Temperature dependent phase transition of (Bi0.5Na0.5)1−xBaxTiO3 lead-free piezoelectric

Phase transformation and electric properties of lead-free piezoceramics (Bi_0.5Na_0.5)_1?xBa_xTiO₃ with x=0.05, 0.06, and 0.07(BNB5T, BNB6T and BNB7T) were investigated using dielectric, piezoelectric and ferroelectric measurements. Electric field induced strain measurement shows “W” shape bipolar strain characteristics for BNB5T with typical ferroelectric P–E curve, while BNB6T and BNB7T, possessing pinch-off P–E, exhibit “V” shape field-induced strain. All the BNBxT specimens exhibit relaxor characteristic, identified by the Debye Law. Dielectric properties measured at elevated temperatures with the frequency variation (10–500 kHz) reveal frequency dispersion below the T_d point, but no dispersion between T_d and T_m, which may be ascribed to an intermediate phase transition. By adding more Ba²⁺ ions, the region of intermediate phase, distinguished by frequency dependence dielectric constant, expands to lower temperature. Moreover, the ferroelectric properties measured at elevated temperature were carried out below and at the depolarization temperature to well investigate the existence of this phase. Much less ε–T profile dispersion were observed during the investigation of BNB6T and BNB7T, leading to possible existence of an intermediate phase in the investigated compositions. The results suggest that the linear field-induced-strain of (Bi_0.5Na_0.5)_1?xBa_xTiO₃ are expected to be attributed to the intermediate phase.     

Microwave dielectric properties of (Ba1−xSrx)(Mg0.5W0.5)O3 ceramics

The densification, microstructural evolution and microwave dielectric properties of (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics with x=0, 0.25, 0.5 and 0.75 are investigated in this study. The sintering temperature of the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ is significantly reduced from 1575 °C to 1400 °C as the x value increases from 0 to 0.25 and 0.50; this result is accompanied by the formation of the (Ba_1−ySr_y)WO₄ phase and a small quantity of second phase surrounding the grains. The grain size of the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics is increased by raising the Sr²⁺ content, which significantly lowers the sintering temperature. The microstructure of the (Ba_0.75Sr_0.25)(Mg_0.5W_0.5)O₃ ceramic displays the smallest average grain size of approximately 0.8 μm, with a narrow grain size distribution. Without long annealing time, very high Q×f values are obtained for the (Ba_1−xSr_x)(Mg_0.5W_0.5)O₃ ceramics sintered at 1400–1575 °C for a duration of only 2 h. The (Ba_0.75Sr_0.25)(Mg_0.5W_0.5)O₃ ceramic sintered at 1400 °C results in the best microwave dielectric properties, including ε_r of 20.6, Q×f of 152,600 GHz and τ_f of +24.0 ppm/°C.     

Microwave dielectric properties and microstructures of Nd(Mg0.5Sn0.5−xTix)O3 ceramics

This study elucidates the microwave dielectric properties and microstructures of Nd(Mg_0.5Sn_0.5?xTi_x)O₃ ceramics with a view to their potential for microwave devices. The Nd(Mg_0.5Sn_0.5?xTi_x)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The X-ray diffraction patterns of the Nd(Mg_0.5Sn_0.4Ti_0.1)O₃ ceramics revealed no significant variation of phase with sintering temperatures. A dielectric constant (?_r) of 21.1, a quality factor (Q × f) of 50,000 GHz, and a temperature coefficient of resonant frequency (τ_f) of ?60 ppm/°C were obtained for Nd(Mg_0.5Sn_0.4Ti_0.1)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Reduced leakage current and improved multiferroic properties of 0.5((1−x)BLPFO-xPZT)-0.5PVDF composite films

0.5((1−x)Bi_0.8La_0.1Pr_0.2FeO₃ (BLPFO)-xPb(Zr_0.52Ti_0.48)O₃ (PZT))-0.5Polyvinylidene difluoride (PVDF) composite films with x variations 0.25, 0.40 and 0.50 were synthesized using two step mixing, followed by hot pressing. The structural, microstructural, dielectric, magnetic, ferroelectric and magnetodielectric properties of composite films have been systematically investigated. The measurement of the dielectric properties at 1 kHz shows that the dielectric loss (tan δ) decreases with increasing the volume fraction of PZT. The value of maximum room temperature ε_r ~78 and low tan δ ~0.061 for 0.5((1−x)BLPFO-xPZT)-0.5PVDF composite film with x=0.50 suggests its usefulness for capacitor applications. For predictions of effective dielectric constant of composite films experimental data were fitted with Lichtenecker model. Among all the composite films, the film with x=0.50 was found to exhibit smallest leakage current density ~7×10⁻⁸ A/cm² and hence improved electrical resistivity. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component at 5 K. The value of remnant polarization (2P_r) is found to increase with increase of PZT content in composite films. In the present composite films a significant dependence of dielectric constant on magnetic field has been observed, and highest value of magnetodielectric response of 2.85% is observed for composite film with x=0.50.     

Phase-microstructure evolution and microwave dielectric characteristic of (1−x)(Sr0.5Ce0.5)TiO3+δ−xNdAlO3 solid solution

A perovskite solid solution (1−x)(Sr_0.5Ce_0.5)TiO_3+δ−xNdAlO₃, x = 0.1 to 0.4 was prepared by conventional solid state method. X-ray diffraction spectra revealed a single phase with tetragonal structure, indicating that doping of NdAlO₃ significantly stabilized the perovskite-like structure. The addition of NdAlO₃ facilitated the formation of large plate-like grains with porous microstructure. The dielectric constant (ε_r) decreased with increasing x because of the small ionic polarizability of NdAlO₃. The Q × f value was strongly dependent on the microstructure of these ceramics. The temperature coefficient of resonant frequency (τ_f) gradually shifted to near zero with a rise of x, which resulted from the decrease in tolerance factor (t). The solid solution with x = 0.4 sintered at 1550 °C for 4 h showed a good combination of dielectric properties: ε_r = 72, Q × f = 12052 GHz and τ_f = +5 pmm/°C.     

Structural,dielectric and ferroelectric properties of Ba1−x(Bi0.5Na0.5)xTiO3 ceramics

Lead free Ba_1?x(Bi_0.5Na_0.5)_xTiO₃ (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) ferroelectric ceramics were synthesized by conventional solid state reaction technique. Sintering was done at 1200 °C for 2 h in air atmosphere. The final products have tetragonal symmetry with decreasing c/a ratio confirmed by X-ray diffraction analysis. The grain size varies between 300 nm to 1000 nm for x=0 to 0.1. With increase in Bi_0.5Na_0.5TiO₃ [BNT] content, the room temperature permittivity decreases whereas the Curie temperature (T_c) increases and its highest value was found to be 155 °C for 10 mol% of BNT addition. The ceramics show stable and low dielectric loss characteristics. The remnant polarization (P_r) and the coercive field (E_c) increases monotonously with increase in BNT content. The highest value of 2P_r (=17 μC/cm²) and 2E_c (=22 Kv/cm) was obtained for x=10 mol% BNT addition.     

Crystal structure,microstructure and electrical properties of (1−x−y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBiFeO3 ceramics near MPB prepared via the combustion technique

(1?x?y)Bi_0.5Na_0.5TiO₃–xBi_0.5K_0.5TiO₃–yBiFeO₃ (BNKFT-x/y with 0.12≤x≤0.24, 0≤y≤0.07) lead-free piezoelectric ceramics have been prepared by the combustion technique. The effects of amounts of x and y on structures and electrical properties were examined. Powders and ceramics can be well calcined and sintered at 750 °C for 2 h and 1025–1050 °C, respectively. The results indicated that the crystalline structure and microstructure changed with the increase of x and y concentrations. XRD results of BNKFT-x/0.03 and BNKFT-0.18/y ceramics with 0.12≤x≤0.24 and 0≤y≤0.07 showed the rhombohedral–tetragonal morphotropic phase boundary (MPB). The addition of y caused a promoted grain growth while the addition of x suppressed the grain growth. The highest density (ρ=5.85 g/cm³), superior dielectric properties at T_c (ε_r=7846 and tan δ=0.02), remnant polarization measured at 40 kV/cm (P_r = 20.1 μC/cm²) and piezoelectric coefficient (d₃₃=213 pC/N) were obtained for x=0.18 and y=0.03.     

Relationships between crystal structure and electrical properties of Li0.055[Agx(K0.5Na0.5)1−x]0.945(Nb1−yTay)O3 ceramics

Electrical properties of perovskite Li_0.055[Ag_x(K_0.5Na_0.5)_1?x]_0.945(Nb_1?yTa_y)O₃ (0.00 ≤ x ≤ 0.04, 0.01 ≤ y ≤ 0.09) ceramics were investigated based on the structural characteristics. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phase was detected through the entire range of compositions. With increasing of Ta⁵⁺ content, the dielectric constant (?_r), piezoelectric coefficient (d₃₃) and electromechanical coupling factor (k_p) of Li_0.055(K_0.5Na_0.5)_0.945(Nb_1?yTa_y)O₃ ceramics were increased up to y = 0.07 and then decreased, while mechanical quality factor (Q_m) was increased. However, the ?_r, d₃₃, k_p and Q_m of Li_0.055[Ag_x(K_0.5Na_0.5)_1?x]_0.945(Nb_0.07Ta_0.03)O₃ ceramics were not changed remarkably with Ag⁺ content. The dependence of temperature coefficient of k_p (TCk_p) on the oxygen octahedral distortion was also discussed by Raman-active vibrations modes.     

Calcium fluorosilicates: The Ca6−0.5xSi2O10−xFx phase

The identity of Ca_6−0.5xSi₂O_10−xF_x with other germanate and silicate phases reported in the literature is confirmed by X-ray methods. The crystals exhibit superstructure which is interpreted as arising from ordering of Ca vacancies in the [203] direction. Its crystallochemical relationships with other fluorosilicate and germanates is discussed.     

Finite size effect on Sm3+ doped Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) ferrite nanoparticles

Samarium doped Mn–Zn ferrite nanoparticles of composition Mn_0.5Zn_0.5Sm_xFe_2−xO₄ (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques for their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter and lattice strain increases with the increase in Sm³⁺ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm³⁺ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced by EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetism for x=0, 0.1 the samples with saturation magnetization of 23.95 emu/g for Mn_0.5Zn_0.5Fe₂O₄ sample which increases with rise in Sm³⁺ ions content. The results are explained and correlated with the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.     

Field-induced large strain in lead-free 0.99[(1−x) Bi0.5(Na0.80K0.20)0.5TiO3–xBiFeO3]–0.01(K0.5Na0.5)NbO3 piezoelectric ceramics

Lead-free 0.99[(1−x) Bi_0.5(Na_0.80K_0.20)_0.5TiO₃–xBiFeO₃]–0.01(K_0.5Na_0.5)NbO₃ (BNKT20–100xBF–1KNN) piezoelectric ceramics were fabricated through conventional techniques. Results showed that changes in BF content of BNKT20–100xBF–1KNN induced transition from the ferroelectric phase to the ergodic relaxor phase. These changes also significantly disrupted long-range ferroelectric order, thereby correspondingly adjusting the ferroelectric-relaxor transition point T_F-R to room temperature. A large strain of 0.39% at the electric-field of 80 kV/cm (corresponding to a large signal d₃₃^* of 488 pm/V) was obtained at x=0.06, which originated from the composition proximity to the ferroelectric-relaxor phase boundary. Moreover, the high-strain material exhibited exceptional fatigue resistance (up to 10⁶ cycles) as a result of the reversible field-induced phase transition. The proposed material exhibits potential for novel ultra-large stroke and nonlinear actuators that require enhanced cycling reliability.     

High- and low-field dielectric responses and ferroelectric properties of (Bi0.5Na0.5)Zr1−xTixO3 ceramics

Bismuth sodium zirconate titanate (Bi_0.5Na_0.5)Zr_1?xTi_xO₃ with (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ceramics was fabricated by a conventional sintering technique at 850–1000 °C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0≤x≤0.2), mixed-phase region (0.3≤x≤0.4), and rhombohedral phase region (0.5≤x≤0.6). It was observed that the phase evolution from orthorhombic to rhombohedral symmetry resulted in a noticeable increase of the dielectric properties. The results from the high- and low-field dielectric responses indicated that the dielectric properties of both BNZ and BNZT ceramics were dominantly attributed to the reversible contribution. It was also noticed that grain size showed only partial influence on the increase of low-field dielectric constant in Ti-rich BNZT ceramic.     

Phase evolution and microwave dielectric properties of novel LiAl5−xZnxO8−0.5x-based (0 ≤ x ≤ 0.5) ceramics

Novel LiAl_5−xZn_xO_8−0.5x microwave dielectric ceramics were synthesized through a solid-state reaction route. Phase evolution of LiAl_5−xZn_xO_8−0.5x was determined by XRD analysis. The XRD results indicated that the phase compositions had a P4₃32 space group when 0 ≤ x ≤ 0.2 and a spinel structure when 0.3 ≤ x ≤ 0.5. The dielectric constant (ε_r) of this series’ solid solutions decreased with the increase in Zn doping content, which was in good agreement with the Clausius-Mossotti relation. Oxygen vacancy and the decreased degree of order degraded the quality factor (Q × f) of the two structures. The deterioration in quality factor was further verified by impedance spectroscopy. The temperature coefficient of the resonant frequency (τ_f) decreased with the increase in x and was correlated with the unit cell volume. Finally, CaTiO₃ was used as a compensation material to obtain a near-zero τ_f of the LiAl₅O₈ ceramic.     

A novel series of Ba0.5Sr0.5Al0.2−xMgxFe0.8O3−ξ (x ≤ 0.2) membranes for oxygen permeation application

The pervoskite-type oxides have received attention due to their potential applications in catalysis, fuel cells, sensors, gas separable membranes, and electrolytes. In view of the importance of oxygen separation from air, stable Ba_0.5Sr_0.5Al_0.2−xMg_xFe_0.8O_3−ξ (x = 0–0.2) powders have been synthesized by decomposition of sol–gel derived oxalate at 950 °C for 5 h and characterized with regard to formation, nature of iron species, oxygen permeation, and electrical conductivity. It is shown that magnesium substitution leads to (i) a stable perovskite-type cubic phase with ‘a’ = 3.953–3.978 Å, (ii) weakening of metal–oxygen bond, (iii) reduction of Fe⁴⁺ ions, and (iv) enhancement of oxygen deficiency and electrical conductivity. Their compact discs act as stable oxygen permeable filters with flux density of ∼3.013–3.355 μmol cm⁻² s⁻¹ at 1000 °C. The maximum value corresponds to composition x = 0.2 and hence can be a potential membrane for oxygen separation technology.     

Temperature Stability of Electrical Properties of (K0.5Na0.5)1−xLixNb0.95Sb0.05O3 Lead-Free Ceramics

(K_0.5Na_0.5)_1−xLi_xNb_0.95Sb_0.05O₃ (KNLNS-x, x=0–10 mol%) lead-free piezoelectric ceramics were prepared by the conventional mixed-oxide method. The temperature stability of the dielectric, piezoelectric, and ferroelectric properties of the two typical compositions (KNLNS-2 with orthorhombic phase, and KNLNS-7 with mixed phases) was investigated systematically. The relationship between the orthorhombic–tetragonal polymorphic phase transition (PPT) of the ceramics and the temperature stability of their electrical properties was also discussed. The electromechanical coupling factors (k_p and k₃₁) of the ceramics show the maximum values near the PPT, where the temperature stability of the resonance frequency is relatively poor. After the occurrence of the PPT, the remnant polarization (P_r) of the ceramics shows a marked decrease, and a maximum peak in the coercive field (E_c) is observed. Related mechanisms for the temperature stability of electrical properties were also discussed.     

The electrical properties of (1−x)(Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3)–xCaZrO3 lead-free piezoelectric ceramics

Lead-free (1−x)(0.0852Bi_0.5Na_0.5TiO₃–0.12Bi_0.5K_0.5TiO₃–0.028BaTiO₃)–xCaZrO₃ piezoelectric ceramics (BNT−BKT−BT−xCZ, x=0, 0.01, 0.02, 0.03, 0.04 and 0.05) were prepared by using a conventional solid-state reaction method. The effects of CZ-doping on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT−BKT−BT−xCZ system were systematically investigated. The polarization and strain behaviors indicated that the long-range ferroelectric order in the unmodified BNT−BKT−BT ceramics was disrupted by the increase of CZ-doping content, and correspondingly the depolarization temperature (T_d) shifted down from 109 °C to below room temperature. When x>0.03, accompanied with the drastic decrease in the remnant polarization (P_r) and piezoelectric coefficient (d₃₃), the electric-field-induced strain was enhanced significantly. A large unipolar strain of 0.35% under an applied electric field of 70 kV/cm (S_max/E_max=500 pm/V) was obtained in the BNT−BKT−BT−0.04CZ ceramics at room temperature, which was attributed to the reversible electric-field-induced phase transition between the relaxor and ferroelectric phases.     

四元复合氧化物La_(0.5)Sr_(0.5)Ni_(0.5)Cu_(0.5)O_3的抗硫性能

以SO2 为毒物 ,采用脉冲中毒方法 ,再以CO氧化反应为探针 ,对三元复合氧化物催化剂La0 .5Sr0 .5NiO3 与La0 .5Sr0 .5CuO3 以及四元复合氧化物催化剂La0 .5Sr0 .5Ni0 .5Cu0 .5O3 等三种催化剂样品的抗硫毒能力、失活曲线、中毒催化剂的再生性能以及毒物残留形态等进行了全面考察和对比分析。实验结果表明四元复合氧化物催化剂La0 .5Sr0 .5Ni0 .5Cu0 .5O3 在SO2 毒物含量是 1 2 2×10 -2 mmol时 ,特别是在高温 (≥ 30 0℃ )条件下 ,具有优异的抗硫性能     

Lilac ceramic pigments based on Ba0.5Sr0.5Zn2−xNixSi2O7 solid solutions

Lilac pigments were prepared within the solid solution series Ba_0.5Sr_0.5Zn_2−xNi_xSi₂O₇ with 0.1≤x≤0.5 from the corresponding oxides and carbonates via solid-state reactions. Depending on the composition, the solid solutions exhibit the crystal structure of the low-temperature and the high-temperature phases of BaZn₂Si₂O₇. This structural change leads to a change in the optical spectra, i.e. the coloration of the ceramic powders. The different colors are attributed to the variation of the coordination sites of Ni²⁺. In the case of samples with the structure of HT-BaZn₂Si₂O₇, Ni²⁺-ions are incorporated into tetrahedrally coordinated sites. Spectra of samples with the crystal structure of LT-BaZn₂Si₂O₇ are attributed to a mixture of Ni²⁺ in tetrahedral coordination but also to distorted sites with higher coordination numbers.     

Phase structure,ferroelectric properties,and electric field-induced large strain in lead-free 0.99[(1−x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3]–0.01Ta piezoelectric ceramics

Lead-free 0.99[(1−x)(Bi_0.5Na_0.5)TiO₃-x(Bi_0.5K_0.5)TiO₃]–0.01Ta piezoelectric ceramics were prepared by a conventional solid-state reaction process. The ferroelectric properties, and strain behaviors were characterized. Increase of the (Bi_0.5K_0.5)TiO₃ content induces a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic phase. Accordingly, the ferroelectric order is disrupted significantly with the increase of (Bi_0.5K_0.5)TiO₃ content and the destabilization of the ferroelectric order is accompanied by an enhancement of the unipolar strain, which peaks at a value of 0.35% (corresponding to a large signal d₃₃ of 438 pm/V) in samples with 20 mol% (Bi_0.5K_0.5)TiO₃ content. Temperature dependent measurements of both polarization and strain from room temperature to 120 °C suggested that the origin of the large strain is due to a reversible field-induced nonpolar pseudocubic-to-polar ferroelectric phase transformation.     

The magnetization reversal and high temperature dielectric response in Y1−xHoxFe0.5Cr0.5O3

The structural, magnetic, and dielectric properties of the Y_1−xHo_xFe_0.5Cr_0.5O₃ (x=0, 0.05, 0.1, 0.3, and 0.5) compounds have been investigated. Rietveld refinement of the XRD patterns shows that the compounds possess orthorhombic perovskite structure. The dual magnetization reversal is observed in the samples with x=0.05 and 0.1, and it vanishes when x≥0.3. Ferromagnetic-like behavior with large coercive fields is observed in all Ho³⁺ doped YFe_0.5Cr_0.5O₃ samples, indicating a doping induced metamagnetic behavior. This abnormal magnetization behavior can be explained by the antiparallel magnetic coupling between the Ho³⁺ and the canted Cr³⁺/Fe³⁺ moments, as well as the Ho–O–Ho magnetic interaction. The dielectric behavior in the frequency range from 100 Hz to 10 MHz is investigated. The low doped samples (x=0, 0.05, and 0.1) exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. The dual magnetization reversal under low magnetic field makes these materials attractive candidates for the magnetic dual sensor devices.