Influence of calcination and sintering temperatures on the structure of (Pb1 − xBax )ZrO3

(Pb1–xBax)ZrO3 powders are synthesized below 800 °C for x 0.25 using a semi-wet route involving solid-state thermochemical reaction in a mixture of ZrO2 and (Pb1–xBax)CO3. The (Pb1–xBax)CO3 precursors were obtained by a forced coprecipitation technique. These powders can be sintered to achieve nearly 99% of the theoretical density at 1050 °C, which is 200 to 300 °C lower than that employed for the solid state route. The structure of as-calcined powder is orthorhombic for x 0.10 and rhombohedral for 0.25 > x 0.35, whereas the two phases coexist for 0.15 x 0.25. The structure of sintered material is orthorhombic for 0 x 0.10, rhombohedral for 0.20 x 0.30, and cubic for x 0.35, whereas orthorhombic and rhombohedral phases coexist at x = 0.15. The difference in the structure of the as-calcined and sintered powders is discussed in terms of particle size effect and chemical homogenisation of Ba2+ in the PBZ matrix.     

Dielectric,ferroelectric, and field-induced strain properties of Ta-doped 0.99Bi0.5(Na0.82K0.18)0.5TiO3–0.01LiSbO3 ceramics

Ta-doped 0.99Bi_0.5(Na_0.82K_0.18)_0.5TiO₃–0.01LiSbO₃ (BNKTT–LS) ceramics were prepared through a conventional mixed oxide solid-state sintering route. Partial substitution of Ta for Ti decreased the dielectric constant and depolarization temperature. The dielectric curves, polarization and strain hysteresis loops demonstrated that the incorporation of Ta stabilized the canonical relaxor phase of BNKT–LS ceramics leading to the degradation of piezoelectric and ferroelectric responses. The destabilization of field-induced ferroelectric order at x = 0.013 was accompanied by substantial enhancement in strain level. A unipolar field-induced strain of 0.39 % with a normalized strain (S _max/E _max =  $ d_{33}^{*} $ ) of 650 pm/V was achieved at a driving field of 6 kV/mm. The observed large strain can be attributed to the non-ergodic relaxor phase at zero electric field that transformed into an ergodic relaxor phase under the influence of the applied electric field.     

Dielectric properties of Na1 − x K x NbO3 and Na1 − x Li x NbO3 ceramics

The dielectric properties of solid solutions based on sodium potassium and sodium lithium niobates have been studied in wide ranges of temperatures (25–750°C), frequencies (25 to 10⁶ Hz), and electric fields (up to 30 kV/cm). We have identified solid-solution regions differing in the temperature and frequency dependences of the dielectric permittivity. It is reasonable to take into account the present results in device applications where wide variations in dc bias field and frequency are needed.     

Dielectric and thermal properties of xPbTiO3-(1 − x)SrTiO3 Polycrystals

SrTiO₃ and PbTiO₃ perovskites are combined to form the xPbTiO₃-(1 – x)SrTiO₃ (PST) solid solution. In this work, a study of its dielectric and thermal properties is reported as a function of PbTiO₃ content. The dielectric properties of the xPbTiO₃-(1 – x)SrTiO₃ solid solution are determined through a thermoelectric analysis technique and hysteresis measurements. Such measurements made at room temperature for all compositions show the influence of one component upon the other resulting in a response to the electric field that involves a strained lattice behavior. A limiting case of antiferroelectric-like behavior is observed for x = 0.5. The thermal properties such as the specific heat capacity (c) and thermal diffusivity () were determined using a photoacoustic technique (PA) and the temperature relaxation method (TRM). The thermal conductivity was calculated from the results obtained for c and .     

Ultrasonic investigation of the relaxor behaviour of ferroelectric ceramics (Pb1−xCax)TiO3 for x = 0.475, 0.50 and 0.55

Three samples of calcium modified lead titanate (Pb_1?xCa_x)TiO₃ with x = 0.475, 0.50 and 0.55 were studied in terms of their ultrasonic properties. The samples were prepared using the solid state reaction technique. Ultrasonic attenuation and velocity were measured as a function of the temperature at 5 MHz and 10 MHz with X-cut quartz transducers, using the ultrasonic pulse-echo technique and Papadakis method for accuracy determination of the transit time of ultrasonic RF pulses. An equation regarding elastic–electric coupling between strain and spontaneous polarization was used in order to fit the elastic modulus. The nature of the phase transition was characterized through the diffusivity exponent obtained from this fit. Our results show that, as calcium concentration increases from 0.475 to 0.55, the behaviour of ferroelectric phase transition changes from normal to relaxor. This process is accompanied by a systematic decrease of the critical temperature.     

Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

Dielectric properties of (Na0.5Bi0.5)1 − xMexTiO3 ceramics near morphotropic phase boundary

Ceramic samples of modified ferroelectric sodium-bismuth titanate (Na_0.5Bi_0.5)_0.87 Me_0.13TiO₃ (Me = Pb, Sr and Pb + Sr), were prepared using conventional solid state reaction techniques. The studies of powder X-ray diffraction of the obtained compounds revealed their rhombohedral symmetry at room temperature, the increase of lattice constant and the increase of rhombohedral lattice distortion (except for the material with Sr dopand, where distortion decreases). Temperature (at room temperature to 400°C) and frequency (at 20 Hz to 1 MHz) dielectric measurements reveal that A-site cations addition of Pb and/or Sr have resulted in the increase of relative electric permittivity. However, the temperature T _m (when the electric permittivity is a maximum) increases after Pb or Sr doping and it decreases after (Pb + Sr) doping. The pyroelectric and current loop measurements have shown that all samples were ferroelectric. The results of these measurements also allowed us to determine the temperature variation of the remanent and spontanous polarizations. The polarizations are found to decrease after Pb or Sr doping and increase after (Pb + Sr) doping. The piezoelectric constants (d ₃₃ and d ₃₁) and electromechanical coupling factors (k ₃₃ and k ₃₁) were obtained from resonance-antiresonance measurements method. The best piezoelectric and electromechanical properties have NBT doped by Pb. This ceramic may be good candidate for device applications. The diffuse ferroelectric phase transition of the investigated materials, similarly as for pure NBT, has been revealed. The properties of these materials (especially in diffuse phase transition range) can be explained by the behaviour of polar regions.     

Dielectric and impedance spectroscopic studies of (Sr1−x Pb x )TiO2 glass ceramics with addition of Nb2O5

Glasses were made by melt-quench method in the system [(Sr_1?x Pb _x )O·TiO₂]-[2SiO₂·B₂O₃]-5[K₂O-BaO] (0·0 ≤ x ≤ 0·4) with addition of 1 mol% Nb₂O₅. Perovskite strontium lead titanate in solid solution phase has been crystallized in borosilicate glassy matrix with suitable choice of composition and heat treatment schedule. Addition of 1 mol% of Nb₂O₅ enhances the crystallization of lead strontium titanate phase in the glassy matrix. Scanning electron microscopy (SEM) is performed to study the surface morphology of the crystallites and crystalline interface to the glass. Dielectric properties of these glass ceramics were studied by measuring capacitance and dissipation factor as a function of temperature at a few selected frequencies. Nb₂O₅ doped strontium lead titanate glass ceramic shows a high value of dielectric constant. It is of the order of 10,000 while the dielectric constant of undoped glass ceramic sample is of the order of 500. Complex impedance and modulus spectroscopic techniques were used to find out the contributions of polarization of crystallites and glass crystal interfaces to the resulting dielectric behaviour.     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

Dielectric and ferroelectric characteristics of [(Bi0.5Na0.5)0.94Ba0.06]1−xSrxTiO3 ceramics

Effects of Sr-substitution upon dielectric and ferroelectric characteristics of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ ceramics have been investigated together with the structure. [(Bi_0.5Na_0.5)_0.94Ba_0.06]_1?xSr_xTiO₃ solid solutions are formed in the entire composition range investigated here (x = 0–0.3), and there are two kinds of symmetries: P4bm and R3c. A morphotropic phase boundary separating P4bm and R3c is observed at x = 0.025. There are two dielectric anomalies in the permittivity versus temperature curve. Sr-substitution significantly enhances the low-temperature dielectric relaxation (around T _d ) and lowers the phase transition temperature (high-temperature dielectric anomaly at T _m ). The saturated polarization–electric field (P–E) hysteresis loops are determined further below T _d , and the pinched P–E hysteresis loops are generally indicated between T _d and T _m . With increasing Sr-content, T _d increases at first and then turns to decrease above x = 0.10, while T _m decreases continuously. Moreover, the pinched P–E hysteresis loops become very weak at x > 0.25. Sr-substitution changes the stabilization of the nonpolar state above T _d , and suppresses the electric field induced phase transition.     

Microwave sintering effect on structural and dielectrical properties of Ba1−x(Sr/Pb)xTiO3 (x = 0.2 for Sr and Pb) ceramics

Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. Sr and Pb doped BaTiO₃ ceramics has been prepared by the high energy ball milling followed by conventional and microwave sintering. The phase formation was confirmed by X-ray diffractometer followed by Scanning electron microscopy, atomic force microscopy and Transmission electron microscopy. Dielectric constant was measured on both the samples and it is observed that, in Ba_0.8Pb_0.2TiO₃ (abbreviated as BPT), it increased more than one order of magnitude and in Ba_0.8Sr_0.2TiO₃ (abbreviated as BST), it increased two orders of magnitudes at room temperature and Curie transition temperature by microwave sintering. Interestingly the Curie transition temperature of BPT value decreased from 224 to 210 °C, where as in BST ferroelectric ceramics, no variation of transition temperature by conventional sintering and microwave sintering respectively. This promising technique has distinguished characteristics of energy saving, rapid processing and uniform temperature distribution throughout the samples.     

Dielectric and electromechanical properties of Mn-doped 0.2875 Pb(Mg1/3Nb2/3)O3–0.2875 Pb(Yb1/2Nb1/2)O3–0.425 PbTiO3 ceramics

In this study, 0.2875 Pb(Mg_1/3Nb_2/3)O₃–0.2875 Pb(Yb_1/2Nb_1/2)O₃–0.425 PbTiO₃ (0.2875PMN–0.2875PYbN–0.425PT) ternary ceramic composition was doped with 1 mol% MnCO₃ in order to induce hard character for potential high-power applications. Dense 0.2875PMN–0.2875PYbN–0.425PT ceramics with 1 mol% MnCO₃ addition were fabricated after sintering at 1100 °C. ε _r = 1728, tanδ = 0.35 %, d ₃₃ = 320 pC/N, d ₃₁ = ?103 pC/N, Q _m = 467, k _p = 0.40, k ₃₁ = 0.24, k ₃₃ = 0.49, and T _c = 280 °C were measured for Mn-doped ceramics. However, undoped ceramics had ε _r = 2380, tanδ = 1.95 %, d ₃₃ = 433 pC/N, d ₃₁ = ?145 pC/N, Q _m = 60, k _p = 0.43, k ₃₁ = 0.27, k ₃₃ = 0.48, and T _c = 285 °C. Acceptor Mn²⁺/Mn³⁺ ions presumably substituted B-site ions in the perovskite structure and formed defect dipole pairs. The electrically “hard” character was induced as a result of the domain wall pinning due to the existing defect pairs. Particularly, increasing Q _m from 60 to 467 and decreasing tanδ from 1.95 to 0.35 % after Mn doping showed that Mn-doped 0.2875PMN–0.2875PYbN–0.425PT ceramics with “hard” character are potential candidates for high-power projector and transducer applications.     

The evolution of structure and properties in GdMn(1−x)TixO3 ceramics

In this work, the effects of Ti doping on the microstructure, dielectric, and magnetic properties of GdMn_(1?x)Ti_xO₃ (x?=?0.00–0.15) ceramic samples synthesized using a solid-state reaction were investigated. All the experimental samples formed a single-phase structure, and no structural transformation occurred within the experimental doping range; however, Ti doping caused lattice shrinkage. Ti doping reduced the grain size, and the microstructure of the synthesized samples appeared more compact in scanning electron microscopy images. The lattice distortion of GdMn_(1?x)Ti_xO₃ caused by Ti substitution at the Mn sites resulted in changes in the Raman vibration modes. X-ray photoelectron spectroscopy results showed that the valence state transition of the Ti and Mn ions occurred and the concentration of Ti⁴⁺, Mn³⁺ ions and oxygen vacancies changed due to the charge compensation induced by Ti doping. Ti doping had a significant influence on the size and concentration of cation vacancies in the GdMn_(1?x)Ti_xO₃ samples. Appropriate Ti doping was shown to reduce the dielectric loss, improve the frequency stability of the dielectric constant, and significantly affect the long-range ordering of Gd³⁺ magnetic moments and clearly reduce magnetization.

     

Phase transitions in the (BaTiO3)x/(BiFeO3)1−x composite ceramics: Dielectric studies

Dielectric studies were carried out for composite ceramics (BaTiO₃)_x/(BiFeO₃)_1−x (0 < x < 1) within a temperature range 23–450 °C. Linear permittivity studies at various frequencies showed the emergence of peaks near the temperatures of the ferroelectric phase transition in the BaTiO₃ grains and of the antiferromagnetic phase transition in the BiFeO₃ grains. The positions of the peaks did not depend visibly on frequency. The permittivity peaks near the antiferromagnetic phase transition shifted to low temperature with increasing the barium titanate fraction which suggests the reduction of the Neel temperature. The decrease in the Neel temperature in the composite ceramics was confirmed by measurements of the temperature dependence of the third harmonic generation.     

A comparison of strain relief behaviour of In x Ga1− x As alloy on GaAs (001) and (110) substrates

A comparative study on the strain relief behaviour of epitaxially grown In _x Ga_{1 – x} As (where 0.1 × 1) alloys on GaAs (001) and (110) were carried out using transmission electron microscopy (TEM) and high resolution X-ray diffraction (XRD). Three different strain relief mechanisms related to the formation of misfit dislocations (MDs) were observed. The dominant strain relief process can be a single mechanism or a combination of two of the three mechanisms depending on the substrate orientation and the in content.     

90‡ domain reversal in Pb(Zr x Ti1−x )O3 ceramics

A simple and direct method has been proposed, which may be used for quantitatively distinguishing the mechanisms of domain reorientation processes in polycrystalline materials. Using this method, the 90 domain reorientation in the Pb(Zr _x Ti_1–x )O₃ ceramic under an electric field was examined through the X-ray diffraction analysis. It was found that polarization switching in the PZT ceramic with a composition near the morphotropic phase boundary, is predominantly controlled by the two successive 90 domain processes rather than only the 180 domain reversal process. Experimental results also indicate that the coercive field of ferroelectric ceramics is related to the cooperative deformation associated with each grain. This cooperative deformation arises from the 90 domain-reversal process.     

Dielectric and Magnetic Properties of Pb(Fe1 /2Nb1 /2)O3–Pb(Fe2 /3W1 /3)O3Solid Solutions

Pb(Fe_1/2Nb_1/2)O₃–Pb(Fe_2/3W_1/3)O₃solid solutions were characterized by dielectric measurements at low frequencies and in the microwave range and magnetic measurements at high frequencies. The observed microwave dispersion was tentatively attributed to the domain mechanism of polarization. The obtained results suggest that the solid solutions studied are potential microwave-absorbing materials.