Lead-free Solid Solution Research Articles

Chemical and technological aspects of increasing the functional characteristics of hard piezoceramics

Objectives. Ferroelectrically hard piezoelectric ceramics are in demand for high-power applications in piezotransformers, ultrasonic emitters, and piezo motors, which requires a combination of high piezoelectric characteristics and mechanical quality factors in it. The aim of this research was to reveal the main regularities in the microstructure and functional characteristic formation of ferroelectrically hard piezoceramics based on two widespread chemical systems, Pb(ZrxTi1-x)O3 and (Na1-xKx)NbO3, through various technological modes of production. In this study, two fundamentally different technological ways of forming a dense microstructure on the example of above systems have been employed to obtain the best set of dielectric, piezoelectric, and mechanical parameters for practical applications. In the case of lead-containing ceramics, various sintering technologies have been used, including conventional ceramic, hot pressing, and spark plasma sintering.Methods. The microstructure of the piezoelectric ceramics was investigated using electron microscopy, and the functional characteristics were assessed in terms of mechanical and piezoelectric properties. The density values were determined by hydrostatic weighing in octane, the relative dielectric permittivity was measured using an LCR meter, and the values of the piezoelectric coefficient and mechanical quality factor were gathered using the resonance–antiresonance method.Results. This research has identified that spark plasma sintering technology makes it possible to obtain high-density samples, which contain a homogeneous microstructure and double the figure-of-merit values, for use in high-power piezoelectric devices that operate at piezoresonance frequencies. It also found that the addition of a small amount of CuNb2O6 (x = 0.025) to lead-free solid solutions leads to the formation of a liquid phase during sintering, thereby creating a compacted microstructure with relative density values (96%) that have practical limitations in conventional ceramic technology. An increase in both the piezoelectric and mechanical properties, which leads to a twofold increase in the values of the quality indicator, was also observed.Conclusions. It is possible to increase, and even to double, the functional characteristics of both lead-containing and lead-free ferroelectrically hard piezoceramics by varying the technology used in the manufacturing process. By using spark plasma sintering technology with lead-containing ceramics, it is possible to reduce the optimum sintering temperature by 200 °C and the sintering time by more than 20 times, thus reducing production costs.

Effect of BFCO Doping on Phase Structure, Microstructure, Electric and Magnetic Properties of BNKLT Ceramics Prepared by the Combustion Method

Lead free solid solution Bi0.5(Na0.68K0.22Li0.10)0.5TiO3-xmol%Bi2FeCrO6 (BNKLT-xBFCO), with x = 0, 0.004, 0.007, 0.013 and 0.019, ceramics were calcined at 750 °C and sintered at 1150 °C for 2 h using the solid state combustion technique. The effect of the x content on the phase formation, microstructure, electric and magnetic properties of the produced ceramics were investigated. All samples exhibited a pure perovskite phase with the co-existence of rhombohedral and tetragonal phases. The doping of BFCO enhanced the density and dielectric properties of the BNKLT ceramics. The BNKLT-0.013BFCO ceramics showed the highest density (5.87 g/cm3), excellent dielectric properties (ε R ∼1390, tan δ R ∼0.039, ε m ∼4986 and tan δ m ∼0.075) and the highest piezoelectric constant (d33∼194 pC/N). The sample with x = 0 showed diamagnetic behavior, while the samples with 0.004-0.019 content exhibited paramagnetic behavior with higher magnetization at higher x content.

First-principles study on structural, electronic and optical properties of perovskite solid solutions KB1-x Mg x I3 (B = Ge, Sn) toward water splitting photocatalysis.

Perovskite materials have been recently attracting a great amount of attention as new potential photocatalysts for water splitting hydrogen evolution. Here, we propose lead-free potassium iodide perovskite solid solutions KBI3 with B-site mixing between Ge/Sn and Mg as potential candidates for photocatalysts based on systematic first-principles calculations. Our calculations demonstrate that these solid solutions, with proper Goldschmidt and octahedral factors for the perovskite structure, become stable by configurational entropy at finite temperature and follow Vegard’s law in terms of lattice constant, bond length and elastic constants. We calculate their band gaps with different levels of theory with and without spin–orbit coupling, revealing that the hybrid HSE06 method yields band gaps increasing along the quadratic function of Mg content x. Moreover, we show that the solid solutions with 0.25 ≤ x ≤ 0.5 have appropriate band gaps between 1.5 and 2.2 eV, reasonable effective masses of charge carriers, and suitable photoabsorption coefficients for absorbing sunlight. Among the solid solutions, KB0.5Mg0.5I3 (B = Ge, Sn) is found to have the most promising band edge alignment with respect to the water redox potentials with different pH values, motivating experimentalists to synthesize them.

Exceptionally High Transduction Coefficient in BaTiO <sub>3-</sub>Based Piezoceramic Through Phase Boundary Engineering

Transduction coefficient ( d33 × g33 ) is the core parameter for evaluating piezoelectric energy harvesting materials. However, due to the thermodynamic constraints, the synergistic variation between piezoelectric charge constant ( d33 ) and dielectric constant ( er ) indeed hinder the further increase of d33 × g33 . Herein, an exceptionally high d33 ×g33 of 13167×10−15m2 /N was achieved in 0.80BaTiO3 -0.10CaTiO3 -0.10BaZrO3 (BC0.1ZT) lead-free solid solution for the first time through a phase boundary engineering strategy. The high d33 × g33 mainly stems from non-synergistic variation of dielectricity and piezoelectricity in a new R-O phase boundary , in which the low er comes from the increased domain size and reduced domain wall density , while the high configurational sensitivity of the unique domains to external electric field contributed to the high d33 on the left side of polymorphic phase boundary (PPB). Our findings provide an alternative approach for enhanced energy harvesting performance by tracing the strategy of designing phase boundary to decouple d33 and er .

High energy storage density of NBT-0.10BFO solid solution films

To reduce the leakage current of the Na0.5Bi0.5TiO3 film and improve its energy storage properties, the sol-gel method was implemented to prepare (1-x)Na0.5Bi0.5TiO3-xBiFeO3 (NBT-xBFO) (x = 0.00, 0.05, 0.10, 0.15) lead-free perovskite-phase solid solution films. The point defects formed by Fe3+ occupying Ti4+ and oxygen vacancies formed composite defects FeTi′−Vo··−FeTi′, which reduced oxygen vacancies, cut down the domain wall pinning, and improved the polarization, thereby enhancing the recoverable energy density. Among all the films, the NBT-0.10BFO film exhibited a high recoverable energy density of 38.5 J/cm3 and an energy storage efficiency of 52.0% under an electric field of 2000 kV/cm. In addition, this film had fatigue resistance up to 1 × 109 cycles and suitable thermal stability within a wide temperature range of 20~110 °C. The NBT-0.10BFO film is expected to have broad application prospects in the field of energy storage.

Structural evidence for the polymorphic phase boundary in (Na,K)NbO3 based perovskites close to the rhombohedral-tetragonal phase coexistence zone

The multi-phase coexistence is a technologically important concept in high-performance piezoelectric ceramics owing to the ability of achieving extremely increased electromechanical properties. However, in fact it cannot always produce desirable thermal stability of small-field piezoelectric properties relevant to the device application. In this work, a typical lead-free piezoelectric composition of (Na0.52K0.4)(Nb0.84Sb0.08)O3–0.055LiTaO3–0.025BaZrO3 coexisted with rhombohedral (R) and tetragonal (T) phases at room temperature was investigated as a case study by means of ex/in-situ synchrotron x-ray diffraction, Rietveld structure refinement and measurements of temperature-dependent electrical properties. The refined crystal structure proves to be a three-phase coexistence of R, orthorhombic (O) and T at virgin state, and evolves into the R+monoclinic (MC)+T phase coexistence at poled state owing to an electric field induced irreversible O-MC phase transition. Particularly, the field induced MC phase can stably exist and maintain its concentration as long as the annealing temperature is below the Curie temperature. An interesting finding is that the poled sample still retains the polymorphism of phase transition like its virgin state featuring the temperature driven R-O(MC)-T phase transition, leading to seriously degraded piezoelectric coefficients after thermal cycles due to domain de-texturing of not only MC phase, but also R and T phases during repeated phase transition. The present study would benefit to understanding of the nature of polymorphic phase boundary and the structure origin of temperature-dependent piezoelectric properties in R-T coexisted (Na,K)NbO3-based lead-free solid-solution ceramics.

Expanded linear polarization response and excellent energy-storage properties in (Bi0.5Na0.5)TiO3-KNbO3 relaxor antiferroelectrics with medium permittivity

Dielectric materials with both high recoverable energy-storage density Wrec and efficiency η have attracted a lot of attention in recent years. Permittivity plays a crucial role in simultaneously achieving high polarization strength and large applied electric fields for any kinds of dielectric materials, among which antiferroelectric ceramics exhibit giant potentials in energy storage. Adjustment of permittivity has seemed to be more in linear dielectrics, but much less cared about in polar dielectrics so far for high-power energy-storage applications. In this work, a novel lead-free solid solution of (1-x)(Bi0.5Na0.5)TiO3-xKNbO3 was reported to show excellent comprehensive energy-storage performances of Wrec of ~5.2 J/cm3, large η of ~88%, fast discharge rate of t0.9 < 200 ns and outstanding temperature and frequency stability at x = 0.16. The X-ray, Raman spectra and scanning electron microscopy and so on demonstrate that it was basically ascribed to the formation of relaxor antiferroelectric phases with temperature-stable dielectric response and expanded linear polarization response, as well as enhanced dielectric breakdown strength induced by sub-micron grains. Particularly, selection of an appropriately medium permittivity value of about one thousand enables the studied AFE composition bring its superiority into full play in energy-storage properties, as demonstrated by a comparison between Wrec values of most previously-reported lead-free ceramics and theoretically predicted ones for linear dielectrics. These findings achieved in current work would provide an important guidance for compositionally designing high-performance energy-storage dielectrics in terms of modifying dielectric properties and polarization responses, particularly for relaxor antiferroelectrics with linear-like characteristics.

Multiphase coexistence and enhanced piezoelectric properties in (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 lead-free ceramics

A new lead-free piezoelectric solid solution system with the formula of (1−x)(K0.45Na0.55)(Nb0.965Sb0.035)O3−xBi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 were prepared using a conventional solid-phase sintering method, and we investigated the relationship between the composition, microstructure, phase structure and electrical properties of the ceramics. It was found that adding Bi0.5(K0.91Li0.09)0.5(Hf0.3Zr0.7)O3 induced the ceramics transition from a single orthorhombic structure to a coexistence of multiple phases, and a three-phase coexistence of rhombohedral, orthorhombic and tetragonal phases was present in the composition range x = 0.03 to 0.035. Enhanced piezoelectric properties were obtained for the ceramics near the three-phase coexistence region, with the largest piezoelectric constant d33 of 253 pC/N and the highest planar electromechanical coupling coefficient of 0.36. Additionally, a rough phase diagram for the solid solution system was established by using the critical temperatures determined by the temperature-dependent dielectric properties. The authors believe that these results can provide a useful reference for the development of (K,Na)NbO3-based lead-free piezoelectric ceramics.

Electric-Field-Induced Phase Transformation and Frequency-Dependent Behavior of Bismuth Sodium Titanate-Barium Titanate.

The electric field response of the lead-free solid solution (1−x)Bi0.53Na0.47TiO3–xBaTiO3 (BNT–BT) in the higher BT composition range with x = 0.12 was investigated using in situ synchrotron X-ray powder diffraction. An introduced Bi-excess non-stoichiometry caused an extended morphotropic phase boundary, leading to an unexpected fully reversible relaxor to ferroelectric (R–FE) phase transformation behavior. By varying the field frequency in a broad range from 10−4 up to 102 Hz, BNT–12BT showed a frequency-dependent gradual suppression of the field induced ferroelectric phase transformation in favor of the relaxor state. A frequency triggered self-heating within the sample was found and the temperature increase exponentially correlated with the field frequency. The effects of a lowered phase transformation temperature TR–FE, caused by the non-stoichiometric composition, were observed in the experimental setup of the freestanding sample. This frequency-dependent investigation of an R–FE phase transformation is unlike previous macroscopic studies, in which heat dissipating metal contacts are used.

Influence of lanthanides (Ln = La, Nd, and Y) in [Ba0.95Ln0.05] [Zr0.25Ti0.75]O3 lead-free piezoelectric solid solutions

Influence of lanthanides (Ln = La, Nd, and Y) in [Ba0.95Ln0.05] [Zr0.25 Ti0.75]O3 ceramics, synthesized by high-temperature solid-state reaction technique. Investigation on the phase structure, ferroelectric, piezoelectric and energy storage performance of BZT-Ln ceramics was done. X-ray diffraction studies revealed that the specimen belongs to cubic phases with the space group of Pm3m. Maximum ferroelectric properties at room temperature were observed an electric field of 65 kV/cm. A maximum energy storage density of 1.03 J/cm3 was achieved at 65 kV/cm for BZT-Nd. The piezoelectric (d33) and piezoelectric voltage (g33) coefficients exhibited a maximum of 21 pC/N and 9.11 (mV.m/N) respectively when Nd3+ substituted with BZT. The dielectric properties of BZT-Nd showed maximum dielectric constant (εr) ∼2148 at 573 K. Thus, the obtained good electrical properties of the ceramics enhance its potential use in sensor and energy storage applications.

Tailoring electromechanical performance in BiScO3-modified Bi0.5Na0.5TiO3-based lead-free piezoceramics

The strain response of lead-free ternary solid solution (1 − x) (0.94 Bi0.5Na0.5TiO3–0.06BaTiO3)–xBiScO3 (BNT–BT–BS) have been tailored by controlling the phase transition temperature. The effects of BiScO3 on the phase structure, dielectric, ferroelectric, piezoelectric properties, and electric field-induced strain are systematically investigated. A schematic phase diagram has also been established to clarify the relationship between strain behavior and structure evolution. The field-induced strain increases progressively, and a large strain of 0.35% with Smax/Emax = 471 pm/V is achieved at the critical composition x = 0.03, owing to the shift of the ferroelectric-to-relaxor transition temperature TF–R to ambient temperature. Intriguingly, the established correlation between strain response and TF–R demonstrates that the optimization of strain behavior of BNT-based ceramics can be realized though the regulation of TF–R to room temperature. Furthermore, a high and thermally stable electrostrictive coefficient Q33 of 0.018 m4/C2 can also be attained at the composition x = 0.06. In this study, it is believed that the modulation of phase transition temperature is feasible to achieve the large strain response in BNT-based ceramics.

Bipolar and unipolar fatigue property in Bi0.5Na0.5TiO3–Bi0.5K0·5TiO3–SrTiO3 lead-free piezoelectric ceramics

The bipolar and unipolar fatigue property of lead-free piezoelectric solid solution Bi0.5Na0.5TiO3–Bi0.5K0·5TiO3–SrTiO3(BNKST) was studied. Under a bipolar electric field of 4 kV/mm at 10 Hz, the remnant and maximum polarization, maximum strain value of all the studied compositions changed less than 2% after 106 bipolar cycles, while the coercive field exhibited different behavior for BNKST composition with different ferroelectric order states. The unipolar fatigue results also indicated that the BNKST with SrTiO3 concentration of 0.15 had excellent fatigue property after 107 unipolar cycles under 4 kV/mm. The underlying mechanism was discussed. The excellent fatigue property and large strain response make this system suitable for piezoelectric actuator applications.

A high-tolerance BNT-based ceramic with excellent energy storage properties and fatigue/frequency/thermal stability

A novel perovskite lead-free solid solution of (Ba0.06Bi0.47Na0.47)1-xLaxTi1-yZryO3 were designed by dual-substitution of La3+ and Zr4+ for (Ba0.06Bi0.47Na0.47)2+ and Ti4+. The frequency-, temperature- and fatigue-dependent energy storage properties of the materials were investigated. After the dopings of La3+ and Zr4+, the crystal structure of the ceramics remains unchanged; and tetragonal and rhombohedral phases coexist in all ceramics which exhibit a relaxor phase transition. The co-substitution of La3+ and Zr4+ leads to the high dielectric breakdown strength (DBS), large spontaneous polarization (Ps) and small remnant polarization (Pr) of the materials. The optimum energy storage properties are achieved at x/y = 0.02/0.04, giving high recoverable energy storage density of Wrec ~1.55 J/cm3, excellent energy storage efficiency of ƞ ~72.6% and large dielectric breakdown strength of DBS ~136 kV/cm. Furthermore, the ceramic with x/y = 0.02/0.04 possesses superior durability of frequency (~2–60 Hz), fatigue (~ 103) and temperature (~ 25–245 °C).

‘Domain structures – heterophases – phase contents’ relations in lead-free ferroelectric solid solutions

Examples of two- and three-phase structures in BaTiO3-based ferroelectric solid solutions are first analyzed within the framework of the united model. The role of domain orientations and heterophases containing the tetragonal phase are discussed in the context of the stress relief at interfaces that separate the ferroelectric phases and two-phase regions. Relations between the domain (twin) structures and phase contents are studied for three-phase states in (1 − x)BaTiO3 − xCaHfO3, (1 − x)BaTiO3 − xCaSnO3, and (1 − x − y)BaTiO3 − xCaTiO3 − yBaZrO3 with compositions near the morphotropic phase boundary. In these materials, volume fractions of the tetragonal, orthorhombic and rhombohedral phases are interpreted in terms of the united model by taking into account analogies between domain orientations in the adjacent phases and minimum numbers of domain types (mechanical twins) therein. Calculated results on the phase content are consistent with experimental room-temperature data on the three aforementioned solid solutions.

Ultra-slim pinched polarization-electric field hysteresis loops and thermally stable electrostrains in lead-free sodium bismuth titanate-based solid solutions

Electric field-induced strains (electrostrains) with high amplitude, high thermal stability and ultra-low hysteresis are of great interest both in fundamental researches and industrial applications, such as high-precision displacement actuators. In this work, we present a strategy to fulfil these requirements via a relaxor antiferroelectric-like material that possesses intriguing antiferroelectric and relaxor characteristics simultaneously. Its antiferroelectric state would result in high electrostrains because of the electric-field induced antiferroelectric-to-ferroelectric phase transition, while the relaxor state would boost the temperature stability and ultra-slim hysteresis of electrostrains. According to this strategy, we obtained high electrostrains (>0.1% at 60 kV/cm) accompanying with good temperature stability (variation of strain < 20% from 30 °C to 120 °C) and ultra-low hysteresis (<7%) in lead-free (Bi0.5Na0.5)TiO3-x(Sr0.7Bi0.2)TiO3 (BNT-xSBT) solid solutions. The thermal stability of the electrostrains is directly correlated to the thermal stability of polarization based on electrostrictive effect. The electrostrictive coefficient in this system is discussed in detail. This work not only proves the effectiveness of this strategy, but also paves a way to search high electrostrains with good thermal stability and ultra-low hysteresis in unique BNT-based solid solutions.

Antiferroelectricity in new silver niobate lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01)

The critical need for clean energy has led to the development of lead-free electroceramics. However, lead-free antiferroelectrics seldom have been reported because of the difficulties in materials fabrication and their low electrical performance. In this work, we successfully synthesized lead-free antiferroelectric ceramics (1-x)AgNbO3-xCaZrO3 (x = 0.00–0.01) using the solid state reaction method in flowing oxygen (O2) atmosphere. Calcium zirconate (CaZrO3) dopant effectively stabilized the antiferroelectricity of silver niobate (AgNbO3) by dramatically decreasing the tolerance factor t. Additionally, we identified an orthorhombic Pbcm structure similar to that of pure AgNbO3. With the introduction of CaZrO3, phase transition temperatures M1–M2, M2–M3 and the freezing temperature Tf decreased. The shift of the M1–M2 phase transition temperature and Tf was the result of the restriction of the M1 phase due to CaZrO3 substitution. The compositions of x < 0.001 displayed a double hysteresis loop with a raised critical field EF. However, when the doping concentration exceeded 0.002, the double hysteresis loop with a higher polarization could not be obtained until the breakdown strength of EB exceeded 200 kV/cm because of the tremendously enhanced free energy barrier between the virgin antiferroelectric state and the field-induced ferroelectric state. We also evaluated the polarization hysteresis loops are also evaluated at temperatures up to 100 °C for the compositions x = 0.00–0.005. With an elevated temperature, at which the free energy barrier was reduced, the double hysteresis loop was obtained at a lower electric field when compared with that at room temperature for the compositions x = 0.004 and 0.005. These results demonstrated that by adjusting the tolerance factor t and average electronegativity difference X, the antiferroelectricity could be predicted in AgNbO3-based lead-free solid solution systems, thus providing a new strategy for designing a new class of antiferroelectric materials.

Piezoelectric, Dielectric and Ferroelectric Properties of (1−x)(K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3-xBa0.5(Bi0.5Na0.5)0.5ZrO3 Lead-Free Solid Solution

The lead-free solid solution $$ (1-x) $$ (K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3-xBa0.5(Bi0.5Na0.5)0.5ZrO3 [KNLNS-xBBNZ] with 0.02 < x < 0.05 was successfully prepared by a conventional solid-state route. The effect of BBNZ on the KNLNS phase structure, microstructure and electrical properties was investigated. X-ray diffraction patterns demonstrated a single-phase perovskite-type structure and for 0.02 < x < 0.03 a rhombohedral–tetragonal (R–T) phase coexistence. In addition, the average crystal size greatly decreased with BBNZ doping. Furthermore, the piezoelectric and ferroelectric properties of the KNLNS-xBBNZ ceramics were enhanced at x = 0.02 ( $$ d_{33} $$ = 292 pC/N, $$ - \;d_{31} $$ = 100 pC/N, $$ k_{\rm{p}} $$ = 48%, $$ \varepsilon_{\rm{r}} $$ = 5876, $$ \tan \delta $$ = 0.03) due to a high polarizability at a local level. For x = 0.02, the solid solution showed good thermal stability of the $$ d_{33} $$ piezoelectric constant. As a result, this lead-free solid solution holds potential for applications in electric generators and high-temperature sensors.

Structural, dielectric and impedance characteristics of (Bi0.5Na0.5)TiO3-BaTiO3 electronic system

A lead-free solid solution of two ferroelectrics, bismuth sodium titanate and barium titanate, of a composition 0.96(Bi0.5Na0.5TiO3)-0.04(BaTiO3) (termed as BNT-BT-4) was prepared by a standard low-cost ceramic technology. The phase analysis of the solid solution, carried out using X-ray diffraction pattern, shows a major tetragonal phase and a minor impurity phase at room temperature. The surface morphology of the prepared system showed the formation of the high-density sample. The phonon mode statistics, width location and intensity of the peaks were analyzed by Raman spectroscopy. The temperature-frequency dependence of dielectric parameters (permittivity and tangent loss) and AC conductivity were analyzed. The apparent activation energy of BNT-BT-4 was evaluated with help of AC conductivity data. The effect of grain on the capacitive and resistive properties has been studied using an impedance spectroscopy technique. The decrease in the value of grain resistance on rising temperature shows the semiconductor or negative temperature coefficient behavior of the material. Based on an analysis of complex modulus spectrum, the conduction mechanism in the material has been suggested. As BNT-BT-4 shows a remarkable temperature independent relative dielectric properties and low tangent loss, it is a potential candidate for devices.

Structural, dielectric, electrical and magnetic characteristics of lead-free multiferroic: Bi(Cd0.5Ti0.5)O3[sbnd]BiFeO3 solid solution

This communication provides the detailed description of the synthesis and characterization of a lead-free multiferroic solid solution of Bi(CdTi)O3 and BiFeO3 of a general chemical composition Bi(Cd0.45Ti0.45Fe0.10)O3 (abbreviated as BCTFO). The material has been synthesized via a solvent-free solid-state reaction approach by utilizing high-purity oxides and carbonate in appropriate stoichiometric amount. The structural, morphological, molecular structure, electrical and magnetic characteristics of as-synthesized electronic system were examined by the powder X-ray diffraction, field emission scanning electron microscopy, vibrating sample magnetometer and impedance spectroscopy techniques respectively in different experimental conditions. Analysis of X-ray diffraction data of BCTFO shows a single-phase formation of the material in orthorhombic crystal symmetry with very fine powder (average linear crystallite dimension = 30 nm). Detailed studies of dielectric parameters (dielectric constant, tangent loss and polarization) in a selected frequencies (1 kHz–1.5 MHz) and temperatures (300 K–773 K) clearly exhibit one of the important components of multiferroics (i.e., ferroelectricity). Studies of some components of electrical parameters (dielectric, impedance, electric modulus and conductivity) of complex spectroscopy confirmed the existence of non-Debye type and other type of dielectric relaxation process in the material. The correlation between the real and idealized circuit response at several temperatures has been investigated by using ZSIMP WIN software and impedance data. Study of another component of multiferroics (i.e., field dependent magnetization) of BCTFO shows the significantly higher value of remnant and spontaneous magnetization. Thus, the existence of dielectric polarization and magnetization is single phase (orthorhombic) in a distorted perovskite confirms the multiferroicity of bismuth ferrite modified bismuth cadmium titanate (BCTFO) at room temperature, and hence the material can be used for some multifunctional applications.

Influence of K0.5Bi0.5TiO3 on the structure, dielectric and ferroelectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics

A new lead-free ferroelectric solid solution between (Ba,Ca)(Zr,Ti)O3 (BCZT) and K0.5Bi0.5TiO3 (KBT) has been systematically investigated in terms of its phase transformations, microstructure, dielectric and ferroelectric properties. The incorporation of KBT into BCZT was found to enhance the sintering behavior, although secondary phases of K4Ti3O8 and BaBi4Ti4O15 were detected at high KBT contents. Chemical heterogeneity was also observed in the form of core-shell grain structures comprising tetragonal ferroelectric BCZT-rich cores with pseudo-cubic relaxor ferroelectric KBT-rich shell regions. Temperature-dependent dielectric property measurements revealed that the BCZT-KBT ceramics exhibited both normal and relaxor ferroelectric behaviour simultaneously, associated directly with the core-shell structure. Ferroelectric hysteresis measurements indicated that the remanent polarisation and coercive field were strongly dependent on KBT content. In common with other lead-free relaxor ferroelectrics, increasing temperature led to the formation of constricted polarisation-electric field hysteresis loops, indicating the occurrence of a reversible electric field-induced nanopolar to long-range ordered ferroelectric state.