Improvement of dielectric loss of (Ba,Sr)(Ti,Zr)O3 ferroelectrics for tunable devices

(Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ (0.05 ≤ x ≤ 0.3) ferroelectric materials have cubic perovskite structure and show paraelectric properties at room temperature. Curie point shifted to a negative value as increasing Zr content in (Ba_0.6Sr_0.4)(Ti_1−xZr_x)O₃ system. When Zr substituted 0.1 mol, the dielectric constant, dielectric loss, tunability, Curie point and FOM were 4500, 0.0005, 63%, −1.6 °C and 1260, respectively. This composition shows excellent microwave dielectric properties than those of (Ba_0.6Sr_0.4)TiO₃ ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters and frequency agile filters, etc.     

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.     

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.     

Property improvement of 0.3Pb(Zn1/3Nb2/3)O3-0.7Pb0.96La0.04(ZrxTi1−x)0.99O3 ceramics by hot-pressing

The piezoelectric ceramics of the compositions expressed by the formula: 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb_0.96La_0.04(Zr_xTi_1−x)_0.99O₃ (x = 0.50–0.53) were prepared by two kind of sintering processes: conventional sintering (CS) and hot-pressing (HP) sintering. By comparing the properties of these two series of ceramics, piezoelectric coefficients (d₃₃), electromechanical coupling factors (k_p), dielectric constants (ɛ_r), etc. were enormously improved by HP sinter procedure, which can be attributed to the highly dense microstructure (bulk density >99%). The most impressive results are the d₃₃ (845pC/N) and k_p (0.703) in the HP specimen with Zr/Ti = 51/49, which have not been observed in the previous relative reports. Additionally, according to the contrast of the experiment data, the origin of the property improvement was analyzed in details.     

Microstructure,electrical and mechanical properties of MgO nanoparticles-reinforced porous PZT 95/5 ferroelectric ceramics

Porous Pb (Zr_0.95Ti_0.05) O₃/xMgO (PZT/MgO, x=0, 0.1, 0.2, 0.5 and 1.0 wt%) ferroelectric ceramics were prepared with MgO nanoparticles as reinforcing phase. The effects of MgO nanoparticles on the phase, microstructure, electrical and mechanical properties of as-prepared ceramics were investigated. The results show that the grain size is reduced obviously when increasing the amount of MgO. Compared with pure porous PZT, T_C of MgO-added PZT ceramics shifts to higher temperature. Moreover, dielectric, ferroelectric and piezoelectric properties show no much degradation. Further, PZT/MgO ceramics possess enhanced mechanical properties compared to pure porous PZT ceramics, the largest increment of the fracture toughness and hardness being 31.3% and 19.8%, respectively. The optimal electrical and mechanical properties are obtained with the addition of less than 0.5 wt% MgO nanoparticles.     

Morphotropic phase boundary and electrical properties of lead-free (K0.5Bi0.5)TiO3–Bi(Ni0.5Ti0.5)O3 relaxor ferroelectric ceramics

Lead-free relaxor ferroelectric ceramics (1?x)(K_0.5Bi_0.5)TiO₃–xBi(Ni_0.5Ti_0.5)O₃ were prepared by a conventional solid-state route, the phase transition behavior and corresponding electrical properties were investigated. A typical morphotropic phase boundary (MPB) between rhombohedral and tetragonal ferroelectric phases was identified to be in the range of 0.05<x<0.07 where the optimum piezoelectric and electromechanical properties of d₃₃=126 pC/N and k_P=18% were achieved. Most importantly, a high Curie temperature ~320 °C, around which the material shows a typical relaxor ferroelectric behavior characterized by the presence of diffuse phase transition and frequency dispersion, was obtained in MPB compositions, significantly higher than those of some existing MPB lead-free titanate systems. These results demonstrate a tremendous potential of the studied system for device applications.     

X-ray diffraction,dielectric, pyroelectric,piezoelectric and Raman spectroscopy studies on (Ba0.95Ca0.05)0.8875Bi0.075TiO3 ceramic

The (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic composition was prepared using the conventional mixed-oxide technique. X-ray diffraction at room temperature and dielectric permittivity in the temperature range from 85 to 450 K and frequency range from 10² to 2 × 10⁵ Hz, respectively, were studied. The X-ray spectra were investigated by profile refinement technique with the use of specialized software at room temperature, the (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ composition crystallizes in quadratic perovskite structure. The dielectric measurements show classical ferroelectric behavior. The pyroelectric and piezoelectric results confirm the dielectric measurements. The pyroelectric coefficient is about 69.2 nC/cm² K at the transition temperature (T_C = 367 K). The piezoelectric constant is d₃₁ = 31.1 pC/N and the electromechanical coupling factor is k_P = 0.14679. Raman spectra of (Ba_0.95Ca_0.05)_0.8875Bi_0.075TiO₃ ceramic were taken at various temperatures and measured over the wave number range from 50 to 1000 cm^?1. All the Raman bands were assigned as the transitional modes of Ba²⁺, Ca²⁺, Bi³⁺ and Ti⁴⁺ cations. The temperature evolution of Raman spectra across the transition shows an important evolution characterizing the disorder of the high temperature phase.     

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.     

Microstructure and electrical properties of (Ba0.85Ca0.15)1−xLix(Ti0.90Zr0.10)1−xNbxO3 ceramics with a low dielectric loss and a low sintering temperature

A low sintering temperature is demonstrated for (Ba_0.85Ca_0.15)_1?xLi_x(Ti_0.90Zr_0.10)_1?xNb_xO₃ (BCLTZN-x) piezoelectric ceramics, where BCLTZN-x lead-free piezoelectric ceramics were prepared by the normal sintering. Effects of Li and Nb on the microstructure and electrical properties of these ceramics were investigated. The sintering temperature of BCLTZN-x ceramics was decreased greatly by introducing Li and Nb, and the grain size of these ceramics decreases with increasing x. These ceramics with a small amount of Li and Nb maintain good piezoelectric properties, together with a low sintering temperature and a lower dielectric loss. These ceramics with x = 0.01 demonstrate optimum electrical properties: d₃₃ ～ 353 pC/N, k_p ～ 41.1%, T_c ～ 86 °C, ?_r ～ 4236, and tan δ ～ 0.75%.     

Phase transition,microstructure and electrical properties of Fe doped Ba0.70Ca0.30TiO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of Ba_0.70Ca_0.30Ti_1?xFe_xO₃ (x=0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x≤0.02 are diphasic composites of tetragonal Ba_0.80Ca_0.20TiO₃:Fe and orthorhombic Ba_0.07Ca_0.93TiO₃:Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x=0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128 °C to 58 °C. However, the ferroelectricity enhances slightly and reaches the maximum near x=0.005, and then weakens with increasing x. On the other hand, the piezoelectric coefficient (d₃₃) and the electromechanical coupling coefficient (k_p) decrease simultaneously with increasing x, whereas the mechanical quality factor (Q_m) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO₃-based lead-free piezoelectric ceramics.     

Barium modified lead lanthanum strontium zirconium niobium titanate for dielectric and piezoelectric properties

The isovalent Ba²⁺ modified lead lanthanum strontium zirconium niobium titanate (PLSZNT) solid solutions were prepared by solid-state reaction method with the compositional formula [Pb_{1−x−w−y}La_xSr_wBa_y][(Zr_zTi_1−z)_{(1−(x/4)−(5/4)k)}Nb_k]O₃ where Ba content, y, was varied from 0, 0.5, 1 and 1.5 mol%. X-ray diffraction (XRD) studies revealed that all the samples have ferroelectric tetragonal structure (FE_TET). The presence of multiple ions at Pb-site enhanced grain growth and further addition of Ba concentration resulted in restrained grain growth. Dielectric studies suggested that the ɛ_RT increased up to 1 mol% Ba while T_c has shown a continuous decreasing trend throughout the series. The piezoelectric parameters as a function of grain growth were characterized. The optimum piezoelectric charge coefficient (d₃₃ = 538 pC/N) and piezoelectric planar coupling coefficient (k_p = 0.521) was found to be in 1 mol% Ba modified PLSZNT ceramic, respectively, and this composition may be suitable for possible sensor and actuator applications.     

Effect of compositional variations on phase transition and electric field-induced strain of (Pb,Ba) (Nb,Zr, Sn,Ti)O3 ceramics

(Pb_0.97Ba_0.02)Nb_0.02(Zr_0.55Sn_0.45?xTi_x)_0.98O₃ (PBNZST, 0.03≤x≤0.06) ceramics were prepared by conventional solid state synthesis and their crystal structure, ferroelectric, dielectric, and electric field-induced strain properties were systemically investigated. A transformation from antiferroelectric (AFE) phase to ferroelectric (FE) phase was observed at 0.05<x<0.06. Besides, with the increase of Ti content, the electric field-induced strain decreased, due to the larger strain of AFE ceramics compared to FE ceramics. Further, when the measuring frequency decreased, the strain improved, because the electric field at low frequency allows a more efficient switching of domains, resulting in larger strain. The maximum strain of 0.55% was obtained in (Pb_0.97Ba_0.02)Nb_0.02(Zr_0.55Sn_0.45?xTi_x)_0.98O₃ antiferroelectric ceramics with x=0.03 at 2 Hz.     

Composition design,phase transitions and electrical properties of Sr2+-substituted xPZN–0.1PNN–(0.9−x)PZT piezoelectric ceramics

The influences of PZN content and Sr²⁺ substitution on the structure and electrical properties of Pb(Zn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_0.52Ti_0.48)O₃ (abbreviated as PZN–PNN–PZT) piezoelectric ceramics were studied. All as-prepared PZN–PNN–PZT ceramics presented single phase of perovskite structure, while higher PZN contents favored rhombohedral symmetry and larger grain size. Meanwhile, with the increase in Sr²⁺ content, the phase structure changed from a mix of tetragonal and rhombohedral symmetries to a pure rhombohedral symmetry. Although the ferroelectric Curie temperature (T_C) was decreased with increasing the PZN and Sr²⁺ contents, the piezoelectric constant (d₃₃) exhibited the opposite trend. As a result, optimum comprehensive electrical properties were obtained in the 0.1PZN–0.1PNN–0.8PZT composition with 10 mol% Sr²⁺ substitution: d₃₃~800 pC/N, k_p ~0.65, ɛ_r~4081, T_C~176 °C, P_r~30.92 µC/cm². Thus, the 10 mol% Sr²⁺-substituted 0.1PZN–0.1PNN–0.8PZT ceramic is a promising candidate for high performance applications.     

Morphotropic phase boundary in the BNT–BT–BKT system

Lead-free x Bi_0.5Na_0.5TiO₃–y BaTiO₃–z Bi_0.5K_0.5TiO₃ piezoelectric ceramics were synthesized by a conventional solid state reaction method. The microstructure, ferroelectric and piezoelectric properties of the ceramics were investigated. Structure measurements by X-ray diffraction with Rietveld refinement have allowed us to specify more precisely the morphotropic phase boundary (MPB) in this system. For (1 ? x) BNT–x BT solid solution ceramics, the 0.94 BNT–0.06 BT morphotropic composition shows the higher values with d₃₃ = 170 pC/N, k_p = 0.35 and k_t = 0.53. In the case of (1 ? x) BNT–x BKT compositions, the d₃₃, k_p and k_t are, respectively, 137 pC/N, 0.39 and 0.54 for the 0.80 BNT–0.20 BKT ceramic. On the other hand, the ternary 0.865 BNT–0.035 BT–0.100 BKT morphotropic composition shows high piezoelectric constant and electromechanical coupling factors (d₃₃ = 133 pC/N, k_p = 0.26 and k_t = 0.57).     

Strong photoluminescence and piezoelectricity properties in Pr-doped Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 ceramics: Influence of concentration and microstructure

(Ba_0.85Ca_0.15)_1−xPr_x(Zr_0.1Ti_0.9)O₃ (where 0 < x < 0.01, abbreviated as BCZT:xPr) ceramics were fabricated by conventional solid-state reaction method. The influence of dopant concentration and microstructure on photoluminescence, ferroelectric, and piezoelectric properties was systematically investigated. The results showed that the photoluminescence spectra of the samples exhibited strong green (530 nm) and red (602 nm) emissions upon excitation of the 430 nm to 500 nm light, which couples well with to the emission band of the commercial blue light-emitting diodes chips. The emission intensities were strongly dependent on the dopant concentration and crystallite size, which reached the optimal value when the crystallite size and dopant concentration were 8 μm and 0.002 mol, respectively. Meanwhile, a large piezoelectric response with d₃₃ = 325 pC/N was obtained for BCZT:0.002Pr near the morphotropic phase boundary. Therefore, the Pr-doped BCZT materials, simultaneously exhibiting excellent luminescent properties and high piezoelectric properties, may have significant technological promise in novel multifunctional devices.     

Piezoelectric and ferroelectric properties of lead-free [Bi1−y(Na1−x−yLix)]0.5BayTiO3 ceramics

Lead-free [Bi_1−y(Na_1−x−yLi_x)]_0.5Ba_yTiO₃ (BNLB-x/y) piezoelectric ceramics were prepared by sintering the constituent oxides, and their piezoelectric and ferroelectric properties studied. The results of X-ray diffraction (XRD) suggest that Li⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ (BNT) lattices to form a solid solution with a single-phase perovskite structure. The ceramics can be well sintered at 1100–1150 °C. The introduction of Li⁺ and Ba²⁺ into Bi_0.5Na_0.5TiO₃ significantly decreases the coercive field, E_c but maintains the large remanent polarization, P_r of the materials. The ceramics exhibit relatively good piezoelectric properties and very strong ferroelectricity: piezoelectric constant, d₃₃ = 208 pC/N, planar electromechanical coupling factor, k_p = 37.0%, remanent polarization, P_r = 38.5 μC/cm², coercive field, E_c = 3.27 kV/mm. The depolarization temperature, T_d of BNLB-0.075/0.04 ceramics is about 190 °C.     

Large enhancement of piezoelectric properties in Mn-modified SrBi4Ti4O15 and its thermal stabilities at elevated temperatures

Manganese-modified strontium bismuth titanate (SrBi₄Ti₄O₁₅, SBT) ceramic oxides were synthesized by substituting a small amount of manganese ions into the Ti⁴⁺ sites using conventional solid-state reaction. The resultant Mn-modified SBT (SBT-Mn) exhibits better piezoelectric properties in comparison to unmodified SBT. The piezoelectric properties of Mn-modified SBT is optimized with only 4 mol% Mn substitution. SBT-4Mn exhibits a large piezoelectric constant (d₃₃=30 pC/N), approximately twice the value of unmodified SBT (d₃₃=13 pC/N), while its Curie temperature, T_c, remains almost unchanged at ~530 °C. The temperature-dependent electrical impedance and electromechanical coupling factors k_p and k_t reveal that the SBT-4Mn exhibits thermally stable electromechanical coupling characteristics up to 300 °C but electromechanical coupling factors deteriorate significantly at a higher temperature due to increased conductivity. Our work suggested that Mn-modified SBT ceramics are promising materials for high temperature piezoelectric applications.     

The temperature-dependent piezoelectric and electromechanical properties of cobalt-modified sodium bismuth titanate

Lightly cobalt-modified, Aurivillius-type, sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) ceramics were synthesized by substituting a small amount of cobalt ions onto the Ti⁴⁺ sites using conventional solid-state reaction. X-ray photoelectron spectroscopy (XPS) analysis coupled with bond valence sum calculations show that the dopant cobalt ions substitute for Ti⁴⁺ ions in the form of Co³⁺. The resultant cobalt-modified NBT ceramics (NBT-Co) exhibit better piezoelectric and electromechanical properties by comparison with pure NBT. With only 0.3 wt% Co³⁺ substitution, the piezoelectric properties of the NBT-Co ceramics are optimal, exhibiting a high piezoelectric coefficient (d₃₃~33 pC/N), a low dielectric loss tan δ (~0.1% at 1 kHz), a high thickness planar coupling coefficient (k_t~34%) as well as a high Curie temperature (T_c~663 °C). Such NBT-Co ceramics exhibit nearly temperature-independent piezoelectric and electromechanical properties up to 400 °C, suggesting that these cobalt-modified NBT ceramics are promising materials for high temperature piezoelectric applications.     

Phase structure and enhanced piezoelectric properties in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 lead-free piezoelectric ceramics

The piezoelectric properties of KNN lead-free piezoelectric ceramics could be greatly enhanced by forming multiphase coexistence. In this work, binary system (1-x)(K_0.48Na_0.52)(Nb_0.95Sb_0.05)O₃-x(Bi_0.5Na_0.42Li_0.08)_0.9Sr_0.1ZrO₃ [(abbreviated as (1-x)KNNS-xBNLSZ] ceramics with rhombohedral-tetragonal (r-T) phase boundary was designed and synthesized using the conventional solid-state sintering method, and effects of BNLSZ contents on their micrograph, phase structure and electrical properties were also investigated. According to phase diagram from the results of temperature-dependent capacitance and dielectric constant, the ceramics exhibit the R-T phase coexistence in the composition range of 3.5%≤x<4.5%, and an enhanced dielectric, ferroelectric, and piezoelectric behavior was obtained at such a phase boundary zone. As a result, the ceramics with x=0.04 exhibit optimum electrical properties of d₃₃~461 pC/N, k_p~46%, tan δ~0.03, P_r~16.9 μC/cm², and E_c ~9 kV/cm, together with a Curie temperature (T_C) of ~228 °C. Such a good comprehensive performance obtained in this present work is due to the R-T phase transition and enhanced ɛ_rP_r. It was believed that this ceramic system would promote the development of KNN-based lead-free ceramics.