Coexistence Of Tetragonal Phase Research Articles

Structure, dielectric tunability, thermal stability and diffuse phase transition behavior of lead free BZT–BCT ceramic capacitors

This paper reports the development of a lead free {Ba(Zr0.2Ti0.8)O3}(1−x){(Ba0.7Ca0.3)TiO3}x – x=0.10, 0.15 and 0.20 – BZT–BCT ceramic solid solution system prepared using a solid-state reaction technique. The evolution of the Raman spectra with temperature was used to study the variation of the basic phase transition of BaTiO3 in these compositions. The phase transition temperature on heating was found to decrease to 310K, 300K, and 300K, respectively, with increasing Ca content on BCT end and decreasing Zr content on BZT end of lead free pseudobinary ferroelectric BZT–BCT system. Tetragonal and rhombohedral phase coexistence is observed at room temperature from X-ray diffraction (XRD) spectra. Rhombohedral phase is identified between the 83K and 273K from temperature dependent Raman studies. Raman results are in excellent agreement with those obtained from temperature dependent dielectric measurements. Bulk ceramic BZT–BCT materials have shown interesting temperature dependent dielectric properties and as well as higher values of room temperature dielectric constant ∼7800, 8400, 5200, dielectric tunability ∼82%, figure of merit (FOM) ∼93.71 % with low dielectric loss (tan δ) ∼0.015 to 0.024 and good thermal stability at high sintering temperature (1600°C); they might be one of the strong candidates for dielectric tunable capacitor applications in an environmentally protective atmosphere.

Structural, Dielectric And Conductivity Properties Of Ba2+ doped (Bi0.5Na0.5)TiO3 ceramic

Polycrystalline (Bi0.5Na0.5)1-xBaxTiO3 [here after BNBT], x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1 ceramics have been synthesized by conventional solid state reaction process and were characterized by X-ray diffraction technique, which indicates that on substitution of Ba 2+ in Bi0.5Na0.5TiO3 (BNT) ceramic there is splitting of the (2 0 0) peak for x ≥ 0.06. This splitting in the peak position reveals that the composition BNBT-0.06 is well in Morphotropic Phase Boundary (MPB) region where rhombohedral and tetragonal phase co-exist. Scanning electron micrograph shows decrease in grain size from 0.66 to 0.53 μm with increasing concentration of Ba 2+ ; and the dielectric constant of Ba 2+ doped BNT ceramics increased with decreasing grain sizes and a maximum value was attained at size of 0.54 ~ 0.56 μm. Doped BNT ceramic also exhibit diffuse phase transition and are characterised by a strong temperature and frequency dispersion of the permittivity which would be connected with the cation disorder in A-site of perovskite unit cell. Complex impedance spectroscopy is used to analyze the electrical behaviour of BNBT, which indicates the presence of grain effect and the composition exhibits Negative Temperature coefficient of resistance (NTCR) behaviour. The compounds exhibit Arrhenius type of electrical conductivity and the presence of non-Debye type of relaxation has been confirmed from impedance analysis.

Investigation of a new lead-free (0.89 − x)(Bi0.5Na0.5)TiO3–0.11(Bi0.5K0.5)TiO3–xBa0.85Ca0.15Ti0.90Zr0.10O3 ceramics

(0.89−x)(Bi0.5Na0.5)TiO3–0.11(Bi0.5K0.5)TiO3–xBa0.85Ca0.15Ti0.90Zr0.10O3 (BNT–BKT–BCTZx) ceramics were prepared by the conventional solid-state method. The dependence of BCTZ content on the microstructure and electrical properties of BNT–BKT–BCTZx ceramics is investigated. The BCTZ diffuses into the BNT–BKT lattice to form a stable solid solution, and a coexistence of rhombohedral and tetragonal phase is observed in these ceramics with the composition of 0.04≤x≤0.08. An enhanced piezoelectric behavior of d33∼198 pC/N and kp∼25.4% is demonstrated in the ceramic with x=0.06. Moreover, the introduction of BCTZ also improves the remanent polarization and decreases the coercive field, and the improvement in ferroelectric properties of 2Pr∼48.77μC/cm2 and 2Ec∼52.92kV/cm is observed in such a ceramic with x=0.06. As a result, the BNT–BKT–BCTZx ceramic is a promising candidate for lead-free piezoelectric materials.

(1-x)Pb(Yb1/2Nb1/2)O3-xPbTiO3(0.40 ≤ x ≤ 0.60) 고용계에서의 PbTiO3치환에 따른 상전이 영역의 상전이 거동과 유전특성

In this study, crystal structural changes and dielectric properties of (1-x)Pb(Yb 1/2 Nb 1/2 )O₃-xPbTiO₃ ((1-x)PYN-xPT) solid solutions were measured and analyzed with respect to the PbTiO₃ (PT) contents (0.40 ≤ x ≤ 0.60). From X-ray diffraction (XRD) measurements, (1-x)PYN-xPT solid solutions showed changes of the crystal structure from pseudocubic (0.40 ≤ x ≤ 0.44) to tetragonal (0.52 ≤ x ≤ 0.60) on increasing PT contents and exhibited the coexistence of pseudocubic and tetragonal phase near the morphotropic phase boundary (MPB) composition (0.46 ≤ x ≤ 0.50). The dielectric constant showed a maximum value at x = 0.46 and the maximum values in (1-x)PYN-xPT decreased with higher PT contents. The phase transition temperatures of (1-x)PYN-xPT solid solutions increased over the whole composition ranges tested (0.40 ≤ x ≤ 0.60).

Modified structure and electrical properties of BSZT doped KNN hybrid ceramic

Lead free (1−x)(K0.5Na0.5)NbO3–x(Ba0.9Sr0.1)(Zr0.1Ti0.9)O3 [(1−x)KNN–xBSZT] (x=0,0.02,0.04 and 0.06) ceramic were synthesized by a solid-state reaction method and the effects of BSZT doping on the electrical properties of KNN have been studied. X-ray diffraction (XRD) indicates that all the samples have single-phase perovskite structure and addition of BSZT forms a morphotropic phase boundary (MPB) i.e. the coexistence of orthorhombic and tetragonal phase in the region 0.02≤x≤0.04. Field emission scanning electron microscopy (FESEM) indicates the reduction in the grain size with the addition of BSZT. Small broadening in the dielectric peak arises at higher concentration of BSZT. The value of remnant polarization at x=0.04 is found to be higher than any other value of x except x=0 and also results in enhancement of dielectric constant at room temperature. Thereby it makes it useful for application at room temperature.

Preparation of Pb(Mg1/3Nb2/3)O3-PbTiO3ceramics by reaction-sintering method and their electrical properties

Pure phase perovskite relaxor-based (1 – x )Pb(Mg 1/3 Nb 2/3 )O 3 – x PbTiO 3 (PMN–PT, x = 0.2–0.4) ferroelectric ceramics were prepared by the reaction-sintering method sintered at 1240–1250 °C. The synthesized ceramics exhibit rather homogeneous microstructure morphology and relatively high density. The content of PbTiO 3 (PT) exerts successive influences on sintering capability, phase structure and electrical properties of the PMN-PT ceramics. With the increase of the PT content, the crystal structure of the PMN–PT ceramics changes gradually from the rhombohedral phase, across the coexistence of rhombohedral phase and tetragonal phase, and to the tetragonal phase, accompanied by the change of the dielectric response character from typical relaxor ferroelectrics to normal ferroelectrics. The morphotropic phase boundary (MPB) of the PMN–PT system is determined locating at x = 0.3–0.34 based on the structure analysis and the electrical properties measurements, in which the PMN–PT ceramics with the MPB composition exhibit enhanced microstructure and excellent electrical properties, especially superior piezoelectric properties.

Phase structure and electrical properties of (Li,Ta)-doped (K,Na)NbO3 lead-free piezoceramics in the vicinity of Na/K = 50/50

The phase structure and electrical properties of (K,Na)NbO3 (KNN)-based lead-free piezoelectric ceramics with nominal composition Li0.03 (NaxK1−x)0.97Nb0.8Ta0.2O3 (LKNNT, x = 0.50−0.55) were investigated with an emphasis on the influence of Na/K ratio. By XRD and Raman measurements, it was revealed that the phase transition from the co-existence of O1 and T1 to the co-existence of O2 and T2 occurs when x = 0.52. At this Na/K ratio, a peak of dielectric constants was obtained, which also corresponds to a morphotropic phase boundary between T1 and T2 besides that between O1 and O2 in LKNNT ceramics. All the Li0.03 (NaxK1−x)0.97Nb0.8Ta0.2O3 ceramics with x = 0.50 − 0.55 show excellent piezoelectric performance, and the piezoelectric coefficient d*33 can reach as high as 335 pm/V. The room-temperature piezoelectric properties in the present LKNNT ceramics are not sensitive to the change of Na/K ratio, indicating that the orthorhombic to tetragonal phase co-existence dominates the enhancement of piezoelectric properties. However, the results on the piezoelectricity measurement at elevated temperature showed possible to further enhance piezoelectric properties by adjusting Na/K ratio in the tetragonal LKNNT ceramics.

Normal to Relaxor Ferroelectric Transition and Domain Morphology Evolution in (K,Na)(Nb,Sb)O3–LiTaO3–BaZrO3 Lead‐Free Ceramics

A normal to relaxor ferroelectric transition was induced by the substitution of BaZrO3 for LiTaO3 in a typical lead‐free (K,Na)(Nb,Sb)O3–LiTaO3–BaZrO3 system and this was found to accompany a tetragonal to rhombohedral phase structural transformation. The typical relaxor behavior characterized by diffuse phase transition and frequency dispersion was identified by the measurement of frequency‐dependent dielectric permittivity. The transmission electron microscopy studies demonstrated that the above phenomenon would be closely related to the domain morphology evolution from normal micron‐sized lamellar domains, to tweed‐like domains and finally to polar nanodomains. Selected area and convergent beam electron diffraction patterns further confirmed that the composition (2.5 mol% BaZrO3) exhibited rhombohedral and tetragonal phase coexistence. The evolution of domain morphology with temperature also disclosed the diffuseness of ferroelectric phase transition.

Influence of Cobalt Ion Doping on Tetragonal–Orthorhombic Polymorphic Transformation and Dielectric Behavior of Barium Titanate Nanoparticles

Cobalt (Co) ion‐doped barium titanate (BaTiO3, BT) nanoparticles were synthesized through the sol–gel route using polyvinyl alcohol. The concentration of Co2+ varies from 0 to 1.6 mol% in the specimens. Grain size (D) ranges from 21 to 29 nm. There exist a new phase of Pnma orthorhombic crystal structure (o‐BT‐II) with lattice parameters a=0.6393 nm, b=0.5268 nm, and c=0.8824 nm in addition to P4mm tetragonal phase in the specimens. The lattice volume V=0.2971 nm3 of o‐BT‐II with z=4 formula units, yields a density ρ=5.214 g/cm3. This is a new polymorph in comparison to well‐known P4mm tetragonal (t) structure, V=0.0644 nm3 or ρ=6.016 g/cm3 (z=1). In 0.6 mol% Co2+‐doped specimen o‐BT‐II phase exists with maximum volume fraction of 64. Measurement of dielectric properties showed that the room temperature ɛr value increases with doping. Curie transition temperature TC decreases from 128°C to a minimum value of 43°C in the specimens doped with 0.6 mol% dopant. The presence of space charge polarization in system is clear from dielectric‐frequency dispersion study. The coexistence of tetragonal and orthorhombic (o‐BT‐II) phase results an unusual TC shift and diffuse nature of the dielectric behavior.

Structure, photoluminescence and electrical properties of Eu–Nd codoped CaBi4Ti4O15 synthesized by sol–gel method

Eu–Nd codoped CaBi3.75−xEuxNd0.25Ti4O15 (CBENT) powders were synthesized by a simple sol–gel method. Their structures were examined by X-ray diffraction, Raman spectrum, respectively. The coexistence of orthorhombic and tetragonal phase was found when the Eu3+ doping content varied from 0.3 to 0.6. The photoluminescence properties of the CBENT powders show that the intense emission bands centered at around 574, 590 and 612 nm are due to the transitions of 5D0 → 7F0, 5D0 → 7F1 and 5D0 → 7F2 of the Eu3+ ions, respectively. The spectra of the temperature dependence of dielectric constant indicate that the Curie temperature TC gradually decreases from 785 to 765 °C. The peaks of dielectric constant are restrained with increasing Eu3+ doping concentration, suggesting the weakness of the ferroelectricity. Combining the photoluminescence with the ferroelectric property in the CBENT, the optimal Eu3+ doping concentration x is 0.2.

Impedance spectroscopy and dielectric properties of Ce and La substituted Pb 0.7Sr 0.3(Fe 0.012Ti 0.988)O 3 nanoparticles

We present the structural, microstructural, dielectric and impedance behavior of Pb 0.7Sr 0.3[(Fe 2/3Ce 1/3) 0.012Ti 0.988]O 3 (PSFCT) and Pb 0.7Sr 0.3[(Fe 2/3La 1/3) 0.012Ti 0.988]O 3 (PSFLT) nanoparticles. These nanoparticles were prepared by a chemical synthesis route using polyvinyl alcohol as surfactant. The X-ray diffraction pattern shows polycrystalline nature with coexistence of tetragonal and cubic phase in both PSFCT and PSFLT nanoparticles. The average particle size has been measured using Scherer's relation. The average particle sizes also measured by TEM are 10 and 11 nm, and by SEM 9 and 12 nm, respectively, of PSFCT and PSFLT nanoparticles. By measuring the value of relative permittivity ( ɛ′) and loss (tan δ) at lower frequency, the dielectric properties show Maxwell–Wagner type interfacial polarization. However, due to nano size effect of PSFCT and PSFLT, dispersionless dielectric response has been observed up to higher frequency of 15 MHz. The frequency dependent real ( Z′) and imaginary ( Z″) parts of impedance confirmed the variation which was observed in dielectric properties. The values of resistance of grain boundaries, R gb is higher than grains, R g indicates that the effect of grain boundaries is dominant on electrical properties when the size of nanoparticles is quite small.

The Preparation of Lead Strontium Titanate Ceramics by the Combustion Method

In this work, (Pb1-xSrx)TiO3 (PST) ceramics with 0.25 ≤ x ≤ 0.75 were successfully prepared by the combustion method. The calcination and sintering temperatures were 800°C–1050°C and 1050°C–1250°C for 2 h, respectively. A single perovskite phase of the PST powders was found with calcination temperatures above 1000°C. The samples were indexed in a tetragonal system when x = 0.25. The lattice parameter c and c/a ratio increased while, the lattice parameter a decreased with increasing firing temperatures. For x = 0.75, the samples were indexed in a cubic phase and the lattice parameter a decreased with an increase in the firing temperatures. The samples were indexed in a tetragonal and cubic phase coexist when x = 0.50. The pure perovskite phase was found in all the sintered pellet samples. The average particle size and average grain size tended to increase with increasing calcining and sintering temperatures. The maximum density was 7.67, 6.52 and 5.59 g/cm3 obtained from the samples sintered at 1150°C with x = 0.25, 0.50 and 0.75, respectively.

Crystal Structure and Microstructure of (Pb1−xBax)(Zr1−yTiy)O3 Ceramics Prepared by the Solid State Reaction Method

Lead Barium Zirconate Titanate [(Pb1−xBax)(Zr1−yTiy)O3]: PBZT ceramics with x = 0.05 and 0.10 and 0 ≤ y ≤ 1 were prepared by the solid state reaction method. The calcination temperatures were between 800 and 1000°C for 1 h and the sintering temperature was 1300°C for 3 h. The crystal structure and microstructure were characterized by a X-ray diffractrometer (XRD) and scanning electron microscopy (SEM). It was found that the structure of calcined powders and sintered pellets of x = 0.05 and 0.10 were in an orthorhombic phase for y = 0, and tetragonal phase for 0.5 ≤ y ≤ 1; the c/a ratio increase with an increasing in the y content, whereas the orthorhombic and tetragonal phase coexist for y = 0.25. Microstructurally, the average particle size and average grain size slightly decreased with an increasing in the y content. The density and shrinkage increased when the x content increased.

Dielectric Ba(Ti1−x Sn x )O3 (x = 0.13) ceramics, sintered by spark plasma and conventional methods

A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti0.87Sn0.13)O3 ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti0.87Sn0.13)O3 ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were ~92% of the theoretical value of Ba(Ti0.87Sn0.13)O3. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature of 63 °C and 10 Hz.

Fabrication and properties of PYN–PMN–PZT quaternary piezoelectric ceramics for high-power, high-temperature applications

xPb(Yb 1/2Nb 1/2)O 3 – 0.05Pb(Mn 1/3Nb 2/3)O 3 – (0.95 – x)Pb(Zr 0.48Ti 0.52)O 3 (PYN–PMN–PZT) quaternary piezoelectric ceramics were prepared by a traditional ceramics process. The effects of Pb(Yb 1/2Nb 1/2)O 3 (PYN) content on the phase structure, electrical properties and Curie temperature of the quaternary system were investigated in detail. The phase structure of PYN–PMN–PZT ceramics changed from tetragonal to rhombohedral with increasing PYN content. The piezoelectric coefficient ( d 33), the electromechanical coupling factor ( K p ) and the dielectric constant (ε 33 T/ε 0) reach maximum values near the morphotropic phase boundary (MPB), whereas the mechanical quality factor ( Q m ) decreases. The sintered PYN–PMN–PZT ceramics exhibit high T C , and as the PYN content increases, T C decreases slightly. The MPB of the tetragonal and rhombohedral phase coexist and are located at a PYN composition of 0.12 ≤ x ≤ 0.14.The composition of PYN–PMN–PZT around the MPB showed high d 33 (> 300pC/N), K p (> 0.50), Q m (> 1000) and T C (> 350 °C), meaning it is a very promising piezoelectric material for high-power and high-temperature applications.

Ferroelectric properties of highly (1 1 1)-oriented Pb(Zr 1− x, Ti x)O 3 thin films with different Zr/Ti ratios

Pb(Zr 1− x , Ti x )O 3 thin films with different Zr/Ti ratios (0.45 ≤ x ≤ 0.49) were prepared by a sol–gel method using nitrate zirconium as starting material and 2-methoxyethanol as solvent. The films were deposited on Pt (1 1 1)/Ti/SiO 2/Si (1 0 0) substrates by spin-coating process and annealed at 650 °C for 3 min by rapid thermal annealing (RTA). X-ray diffraction (XRD) revealed that the films crystallized in perovskite phase and were all (1 1 1)-oriented. The effect of Zr/Ti ratios on the phase components and ferroelectric properties of the thin films was investigated. The result suggests that monoclinic phase and tetragonal phase coexists for the films with 0.47 ≤ x ≤ 0.49 and there is a pure monoclinic phase for the films with x ≤ 0.46. The films with x ≤ 0.46 exhibit higher remnant polarizations ( 2 P r max = 44.9 μ C/c m 2 ) compared with the other films, as is explained by more monoclinic phase content and higher (1 1 1) orientation degree.

Structure and electrical properties of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BiCoO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiCoO3 (x = 0.12–0.24, y = 0–0.04) have been fabricated by a conventional solid-state reaction method, and their structure and electrical properties have been investigated. The XRD analysis shows that samples with y ≤ 0.03 exhibit a pure perovskite phase and very weak impurity reflections can be detected in the sample with y = 0.04. With x increasing from 0.12 to 0.24 and y increasing from 0 to 0.04, the ceramics transform gradually from a rhombohedral phase to a tetragonal phase and rhombohedral–tetragonal phase coexistence to a pseudocubic phase, respectively. The morphotropic phase boundary (MPB) of the system between rhombohedral and tetragonal locates in the range of x = 0.18–0.21, y = 0–0.03. The ceramics near the composition of the MPB have good performances with piezoelectric constant d33 = 156 pC/N and electromechanical coupling factor kp = 0.34 at x = 0.21 and y = 0.01, which attains a maximum value in this ternary system. Adding content of BiCoO3 leads to a disappearance of the response in the curves of dielectric constant-temperature to the ferroelectric–antiferroelectric transition. The temperature dependence of dielectric properties suggests that the ceramics are relaxor ferroelectrics. The results show that (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiCoO3 ceramics are good candidate for use as lead-free ceramics.

Modeling on domain switching in ferroelectric ceramics near the morphotropic phase boundary

In this paper, domain switching in ferroelectric ceramics near the morphotropic phase boundary (MPB), where tetragonal phase and rhombohedral phase coexist, is analyzed by a micromechanical model using an inverse-pole-figure (IPF) method. Charge screening effect in ferroelectric ceramics is taken into account, thus the depolarization field by polarization switching vanishes. The mechanical constraint caused by non-180° switching, however, cannot be neglected and is assumed to be proportional to the switching strain caused by non-180° domain switching with a factor β as the measure of the constrained level. Using the IPF method, the domain switching induced polarization and strain can be explicitly obtained via integrations over the unit spherical surface. Two limiting cases are studied in this paper, i.e., the energy barrier for the interphase non-180° domain switching is equal to or much larger than that for the in-phase non-180° switching. In the former case, it is found that domains always tend to switch to the rhombohedral phase especially when the constrained level is high, i.e., at a large value of β. If the mechanical constraint is neglected, i.e., β=0, the maximum achievable polarization and strain can be analytically obtained in this case. While in the latter case, interphase domain switching is suppressed, thus domain switching in MPB ceramics is only a superposition of independent in-phase domain switching in tetragonal ceramics and rhombohedral ceramics.

Structural Phase Transition Studies on PMN-0.35PT using Infrared Spectroscopy

The purpose of the present work is to report studies on structural phase transition for PMN-xPT ferroelectric, with melt PbTiO 3 composition around the MPB (x = 0.35 mol %), using infrared spectroscopy technique. The study was centered on monitoring the behavior of the ν 1 -(Nb─O), ν1-(Ti─O) and ν 1 -(Mg─O) stretching modes as a function of temperature. The increasing as a function of temperature for ν 1 -(Ti─O) and ν 1 -(Mg─O) modes, observed between 230 and 300 K, can be related to the monoclinic (M C ) + tetragonal (T) phase coexistence in the PMN-PT.

Evidence for the monoclinic–tetragonal phase coexistence inPb(Zr0.53Ti0.47)O3 thin films

The structure and ferroelectric properties ofPbZr0.53Ti0.47O3 thin films were investigated in detail by using the x-ray diffraction technique. Thesurface morphology of the film was studied by using the atomic force microscopytechnique, showing a film with a dense morphology and a smooth surface. Basedon recent results reported by Pandey et al (2008 Acta Crystallogr. A64 192),Rietveld refinements of the structure were conducted considering different modelsproposed in the literature. Results suggested the monoclinic and tetragonal(M+T) phasecoexistence, with P4mm and Cm space groups, respectively. The monoclinic phase (68 mol%) is dominant over the tetragonalphase (32 mol%) for this PZT film composition.