Effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics prepared by Plasma Activated Sintering

Lead-free [Ba(Zr_0.2Ti_0.8)O₃-x(Ba_0.7Ca_0.3)TiO₃, BZT-xBCT] ceramics were prepared by Plasma Activated Sintering (PAS). The effect of composition fluctuation on structural and electrical properties of BZT-xBCT ceramics was investigated. It was found PAS can obtain compact BZT-xBCT ceramics and BZT-0.50BCT ceramic possessed a MPB structure consisting of rhombohedral and tetragonal phases. Impedance spectroscopy confirmed two contributions from grains and grain boundaries, and the ceramics showed typical characteristic of diffuse phase transition. As compared with the BZT-xBCT ceramics with the pseudo-cubic phase, PAS-ed BZT-0.50BCT ceramic exhibited better properties of d₃₃ = 127 pC/N, k_p = 25.1%, ε_r = 2614, ε_m = 6655, and 2P_r = 25.2 μC/cm² due to the existence of the MPB structure.     

Relaxor behavior and ferroelectric properties of a new Ba4SmFe0.5Nb9.5O30 tungsten bronze ceramic

Unfilled tungsten bronze ceramics with a composition of Ba₄SmFe_0.5Nb_9.5O₃₀ were prepared by the conventional solid-state sintering method. The phase, microstructure, dielectric and ferroelectric properties were studied. Room temperature XRD results indicated that the ceramic occurs in the tetragonal space group P4bm phase with cell parameters of a=b=12.4712(2) Å and c=3.9430(2) Å. The temperature-dependent dielectric properties, XRD data and Raman spectra data indicated that BSFN ceramics exhibit no phase changes from 35 °C to 450 °C. Fitting of a Vogel-Fulcher relationship with an activated energy E_a of 0.11 eV indicates an unambiguous dielectric relaxor state near room temperature. Furthermore, the BSFN ceramics exhibited residual polarization and coercive field of 3.45 µC/cm² and 24.65 kV/cm, respectively.     

Influence of Ca substitution on microstructure and electrical properties of Ba(Zr,Ti)O3 ceramics

In the present work, lead-free (Ba_1?xCa_x)(Zr_0.04Ti_0.96)O₃ (x=0.00–0.09) ceramics were fabricated via a solid-state reaction method. The microstructure and electrical properties of the ceramics were investigated. The microstructure of the BCZT ceramics showed a core shell structure at compositions of x=0.03 and 0.06. The substitution of small amount of Ba²⁺ by Ca²⁺ resulted in an improvement of the piezoelectric, dielectric and ferroelectric properties of the ceramics. The orthorhombic–tetragonal phase transition was found in the composition of x≤0.03. Piezoelectric coefficient of d₃₃～392 pC/N and lowest E_c～3.3 kV/cm with highest P_r～14.1 μC/cm² were obtained for the composition of x=0.03 while its Curie temperature (T_C) was as high as 125 °C. However, the ferroelectric to paraelectric transition temperature had slightly shifted towards room temperature with increasing Ca²⁺ concentration.     

Effects of CaO–B2O3–SiO2 glass additive on the microstructure and electrical properties of BCZT lead-free ceramic

Addition of CaO–B₂O₃–SiO₂ (CBS) glass was performed to lower the sintering temperature of lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ceramics. Orthorhombic and tetragonal phases coexisted in CBS-free BCZT ceramics. The BCZT ceramics transformed into a pseudo-cubic phase when sintered at 1300 °C with increasing CBS glass content. Additionally, the secondary phase, Ba₂TiSi₂O₈, was observed when CBS glass was added. The density initially increased, reached a maximum value with 2 wt% CBS glass, and then decreased rapidly with further increase in CBS glass content, which was consistent with the microstructure. The ɛ, T_c, P_r, and d₃₃ depend on microstructure, and the results agree with the density. Evident relaxation behavior was observed. Observed results were inferred to be dependent on the microstructure, phase structure, lattice distortion, and secondary phase. The sample with 2 wt% CBS glass showed the excellent performance, which could be a promising substitute to lead-free piezoelectric ceramics for lead-based materials.     

Low temperature sintering and dielectric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3−xCu2+ ceramics obtained by the sol-gel technique

Lead-free Cu²⁺-modified (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ (BCZT−xCu²⁺) piezoelectric ceramics was synthesized by sol-gel method. The effects of Cu²⁺ additions on sintering characteristics, the phase structure, microstructure, electrical properties and complex impedance characteristic were investigated systematically. The XRD patterns exhibited a pure perovskite structure without impurity phase in all samples. SEM micrographs, temperature dependence of dielectric constant and polarization-electric field (P-E) hysteresis loops indicated that a small amount of Cu²⁺ addition affected the properties obviously. The results revealed that the addition of Cu²⁺ significantly improved the sinterability of BCZT ceramics which resulted in a reduction of sintering temperature from 1440 °C to 1230 °C. The TG-DSC was analyzed to verify the reaction process of BCZT−Cu²⁺ materials. (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃ ceramics with x=0.020 Cu²⁺ exhibited good electrical properties: ε_m=12,112, T_c=360 K, ε_r=2614, tan δ=0.026, K_p=0.47 and d₃₃=382 pC/N. The results indicated that Cu²⁺-modified BCZT ceramics could be a promising candidate for commercial purposes.     

Phase formation and electrical properties of Ba(ZrxTi1−x)O3 ceramics synthesized through a novel combustion technique

High quality Ba(Zr_xTi_1?x)O₃ (BZT, 0.025≤x≤0.150, step=0.025) ceramic has been prepared by the combustion technique. The raw materials were mixed with CH₄N₂O and calcined at 1000 °C and sintered at 1375 °C. For Ba(Zr_xTi_1?x)O₃ with x=0.025, the ceramics exhibited orthorhombic structure at room temperature. The crystal structure was transformed to rhombohedral, tetragonal and cubic phase, respectively with increasing zirconium content. The effect of x on dielectric properties has been studied intensively. It is found that the phase formation, which was affected from zirconium substitution, strongly influences the dielectric behavior. The rhombohedral phase decreases the maximum dielectric constant while the tetragonal phase enhances it. An extrapolation studied revealed the phase transition peaks merged into one peak at x ～0.094. The highest diffuseness constant of 1.95 was observed in BZT with 0.075 mol% zirconium. This was caused by the broadest dielectric peak of ferroelectric phase transition and the imminent diffusion between ferroelectric phase transition peak and Curie phase transition peak. The ferroelectric properties were sensitive to the phase exhibited in BZT system.     

Enhanced electrical properties in lead-free NBT–BT ceramics by series ST substitution

Comprehensive electrical properties of 0.94(Na_1/2Bi_1/2)TiO₃–0.06BaTiO₃ lead-free ceramics by doping series SrTiO₃ were investigated. High piezoelectric constant of 205 pC/N and electromechanical coupling factor of 0.34 were obtained due to the forming of the rhombohedral–tetragonal morphotropic phase boundary at x=0.02–0.06. Very large recoverable strain of 0.34% was obtained at x=0.10 due to the coexistence of ferroelectric and relaxor pseudocubic phases. A large electrocaloric effect (ΔT_max=1.71 K and ΔT/ΔE=0.34 K mm kV⁻¹ at 50 kV cm⁻¹) which determined by indirect measurements method was obtained at 120 °C at x=0.02, which is significantly higher than that of lead-free ferroelectric ceramics reported so far. Moreover, lower operating temperatures of 50 °C and 30 °C were proposed when x=0.10 and 0.20 with ΔT_max=0.79 K and 0.6 K, respectively. These properties added together indicate a promising material for applications in cooling systems and actuators.     

Enhanced dielectric and piezoelectric properties in Li/Sb-modified (Na,K)NbO3 ceramics by optimizing sintering temperature

In this paper, lead-free (Na_0.474K_0.474Li_0.052)(Nb_0.948Sb_0.052)O₃ ceramics were synthesized by a conventional solid-state reaction route. The effects of sintering temperature on the crystal structure, microstructure, densification, dielectric properties, and ferroelectric properties of the KNNLS ceramics were addressed. X-ray diffraction patterns and Raman spectrum indicated a transition from orthorhombic to tetragonal phase during the sintering temperature region. This transition is attributed to the migration of Li between the matrix grain and grain boundary. Scanning electron microscopy study revealed increased grain size and enhanced densification with increasing sintering temperature. The density of the ceramics sintered at 1080 °C reached a maximum value of 4.22 g/cm³. KNNLS ceramics sintered at an optimum temperature of 1080 °C exhibited high piezoelectric properties, that is 242 pC/N for d₃₃, 0.42 for k_p and 18.2 μC/cm² for P_r.     

Influence of cobalt and sintering temperature on structure and electrical properties of BaZr0.05Ti0.95O3 ceramics

Pure and Co-modified BaZr_0.05Ti_0.95O₃ ceramics were fabricated by the traditional solid state reaction technique. The influence of cobalt and sintering temperature on structure, dielectric, ferroelectric properties and diffuse phase transition of BZT ceramics were investigated systematically. 1300 °C was the optimal sintering temperature for BZT ceramics. The solid solubility limit of Co ions in BZT matrix was determined to be 0.4 mol%. The introduction of a moderate amount of Co ions was believed to benefit the microstructure development and make the grain size more uniform. Compared with undoped counterparts, 0.4 mol% Co-modified ceramics showed equivalent ferroelectric properties with a high remnant polarization (P_r=9.6 μC/cm²) and a low coercive field (E_c=0.21 kV/mm). Besides these, a relative high dielectric coefficient (ε_r=2030) and a low dielectric loss (tan δ=1.85%) were also obtained on this composition. The degree of diffuse phase transition was enhanced by the addition of Co ions. The related mechanism of the diffused phase transition behavior was discussed.     

Effect of Fe substitution on the piezoelectric,dielectric and ferroelectric properties of PNZST ceramics

Fe-doped (Pb_0.99Nb_0.02)[(Zr_0.70Sn_0.30)_0.52Ti_0.48]_0.98O₃ (PNZST) ceramics were prepared via conventional solid state reaction method, and the effect of Fe doping on their structural and electrical properties was investigated in detail. Results showed that Fe³⁺ cations could dissolve into readily the B-sites of perovskite structure for the PNZST ceramics with the less amount of Fe content (≤0.8 wt%), resulting in the full densification after sintered at 1300 °C. Meanwhile, Fe doping caused a structure transform from the tetragonal to the rhombohedral. The better electric properties for PNZST ceramic with 0.6 wt% Fe content were obtained, i.e. piezoelectric constant d₃₃=380 pC/N, electromechanical coupling factor k_p=0.57, mechanical quality factor Q_m=225, dielectric constant ε_r=1190, loss tangent tan δ=0.007 and curie temperature T_c=318 °C.     

Structural,microstructural, ferroelectric and photoluminescent properties of praseodymium modified Ba0.98Ca0.02Zr0.02Ti0.98O3 ceramics

The ‘x’ wt% (x = 0, 0.02, 0.04 and 0.06) Pr₆O₁₁ modified Ba_0.98Ca_0.02Zr_0.02Ti_0.98O₃ (BCZT – x Pr) piezoelectric ceramics have been fabricated by the solid state reaction method with sintering at 1450 °C (x = 0) and 1350 °C (0.02 ≤ x ≤ 0.06) for 2 h. The impact of Pr concentration on the structural, microstructural, photoluminescence and ferroelectric properties has been systematically investigated. The x-ray diffraction (XRD) patterns revealed the co-existence of tetragonal and orthorhombic phases at room temperature upto x = 0.04 Pr concentration. The grain size was found to decrease upto x = 0.04 Pr content. Room temperature Raman spectroscopy results were consistent with the XRD results. The photoluminescence (PL) spectra showed significant emissions consisting of strong blue (489 nm), green (528 nm) and red (649 nm) wavelengths. The emission intensities of PL spectrum were strongly Pr concentration dependent and a maximum value was obtained for 0.04 Pr modified BCZT ceramic. Further, a large remnant polarization (2P_r ~ 13 µC/cm²) and low coercive field (E_C ~ 22 V/cm) were obtained for BCZT – 0.04 Pr ceramic. The crystal structure and microstructure affect the photoluminescence and ferroelectric properties. Such properties of 0.04 Pr modified BCZT ceramic make it the potential candidate for novel integrated and multifunctional devices.     

Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3–CeO2 ceramics with high piezoelectric coefficient obtained by low-temperature sintering

Lead-free (Ba_0.85Ca_0.15)(Ti_0.9Zr_0.1)O₃–x%CeO₂(BCZT–xCe) piezoelectric ceramics have been prepared by the traditional ceramic process and the effects of CeO₂ addition on their phase structure and piezoelectric properties have been studied. The addition of CeO₂ significantly improves the sinterability of BCZT ceramics which results in a reduction of sintering temperature from 1540 °C to 1350 °C without sacrificing the high piezoelectric properties. X-ray diffraction data show that CeO₂ diffuses into the lattice of BCZT and a pure perovskite phase is formed. SEM images indicate that a small addition of CeO₂ greatly affects the microstructure. Main piezoelectric parameters are optimized at around x = 0.04 wt% with a high piezoelectric coefficient (d₃₃ = 600 pC/N), a planar electromechanical coefficient (k_p = 51%), a high dielectric constant (?_r = 4843) and a low dissipation factor (tan δ = 0.012) at 1 kHz, which indicates that the BCZT–xCe ceramics are promising for lead-free practical applications.     

High piezoelectricity in CuO-modified Ba(Ti0.90Sn0.10)O3 lead-free ceramics with modulated phase structure

High piezoelectricity was achieved in Ba(Ti_0.90Sn_0.10)O₃ lead-free ceramics by optimizing CuO addition and sintering temperature. The phase structure of 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramic is coexisting rhombohedral and tetragonal phases as sintered at 1300 °C. The coexistence of rhombohedral, tetragonal and orthorhombic phases appears in 1.0 mol% CuO-doped Ba(Ti_0.90Sn_0.10)O₃ ceramics as sintered at 1350–1450 °C, which leads to highly enhanced d₃₃ up to 650pC/N. This work demonstrates that high piezoelectric property (d₃₃ = 650pC/N) can be obtained in BaTiO₃-based lead-free piezoceramics with a simple composition modification by modulating phase structures, which also indicates that Ba(Ti,Sn)O₃ is a promising candidate to replace the lead-based piezoceramics.     

Microstructure,ferroelectric and piezoelectric properties of Bi0.5K0.5TiO3-modified BiFeO3–BaTiO3 lead-free ceramics with high Curie temperature

The effects of composition, sintering temperature and dwell time on the microstructure and electrical properties of (0.75 ? x)BiFeO₃–0.25BaTiO₃–xBi_0.5K_0.5TiO₃ + 1 mol% MnO₂ ceramics were studied. The ceramics sintered at 1000 °C for 2 h possess a pure perovskite structure and a morphotropic phase boundary of rhombohedral and pseudocubic phases is formed at x = 0.025. The addition of Bi_0.5K_0.5TiO₃ retards the grain growth and induces two dielectric anomalies at high temperatures (T₁ ～ 450–550 °C and T₂ ～ 700 °C, respectively). After the addition of 2.5 mol% Bi_0.5K_0.5TiO₃, the ferroelectric and piezoelectric properties of the ceramics are improved and very high Curie temperature of 708 °C is obtained. Sintering temperature has an important influence on the microstructure and electrical properties of the ceramics. Critical sintering temperature is 970 °C. For the ceramic with x = 0.025 sintered at/above 970 °C, large grains, good densification, high resistivity and enhanced electrical properties are obtained. The weak dependences of microstructure and electrical properties on dwell time are observed for the ceramic with x = 0.025.     

Band gap narrowing and magnetic properties of transition-metal-doped Ba0.85Ca0.15Ti0.9Zr0.1O3 lead-free ceramics

Transition metal (TM = Mn, Fe, Co, and Ni)-doped Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃ (BCZT) lead-free ceramics with excellent optical and magnetic properties are synthesized via a solid-state reaction method. The effects of TM elements on the sintering, structure, optical, and magnetic properties of BCZT ceramics are investigated in detail. Structural phase transition from the coexistence of rhombohedral and tetragonal phases to a single rhombohedral phase is observed owing to grain refinement. A narrow band gap of 1.68 eV is achieved in the Co-doped BCZT. The optical absorption of TM-doped BCZT is enhanced, which is ascribed to the molecular orbital rearrangement caused by lattice distortion. Moreover the magnetic behaviors of TM-doped BCZT are observed. The Fe-doped BCZT presents the most evident ferromagnetism, resulting from the exchange coupling interaction between the Fe³⁺ ions and oxygen vacancies. These results provide additional insight into the use of TM-doped BCZT lead-free ferroelectric ceramics for various applications.     

Influence of Li2O–B2O3–SiO2 glass on the sintering behavior and microwave dielectric properties of BaO–0.15ZnO–4TiO2 ceramics

This paper reports the investigation of the performance of Li₂O–B₂O₃–SiO₂ (LBS) glass as a sintering aid to lower the sintering temperature of BaO–0.15ZnO–4TiO₂ (BZT) ceramics, as well as the detailed study on the sintering behavior, phase evolution, microstructure and microwave dielectric properties of the resulting BZT ceramics. The addition of LBS glass significantly lowers the sintering temperature of the BZT ceramics from 1150 °C to 875–925 °C. Small amount of LBS glass promotes the densification of BZT ceramic and improves the dielectric properties. However, excessive LBS addition leads to the precipitation of glass phase and growth of abnormal grain, deteriorating the dielectric properties of the BZT ceramic. The BZT ceramic with 5 wt% LBS addition sintered at 900 °C shows excellent microwave dielectric properties: ε_r=27.88, Q×f=14,795 GHz.     

Low temperature fabrication of lead-free KNN-LS-BS ceramics via the combustion method

Lead-free piezoelectric 0.992(0.95K_0.5Na_0.5NbO₃–0.05LiSbO₃)–0.008BiScO₃; KNN-LS-BS ceramics were successfully prepared using the combustion method. The highest % perovskite phase was found in the sample calcined at 700 °C for 1 h. The structural phase of orthorhombic structure was also detected in this sample. For the sintered ceramics, a pure tetragonal perovskite phase was observed in the samples sintered between 1025 and 1100 °C. The microstructure of ceramics showed a square or rectangular shape and the average grain size increased with increasing of sintering temperature. The density of the ceramics increased with increasing of sintered temperature up to 1075 °C, were it reached 97.5% of theoretical density and then dropped in value when the sintered temperature further increased. The excellent electrical properties of ε_r at T_c=6600, tanδ at T_c=0.04, P_r (at 40 kV/cm)=19.4 μC/cm² and E_c (at 40 kV/cm)=24.1 kV/cm were obtained in the most dense ceramic. The results indicate that the KNN-LS-BS ceramics are promising lead-free piezoelectric materials.     

Effect of Ba0.85Ca0.15Ti0.90Zr0.10O3 content on the microstructure and electrical properties of Bi0.51(Na0.82K0.18) 0.50TiO3 ceramics

(1?x)Bi_0.51(Na_0.82K_0.18)_0.50TiO₃–xBa_0.85Ca_0.15Ti_0.90Zr_0.10O₃ [(1?x)BNKT–xBCTZ] ceramics were prepared by the conventional solid-state method, and the effect of BCTZ content on their microstructure and electrical properties was investigated. A stable solid solution with a pure perovskite phase is formed between BNKT and BCTZ, and these ceramics have a coexistence of rhombohedral and tetragonal phases in the range of 0 ≤ x < 0.15. Their T_m and T_d values are strongly independent on the BCTZ content. Moreover, the sintering temperature strongly affects the ferroelectric and piezoelectric properties of these ceramics with x = 0.02. These ceramics with x = 0.02 exhibit an optimum electrical behavior of d₃₃ ～ 205, k_p ～ 0.25, P_r ～ 31.8 μC/cm², and E_c ～ 19.1 kV/cm together with a high T_d value of ～91 °C when sintered at 1180 °C and poled at an optimum condition. As a result, the (1?x)BNKT–xBCTZ ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Characterization of 0.93Pb(Zn1/3Nb2/3)O3–0.07BaTiO3 ceramics derived from a novel Zn3Nb2O8 B-site precursor

In this work, perovskite relaxor ferroelectric lead zinc niobate–barium titanate (0.93PZN–0.07BT) ceramics were fabricated by using a combination of Zn₃Nb₂O₈ B-site precursor and reactive sintering process. The effects of sintering condition on phase formation, densification, microstructure and dielectric properties of the final products have been investigated using a combination of X-ray diffraction, Archimedes density measurement, scanning electron microscopy and dielectric measurement techniques. It is seen that pure perovskite phase of PZN-BT solid solutions can be achieved in all samples. Density and average grain size values of sintered samples increased with sintering temperatures and dwell time. With appropriate sintering at 1150 °C for 5 h, 0.93PZN–0.07BT ceramics exhibited a peak dielectric constant of 11,497 and dielectric loss of 0.05 at the Curie temperature of 99 °C measured at 1 kHz.