Enhanced electrical properties of lead-free BNLT–BZT ceramics by thermal treatment technique

Electrical properties of lead-free solid solution ceramics from the Bi_0.4871Na_0.4871La_0.0172TiO₃ (BNLT) and BaZr_0.05Ti_0.95O₃ (BZT) system have been improved by a thermal treatment technique. A modified two step mixed-oxide method was employed for the preparation of the (1?x)BNLT–xBZT ceramics, where x=0.06, 0.09, 0.12 and 0.20. After sintering at 1125 °C for 4 h, the BNLT–BZT ceramics were annealed at 825, 925 and 1025 °C. The annealing treatment caused an increase in dielectric constant of BNLT–BZT ceramics with x≤0.09 mol% and with x higher than 0.09 mol% the dielectric value dropped considerably. The ferroelectric properties of all annealed ceramic samples tend to decrease with increasing annealing temperature as confirmed by the slimmer P–E loops. The piezoelectric coefficient (d₃₃) increased with annealing temperatures and a maximum value of ～170 pC/N was obtained from the ceramic samples annealed at 1025 °C with x=0.02.     

Lead-free high performance Bi(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 piezoceramics

In this article, structure, dielectric, ferroelectric and piezoelectric properties of Bi rich Bi_1.05(Zn_0.5Ti_0.5)O₃-modified BiFeO₃-BaTiO₃ (BF-BT-xBZT) ceramics were investigated experimentally. Crystal structure, phase purity and microstructure were examined through X-ray diffractometry and scanning electron microscopy, respectively. The crystallographic results show the formation of single-phase solid solutions for all compositions except x?=?10?mol%. The BF-BT modification through BZT instigates variation in grain size, enhancement in Curie temperature (T_C) and field induced polarization and strain response. Large field induced strain of ～0.24% at low driving field along with a small hysteresis of ～38% was observed for 2?mol% BZT modified BF-BT ceramics. These investigated results signpost the potentiality of BF-BT-xBZT ceramics in high temperature piezoelectric device applications.     

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.     

Electrical and magnetic properties of La1−xSrxMnO3 (0.1 ≤ x≤ 0.25) ceramics prepared by sol–gel technique

La_1−xSr_xMnO₃ (0.1 ≤ x ≤ 0.25) high density ceramics were prepared by sol-gel method using methanol as solvent. X-ray diffraction analysis showed that all samples exhibited single perovskite structure and no second phase was detected. Scanning electron microscopy images exhibited good particle connectivity on the surface of sample, and grain size increased with the increase in Sr doping. Resistivity-temperature curves of samples were measured by standard four-probe method, and curves exhibited significant differences in studied range of Sr doping. Magnetic measurement results indicated that the variation of susceptibility of different samples was quite different, and the Curie temperature of samples increased with the increase in Sr content. For x = 0.2, temperature coefficient of resistance value of the sample was larger, and corresponding peak TCR temperature was 307.1 K, which is very close to room temperature. Thus, La_0.8Sr_0.2MnO₃ ceramics exhibited high TCR value close to room temperature. Combined with its excellent magnetic properties, La_0.8Sr_0.2MnO₃ ceramics may potentially act as effective candidates for uncooled radiation calorimeter and uncooled magnetic sensor. Applications of La_0.8Sr_0.2MnO₃ ceramics in uncooled infrared radiation calorimeter at room temperature will be highly beneficial.     

The effects of sintering temperature and content of x on phase formation,microstructure and dielectric properties of (1−x)(Bi0.4871Na0.4871La0.0172TiO3)−x(BaZr0.05Ti0.95O3) ceramics prepared via the combustion technique

(1?x)(Bi_0.4871Na_0.4871La_0.0172TiO₃)?x(BaZr_0.05Ti_0.95O₃) ceramics (abbreviated (1?x)BNLT?xBZT) where 0.1≤x≤0.3 were fabricated by the combustion technique using glycine as fuel. BNLT and BZT powders were calcined at temperatures of 825 °C for 4 h and 925 °C for 6 h, respectively. After that they were mixed with the different compositions. It was found that the optimum sintering temperature of (1?x)BNLT?xBZT ceramic was obtained at 1125 °C for 2 h. This ceramic had the highest density. The structure of the (1?x)BNLT?xBZT ceramics exhibited the co-existence of tetragonal and rhombohedral phases with x≤0.1. The tetragonality increases with the increase of x content. The average grain size, the density and the Curie temperatures decrease with increasing x content. The maximum dielectric constant and the highest P_r were at about 4850 and 12.7 μC/cm², respectively, and were obtained by the 0.85BNLT?0.15BZT sample.     

Oxygen evolution on La1−xSrxMnO3 electrodes in alkaline solutions

Anodic characteristics of La_1?xSr_xMnO₃ electrodes were investigated in alkaline solutions. It was found that the catalytic activity for the oxygen evolution reaction was relatively high and increased with the increase of x in La_1?xSr_xMnO₃. The primary discharge step of hydroxide ion is rate-controlling in the anodic evolution of oxygen at La_1?xSr_xMnO₃ electrodes. The catalytic property for this reaction is discussed by applying the theory of σ* band formation to the interaction between the e_g orbital of Mn cation and the electron orbital of hydroxide ion.     

Hydrothermal synthesis,sintering and characterization of nano La-manganite perovskite doped with Ca or Sr

Two lanthanum manganite perovskite-nanostructures, namely; La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ (x?=?0.1, 0.3, 0.5 and 1.0), were synthesized by hydrothermal method. To follow up the composition of formed phases, the synthesized powders were calcined at different temperatures. The obtained materials were investigated by X-ray diffraction (XRD) and transmission electron microscope (TEM). Moreover, the calcined powders were pressed at 100?MPa and sintered at variable temperatures; i.e. 1250, 1300, 1350 and 1450?°C. The phase composition and microstructural characteristics of sintered pervoskites were examined by XRD and scanning electron microscope (SEM). Furthermore, physical (bulk density and apparent porosity), electrical resistivity and magnetic properties were also determined. The results revealed that La_xCa_(1-x)MnO₃ and La_xSr_(1-x)MnO₃ nanostructures were successfully prepared by hydrothermal method. The physical properties of sintered pervoskites were strongly depended on dopant type and concentration. The maximum sintering temperature for La_xCa_(1-x)MnO₃ was 1400?°C while for La_xSr_(1-x)MnO₃ was 1450?°C, after which the materials have been fused. Materials doped with Ca or Sr exhibited lower resistivity. On the other side, the magnetic properties have been also improved after addition of Ca or Sr. This has been discussed based on the double exchange mechanism. La_xSr_1-xMnO₃ exhibited better magnetic properties than La_xCa_1-xMnO₃ and LaMnO₃. La_0.5Ca_0.5MnO₃ and La_0.5Sr_0.5MnO₃ exhibited the highest magnetization among the other pervoskites.     

La1-xSrxMnO3:Ag0.2 (0.1 ≤ x ≤ 0.2) ceramics with large room-temperature TCR for uncooled infrared bolometers

In this study, high-density La_1-xSr_xMnO₃:Ag_0.2 (x = 0.1, 0.125, 0.15, 0.175, and 0.2) ceramics were prepared by the conventional sol-gel method. The peak values of temperature coefficient of resistivity (TCR) in all La_1-xSr_xMnO₃:Ag_0.2 samples were systematically controlled by changing the Sr content. A significant improvement in peak TCR have been observed through adjusting the Sr content. At doping molar ratio of x = 0.15 in La_1-xSr_xMnO₃:Ag_0.2 ceramics, the peak TCR value reached 14.7% K⁻¹, and peak TCR temperature (T_K, 288.2 K) was estimated to room-temperature (290 K). Visibly, it is encouraging to get such a high room-temperature TCR value. These findings suggested that La_0.85Sr_0.15MnO₃:Ag_0.2 ceramics could be used to prepare room-temperature uncooled infrared bolometers.     

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.     

Effect of ZnO doping on structural,dielectric, ferroelectric and piezoelectric properties of BaZr0.1Ti0.9O3 ceramics

This study provides a fundamental understanding of structural, dielectric, ferroelectric and piezoelectric properties of bare and ZnO-doped BaZr_0.1Ti_0.9O₃ (BZT) solid solutions synthesized using mechanochemical activation technique. Structural investigation has been carried out using XRD patterns of the synthesized compositions by Rietveld refinement method. It confirms the formation of tetragonal phase with P4mm space group for ZnO doping up to 2.5 wt%, while in 5.0 wt% ZnO-doped sample, BZT and ZnO are distributed as individual phases of tetragonal (P4mm) and hexagonal (P6₃mc), respectively. Microstructural analysis shows that average grain size increases quite rapidly with the increase of ZnO content. Detailed analysis of dielectric constant as a function of temperature for the prepared samples shows that the frequency independent dielectric constant maximum shifts to lower temperature with increase in ZnO doping. The ferroelectric ordering is confirmed using P-E loop measurements. The piezoelectric constant of the synthesized specimens were found to decrease with increasing ZnO content.     

Piezoelectric and dielectric properties of (Bi0.5Na0.5)0.94Ba0.06TiO3–Ba(Zr0.04Ti0.96)O3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics of (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃–xBa(Zr_0.04Ti_0.96)O₃ (abbreviated as BNBT–BZT100x, wherein x from 0 to 10 mol%) were fabricated. We have studied effects of amount of BZT content on the electrical properties and microstructures. X-ray diffraction analysis indicates that a solid solution is formed when BZT diffuses into the BNBT lattice, and further the crystal structure of sintered hybrid changes from rhombohedral to tetragonal symmetry along with increasing BZT content. Piezoelectric property measurements reveal that the BNBT–BZT4 ceramics has the highest piezoelectric performance, for example, the piezoelectric constant d₃₃ reaches to 167 pC/N and planar electromechanical coupling factor k_p is up to 0.27. In addition, the effect of Bi₂O₃ on the electrical properties and microstructure of the BNBT–BZT4 ceramics have also been studied, and found that the doping of Bi enhances the piezoelectric properties of ceramics.     

Improved ferroelectric properties of BiFeO3-based piezoelectric ceramics through morphotropic phase boundary construction

The ceramic (1-x)BiFe_0.985Sc_0.015O₃-xBaZr_0.2Ti_0.8O₃ + 1mol% MnO₂ (x = 0.20, 0.25, 0.30, 0.35) (BFS-xBZT) was synthesized using the traditional ceramic sintering method. The components of the ceramic were determined by constructing a morphotropic phase boundary (MPB) which consists of rhombohedral (R) and tetragonal (T) phases (0.24≤ x ≤ 0.26). With the accumulation of BZT content, relax behaviors were observed by dielectric properties measurements. At the MPB, the crystal structures of the R phase and T phase change abruptly. The distortion degree of the R phase increases, and the differences between a and c of the T phase decrease. An enhanced ferroelectricity Pr of ~27.8 μC/cm² and apex piezoelectric coefficient d₃₃ of 131 ± 4 pC/N are obtained near the MPB (x = 0.25), due to the R-T phase coexistence near room temperature. The results show that BFS-xBZT ceramics could be a candidate for lead-free piezoelectric ceramics at high operating temperatures.     

Morphotropic phase boundary and electrical properties of 1−x[Bi0.5Na0.5]TiO3 –xBa[Zr0.25Ti0.75]O3 lead-free piezoelectric ceramics

Lead-free solid solutions (1?x)Bi_0.5Na_0.5TiO₃ (BNT)–xBaZr_0.25Ti_0.75O₃ (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1?x(BNT)–x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO₃) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05.     

Efficient and robust ceramic interconnects based on a mixed-cation perovskite for solid oxide fuel cells

To achieve a required output voltage, a solid oxide fuel cell (SOFC) stack has multiple unit cells connected in series through interconnects (ICs). A dual-layer IC film comprising p- and n-type conducting perovskite oxides is considered to be a promising design in terms of electrical properties and stability; however, its fabrication is materials-intensive and time-consuming. Here, we propose an advanced design of a single-layer IC film inspired by the interfacial nature of the dual-layer IC film. Based on an understanding of cross-diffusion phenomena across the interface between Sr_0.7La_0.2TiO₃ and La_0.8Sr_0.2MnO₃ during the co-sintering process revealed by secondary ion mass spectroscopy, we design and synthesize mixed-cation perovskite oxides, (Sr_0.6La_0.4)_0.9(Ti_1–xMn_x)O₃ (SLTM), for IC applications in SOFCs. Among various compositions, Ti-rich SLTM (x?=?0.25) shows high sinterability, leading to the formation of a thin, gas-tight IC film on a porous anode support via simple screen printing and sintering. When exposed to both reducing and oxidizing atmospheres, the fabricated SLTM-IC film is highly conductive and remains stable during continuous operation. The ceramic IC design proposed in this work may provide great benefits in terms of reduced costs of IC materials and fabrication, while maintaining the IC performance required for SOFCs.     

Structural,dielectric and piezoelectric properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–Bi(Zn0.5Ti0.5)O3 thin films prepared by sol–gel method

Lead free (1−x)(0.8Bi_0.5Na_0.5Ti_0.5O₃–0.2Bi_0.5K_0.5TiO₃)–xBiZn_0.5Ti_0.5O₃ (x=0–0.06) (BNT–BKT–BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel processing technique. The effects of BZT content on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT–BKT–BZT thin films were investigated systematically. The BNT–BKT–BZT thin films undergo a transition from ferroelectric to relaxor phase with increasing temperature. The phase transition temperature decreases with the increase of BZT content. The BNT–BKT–BZT thin film with x=0.04 exhibits the best ferroelectric properties (P_max=40 µC/cm² and P_r=10 µC/cm²), largest dielectric constant (ε=560) and piezoelectric constant (d₃₃=40 pm/V). This finding demonstrates that the BNT–BKT–BZT thin film has an excellent potential for demanding high piezoelectric properties in lead free films.     

Structural,ferroelectric, magnetic and magnetoelectric properties of (1-x) Ba0.85Ca0.15Zr0.1Ti0.9O3 -x La0.67Sr0.33MnO3 lead-free magnetoelectric composites

The influence of an additional La_0.67Sr_0.33MnO₃ (LSMO) magnetic phase on the structural, ferromagnetic, ferroelectric, and magnetoelectric properties of Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ferroelectric phase was studied for composites of (1-x)BCZT -xLSMO (x = 0, 25, 50, 75 and 100%). The ferroelectric BCZT sample showed a perovskite single phase formation with a tetragonal crystal structure of the P4mm space group, and the magnetic phase of LSMO presented a rhombohedral crystal structure of R3c space group as shown by XRD. The composite sample with 25% LSMO exhibited large ferroelectric and piezoelectric properties with remnant, saturation polarization, and coercive electric field P_r ~7.74 μC/cm², P_s ~11.69 μC/cm² and E_C ~12.22 kV/cm with a piezoelectric coefficient d₃₃ ~ 231 pC/N. The magnetic characterization for the composites showed that the sample containing 75% of LSMO revealed the highest remnant, saturation magnetization, and coercive field of M_r ~1.358 emu/g, M_s ~19.17 emu/g, and H_C ~33.19 Oe, respectively. Moreover, it revealed the largest magnetoelectric coupling coefficient α_ME ~2.51 mV/cm.Oe with high coupling quality at a lower applied magnetic field. The results highlight the value of these composites as lead-free room temperature magnetoelectric sensors and actuators.     

Preparation,thermal and phase evolution and functional properties of non-stoichiometric strontium-doped lanthanum manganite perovskite ceramics

Powders of (La_0.85Sr_0.15)_0.98MnO_3-δ (LSM85) and (La_0.80Sr_0.20)_0.98MnO_3-δ (LSM80) perovskites have been synthesized and characterized in detail, and then sintered to evaluate their electrical and magnetic properties at low temperatures and at near room temperature. Microstructural observations/analyses after the dilatometric essays show that the perovskites have compositions that deviate from the nominal ones. Furthermore, magnetic characterization of both samples reveals a ferromagnetic behavior with a Curie temperature above 300 K for LSM80 and of 260 K for LSM85. In addition, LSM85 is insulator from 15 up to 300 K, whereas LSM80 is metallic up to 160 K and insulator up to 300 K. This significant discrepancy of behaviour is attributable to structural and compositional differences between the two perovskites.     

Effect of MnO2 addition on relaxor behavior and electrical properties of PMNST ferroelectric ceramics

A novel ferroelectric system, 0.2Pb(Mg_1/3Nb_2/3)O₃–0.8Pb(Sn_0.46Ti_0.54)O₃ with MnO₂ addition (PMNST-Mn), was prepared. The dielectric, ferroelectric and piezoelectric properties were investigated. The results demonstrated that the addition of MnO₂ suppressed the dielectric relaxor behavior of PMNST. With the increase of MnO₂ addition, the diffuse phase transition (DPT) behavior weakened gradually. The addition of MnO₂ contributed to the decrease of the dielectric loss (tanδ) and the enhancement of ferroelectric polarization. The optimum ferroelectric and piezoelectric properties were obtained when the addition of MnO₂ is 0.75 mol%, and the remnant polarization (P_r) and mechanical quality factor (Q_m) were about 25% and 60% higher than those of PMNST, respectively. It was suggested that the formation of oxygen vacancies made the important contribution to suppressing relaxor behavior and improving the electrical properties of PMNST due to the substitution of Mn for B-site. This work provided a practicable strategy to tune electrical properties of ferroelectrics.     

A-site Ca/Sr co-doping to optimize room-temperature TCR of La0.7Ca0.3-xSrxMnO3 films

Based on the analysis of crystal structure, Mn³⁺/Mn⁴⁺ pairs, distortion of MnO₆ octahedron, and electrical transport properties of La_1-xCa_xMnO₃ and La_1-xSr_xMnO₃ materials, room-temperature coefficient of resistivity (TCR) of La_0.7Ca_0.3-xSr_xMnO₃ (LCSMO) films was optimized by Ca/Sr co-doping at the A-site. LCSMO films are successfully fabricated on LaAlO₃ (100) substrates via facile spin coating technology. The microstructure of LCSMO films is characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy and X-ray photoemission spectroscopy. Results reveal that A-site Ca/Sr co-doping significantly influenced crystal structure, formation of Mn³⁺/Mn⁴⁺ pairs, and distortion of MnO₆ octahedron. The correlation between microstructure and electrical transport properties was explained through the phenomenological percolation model, double-exchange mechanism and Jahn-Teller effect. Furthermore, the TCR reached 10.2% K^-1 at 296.1 K in La_0.7Ca_0.18Sr_0.12MnO₃ films.     

Disappearance of Fatigue Heterogeneity Due to an Introduction of La0.8Sr0.2MnO3 Buffer Layers in Modified Lead Zirconate Titanate Ceramics

A disappearance of fatigue heterogeneity has been observed with an introduction of La_0.8Sr_0.2MnO₃ (LSM) buffer layers in modified lead zirconate titanate ceramics. This disappearance provides clear evidence for the presence of trapped charge defects near the ferroelectric‐electrode interface. The time‐dependent polarization switching curves reveal that the modified lead zirconate titanate ceramics with LSM buffer layers displayed much less retardation after fatigue cycles. These results point to the essential role of oxygen vacancy during fatigue.