bias field, modified model needs to be constructed for the relaxor ferroelectrics. The dielectric constant curve as a function of temperature without and under DC field was well fitted using the equation of diffuse phase transition. The lower ε_max, higher T_max and higher diffuseness parameter under DC field were observed and only the lower ε_max contributed to positive tunability.     

Phase transition and electrical studies of wolframium doped SrBi2Ta2O9 ferroelectric ceramics

In this study, crystalline structure, dielectric and impedance properties of SrBi₂Ta₂O₉ (SBT) - based ferroelectric ceramics have been investigated with the substitution of wolframium/tungsten (W) onto the tantalum site. Wolframium doped SrBi₂(W _x Ta_{1 − x} )₂O₉ (0.0 ≤ x ≤ 0.20) ceramics were synthesized by solid state reaction method. The X-ray diffractogram analysis revealed that the substitution formed a single phase layered perovskite structure for the doping content up to x ≤ 0.05. The dielectric measurements as a function of temperature show an increase in Curie temperature (T _c ) over the composition range of x = 0.05 to 0.20. The W^{6 +} substitution in perovskite-like units results in a sharp dielectric anomaly at the ferroelectric phase transition. Furthermore, the dielectric constant at their respective Curie temperature increases with wolframium doping. Both enhanced Curie temperatures and dielectric constants at the Curie points indicate an increase in polarizability, which could be attributed to the increased “rattling space” due to the incorporation of the smaller tungsten cations. The dielectric loss reduces significantly with tungsten addition. AC impedance properties vis-à-vis wolframium content has also been studied.     

Acoustic properties of PLZT ceramics studied by Brillouin scattering

Brillouin spectra of lanthanum lead zirconate titanate (Pb_1−x La_x)(Zr_yTi_1−y )O₃ (PLZT-100(x/y/1−y)) relaxor ferroelectric ceramics with the famous composition of PLZT-10/65/35 have been investigated using a high-resolution Brillouin spectroscopy. The central peak of PLZT-10/65/35 appeared below ∼600 K, which is similar to the Burns temperature. The integrated intensity of the central peak grew on cooling and reached its maximum value at around 370 K, which is higher than the dielectric maximum temperatures. The overall shape and width of central peaks did not change in the electric field range of 0–7 kV/cm at room temperature. These observations were discussed in relation with the dynamics of nano-sized polar clusters, which have been suggested as the origin of the complex dynamical behaviors of ferroelectric relaxors.     

Microwave dielectric properties of temperature stable Ca5A2Ti1−x Hf x O12 (A = Nb, Ta) ceramics

Ca₅A₂Ti_1−xHf_xO₁₂ (A = Nb, Ta) ceramics have been prepared as single-phase materials by conventional solid-state ceramic route. Their structure and microstructure were studied by X-ray diffraction and scanning electron microscopic methods and dielectric properties were characterised in the 4–6 GHz microwave frequency range. We observed an increase in cell volume and theoretical density with compositional variations. In Ca₅Nb₂Ti_1−xHf_xO₁₂ ceramics the dielectric constant varied from 48 to 22 and quality factor from 26000 to 16000 GHz whereas in Ca₅Ta₂Ti_1−xHf_xO₁₂ the variation in dielectric constant was from 38 to 17 and quality factor from 33000 to 18000 GHz with increase in x. In both the ceramic systems the temperature coefficient of resonant frequency shifted from positive to negative values with Hf ⁴⁺ substitution for Ti⁴⁺.     

Temperature dependence of the dielectric dispersion and ferroelectric properties of neodymium doped bismuth titanate ceramics

Nd-doped bismuth titanate Bi_{4 − x} Nd _x Ti₃O₁₂ ceramics (x = 0–1.0) were prepared by the solid state reaction method. The temperature dependence of the dielectric dispersion and ferroelectric properties were investigated. With the increase of the Nd substitution for Bi ion, the Curie temperature decreased and the corresponding dielectric constant peak broadened. In addition, the strong low-frequency dielectric dispersions were exhibited. The Nd doping decreases the temperature dependence of the ac conductivity and increases the temperature dependence of the remanent polarization, which is caused by the induced polarization by defects, such as bismuth and oxygen vacancies.     

Synthesis of (Ba<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>)(Ti<Subscript>0.5</Subscript>Zr<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> ceramics and effect of Sr content on room temperature dielectric properties

The compositions in the system (Ba_1−x Sr _x )(Ti_0.5Zr_0.5)O₃ with different Sr (x) content, were synthesized through solid oxide reaction route. The phase formation behaviors in the system were investigated by XRD. The room temperature dielectric properties of the compositions were investigated in the frequency range 10 Hz to 13 MHz. The solid solution system Ba_1−x Sr _x Ti_0.5Zr_0.5O₃ remains as cubic perovskite up to x < 0.6 and transforms into the tetragonal structure above x > 0.6. Composition with x = 0.6 contains a mixture of cubic and tetragonal phases with broadened diffraction pattern. It is observed that the increasing of Sr substitution results in the decreasing of bulk density, average grain size and dielectric constants etc. in the composition system. The AC dielectric conductivity of the ceramics also decreases with the increase in Sr-substitution due to decrease in loss as well as grain size with that substitution.     

Piezoelectric properties and dielectric behavior of Bi1/2Na1/2[Ti1−x (Sb1/2Nb1/2) x ]O3 lead-free piezoelectric ceramics

New lead-free piezoelectric ceramics of ABO₃ perovskite type, Bi_1/2Na_1/2[Ti_1−x (Sb_1/2Nb_1/2) _x ]O₃, were synthesized by conventional solid state reaction. The effect of the replacement of complex ions of (Sb_1/2Nb_1/2)⁴⁺ in the B cationic site on structural and electrical properties was investigated. The XRD analysis showed that all samples exhibited a single phase of perovskite structure. Piezoelectric and dielectric measurement revealed that the substitution of (Sb_1/2Nb_1/2)⁴⁺ ions lead to an increase in piezoelectric constant(d ₃₃), electromechanical coupling factor(k _t), relative dielectric constant(ɛ _r),and loss tangent (tanδ), while excess of (Nb_1/2Sb_1/2)⁴⁺ ions results in a decrease in d ₃₃, k _t, ɛ _r, but an increase in tanδ. Temperature dependence of dielectric constant ɛ _r measurement indicated these compounds were relaxor ferroelectric. At low frequency and high temperature, dielectric constant increased sharply attributed to the superparaelectric clusters after (Sb_1/2Nb_1/2)⁴⁺ ions substitution.     

Preparation, characterization and dielectric study of new ferroelectric relaxors crystallizing with the tetragonal tungsten bronze structural type

The replacement of sodium and niobium by lanthanum and iron in Pb₂NaNb₅O₁₅, have allowed to prepare the new solid state solution Pb₂Na_1−x La _x Nb_5−x Fe _x 0₁₅ (0 ≤ x ≤ 1), crystallising with the tungsten bronze structure. The latter synthesized, in air, by solid state reaction, has been studied by means of X-ray and dielectric measurements. The composition dependencies of ferroelectric—paraelectric transition temperature and the lattice parameters are reported. The dielectric constants ɛ′_r and ɛ″_r have been also investigated as a function of temperature in the range 20°–700°C, and as a function of frequency in the range 1 k–13 MHz. In the composition range 0 ≤ x ≤ 0.35, the materials exhibit a typical ferroelectric–paraelectric transition while, in the composition range 0.35 < x ≤ 1, a relaxor effect has been evidenced.     

Low-temperature sintering and electrical properties of (1−x)Pb(Zr0.5Ti0.5)O3-xPb(Cu0.33Nb0.67)O3 ceramics

Electrical properties and sintering behaviors of (1 − x)Pb(Zr_0.5Ti_0.5)O₃-xPb(Cu_0.33Nb_0.67)O₃ ((1 − x)PZT-xPCN, 0.04 ≤ x ≤ 0.32) ceramics were investigated as a function of PCN content and sintering temperature. For the specimens sintered at 1050^∘C for 2 h, a single phase of perovskite structure was obtained up to x = 0.16, and the pyrochlore phase, Pb₂Nb₂O₇ was detected for further substitution. The dielectric constant (ε _r), electromechanical coupling factor (K_p) and the piezoelectric coefficient (d ₃₃) increased up to x = 0.08 and then decreased. These results were due to the coexistence of tetragonal and rhombohedral phases in the composition of x = 0.08. With an increasing of PCN content, Curie temperature (T_c) decreased and the dielectric loss (tanδ) increased. Typically, ε_r of 1636, K_p of 64% and d₃₃ of 473pC/N were obtained for the 0.92PZT-0.08PCN ceramics sintered at 950^∘C for 2 h.     

Dielectric properties and morphotropic phase boundaries in the xPb(Zn1/3Nb2/3)O3−(1−x)Pb(Zr0.5Ti0.5O3 pseudo-binary system

Ceramics in the xPb(Zn_1/3Nb_2/3)O₃−(1−x)Pb(Zr_0.5Ti_0.5)O₃ [xPZN–(1−x)PZT] solid solution system are expected to display excellent dielectric, piezoelectric, and ferroelectric properties in compositions close to the morphotropic phase boundary (MPB). The dielectric behavior of ceramics with x = 0.1−0.6 has been characterized in order to identify the MPB compositions in this system. Combined with X-ray diffraction results, ferroelectric hysteresis measurements, and Raman reflectivity analysis, it was consistently shown that an MPB exists between x = 0.2 and x = 0.3 in this binary system. When x ≤ 0.2, the tetragonal phase dominates at ambient temperatures. In the range of x ≥ 0.3, the rhombohedral phase dominates. For this rhombohedral phase, electrical measurements reveal a profound frequency dispersion in the dielectric response when x ≥ 0.6, suggesting a transition from normal ferroelectric to relaxor ferroelectric between 0.5 ≤ x ≤ 0.6. Excellent piezoelectric properties were found in 0.3PZN–0.7PZT, the composition closest to the MPB with a rhombohedral structure. The results are summarized in a PZN–PZT binary phase diagram.     

Synthesis of (Ba0.5Sr0.5)(Ti1 − x Zr x )O3 ceramics: Effect of Zr content on room temperature electrical properties

The phase formation behavior and room temperature dielectric properties of bulk perovskite solid solution composition (Ba_0.5Sr_0.5)(Ti_1 − x Zr _x )O₃ have been investigated. The samples with different Zr-content were prepared through solid state reaction. The XRD investigation showed that Zr⁺⁴ is systematically dissolved in Ba_0.5Sr_0.5TiO₃ lattice up to about 60 atm.% substitution, having cubic Pm3m structure. Eighty atom percent Zr substituted composition showed to contain a cubic phase similar to that of x = 0.6 composition and a tetragonal (I4/mcm) phase. That is the solid solution breaks around at 80 atm.% Zr substitutions. Ba_0.5Sr_0.5ZrO₃ was having orthorhombic Imma structure. Decrease in grain sizes were observed with increase in Zr content. The permittivity of the ceramics decreased with the increase in Zr substitution. The frequency dependency of dielectric loss in the frequency range 10 Hz to 10 MHz, were improved with Zr substitution in the ceramics. The room temperature ac and dc conductivity also decreased significantly with the increase in Zr-content.     

Sintering behavior, structures and microwave dielectric properties of a rutile solid solution system: (AxNb2x)Ti1–3xO2 (A=Cu, Ni)

The sintering behavior, structures and microwave dielectric properties in a rutile solid solution system—(A_xNb_2x)Ti_1–3xO₂ (A=Cu, Ni)—were investigated and the samples were prepared by conventional solid state reaction method. Single phase of tetragonal rutile structure has been obtained through the entire range of compositions (0.02 ≤ x ≤ 0.20). The sintering temperature was lowered to 900°C by (Cu _{x /3}Nb_2x/3)⁴⁺ substituting for Ti⁴⁺ in the solid solution. Comparing with that of rutile TiO₂ (465 ppm/°C), the temperature coefficient of resonant frequency (TCF) of the rutile solid solution is much lower (about 250 ppm/°C), and the dielectric constant and the quality factor (Qf value) of the solid solution are about 70~80 and 7,000G Hz. The substitution of (Cu _{x /3}Nb_2x/3)⁴⁺or (Ni _{x /3}Nb_2x/3)⁴⁺ for Ti⁴⁺ in the solid solution improved the microwave dielectric properties of the rutile TiO₂ ceramics.     

Structural and ferroelectric characterization of BMZ–BF–PT ceramics

Bismuth containing crystalline solid solutions of [(BiMgZrO₃)_1 − y –(BiFeO₃) _y ] _x –(PbTiO₃)_1 − x , (BMZ–BF–PT) have been synthesized by high temperature solid-state reaction technique. The crystalline symmetry varied with the composition, indicating good solid state solubility of BMZ and BF with PT. X-ray diffraction (XRD) reveals that BMZ–PT and BMZ–BF–PT have a single-phase perovskite structure. The MPB of BMZ–PT lies in the region x = 0.55 to x = 0.6, which is supported by the transformation from rhombohedral to tetragonal phase. The SEM photographs exhibit the uniform distribution of grains in the matrix. Polarization–electric field hysteresis studies were carried out at Room Temperature for all the compositions up to an applied electric field of 3.5 kV/mm. It was found that with the increase of BiFeO₃ content in the composition the remnant polarization decreases and the ferroelectric loops get constricted. Variation of dielectric constant with temperature shows that there is an increase in Transition temperature (T _C) with the increase in applied frequency indicating a relaxor characteristic of the compound. Our results show that BMZ–BF–PT is a good low-lead (Pb) high-temperature ferroelectric ceramic.     

Dielectric Properties of Niobium and Lanthanum Doped Lead Barium Zirconate Titanate Relaxor Ferroelectrics

The lead barium zirconate titanate (PBZT) relaxor ferroelectrics are ideal for high voltage capacitor applications due to their high dielectric constant, stability under DC bias, and temperature stability. In this study the composition (Pb_0.65Ba_0.35)(Zr_0.70Ti_0.30)O₃ was selected as the base composition. It exhibited typical relaxor characteristics such as frequency dispersion and diffuse phase transition. The dielectric constant is 6000 at room temperature and remains almost constant under electric field as high as 20 kV/cm. To further enhance the dielectric properties, various amounts of niobium oxide and lanthanum oxide dopants were added to the base PBZT to alter the defect structure and hence the dielectric properties. It was found that the dielectric constant of 1% Nb-doped samples was increased by 20–25% while maintaining similar voltage stability. This increase was attributed to the abnormal grain growth in the Nb-doped sample, and the correlation between microstructure and dielectric constant was drawn through a grain size study. The La addition only caused a monotonic decrease of dielectric constant and slightly improved voltage stability.     

High-ε Microwave Dielectrics in Pb0.6Ca0.4Zr0.6+x (Fe1/2Nb1/2)0.4−x O3 System

Modification of Pb_0.6Ca_0.4Zr_0.6(Fe_1/2Nb_1/2)_0.4O₃ dielectric ceramics was performed by Zr substitution for (Fe, Nb). The XRD patterns showed that the single phase with orthorhombic distortion unit cell was obtained in the present ceramics. The decreasing dielectric constant by Zr substitution was due to its smaller value of /r ³ _ion. The calculated polarizability was compared with the observed one, and the results showed a good fit, considering the polarizability of oxygen dependent on the V _ox. The Zr substitution on B-site reduced the temperature coefficient of dielectric constant effectively due to the reduced dielectric constant. The effects of tilting transition on the temperature coefficient of dielectric constant were also discussed. The modified microwave dielectric properties were obtained in Pb_0.6Ca_0.4Zr_0.6+x (Fe_1/2Nb_1/2)_0.4–x O₃ for x = 0.3: _r = 100, Q × f = 3,300 to 3,600 GHz, _f = 6–8 ppm/°C.     

Co-Modification of Ba5NdTi3Ta7O30 Dielectric Ceramics by Substitution and Introducing Secondary Phase

Co-modification of Ba₅NdTi₃Ta₇O₃₀ dielectrics ceramics was investigated through Pb substitution for Ba and introducing Bi₄Ti₃O₁₂ secondary phase. The dielectric constant increased from 150 to 283, the temperature coefficient of the dielectric constant decreased from –2500 ppm/°C to –1279 ppm/°C, and the dielectric loss decreased to 0.0007 at 1 MHz. Meanwhile, the bi-phase ceramics were investigated to achieve temperature stable ceramics with high dielectric constant and low dielectric loss. As the composition x varied from 0.4 to 0.7 for (1 – x)(Ba_0.8Pb_0.2)₅NdTi₃Ta₇O₃₀/xBi₄Ti₃O₁₂, the temperature coefficient of the dielectric constant changed from negative to zero to positive.     

Temperature-Stable Super High Permittivity Dielectric Ceramics Based on (Ag1 − x Na x )(Nb1 − y Ta y )O3 System

The dielectric properties of (Ag_{1 –x} Na _x )(Nb_{1 –y} Ta _y )O₃ were studied in this paper. The molar ratios of Ag/Na and Nb/Ta were quite important to adjust dielectric properties of the system. The ceramic material with high permittivity and low dielectric loss can be obtained in the cases where Ag/Na ratio is 3/2 and Nb/Ta ratio is 3/2. In addition, the dielectric loss was reduced by preparing the precursor in advance.     

Phase transition and piezoelectric response under electric field in PMN-PT crystals

The phase transition between the ferroelectric and relaxor states for (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-PT) single crystals at low PT (x = 0.21) was identified using high-resolution X-ray diffraction. The characterization of the dielectric and pyroelectric currents determined the properties of the polar state. The temperature stability region of the polar phase was enlarged with increasing bias field, and the corresponding polarization and piezoelectric properties were enhanced. Non-linearity of the electric displacement and loss under high ac fields was investigated by laser interferometry at a frequency of 40 kHz well below the resonant frequency. A linear displacement was obtained up to a large alternating current-field of 125 V/mm with an almost negligible second order harmonic component. The optimal d₃₃ improvement was 1,339 pm/V found for the [001] orientation. Such disclosure of phase stability and enhanced performances under high external field will be useful to determine their practical applications for resonant power transducers and quasi-static actuators.