Phase structure and electrical properties of (0.8 − x) BaTiO3-0.2Bi0.5Na0.5TiO3-xBaZrO3 lead-free piezoceramics

Lead-free piezoelectric ceramics (0.8 − x)BaTiO₃-0.2Bi_0.5Na_0.5TiO₃-xBaZrO₃ (BT-BNT-xBZ, 0 ≤ x ≤ 0.08) doped with 0.3 wt% Li₂CO₃ were prepared by conventional solid-state reaction method. With the Li₂CO₃ doping, all the ceramics can be well sintered at 1170-1210 °C. The phase structure, dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between tetragonal and pseudocubic phases exists at x = 0.03-0.04. The addition of Zr can improve the piezoelectric properties of BT-BNT ceramics. Furthermore, a relaxor behavior is induced and the tetragonal-cubic phase transition shifts towards lower temperatures after the addition of Zr. The ceramics with x = 0.03 possess the optimum electrical properties: d₃₃ = 72 pC/N, k_p = 15.4%, ?_r = 661, P_r = 18.5 μC/cm², E_c = 34.1 kV/cm, T_c = 150 °C.     

Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ + x wt% Dy₂O₃ with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy₂O₃ on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ composition was not changed by adding 0.05-0.3 wt% Dy₂O₃. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy₂O₃ inhibits the grain growth of the ceramics. The addition of Dy₂O₃ shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy³⁺ ions substitute B-site Ti⁴⁺ ions, and increasing the properties for 0.15 < x < 0.3 when Dy³⁺ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d₃₃ = 170 pC/N and the dielectric constant ?_r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3.     

Microstructure, ferroelectric, and piezoelectric properties of (1 − x − y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.5Ag0.5TiO3 lead-free ceramics

Lead-free (1 − x − y)Bi_0.5Na_0.5TiO₃-xBaTiO₃-yBi_0.5Ag_0.5TiO₃ (BNT-BT-BAT-x/y, x = 0-0.10, y = 0-0.075) piezoelectric ceramics were synthesized by conventional oxide-mixed method. The microstructure, ferroelectric, and piezoelectric properties of the ceramics were investigated. Results show that a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases of BNT-BT-BAT-x/0.04 ceramics is formed at x = 0.06-0.08. The addition of BAT has no obvious change on the crystal structure of BNT-BT ceramics while it causes the grain size of the ceramics to become more homogenous. Near the MPB, the ceramics with x = 0.06 and y = 0.05-0.06 possess optimum electrical properties: P_r ∼ 42.5 μC/cm², E_c ∼ 32.0 kV/cm, d₃₃ ∼ 172 pC/N, k_p ∼ 32.6%, and k_t ∼ 52.6%. The temperature dependences of k_p and polarization versus electric hysteresis loops reveal that the depolarization temperature (T_d) of BNT-BT-BAT-0.06/y ceramics decreases with increasing y. In addition, the polar and non-polar phases may coexist in the BNT-BT-BAT-x/y ceramics above T_d.     

Preparation and electrical properties of Bi0.5Na0.5TiO3-BaTiO3-KNbO3 lead-free piezoelectric ceramics

Lead-free (1 − x)Bi_0.47Na_0.47Ba_0.06TiO₃-xKNbO₃ (BNBT-xKN, x = 0-0.08) ceramics were prepared by ordinary ceramic sintering technique. The piezoelectric, dielectric and ferroelectric properties of the ceramics are investigated and discussed. The results of X-ray diffraction (XRD) indicate that KNbO₃ (KN) has diffused into Bi_0.47Na_0.47Ba_0.06TiO₃ (BNBT) lattices to form a solid solution with a pure perovskite structure. Moderate additive of KN (x ≤ 0.02) in BNBT-xKN ceramics enhance their piezoelectric and ferroelectric properties. Three dielectric anomaly peaks are observed in BNBT-0.00KN, BNBT-0.01KN and BNBT-0.02KN ceramics. With the increment of KN in BNBT-xKN ceramics, the dielectric anomaly peaks shift to lower temperature. BNBT-0.01KN ceramic exhibits excellent piezoelectric properties and strong ferroelectricity: piezoelectric coefficient, d₃₃ = 195 pC/N; electromechanical coupling factor, k_t = 58.9 and k_p = 29.3%; mechanical quality factor, Q_m = 113; remnant polarization, P_r = 41.8 μC/cm²; coercive field, E_c = 19.5 kV/cm.     

Phase transition and piezoelectric properties of K0.48Na0.52NbO3-LiTa0.5Nb0.5O3-NaNbO3 lead-free ceramics

Plate-like NaNbO₃ (NN) particles were used as the raw material to fabricate (1 − x)[0.93 K_0.48Na_0.52Nb O₃-0.07Li(Ta_0.5Nb_0.5)O₃]-xNaNbO₃ lead-free piezoelectric ceramics using a conventional ceramic process. The effects of NN on the crystal structure and piezoelectric properties of the ceramics were investigated. The results of X-ray diffraction suggest that the perovskite phase coexists with the K₃Li₂Nb₅O₁₅ phase, and the tilting of the oxygen octahedron is probably responsible for the evolution of the tungsten-bronze-typed K₃Li₂Nb₅O₁₅ phase. The Curie temperature (T_C) is shifted to lower temperature with increasing NN content. (1 − x)[0.93 K_0.48Na_0.52NbO₃-0.07Li(Ta_0.5Nb_0.5)O₃]-xNaNbO₃ ceramics show obvious dielectric relaxor characteristics for x > 0.03, and the relaxor behavior of ceramics is strengthened by increasing NN content. Both the electromechanical coupling factor (k_p) and the piezoelectric constant (d₃₃) decrease with increasing amounts of NN. 0.01-0.03 mol of plate-like NaNbO₃ in 0.93 K_0.48Na_0.52NbO₃-0.07Li(Ta_0.5Nb_0.5)O₃ gives the optimum content for preparing textured ceramics by the RTGG method.     

X-ray diffraction and dielectric studies across morphotropic phase boundary in (1 − x) [Pb(Mg0.5W0.5)O3]-xPbTiO3 ceramics

We present here the results of comprehensive X-ray diffraction and dielectric studies on several compositions of (1 − x)[Pb(Mg_0.5W_0.5)O₃]-xPbTiO₃ (PMW-xPT) solid solution across the morphotropic phase boundary. Rietveld analysis of the powder X-ray diffraction data reveals cubic (space group Fm3m) structure of PMW-xPT ceramics for the compositions with x ≤ 0.42, tetragonal (space group P4mm) structure for the compositions with x ≥ 0.72 and coexistence of the tetragonal and cubic phases for the intermediate compositions (0.46 ≤ x ≤ 0.68). Temperature dependence of the dielectric permittivity above room temperature exhibits diffuse nature of phase transitions for the compositions in the cubic and two phase region while the compositions with tetragonal structure at room temperature exhibit sharp ferroelectric to paraelectric phase transition. The PMW-xPT compositions with coexistence of tetragonal and cubic phases at room temperature exhibit two anomalies in the temperature dependence of the dielectric permittivity above room temperature. Using results of structural and dielectric studies a partial phase diagram of PMW-xPT ceramics is also presented.     

Characterization of sol-gel synthesised lead-free (1 − x)Na0.5Bi0.5TiO3-xBaTiO3-based ceramics

The crystal structure, microstructure, dielectric and ferroelectric properties of (1 − x)Na_0.5Bi_0.5TiO₃-xBaTiO₃ ceramics with x = 0, 0.03, 0.05, 0.07 and 0.1 are investigated. A structural variation according to the system composition was investigated by X-ray diffraction (XRD) analyses. The results revealed that the synthesis temperature for pure perovskite phase powder prepared by the present sol-gel process is much lower (800 °C), and a rhombohedral-tetragonal morphotropic phase boundary (MPB) is found for x = 0.07 composition which showing the highest remanent polarization value and the smallest coercive field. The optimum dielectric and piezoelectric properties were found with the 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃ composition. The piezoelectric constant d₃₃ is 120 pC/N and good polarization behaviour was observed with remanent polarization (P_r) of 12.18 pC/cm², coercive field (E_c) of 2.11 kV/mm, and enhanced dielectric properties ?_r > 1500 at room temperature. The 0.93Na_0.5Bi_0.5TiO₃-0.07BaTiO₃-based ceramic is a promising lead-free piezoelectric candidate for applications in different devices.     

Phase transition and electrical properties of (1 − x)K0.02Na0.98NbO3-xBaTiO3 ceramics

(1 − x)K_0.02Na_0.98NbO₃-xBaTiO₃ ceramics were prepared by the solid state reaction method, and their electrical properties were investigated. The samples showed crystal structure changing from monoclinic to orthorhombic, and then to tetragonal, with an increase in BaTiO₃ content. The addition of BaTiO₃ markedly enhanced ferroelectric and piezoelectric properties of K_0.02Na_0.98NbO₃ ceramics. Remnant polarization increased and coercive field decreased only in the samples with small amount of BaTiO₃. Piezoelectric properties were improved with the addition of BaTiO₃. The 0.9K_0.02Na_0.98NbO₃-0.1BaTiO₃ ceramics showed maximum piezoelectric constant (d₃₃ = 160 pC/N), which was even comparable with that of (1 − x)K_0.5Na_0.5NbO₃-xBaTiO₃ ceramics. Their good piezoelectric properties, along with a low ferroelectric-ferroelectric transition temperature (T_F-F), made the 0.9K_0.02Na_0.98NbO₃-0.1BaTiO₃ ceramics a potential candidate for lead-free piezoelectric applications.     

Polymorphic phase transition-induced electrical behavior of BiCoO3-modified (K0.48Na0.52)NbO3 lead-free piezoelectric ceramics

(1 − x)(K_0.48Na_0.52)NbO₃-xBiCoO₃ [KNN-xBC] lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. The effects of the BiCoO₃ addition on the phase structure, dielectric, piezoelectric and ferroelectric properties of KNN-xBC ceramics were systematically investigated. The polymorphic phase transition (PPT) from rhombohedral to orthorhombic phase around room temperature was identified in the composition range of 0.01 ≤ x ≤ 0.02, and the improved electrical properties were induced by this PPT. The KNN-0.01BC ceramics near PPT exhibit optimum electrical properties: d₃₃ ∼ 165 pC/N, k_p ∼ 0.40, P_r ∼ 31.0 μC/cm², and E_c ∼ 12.6 kV/cm. These results indicate that the enhanced piezoelectric properties for alkali niobate can be achieved by forming the coexistence of rhombohedral and orthorhombic phases.     

The effects of Bi(Mg2/3Nb1/3)O3 on piezoelectric and ferroelectric properties of K0.5Na0.5NbO3 lead-free piezoelectric ceramics

To improve the temperature stability of piezoelectric properties of Na_0.5K_0.5NbO₃ (KNN)-based ceramics, Bi(Mg_2/3Nb_1/3)O₃ (BMN) was used to modify Na_0.5K_0.5NbO₃ (KNN)-based ceramics by a conventional sintering technique. Piezoelectric and ferroelectric properties of 0.99K_0.5Na_0.5NbO₃-0.01Bi(Mg_2/3Nb_1/3)O₃ ceramics were studied. It is found that 0.01BMN-0.99KNN ceramics exhibits stable piezoelectric properties as the temperature changes due to the composition fluctuation on B sites (d₃₃ ≈ 130 pC/N, dielectric loss tg θ ≤ 5% in the range 25-300 °C). These results indicate that these materials are promising lead-free piezoelectric ceramic candidates for practical applications.     

Crystal structure and dielectric properties of La(Mg0.5Ti0.5)O3-Ca0.8Sm0.4/3TiO3 solid solution system at microwave frequencies

The crystal structure and the dielectric properties of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ ceramics have been investigated. Ca_0.8Sm_0.4/3TiO₃ was employed as a τ_f compensator and was added to La(Mg_0.5Ti_0.5)O₃ to achieve a temperature-stable material. The formation of (1 − x)La(Mg_0.5Ti_0.5)O₃-xCa_0.8Sm_0.4/3TiO₃ solid solutions were confirmed by the XRD results and the measured lattice parameters for all compositions. The dielectric properties are strongly correlated to the sintering temperature and the compositional ratio of the specimens. Although the ?_r of the specimen could be boosted by increasing the amount of Ca_0.8Sm_0.4/3TiO₃, it would instead render a decrease in the Q × f. The τ_f value is strongly correlated to the compositions and can be controlled by the existing phases. A new microwave dielectric material 0.45La(Mg_0.5Ti_0.5)O₃-0.55Ca_0.8Sm_0.4/3TiO₃, possessing a fine combination of microwave dielectric properties with an ?_r of 47.83, a Q × f of 26,500 GHz (at 6.2 GHz) and a τ_f of −1.7 ppm/°C, is proposed as a very promising candidate material for today's 3G applications.     

Effect of addition of Ba(W0.5Cu0.5)O3 in Pb(Mg1/3Nb2/3)O3-Pb(Zn1/3Nb2/3)O3-Pb(Zr0.52Ti0.48)O3 ceramics on the sintering temperature, electrical properties and phase transition

In this work, we report on the Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PZN-PZT) ceramics with Ba(W_0.5Cu_0.5)O₃ as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W_0.5Cu_0.5)O₃ significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W_0.5Cu_0.5)O₃-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: (K_p = 0.63, Q_m = 1415 and d₃₃ = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications.     

High-dielectric-constant and low-loss microwave dielectric in the (1 − x)La(Mg0.5Ti0.5)O3-x(Ca0.8Sr0.2)TiO3 solid solution system

The microwave dielectric properties and microstructures of (1 − x)La(Mg_0.5Ti_0.5)O₃-x(Ca_0.8Sr_0.2)TiO₃ ceramics, prepared by a mixed oxide route, have been investigated. The forming of solid solutions was confirmed by the XRD patterns and the measured lattice parameters for all compositions. A near zero τ_f was achieved for samples with x = 0.5, although the dielectric properties varied with sintering temperature. The Q × f value of 0.5La(Mg_0.5Ti_0.5)O₃-0.5(Ca_0.8Sr_0.2)TiO₃ increased up to 1475 °C, after which it decreased. The decrease in dielectric properties was coincident with the onset of rapid grain growth. The optimum combination of microwave dielectric properties was achieved at 1475 °C for samples where x = 0.5 with a dielectric constant ?_r of 47.12, a Q × f value of 35,000 GHz (measured at 6.2 GHz) and a τ_f value of −4.7 ppm/°C.     

Study of structural, dielectric and electrical behavior of (1 − x)Ba(Fe0.5Nb0.5)O3-xSrTiO3 ceramics

Polycrystalline samples of BaFe_0.5Nb_0.5O₃ and (1 − x)Ba(Fe_0.5Nb_0.5)O₃-xSrTiO₃ [referred as BFN and BFN-ST respectively] (x = 0.00, 0.15 and 0.20) have been synthesized by a high-temperature solid-state reaction technique. The XRD patterns of the BFN and BFN-ST at room temperature show a monoclinic phase. The microstructure of the ceramics was examined by the scanning electron microscopy (SEM) and shows the polycrystalline nature of the samples with different grain sizes, which are inhomogeneously distributed through the sample surface. Detailed studies of dielectric and impedance properties of the materials in a wide range of frequency (100 Hz-5 MHz) and temperatures (30-270 °C) showed that properties are strongly temperature and frequency dependent. Complex Argand plane plot of ?″ against ?′, usually called Cole-Cole plots is used to check the polydispersive nature of relaxation phenomena in above mentioned compounds. Relaxation phenomena of non-Debye type have been observed in the BFN and BFN-ST ceramics, as confirmed by the Cole-Cole plots.     

Coexistence of room temperature ferroelectricity and ferrimagnetism in multiferroic BiFeO3-Bi0.5Na0.5TiO3 solid solution

The structure, ferroelectric and magnetic properties of (1 − x)BiFeO₃-xBi_0.5Na_0.5TiO₃ (x = 0.37) solid solution fabricated by a sol-gel method have been investigated. X-ray diffraction and Raman spectroscopy measurements show a single-phase perovskite structure with no impurities identified. Compared with pure BiFeO₃, the coexistence of ferroelectricity and ferrimagnetism have been observed at room temperature for the solution with remnant polarization P_r = 1.41 μC/cm² and remnant magnetization M_r = 0.054 emu/g. Importantly, a magnetic transition from ferrimagnetic (FM) ordering to paramagnetic (PM) state is observed, with Curie temperature T_C ∼ 330 K, being explained in terms of the suppression of cycloid spin configuration by the structural distortion.     

Properties of praseodymium-doped bismuth potassium titanate (Bi0.5K0.5TiO3) synthesised using the soft combustion technique

Bismuth potassium titanate (Bi_0.5K_0.5TiO₃; BKT) and praseodymium-doped BKT (Bi_0.5(1−x)Pr_xK_0.5TiO₃; BPKT) powders were synthesised using the soft combustion technique. Fine particles of 10-100 nm of BKT and BPKT were produced. A single phase BKT was obtained with a minimum of 0.5 mol of glycine. Various compounds of Bi_0.5(1−x)Pr_xK_0.5TiO₃ where x = 0.01, 0.03, 0.05, 0.10, 0.15 and 0.20 were prepared. Pure BKT and BPKT powders were obtained after calcination at 800 °C for 3 h. After sintering at 1050 °C for 5 h, pure BKT and BPKT pellets were obtained for x = 0 and 0.01. However, for BPKT with x = 0.03, 0.05, 0.10, 0.15 and 0.20, a minor amount of Bi₄Ti₃O₁₂ (BIT) secondary phase was present after sintering at 1050 °C for 5 h. The crystallite size and grain size of all the samples followed similar trends, first increasing from x = 0 (undoped BKT) to x = 0.05 and then decreasing above x = 0.05. Among the undoped and doped samples, BPKT with x = 0.05 had the highest dielectric properties (?_r = 713.87) due to its large crystallite size (68.66 nm), large grain size (∼435 nm) and high relative density (93.39%).     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting Mg with Ni

The microwave dielectric properties of La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm³, dielectric constant (?_r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τ_f) of −85 ppm/°C were obtained for La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Phase evolution, crystal structure and dielectric behavior of (1 − x)Nd(Zn0.5Ti0.5)O3 + xBi(Zn0.5Ti0.5)O3 compound ceramics

The phase evolution, crystal structure and dielectric properties of (1 − x)Nd(Zn_0.5Ti_0.5)O₃ + xBi(Zn_0.5Ti_0.5)O₃ compound ceramics (0 ≤ x ≤ 1.0, abbreviated as (1 − x)NZT-xBZT hereafter) were investigated. A pure perovskite phase was formed in the composition range of 0 ≤ x ≤ 0.05. The B-site Zn²⁺/Ti⁴⁺ 1:1 long range ordering (LRO) structure was detected by both XRD and Raman spectra in x ≤ 0.05 samples. However, this LRO structure became gradually degraded with an increase in x. The dielectric behaviors of the compound ceramic at various frequencies were investigated and correlated to its chemical composition and crystal structure. A gradually compensated τ_f value was obtained in (1 − x)NZT-xBZT microwave dielectrics at x = 0.03, which was mainly due to the dilution of dielectric constant in terms of Claussius-Mossotti differential equation.     

The temperature-dependent electrical properties of Bi0.5Na0.5TiO3-BaTiO3-Bi0.5K0.5TiO3 near the morphotropic phase boundary

Bi_0.5Na_0.5TiO₃-BaTiO₃-Bi_0.5K_0.5TiO₃ (BNT-BT-BKT) lead-free piezoceramics with compositions near the rhombohedral-tetragonal morphotropic phase boundary (MPB) were prepared and investigated. At room temperature, all ceramics show excellent electrical properties. In this study, the best properties were observed in 0.884BNT-0.036BT-0.08BKT, with the remnant polarization, bipolar total strain, unipolar strain, piezoelectric constant, and planar electromechanical coupling factor being 34.4 μC cm⁻², 0.25%, 0.15%, 122 pC N⁻¹, and 0.30, respectively. Detailed analysis of the temperature dependence of polarization-electric field (P-E) loops and bipolar/unipolar strain-electric field (S-E) curves of this composition revealed a ferroelectric-antiferroelectric phase transition around 100 °C. Around this temperature, there is a significant shape change in both P-E and S-E curves, accompanied by enhanced strain and decreased polarization; the largest recoverable strain reaches 0.42%. These results can be explained by the formation of antiferroelectric order and the contribution of field-induced antiferroelectric-ferroelectric phase transition to piezoelectric response. Our results indicate that BNT-BT-BKT lead-free piezoceramics can have excellent electrical properties in compositions near the MPB and also reveal some insight into the temperature dependence of the electrical performance with the MPB composition.