Showing papers on "Ferroelectric ceramics published in 2010"

Strong ferroelectric domain-wall pinning in BiFeO3 ceramics

Abstract: We have studied the polarization-electric-field hysteresis, the dielectric permittivity dispersion, the piezoelectric properties, the electric-field-induced strain, and the interrelations between these properties for bismuth ferrite (BiFeO3) ceramics. The results indicate that the domain-wall movement in BiFeO3 is strongly inhibited by charged defects, most probably acceptor-oxygen-vacancy defect pairs. The domain-wall mobility can be considerably increased by preventing the defects from migrating into their stable configuration; this can be achieved by thermal quenching from above the Curie temperature, which freezes the disordered defect state. Similarly, Bi2O3 loss during annealing at high temperatures contributes to depinning of the domain walls and an increase in the remanent polarization. The possible defects causing the pinning effect are analyzed and discussed. A weakening of the contacts between the grains in the ceramics and crack propagation were observed during poling with constant field at 100 kV/cm. This is probably caused by an electrically induced strain associated with ferroelastic domain reversal. A relatively large piezoelectric d33 constant of 44 pC/N was obtained by “cyclic poling,” in which the electric field was released after each applied cycle with the purpose to relax the mechanical stresses and minimize the problem of cracking.

Charge migration in Pb(Zr,Ti)O3 ceramics and its relation to ageing, hardening and softening

Abstract: The dielectric response of hard (Fe-doped) and soft (Nb-doped) rhombohedral Pb(Zr0.58Ti0.42)1−xMexO3 (Me=Fe or Nb) ceramics was studied at subswitching conditions over a wide range of temperatures (50–450 °C) and frequencies (10 mHz to 10 kHz). The results show qualitative differences in the behavior of the acceptor- and donor-doped samples. Hard materials exhibit a steep increase in the complex permittivity with decreasing frequency. The onset of the dispersion is thermally activated with activation energies of about 0.6–0.8 eV and is attributed here to oxygen vacancy hopping. The activation energy for ac conductivity observed in soft materials is estimated to be about 1.7 eV, corresponding to half of the energy gap of Pb(Zr,Ti)O3 and is thus consistent with electronic conduction. The relevance of ionic hopping conductivity in hard materials to ferroelectric aging/deaging and hardening is analyzed. Strong ionic conductivity in hard samples and its absence in soft samples agree well with the dipolar mecha...

Ferroelectric transition of Aurivillius compounds Bi5Ti3FeO15 and Bi6Ti3Fe2O18

Abstract: Single-phase Bi5Ti3FeO15 and Bi6Ti3Fe2O18 ceramics have been synthesized by solid state reaction. The ferroelectric transition of the compounds was studied by differential scanning calorimetry, high-temperature x-ray diffraction, and temperature-dependent dielectric measurements. Two solid-state structural transitions were observed in both compounds, one is the orthorhombic↔tetragonal transition (ferroelectric transition) at 1021 K for Bi5Ti3FeO15 and 973 K for Bi6Ti3Fe2O18, and the other is accompanied by an abrupt lattice expansion of the tetragonal phase at about 1110 K for Bi5Ti3FeO15 and about 1090 K for Bi6Ti3Fe2O18.

Nonmagnetic Fe-site doping of BiFeO3 multiferroic ceramics

Abstract: In this paper, we show that a pure single phase by doping Fe-site of BiFeO3 (BFO) using tetravalent Zr4+ ions can be achieved by introducing cation (Bi3+) vacancies. The structural analysis reveals that the ferroelectric nature of BFO should be weakly affected by 10% of Zr4+ doping as the c/a ratio and the Curie temperature TC remain roughly unchanged compared to that of pure BFO. In contrast, the magnetic properties are affected as a weak ferromagnetism and a change of Neel temperature TN are observed. Beyond the double-exchange interactions arising from the creation of Fe2+, we propose another simple model inducing a local ferromagnetic coupling rather than an antiferromagnetic which considers the replacement of the magnetically active Fe3+, time to time, by a nonactive Zr4+.

Classic and Advanced Ceramics: From Fundamentals to Applications

Abstract: Preface INTRODUCTION TO CLASSIC CERAMICS Ceramics through the Ages, and Technological Progress Classification of Ceramics MINERALOGY, STRUCTURE, AND GREEN PROCESSING OF CLAY MINERALS Natural Clay Minerals Synthetic Raw Materials Processing and Forming of Clay Powders Rheology of Clay Particle Suspensions Drying of Green Clay Bodies IMPORTANT CERAMIC PHASE SYSTEMS Fundamentals of Phase Diagrams Phase Systems with Ceramic Relevance MINERALOGY AND CHEMISTRY OF THE CERAMIC FIRING PROCESS Introduction Crystallography of the Thermal Transformations of Kaolinite Thermal Transformations in Illitic Clays Thermal Transformations and Phase Formation in the System MgO-CaO-Al2O3-SiO2 Thermal Transformations and Phase Formation in the System MgO-(Fe2O3)-Al2O3-SiO2 MINERALOGY AND CHEMISTRY OF CEMENTS Historical Development Portland Cement High Performance Concrete (HPC) Environmental Impact and Concrete Recycling Future Developments and Outlook INTRODUCTION TO ADVANCED CERAMICS General Properties of Advanced Ceramics Current World Market Situation Recent US and Global Forecasts OXIDE CERAMICS: STRUCTURE, TECHNOLOGY, AND APPLICATIONS Alumina Zirconia Titania ELECTROCERAMIC MATERIALS Introduction Physics of Dielectric Materials Ferroelectric Ceramics Microwave Ceramics Pyroelectric and Piezoelectric Ceramics Electro-Optic Ceramics Selected Application of Electroceramic Materials and Devices SUPERCONDUCTING CERAMICS Introduction Definitions Historical Developments Material Classification Crystal Chemistry Theory Materials Processing Application of Ceramic Superconductors Outlook and Future Developments BIOCERAMIC MATERIALS Introduction The Concept and Definition of Biocompatibility The Interaction of Implant Materials and Living Tissue: A Basic Approach Mechanical Properties of Advanced Bioceramics: Alumina versus Zirconia Selected Bioceramic Materials Performance Requirements and Quality Control of Ceramic Femoral Ball Heads Future Developments and Outlook NON-OXIDE CERAMICS: STRUCTURE., TECHNOLOGY, AND APPLICATIONS Introduction Carbides Nitrides ADVANCED CERAMIC APPLICATIONS AND FUTURE DEVELOPMENT TRENDS Design of Monodisperse Ceramic Powders Ceramic Processing in a Microgravity Environment Powder Preparation under Reduced Gravity Ceramic Powder Synthesis by SHS Nanosized Ceramic Powders Future Development Trends APPENDIX A: Construction of the Phase Diagram of a Binary System A-B with Ideal Solid Solution APPENDIX B: Thermodynamics of Displacive Phase Transformation APPENDIX C: Radial Electron Density Distribution (RED) Function APPENDIX D: Thermodynamics of Spinodal Decomposition of Crystals APPENDIX E: Theory of Superconductivity

Low loss microwave ferroelectric ceramics for high power tunable devices

Abstract: In this paper we report the influence of the composition and concentration of Mg-containing additions such as Mg 2 TiO 4 , MgO and a mixture of Mg 2 TiO 4 –MgO on ceramics based on a mixture of BaTiO 3 /SrTiO 3 . Phase relations, crystal structure, microstructures, microwave dielectric properties ( ɛ , tan δ ) and DC tunability have been studied over a wide range of frequencies. The temperature dependence of the dielectric properties has been measured as well. Among the compositions synthesized were low loss bulk ferroelectrics with dielectric constants in the range 150–800 and relatively high DC tunabilities (up to 1.49 under a DC electric field of 40 kV/cm). These materials can be used for high power tunable microwave devices.

Grain size effect on the nonlinear dielectric properties of barium titanate ceramics

Abstract: The nonlinear dielectric properties of dense BaTiO3 ceramics with grain size of 1 μm–90 nm were investigated. In the finest ceramics, the permittivity reduces below 1000 and a remarkable nonhysteretic linear dc-tunability [e(E)] is obtained at high field, above 40 kV/cm. The observed behavior was explained by considering the nanostructured ceramic as a composite formed by ferroelectric grains, whose nonlinearity is reducing, and by low-permittivity nonferroelectric grain boundaries, whose volume fraction increases when decreasing the grain size. Reducing the grain size in ferroelectric dense materials is an alternative route to accomplish the application requirements: nonhysteretic tunability and permittivity below 1000.

Polarization relaxation mechanism of Ba0.6Sr0.4TiO3/Ni0.8Zn0.2Fe2O4 composite with giant dielectric constant and high permeability

Abstract: Ba0.6Sr0.4TiO3/Ni0.8Zn0.2Fe2O4 (BST/NZO) composites were synthesized via the conventional solid-state reaction method. The phase composition and surface morphology of the composites were investigated using x-ray diffractometry and scanning electron microscope, respectively. The dielectric and magnetic properties of the composites were studied. The results show that the BST/NZO composites have giant dielectric constants and very high permeabilities. For the 10%BST/90%NZO composite, the dielectric constant and permeability in low frequency range are about 150 000 and 29, respectively. The giant dielectric behavior of the BST/NZO composites is mainly attributed to the Maxwell–Wagner polarization.

Temperature-pressure phase diagram and ferroelectric properties of BaTiO3 single crystal based on a modified Landau potential

Abstract: A modified eighth-order Landau potential was proposed for the BaTiO3 single crystal by taking account into the quantum mechanical effects at low temperature. While all existing thermodynamic potentials for BaTiO3 fail to accurately describe the pressure dependence of ferroelectric transition temperatures, the temperature and hydrostatic pressure phase diagram constructed using the modified potential shows excellent agreement with experimental measurements by Ishidate, Abe, Takahashi, and Mori [Phys. Rev. Lett. 78, 2397 (1997)]. On the basis of the new proposed Landau potential, we calculated the dielectric coefficients, spontaneous polarizations, temperature-electric field phase diagram, and piezoelectric coefficients, all in good agreement well with existing experimental data.

Structural and piezoelectric properties of high-density (Bi0.5K0.5)TiO3–BiFeO3 ceramics

Abstract: The crystal structures and dielectric, polarization, and piezoelectric properties of high-density x(Bi0.5K0.5)TiO3–(1−x)BiFeO3 ceramics were investigated. The results obtained using x-ray and neutron powder diffractions and transmission electron microscopy showed that a morphotropic phase boundary between the rhombohedral (ferroelectric) and pseudocubic (ferroelectric) phases is present in 0.4

Dynamics of polarization reversal in virgin and fatigued ferroelectric ceramics by inhomogeneous field mechanism

Abstract: Temporal behavior of ferroelectric ceramics during the polarization switching cannot be satisfactorily explained by simple Debye or even stretched exponential laws. These materials exhibit rather a wide spectrum of characteristic times interpreted by different authors as switching or nucleation waiting times, the physical reasons for a wide time distribution still remaining unclear. A new model of polarization switching presented here suggests that the characteristic time variance in the ferroelectrics originates from the random distribution of the local electric fields due to intrinsic randomness of the material. The presented theory allows a direct extraction of the distribution of field values from the experiment. Systematic studies of polarization switching in fatigued lead zirconate titanate demonstrate the evolution of the field distribution with increasing level of fatigue. Plausible cause of the formation of regions subject to different field strengths is the generation of defects such as microcracks, pores, or voids in the course of fatigue. Suitability of the proposed model is demonstrated by an excellent correlation between experimental and calculated data for virgin and differently fatigued samples in a broad time-field region covering the electric field values of 0.5--2.5 kV/mm and nine orders of the magnitude of poling time.

Experimental and theoretical investigation on polarization reversal in unfatigued lead-zirconate-titanate ceramic

Abstract: The dynamics of polarization switching in a soft lead-zirconate-titanate ceramic has been studied over a broad time window ranging from 10−6–106 for applied fields between 0.5 and 2.5 kV/mm. The classical Kolmogorov–Avrami–Ishibashi model of the polarization reversal was not able to satisfactory explain the obtained results. Therefore, a new concept for the polarization dynamics of ferroelectric ceramics has been suggested, which is based on two principal assumptions, (1) a strong dependence of the polarization switching time on the local electric field and (2) a random distribution of the local switching times caused by an intrinsic randomness in the field distribution within the system. Thereby the switching volume is composed as an ensemble of many regions with independent dynamics governed by local field exclusively. Such random field distribution could be well adjusted by a Gaussian distribution around the mean value of the field applied. A total polarization dependence on time and applied field was obtained in explicit form with only three fitting parameters which enabled a good description of the experimental results on polarization reversal in the whole time-field domain.

Relaxor behavior of (Ba,Bi)(Ti,Al)O3 ferroelectric ceramic

Abstract: Perovskite type (Ba0.9Bi0.1)(Ti0.9Al0.1)O3 (BBTA) ceramics have been prepared through solid state reaction route. The room temperature x-ray diffraction study suggests that BBTA ceramics have single phase tetragonal symmetry with space group P4mm. In contrast to the sharp dielectric transition of pure BaTiO3, a broad dielectric anomaly coupled with the shift in dielectric maxima toward a higher temperature with increasing frequency has been observed in BBTA. The quantitative characterization based on empirical parameters (ΔTm, γ, ΔTrelax, and ΔTdiffuse(1 kHz)) confirms its relaxor nature. The dielectric relaxation which follows the Vogel–Fulcher relationship with Eα=0.011 eV, Tf=356 K, and f0=1.38×1010 Hz, further supports spin-glass-like characteristics. In this system, the relaxor behavior can be attributed to the dynamic response of the polar clusters induced by the combined substitutions of Bi3+ and Al3+ on the Ba2+ and Ti4+ site. Moreover, the curie temperature of BBTA shows the decreasing trend comp...

Enhanced multiferroic properties in Ti-doped Bi2Fe4O9 ceramics

Abstract: Structural, magnetic, and ferroelectric properties have been investigated for Bi2Fe4(1−x)Ti4xO9 (0≤x≤0.2) bulk ceramics, which were synthesized by a modified Pechini method. X-ray diffraction reveals that all samples are single phase with no impurities detected. Compared with antiferromagnetic Bi2Fe4O9 compound, doping with Ti ions induces the appearance of weak ferromagnetism at room temperature, which is discussed in terms of the collapse of the frustrated antiferromagnetic spin structure. Moreover, appropriate Ti doping also significantly reduces electric leakage and leads to the enhancement of electrical polarization. Among all samples, the optimal multiferroics with Mr∼0.0188 emu/g and Pr∼0.262 μC/cm2 at room temperature is found for x=0.15 ceramics. It is thus shown that Ti-doped Bi2Fe4O9 is a promising candidate for preparing multiferroic materials.

Piezoelectric PZT / PVDF-copolymer 0-3 composites: aspects on film preparation and electrical poling

Abstract: Composite films of lead zirconate titanate (PZT) and different (non-polar and polar) polyvinylidene fluoride (PVDF) copolymers are prepared as 30 to 150 μm thick freestanding, relatively flexible films. For low ceramic-volume fractions the ceramic fillers are homogeneous distributed within the polymer matrix as indicated by scanning electron microscopy studies. Ceramic-volume fractions higher than approximately 0.5 lead to porous composite films which became brittle. The brittle films are difficult to polarize and not suitable as piezoelectric transducers. The permittivities of non-porous composite films follow the Bruggeman model for dielectric mixtures. Different procedures are presented and verified in order to polarize the ferroelectric PZT particles and the ferroelectric polymer matrix. In detail, the overall polarization is discussed by taking into account the polarities of the applied poling voltage and of the measured piezoelectric signals. In summary, for composites with high ceramic-volume fractions piezoelectric coefficients of up to 8.6 pC/N and 22.1 pC/N (for PZT / P(VDFTrFE) composites) and up to 11.3 pC/N and 24.8 pC/N (for PZT / P(VDF-HFP) composites) are reached after short-term, room-temperature and long-term, high-temperature poling, respectively.

Study of impedance parameters of cerium modified lead zirconate titanate ceramics

Abstract: A high-temperature solid-state reaction technique was used to prepare the polycrystalline samples of cerium (Ce) modified lead zirconate titanate with Zr/Ti ratio 65:35 (i.e., Pb(Zr0.65-xCexTi0.35)O3 (PZCT)). Preliminary X-ray structural analysis exhibits the formation of the new compositions of PZT. In order to study the compositional effects on the electrical properties (complex impedance Z*, complex modulus M*, electrical conductivity and relaxation mechanisms) of PZCT, a nondestructive experimental technique (i.e., complex impedance spectroscopy) was used. The complex impedance analysis with Nyquist plots shows that the impedance parameters of all the PZCT samples contain bulk effect. The presence of single arc in the complex modulus spectra of PZCT confirms the single phase of PZCT with high relaxation time. The asymmetric behaviour of semi-circular arcs and shifting of peaks suggest the existence of non-Debye (Cole-Cole) type of relaxation mechanism in the PZCT systems.

Comparison of the Temperature-Dependent Ferroelastic Behavior of Hard and Soft Lead Zirconate Titanate Ceramics

Abstract: The ferroelastic properties of a hard acceptor-doped lead zirconate titanate (PZT) ceramic are investigated between room temperature and 300°C. Comparison with a soft PZT shows that acceptor doping has a stronger influence on mechanically induced domain switching than on switching caused by electric fields. A quantitative analysis of spontaneous and remanent strain and polarization indicates that poling in the soft material is dominated by 180° domain processes, while non-180° processes dominate the strain behavior. If the mechanical load exceeds a threshold level, the “hardening” effect of the acceptor doping vanishes, and hard and soft materials behave identically. The results are discussed based on the defect dipole model and the charge drift model for hardening and aging in acceptor-doped ferroelectric ceramics.

Morphotropic phase boundary and electrical properties in (1-x)Bi0.5Na0.5TiO3-xBi(Zn0.5Ti0.5)O3 lead-free piezoceramics

Abstract: (1−x)Bi0.5Na0.5TiO3−xBi(Zn0.5Ti0.5)O3 [(1−x)BNT−xBZT, x=0, 0.025, 0.0375, 0.050, and 0.075] lead-free piezoceramics were prepared and their structures and electrical properties were investigated. It is found that BZT can increase the Curie temperature of BNT. A morphotropic phase boundary (MPB) separating rhombohedral and tetragonal phases exists near x=0.0375. As the result, the MPB composition shows improved electrical properties; the saturated polarization, remnant polarization, and coercive field are 42.0 μC/cm2, 36.5 μC/cm2, and 3.5 kV/mm, respectively, while the piezoelectric coefficient, planar electromechanical coupling factor, and unipolar strain are 92 pC/N, 0.22, and 0.08%, respectively. The structures and electrical properties are discussed by comparing with that of other BNT-based piezoceramics. Our results do not only supplement for BNT-based lead-free piezoceramics, but also may provide a way to develop new lead-free piezoceramics with high Curie temperature.

Kinetic electrocaloric effect and giant net cooling of lead-free ferroelectric refrigerants

Abstract: The electrocaloric effect of BaTiO3 multilayer thick film structure was investigated by direct measurement using differential scanning calorimeter. The samples show a giant electrocaloric effect of 0.89 J/g under E=176 kV/cm, which also depends on the varying rate of applied field, following a general power-law relation. Based on the large net-cooling (0.37 J/g) resulting from the difference in the varying rates of rising and falling fields, the kinetic electrocaloric effect provides a solution for the design of refrigeration cycle in ferroelectric microrefrigerator.

The Piezoelectric and Dielectric Properties of 0.3Pb(Ni1/3Nb2/3)O3–xPbTiO3–(0.7−x)PbZrO3 Ferroelectric Ceramics Near the Morphotropic Phase Boundary

Abstract: 0.3Pb(Ni1/3Nb2/3)O3−xPbTiO3–(0.7−x)PbZrO3 (x=0.33–0.43) piezoelectric ceramics were prepared by the one-step solid-state reaction method. X-ray diffraction analysis showed the coexistence of rhombohedral and tetragonal phases at the composition x=0.39, which is the morphotropic phase boundary (MPB) for this system. The dielectric, ferroelectric, and piezoelectric properties of 0.3Pb(Ni1/3Nb2/3)O3–xPbTiO3–(0.7−x)PbZrO3 were investigated as a function of the content of PbTiO3. The ceramics at MPB showed large remnant polarization, low coercive field, and good piezoelectric properties. The results showed that piezoelectric ceramics with high piezoelectric constant and high Curie temperature also can be obtained in Pb(Ni1/3Nb2/3)O3–PbTiO3–PbZrO3 system with low Pb(Ni1/3Nb2/3)O3 content.

Harvesting Single Ferroelectric Domain Stressed Nanoparticles for Optical and Ferroic Applications

Abstract: We describe techniques to selectively harvest single ferroelectric domain nanoparticles of BaTiO3 as small as 9 nm from a plethora of nanoparticles produced by mechanical grinding. High resolution transmission electron microscopy imaging shows the unidomain atomic structure of the nanoparticles and reveals compressive and tensile surface strains which are attributed to the preservation of ferroelectric behavior in these particles. We demonstrate the positive benefits of using harvested nanoparticles in disparate liquid crystal systems.

Temperature-dependent mechanical depolarization of ferroelectric ceramics

Abstract: Mechanical depolarization of poled lead titanate zirconate (PZT) ceramics was conducted at a series of temperatures from 25 to 180??C in a temperature-controlled silicon oil tank. Both the longitudinal strain and polarization of the bar-shaped PZT samples were measured during uni-axial compression up to 400?MPa. It is found that both the stress-induced switchable polarization and the switchable strain of the poled PZT samples decrease steadily with increasing temperature. Unpoled PZT samples were also tested and the switchable strains follow a rule similar to the poled ones but of smaller magnitude. By measuring the P?E hysteresis loops, polarization variations and strain variations of a compression-free, poled PZT sample during a full cycle of heating?cooling, it is found that at elevated temperatures, the reduced switchable polarization by stress is caused by the pyroelectric effect and the reduced switchable strain is mainly due to the decreasing tetragonality (c/a). Furthermore, it was found that both the poled and unpoled PZT ceramics show a recoverable thermal shrinkage effect within the measurement temperature range.

Local probing of magnetoelectric coupling in multiferroic composites of BaFe12O19–BaTiO3

Abstract: The BaFe12O19–BaTiO3 composite ferroelectric/ferromagnetic ceramics were prepared by conventional solid-state sintering technique. The magnetic properties are consistent with the ratio of the magnetic phase present but ferroelectric properties are degraded due to a sufficiently high degree of conductivity in the ceramics. Magnetoelectric coupling was observed at a local level by means of the scanning probe microscopy (SPM). Piezoresponse and magnetic force modes of SPM were both utilized to assess strain-mediated magnetoelectric coupling between neighboring grains. The observed variation in the magnetic signal after the electrical poling with SPM was attested to the changes in the magnetic interactions and magnetic anisotropy leading to broadening of the magnetic domain wall.

Nonstoichiometric BiFe0.9Ti0.05O3 multiferroic ceramics with ultrahigh electrical resistivity

Abstract: BiFeO3, BiFe09Ti01O3, and BiFe09Ti005O3 ceramics of relatively high perovskite phase content were prepared for a comparison study While both BiFe09Ti01O3 and BiFe09Ti005O3 exhibit similarly improved weak ferromagnetism over BiFeO3, there exists a major difference in the x-ray diffraction patterns of BiFe09Ti01O3 and BiFe09Ti005O3, and the leakage current of BiFe09Ti005O3 is decreased by five orders of magnitude from that of BiFe09Ti01O3 With an ultrahigh electrical resistivity, over 1×1014 Ω cm, BiFe09Ti005O3 ceramic displays an especially low dielectric loss, 0015 at 100 Hz, a remanent polarization Pr of 023 μC/cm2 and a remanent magnetization Mr of 013 emu/g at room temperature It is proposed that the Fe-deficiency in BiFe09Ti005O3 decreases the amount of Fe2+ and leads to the ultrahigh electrical resistivity Nonstoichiometric compositions should receive more attention for developing high quality BiFeO3 multiferroic materials

Ferroelectric phase transition in Sn2+ ions doped (Ba,Ca)TiO3 ceramics

Abstract: Solid solutions of BaTiO3 ferroelectric ceramics containing Sn2+ ions have been synthesized by solid state reaction with Ca2+ codoping. The crystal structures of Sn2+ ions doped (Ba,Ca)TiO3 were identified as tetragonal perovskite type BaTiO3 based on x-ray diffraction profiles analysis. (Ba1−xCax)TiO3 (x=0.13) tetragonality increased with Sn ions doping. Temperature dependence of the dielectric properties for Sn2+ ions doped (Ba1−xCax)TiO3 ceramic sample showed a tetragonal-to-cubic phase transition temperature of 155 °C, which is higher than that of undoped (Ba1−xCax)TiO3 (135 °C). By using synchrotron x-ray absorption near-edge structure spectroscopy the valence state of Sn ions in the (Ba1−x−yCaxSny)TiO3 (x=0.13, y=0.05) ferroelectric ceramics was identified to be Sn2+.

Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22: Comparison of ceramics and single crystals

Abstract: We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Ram...

Density functional calculations of the structural, electronic, and ferroelectric properties of high-k titanate Re2Ti2O7 (Re=La and Nd)

Abstract: We have studied the structural, electronic, and ferroelectric properties of La2Ti2O7 (LTO) and Nd2Ti2O7 (NTO) by first-principles density functional theory calculations. The computed structural parameters are found to be in good agreement with experimental findings. In particular, the P21 phase is confirmed to be energetically preferred over the other configurations for both titanates. The calculations revealed the possible existence of an unidentified phase, namely, the P21/m paraelectric structure. From the modern theory of polarization the spontaneous polarization of LTO and NTO was calculated to be 7.72 μC/cm2 and 7.42 μC/cm2, respectively, in accordance with experimental findings. Its origin is ascribed to the displacement of the rare earth (Re) cations in the [100] cleavage plane and parallel to the b axis. Electronic charge density distributions and Bader’s topological analysis indicates that the bonding interactions between Re and O as well as Ti and O are not purely ionic, a noticeable covalent b...

Structural investigation of a novel perovskite-based lead-free ceramics: xBiScO3−(1−x)BaTiO3

Abstract: A full structural investigation was carried out on novel lead-free piezoelectric solid solutions of xBiScO(3)-(1-x)BaTiO3 (BS-BT) between x = 0.0 and 0.35 utilizing x-ray and neutron powder diffraction. This particular system demonstrated an extended tetragonal-pseudocubic phase boundary at room temperature in the region 0.05 = 0.05 demonstrated only one structural phase transition, which is the ferroelectric to paraelectric phase transition, suppressing the other two low temperature phase transitions. High-temperature dielectric properties were also studied in order to examine the physical properties of the ceramics. (c) 2010 American Institute of Physics. [doi:10.1063/1.3309064]