BT Ceramics Research Articles

Electrical Characterization of the Fe-Doped BT Ceramics by an Impedance Spectroscopy

The electric properties of the Fe - doped BaTiO3 ceramics was investigated as a function of frequency and temperature. The structure and morphology of investigated sample were characterized by an X-ray diffraction and scanning electron microscopy. The impedance measurements were carried out at the temperature ranging from 450 K to 600 K, and at the frequency range from 0.1 Hz to 10 MHz. Based on these parameters the electrical properties of the grains and grains boundaries were described. The bulk and grains boundaries resistance of ceramics and the thermal activation energies were determined.

Preparation and dielectric properties of X9R core–shell BaTiO3 ceramics coated by BiAlO3–BaTiO3

The typical “core–shell” structure in BT ceramics can easily obtain double dielectric anomalies, which greatly improve the dielectric temperature stability for multilayer ceramic capacitors. In this paper, BaTiO3 particles were coated with 0.3BiAlO3–0.7BaTiO3 shell [xBT@(0.3BA–0.7BT)] by a sol–gel method. Core–shell structure was proved to exist in ceramic grains by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). High-temperature X9R dielectrics were obtained when x=0.3 and 0.2, with a high dielectric constant (~1200) and low dielectric loss (<2.0%). Furthermore, the impedance data was fitted by an effective 4RC equivalent circuit, which could be assigned to the core, the shell, the grain boundary, and the ceramic/internal electrode interface regions. The activation energy of the core was found to decrease with x decreasing, while opposite tendency exists in the shell and the grain boundary.

Study of the Dielectric Properties of Europium Doped Barium Titanate Ceramics by an Impedance Spectroscopy

The barium titanate (BaTiO3) and the BaTiO3 + 0.1wt.% Eu2O3 ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances.

Stable piezoelectric property of modified BiFeO3–BaTiO3 lead-free piezoceramics

Perovskite-structured 0.696BiFeO3–0.014Bi(Zn1/2Ti1/2)O3–0.29BaTiO3 (BF69.6–BZT1.4–BT29) lead-free piezoceramics with various MnO2 addition were prepared using a refined solid state reaction electroceramic processing. Powder X-ray diffraction measurements showed their crystallographic structure being of rhombohedral structure and scanning electron microscopy observations revealed that MnO2-doping enhances ceramic microstructure grain size growth. In contrast to BF–BT ceramics, low dielectric loss ceramics were obtained with combined strategies of refined electroceramic processing, Mn-doping and adding BZT third member. A good combination of ferroelectric and piezoelectric property was obtained in the 0.22 and 0.26 % in weight MnO2-doped BF69.6–BZT1.4–BT29 coarse-grained ceramics and discussed in relation to microstructure grain size effect and point defect effect. Excellent time and thermal aging stabilities of piezoelectric constant d33 were also experimentally demonstrated and argued resulting from the feature of higher ferroelectric Curie temperature (TC) and no ferroelectric–ferroelectric structural phase transition below TC of BF–BZT–BT system.

Raman spectra and structural stability in B-site manganese doped (Bi0.5Na0.5)0.925Ba0.075TiO3 relaxor ferroelectric ceramics

Soft X-ray absorption (XAS), transmission electron spectroscopy (TEM), Raman spectroscopy, and synchrotron XRD have been studied in B-site 0–2mol% manganese (Mn) doped (Bi0.5Na0.5)0.925Ba0.075TiO3 (BN7.5BT) relaxor ferroelectric ceramics. High-resolution synchrotron XRD and TEM reveal two phase coexistence of rhombohedral R3c and tetragonal P4bm structures in 0 and 0.2%, and an orthorhombic structure in 1 and 2% Mn-doped BN7.5BT at room temperature. Raman spectra of 0% Mn reveal structural transition from two phase coexistence to tetragonal phase near 190°C with a softening anomaly, while 0.2–2% Mn-doped BN7.5BT show softening behavior near 290°C upon heating. Raman spectra and synchrotron XRD indicate that Mn doping can enhance structural thermal stability in BN7.5BT ceramics.

Dielectric, optical, piezoelectric and ferroelectric studies of NBT–BT ceramics near MPB

Solid solutions of the lead free (1−x)Na0.5Bi0.5TiO3–xBaTiO3/NBT–xBT (where x=0.05, 0.06, 0.07, and 0.08) ferroelectric ceramics were synthesized in single perovskite phase by solid state reaction route. Higher values of remnant polarization (Pr) ~31.71μC/cm2, dielectric constant (εr) ~5067, piezoelectric coefficient (d33) ~105pC/N, electromechanical coupling coefficient (kp) ~21.17 and maximum induced strain% of ~0.45 were obtained in the x=0.07 NBT–xBT composition. The bipolar fatigue behavior of the NBT–xBT (x=0.05, 0.06, 0.07, and 0.08) ceramics was carried out by the remnant polarization vs. number of cycles (up to 109) study. Optical band gap of all the NBT–xBT ceramics was found to be ~3eV. Excellent dielectric, piezoelectric and ferroelectric properties suggested that the x=0.07 is the actual MPB composition of the NBT–xBT system.

The relaxor behavior and dielectric temperature stability of 0.85BaTiO3–0.15Na0.5Bi0.5TiO3–xLiBa2Nb5O15 ceramics

0.85BaTiO3–0.15Na0.5Bi0.5TiO3–xLiBa2Nb5O15 (x=0, 0.003, 0.004, 0.005, 0.006) ceramics were prepared by the solid state method. The effects of LiBa2Nb5O15 content on the phase structure, relaxor behavior and dielectric temperature stability were investigated. With the increasing amount of LBN content, the values of tetragonality decreased and the ceramics had a tendency to be a cubic structure. For x≥0.003, dielectric measurements indicated relaxor behavior. The increasing amount of LBN content improved the dielectric temperature stability of 0.85BT–0.15BT ceramics effectively. It was found that the variation ΔC/C25°C was around ±15% for x=0.004 from 25°C to 150°C. This ceramics with a small temperature coefficient of capacitance and a low dielectric loss in a wide temperature range showed a great potential application for high-temperature applications.

Large piezoelectric effect in Bi1/2Na1/2TiO3-based lead-free piezoceramics

The 0.935Bi1/2Na1/2TiO3–0.065BaTiO3–100xBi2FeCrO6 (x=0–0.013) (BNT–BT–100xBFCO) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method and the effect of BFCO addition on the microstructure and electrical properties of the ceramics was investigated. All the samples have a relative density higher than 97% of their theoretical values. X-ray diffraction (XRD) patterns show that all compositions have a pure perovskite structure and BFCO effectively diffused into the BNT–BT lattice during sintering to form a solid solution. SEM images indicate that the grain size of BNT–BT ceramics firstly increases and then decreases with the increase of BFCO content, and all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. Appropriate BFCO doping into BNT–BT ceramics induce the enhancement of piezoelectric and ferroelectric properties. Improved Pr=42.3μC/cm2, low Ec of 28.7kV/cm, and high d33=214pC/N, kp=33% were observed at x=0.007. These results indicate that the modified BNT–BT ceramics might be promising lead-free piezoelectric candidates for practical applications.

Temperature stability of dielectric properties for xBiAlO3–(1 − x)BaTiO3 ceramics

xBiAlO3–(1−x)BaTiO3 [xBA–(1−x)BT] polycrystalline ceramics were prepared by solid-state reaction method and sol–gel method, respectively. The ceramics were in tetragonal phase when x≤0.1, transformed to pseudocubic at x>0.1. The temperature stability of the dielectric constant for BA–BT was improved with BA contents increasing. Of particular interest was that the ceramics prepared by sol–gel method had less secondary phase, exhibiting much improved dielectric behavior. Among them, 0.3BA–0.7BT met the requirement of capacitance variation (ΔC/C≤±15%) in the temperature range of −55 to 440°C with moderate dielectric constant (ɛ=660) and low dielectric loss (tanδ=1.2%) at room temperature (1kHz). Nb-doped 0.2BA–0.8BT ceramics were investigated to improve the dielectric temperature stability at high-temperature end. It is found that all samples with 0.01–0.04mol Nb addition satisfied the X8R specification.

Energy Harvesting Using PLZT and Lead-Free Ceramics and Their Piezoelectric Properties on the Nano-scale

Vibration-electrical energy converters for energy harvesting based on the piezoelectric effect were investigated. The unimorph of PZT with a higher Tc and Mn-doped BaTiO3-based ceramics produced greater power and energy. Two unimorphs consisting of PZT (Tc = 320°C) and Mn-0.2mol% doped BT ceramics produced 3493 mJ and 193 mJ. Thermal energy harvesting using nonlinear pyroelectric effects was investigated in PLZT ceramics with different Tc and BT-based ceramics. PLZT(9.1/65/35) ceramics exhibited energy generation of 52J/L/cycle. Adiabatic temperature change (ΔT), due to electrocaloric effects was estimated from the polarization change. ΔT of 0.015 and 0.023K were estimated for BaTiO3 and PLZT(9.1/65/35) ceramics.

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi0.5Na0.5TiO3–0.07BaTiO3 (BNT–BT) and 0.93Bi0.5Na0.5TiO3–0.06BaTiO3–0.01K0.5Na0.5NbO3 (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (εr) ~1020 and 1370, respectively at 1kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485J/cm3 and 0.598J/cm3 were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.

Local structure investigation and properties of Mn-doped BiFeO3–BaTiO3 ceramics

Bi0.75Ba0.25(Fe,Ti)1−xMnxO3 with x=0, 3 and 5mol% Mn ceramics were prepared by a solid state reaction method. The relationships between site substitution of Mn in Mn-doped 0.75BF–0.25BT ceramics, phase formation and their properties were investigated. The addition of Mn was shown to improve densification, electrical and magnetic properties, especially ME coefficient. The Synchrotron X-Ray Absorption Near Edge Structure (XANES) spectra showed that Mn substituted for Fe/Ti atom and did not affect the oxidation state of Ti and Bi. However, a significant change of oxidation state was observed in Fe, Mn and Ba atoms.

Structure and electrical properties evolution of B-site complex ions (Li1/4Nb3/4) modification BNT–BT ceramics

B-site complex ions (Li1/4Nb3/4)4+ modification (Bi1/2Na1/2)0·94Ba0·06TiO3 ceramics with compositions of (Bi1/2Na1/2)0·94Ba0·06Ti1−x(Li1/4Nb3/4)xO3 (x = 0, 0·01, 0·03 and 0·06) have been synthesised via the conventional solid state reaction. The effect of (Li1/4Nb3/4)4+ content and sintering temperature on structures and electrical properties were investigated. It was found that both compositions and sintering temperatures have no significant effect on the crystal structure, and trace (Li1/4Nb3/4)4+ addition and sintering temperatures have a great influence on the microstructure. Two obvious dielectric anomaly peaks (Td and Tm) were observed and dielectric constant for all poled specimens displayed significant frequency dispersion at Td and diffusion phase transition at Tm. The piezoelectric properties of the ceramics are insensitive to the sintering temperatures, and the composition with x = 0·03 sintering at 1150°C exhibits favourable piezoelectric properties of d33 = 155 pC N−1 and kp = 0·312.

Effect of sintering temperature on the phase structure and electrical properties of Al–N co-doped BaTiO3piezoceramics

BaTiO3 and 1.5 mol% AlN/BaTiO3 (AlN/BT) piezoceramics were prepared via a conventional solid-state reaction method. The effects of sintering temperature on the phase structure, preferential orientation degree of Al3+–N3− pairs and electrical properties of the ceramics were investigated and analyzed. The AlN/BT ceramic sintered at 1325 °C obtains the optimum piezoelectric properties of d33 = 305 pC N−1, kp = 0.33 and Qm = 140 due to the preferential distribution of Al3+–N3− pairs and suitable sintering temperature. The high temperature stability testing reveals that these AlN-doped BT ceramics are useable at temperatures as high as approximately 115 °C. These properties indicate that this system is a potential high piezoelectric lead-free candidate material to be further studied.

Large E-field induced strain and polar evolution in lead-free Zr-doped 92.5%(Bi0.5Na0.5)TiO3–7.5%BaTiO3 ceramics

Abstract Structure, dielectric permittivity, strain, electric ( E ) polarization, and piezoelectric responses of (Bi 1/2 Na 1/2 ) 0.925 Ba 0.075 (Ti 1− x Zr x )O 3 (BNT7.5BT-100 x Zr; x = 0–0.04) ceramics were investigated as functions of poling E field and temperature. The BNT7.5BT ceramic reveals a phase transition from P4bm nanodomains to long-range-ordered P4mm domains. The Zr-doped BNT7.5BT ceramic reveals a reversible change of unit cell with dynamically fluctuating polar nanoregions, which are responsible for the large strain. The poled BNT7.5BT ceramic displays a depolarization temperature of T d = 90 °C, which correspond to a phase transition from ferroelectric to relaxor states. The Zr-doped BNT7.5BT ceramics have Burns temperatures ( T B ) in the region of 400–435 °C, below which polar nanoregions begin to develop. The Zr-doped BNT7.5BT ceramics display wide diffuse phase transitions, suggesting a transition from R + T to T phases. BNT7.5BT-2Zr ceramic shows a temperature dependent linear large strain of 0.482% at 150 °C and can be a potential candidate for lead-free actuator.

Phase structure and piezoelectric properties of NBT–KBT–BT ceramics prepared by sol–gel flame synthetic approach

Sol–gel flame synthetic approach was used to produce powders and the resultant ceramics of (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3–BaTiO3 (NBT–KBT–BT) with different compositions. Detailed analysis of polarization–electric field (P–E) loops and strain–electric field (S–E) curves reveals that a tetragonal antiferroelectric-like phase exists at room temperature with a suitable composition. Because of the morphotropic phase boundary (MPB) behavior, the maximum piezoelectric constant d33 of about 213pC/N with an electromechanical coupling factor kp of about 29% and a remnant polarization Pr of 23.55μC/cm2 were obtained in the 0.90NBT–0.05KBT–0.05BT ceramics. This work provides new insight to further optimized lead-free NBT–KBT–BT piezoelectric ceramics for practical use in different composition ranges at room temperature.

Dielectric and Electromechanical Properties of BaTiO3 Ceramics Prepared by Hot Isostatic Pressing

Lead-free piezoelectric barium titanate (BaTiO3 or BT) ceramics with various grain sizes were prepared by hot isostatic pressing (HIP) and post-annealing. The dielectric, ferroelectric and electromechanical properties were investigated. The average grain sizes of the ceramics were controlled by changing the post-annealing temperature. The BT ceramics obtained by HIP at 800°C without post-annealing with the average grain size 0.48 μm exhibited ferroelectric behaviors as shown by polarization and electromechanical measurements and the piezoelectric response corresponding to the d33 coefficient of 46 pC/N. The polarization hysteresis loops became more saturated with increasing grain sizes. The remanent polarization and the unipolar strain/field of the BT ceramics prepared by HIP at 800°C under 200 MPa and annealed at 1400°C in air for 12 h were 9.4 μC/cm2 and 380 pm/V, respectively.

Phase transition and piezoelectric properties of lead-free (Bi1/2Na1/2)TiO3–BaTiO3 ceramics

(1−x)(Bi0.5Na0.5)TiO3–xBaTiO3 ceramics (x=0.03, 0.06, 0.08, 0.12, 0.15, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 0.90) were fabricated by a conventional solid-state reaction and their phase transitions and piezoelectric properties were investigated using XRD analyses, Curie temperature, the frequency dependance of dielectric constant, and P–E curves. A complete solid solution with a perovskite structure was formed in the whole composition range of BNT–BT and more than two phase transitions arising from a compositional change were found. With increasing BaTiO3 content, the sequence of phase transitions from a rhombohedral structure to unknown tetragonal structures and finally a tetragonal structure with the space group P4mm has been established. While the rhombohedral–tetragonal phase transition led to superior piezoelectric properties in BNT–BT ceramics, other phase transitions between tetragonal structures had a little effect on piezoelectric properties. The d33, εr, kp, kt, and Qm and values lied in ranges of 40–130pC/N, 400–900, 10–30%, 15–30%, and 50–250, respectively.

Enhanced piezoelectric and mechanical properties of AlN-modified BaTiO3 composite ceramics.

BaTiO3-xAlN (BT-xAlN) composite ceramics were prepared by conventional solid state reaction sintering. The effects of the AlN content on the crystalline structures, densities, and electrical and mechanical properties of the BT ceramics were investigated. The BT-1.5%AlN ceramic exhibits a good piezoelectric constant of 305 pC N(-1) and an improved Vickers hardness of 5.9 GPa. The enhanced piezoelectricity originates from interactions between defect dipoles and spontaneous polarization inside the domains due to the occurrence of local symmetry, caused by the preferential distribution of the Al(3+)-N(3-) pairs vertical to the c axis. The hardening of the material is attributed to the improved density, and particle and grain boundary strengthening. Our work indicates that if a suitable doping ion pair is designed, lead-free ceramic systems prepared from ordinary raw materials by a conventional sintering method have a high probability of exhibiting good piezoelectric and mechanical properties simultaneously.

Enhanced thermal stability of lead-free high temperature 0.75BiFeO3–0.25BaTiO3 ceramics with excess Bi content

Lead-free high temperature 0.75BiFeO3–0.25BaTiO3 (0.75BF–0.25BT) ceramics with different excess Bi contents were prepared by solid state reaction method. XRD results indicated that the modified 0.75BF–0.25BT ceramics exhibited single perovskite structure with pseudo-cubic symmetry. The room temperature piezoelectric constant d33 and remnant polarization Pr were improved by the introduction of excess Bi content, while the temperature stability of dielectric and piezoelectric properties were enhanced. The 0.75BF–0.25BT ceramics with 1% excess Bi had a Curie temperature Tc of 508°C, dielectric constant ɛ of 440, loss tanθ (1kHz) of 4.6%, remnant polarization of 34.4μC/cm2, piezoelectric constant d33 of 114 pC/N, and planar electromechanical coupling factor kp of 0.31. The piezoelectric constant d33, and planner electromechanical coupling factor kp of 0.75BF–0.25BT ceramics with 1% excess Bi were stable up to 450°C, about 300°C higher than that of PZT-based ceramics. The combination of improved piezoelectric constant d33 and electrical temperature stability indicated that 0.75BF–0.25BT ceramics with proper concentration of excess Bi were promising candidates for high-temperature and lead-free piezoelectric applications.