TiO3-based Solid Solutions Research Articles

High-power piezoelectric properties of quenched (Bi0.5Na0.5)TiO3-based solid-solution ceramics

Lead-free piezoelectric ceramics based on 0.90(Bi0.5Na0.5)TiO3 – 0.04(Bi0.5Li0.5)TiO3 – 0.06BaTiO3 with additives MnCO3 (0.1 wt%) [BNLBT4-6 + Mn0.1], which have a morphotropic phase boundary composition, were prepared by controlling the quenching rate (QR) and, their high-power piezoelectric and electrical properties were examined. The depolarization temperature Td could be increased by controlling the QR. The Td with QR = 15.0 and 0.05 °C/s was 166 and 119 °C, respectively. Thus, Td was increased by about ∼40 °C due to the quenching effect. Moreover, vibration velocities (v0−p) were observed at 1.3 m/s even after quenching. Additionally, the values of d31, ɛ33T/ɛ0, and s11E decreased, whereas Qm increased after quenching. The quenching effect promoted the dielectric and elastic hardening of BNLBT4-6 + Mn0.1 ceramics. After quenching, Td increased, and the value of d31 × Qm maintained the same value as for ordinary firing (OF) with QR = 0.05. Consequently, quenching was found to be effective for increasing the Td and Qm, hence, a promising effect for high-power piezoelectric applications.

Quenching effects on electrical properties of Cu-doped (Bi1/2Na1/2)TiO3-based solid solution ceramics

Quenching effects on electrical and piezoelectric properties were investigated for Cu-doped (Bi1/2Na1/2)TiO3 (BNT)-based solid solution systems, 0.90(Bi1/2Na1/2)TiO3–0.06BaTiO3–0.04(Bi1/2Li1/2)TiO3 (BNLBT), aiming to increase the depolarization temperature Td without deteriorating the piezoelectric properties. A dense BNLBT ceramics doped with CuO 1.0 wt% was fabricated by a conventional ceramic fabrication process with a low-sintering temperature at 940 °C, which is 200 °C lower than those for non-doped BNLBT ceramics. In addition, the CuO-doped BNLBT ceramic was quenched immediately after the sintering process at 940 °C, and the piezoelectric constant and Td were measured. The Td values of CuO-doped BNLBT systems with and without quenching were 143 and 78 °C, respectively. This showed that Td Cu-doped ceramics increased by approximately 60 °C due to quenching. In addition, the electromechanical coupling factors k33 of quenched and non-quenched Cu-doped BNLBT ceramics were approximately 0.58, showing no significant deterioration of piezoelectric activity caused by quenching.

Dimensional t-factor variation and increase of stability of the ferroelectric state in (Na0.5Bi0.5)TiO3-based solid solutions

The influence of the [Formula: see text]-site ion substitutions in ([Formula: see text](Bi[Formula: see text]Na[Formula: see text]TiO3–[Formula: see text]BaTiO3system of solid solutions on the relative stability of the antiferroelectric (AFE) and ferroelectric (FE) phases has been studied. The ions of zirconium, tin, and (In[Formula: see text]Nb[Formula: see text], (Fe[Formula: see text]Nb[Formula: see text], (Al[Formula: see text]V[Formula: see text] ion complexes have been used as substituting elements. An increase in the concentration of the substituting ion results in a near linear variation in the size of the crystal lattice cell. Along with the cell size variation, a change in the relative stability of the AFE and FE phases takes place according to the changes of the tolerance factor of the solid solution. An increase in the tolerance factor leads to the increase in the temperature of the FE–AFE phase transition, and vice versa. Obtained results indicate the way for raising the temperature of the FE–AFE phase transition in (Bi[Formula: see text]Na[Formula: see text]TiO3-based solid solutions.

Quenching effects on piezoelectric properties and depolarization temperatures of (Bi0.5Na0.5)TiO3-based solid solution systems

Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5(1−x)Li0.5x)TiO3 and (1 − y)(Bi0.5Na0.48Li0.02)TiO3–yBaTiO3 (abbreviated as BNLT100x and BNLBT4-100y, respectively), were fabricated by a quenching procedure after sintering, and then their electrical properties were investigated with the aim of increasing their depolarization temperature Td. From the measurements by a resonance–antiresonance method, the electromechanical coupling factors k33 of BNLT100x and BNLBT4-100y were exactly the same after the quenching treatment as compared with the nonquenched one. The Td of all BNLT100x quenched from 1100 °C reached around 240 °C, and they are almost 60 °C higher for x = 0, 0.02, 0.04, and almost 80 °C higher for x = 0.08 than those of nonquenched ceramics. We also found, from the measurement on BNLBT4-100y quenched from 1100 °C, that the Td values were enhanced to higher temperature by the quenching treatment, even in the case of rhombohedral side (100y < 6), tetragonal side (100y > 6), and MPB composition (100y = 6). Moreover, we confirmed that the rhombohedrality 90-α and the tetragonality c/a values were enhanced by the quenching treatment. This result revealed that, even in the tetragonal symmetry, the lattice distortion (tetragonality) could also be stabilized by the quenching treatment in BNT-based solid solution ceramics.

Lead-free BNT-based composite materials: enhanced depolarization temperature and electromechanical behavior.

The development of (Bi0.5Na0.5)TiO3-based solid solutions with both high depolarization temperature Td and excellent piezoelectric and electromechanical properties for practical application is intractable because improved thermal stability is usually accompanied by a deterioration in piezoelectric and electromechanical performance. Herein, we report a 0-3 type 0.93(Bi0.5Na0.5)TiO3-0.07BaTiO3 : 30 mol%ZnO composite (BNT-7BT : 0.3ZnO), in which the ZnO nanoparticles exist in two forms, to resolve the abovementioned long-standing obstacle. In this composite, Zn ions fill the boundaries of BNT-7BT grains, and residual Zn ions diffuse into the BNT-7BT lattice, as confirmed by XRD, Raman spectroscopy, and microstructure analysis. The BNT-7BT composite ceramics with a 0-3 type connectivity exhibited enhanced frequency-dependent electromechanical properties, fatigue characteristics, and thermal stabilities. More importantly, low poling field-driven large piezoelectric properties were observed for the composite ceramics as compared to the case of the pure BNT-7BT solid solution. A mechanism related to the ZnO-driven phase transition from the rhombohedral to tetragonal phase and built-in electric field to partially compensate the depolarization field was proposed to explain the achieved outstanding piezoelectric performance. This is the first time that the thermal stability, electromechanical behavior, and low poling field-driven high piezoelectric performance of BNT-based ceramics have been simultaneously optimized. Thus, our study provides a referential methodology to achieve novel piezoceramics with excellent piezoelectricity by composite engineering and opens up a new development window for the utilization of conventional BNT-based and other lead-free ceramics in practical applications.

Studying the structural and electronic effects of substituted (Bi0.5Na0.5)TiO3

Significant efforts have been made in the development of (Bi0.5Na0.5)TiO3 ferroelectrics as an alternative to the lead-based industry standard PbTi1-xZrxO3.[1] It has also been shown that doping the A- and B-site of (Bi0.5Na0.5)TiO3 can greatly improve the ferroelectric behavior of these materials,[2] possibly due to the formation of two or more ferroelectric phases at a morphotropic phase boundary (MPB). As such, there is a significant interest in understanding the structural changes in (Bi0.5Na0.5)TiO3-based solid solutions. (Bi0.5Na0.5)TiO3 was originally described as adopting a rhombohedral structure in space group R3c, However, the accuracy of this description has been greatly debated. It was recently suggested that (Bi0.5Na0.5)TiO3 actually adopts a monoclinic structure in space group Cc.[3] Given this recent controversy, we investigated the structural evolution of (Bi0.5Na0.5)TiO3-based solid solutions, particularly the (Bi0.5Na0.5)Ti1-xZrxO3 and (1-x)(Bi0.5Na0.5)TiO3–xBiFeO3 solid solutions., using both diffraction and spectroscopy techniques. Diffraction measurements on (Bi0.5Na0.5)TiO3 confirm that both monoclinic Cc and rhombohedral R3c phases are present at room temperature. Diffraction analysis showed that doping (Bi0.5Na0.5)TiO3 with a small amount of (Bi0.5Na0.5)ZrO3 and BiFeO3 can stabilizes the rhombohedral phase. The Ti/Fe K-edge and Zr L3-edge XANES spectra analysis was performed to determine the effects doping has on the local displacement of the B-site cations.

Bulk response and grain boundary microelectrical activity of high TC BaTiO3–(Bi1/2K1/2)TiO3-based positive temperature coefficient of resistance ceramics

Abstract

Giant electric-field-induced strains in lead-free ceramics for actuator applications – status and perspective

In response to the current environmental regulations against the use of lead in daily electronic devices, a number of investigations have been performed worldwide in search for alternative piezoelectric ceramics that can replace the market-dominating lead-based ones, representatively Pb(Zr x Ti1-x )O3 (PZT)-based solid solutions. Selected systems of potential importance such as chemically modified and/or crystallographically textured (K, Na)NbO3 and (Bi1/2Na1/2)TiO3-based solid solutions have been developed. Nevertheless, only few achievements have so far been introduced to the marketplace. A recent discovery has greatly extended our tool box for material design by furnishing (Bi1/2Na1/2)TiO3-based ceramics with a reversible phase transition between an ergodic relaxor state and a ferroelectric with the application of electric field. This paired the piezoelectric effect with a strain-generating phase transition and extended opportunities for actuator applications in a completely new manner. In this contribution, we will present the status and perspectives of this new class of actuator ceramics, aiming at covering a wide spectrum of topics, i.e., from fundamentals to practice.

Physical and Electrical Properties of Lead-Free (Bi&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;–(Bi&lt;sub&gt;0.5&lt;/sub&gt;K&lt;sub&gt;0.5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt; Ceramics

Extending the investigations on (Bi0.5Na0.5)TiO3-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3 [BNT-BKT]. (Bi0.5Na0.5)TiO3 with 7~ 30 mol% (Bi0.5K0.5)TiO3ceramics have been prepared following the conventional mixed oxide process. A morphotropic phase boundary (MPB) between rhombohedral (R) and tetragonal (T) was found at the composition 0.82BNT-0.18BKT with correspondingly enhanced piezoelectric properties. The electromechanical planar coupling factor is higher for compositions near the MPB. The mechanical quality factor (Qm), planar coupling coefficient (kp) and thickness coupling coefficient (kt) of 0.82BNT-0.18BKT ceramics were 125, 28.8% and 47.4%, respectively.

Effect of lattice occupation behavior of Li+ cations on microstructure and electrical properties of (Bi1/2Na1/2)TiO3-based lead-free piezoceramics

The multisite occupation of Li+ cations in perovskite structure of (Bi1/2Na1/2)TiO3-based solid solution is investigated, which is rarely reported in previous studies. The multisite occupation in relation to the Li2CO3 doping level has been demonstrated with the aid of the microstructure and temperature-dependent conductivity analysis: As the addition of Li2CO3 is below 0.75 mol. %, the introduced Li+ cations precede to enter the A sites of the perovskite lattice to compensate for the A-site deficiency stemming from the high-temperature sintering process. Once the addition exceeds 0.75 mol. %, the excess Li+ cations will occupy B sites to substitute for Ti4+ and give rise to the generation of oxygen vacancies. The proposed multisite occupation behavior of Li+ cations and its derivative effects, involving the clamping effect or grain size effect, have made the piezo-/ferroelectric performances of the 0.85BNT–0.10BKT–0.05BT ceramics optimized at the Li2CO3 addition of 1.0 mol.%:d33 = 163 pC/N, Pr = 40.9 μC/cm2.

Piezoelectric Properties of (Bi0.5Na0.5)TiO3-Based Solid Solution at Large-Amplitude Vibration

The high-power piezoelectric characteristics of (Bi0.5Na0.5)TiO3 based solid solution ceramics, x(Bi0.5Na0.5)TiO3-y(Bi0.5Li0.5)TiO3-zBaTiO3 + MnCO3 w wt% [x + y + z = 1, y = 0.04, z = 0.02–0.08, BNLBT4-100z + Mnw], were focused on under large-amplitude vibration in this study. The BNLBT4-100z system has a morphotropic phase boundary (MPB) at approximately z = 0.06, and BNLBT4-2 and BNLBT4-4 exhibited rhombohedral symmetry, whereas BNLBT-4-8 exhibited tetragonal symmetry. The piezoelectric strain constant, d 33, for the MPB composition (z = 0.06) under small-amplitude vibration was the largest (>40 pC/N) among all compositions and the mechanical quality factor, Q m, of the composition with rhombohedral symmetry was higher than those of compositions with other symmetries. The vibration velocity, which was measured using a laser Doppler vibrometer reached 2 m/s for BNLBT4-2+Mn0.4 and BNLBT4-4+Mn0.4 rhombohedral symmetry and BNLBT4-6+Mn0.4 with the MPB, as compared with 1 m/s for BNLBT4-8+Mn0.4 with tetragonal symmetry. These results indicate that BNLKT4-4+Mn0.4 ceramic with rhombohedral symmetry is a promising candidate material for use in lead-free high-power piezoelectric devices.

Structure and Electrical Properties of Lead-Free (Bi&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt;-Ba(Sn,Ti)O&lt;sub&gt;3&lt;/sub&gt; Ceramics

Extending the investigations on (Bi0.5Na0.5)TiO3-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Bi0.5Na0.5)TiO3-Ba(Sn,Ti)O3. X-ray diffraction analysis revealed that, during sintering, all of the Ba(Sn,Ti)O3 diffuses into the lattice of (Bi0.5Na0.5)TiO3 to form a solid solution, in which a rhombohedral phase with a perovskite structure was found. It was found that the samples with a low content of Ba(Sn0.06Ti0.94)O3 exhibit relatively good physical and electric properties. For 0.98(Bi0.5Na0.5)TiO3-0.02Ba(Sn0.06Ti0.94)O3 ceramics, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.16 and 0.57, respectively, at the sintering of 1100oC for 3 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 3.56. For 0.98(Bi0.5Na0.5)TiO3-0.02Ba(Sn0.06Ti0.94)O3 ceramics, the relative density and the thickness coupling coefficient kt reach 98.1% and 0.58, respectively, at the sintering of 1100oC for 5 h. With suitable Ba(SnxTi1-x)O3 concentration and sintering condition, a dense microstructure and good electrical properties were obtained.

Effect of Bi2O3 addition and sintering time on the physical and electrical properties of lead-free (Na0.5Bi0.5)TiO3-Ba(Zr0.04Ti0.96)O3 ceramics

Although PbZrO3-PbTiO3 (PZT)-based ceramics are playing a dominant role in piezoelectric materials, their evaporation of harmful lead oxide during the sintering process causes a crucial environment problem. It is necessary to search for lead-free piezoelectric materials that have such excellent properties as those found in the PZT-based ceramics. Therefore (Na0.5Bi0.5)TiO3-based solid solutions were studied to improve piezoelectric properties. In the present study, various quantities of Bi2O3 were added into 0.99(Na0.5Bi0.5)TiO3-0.01Ba(Zr0.04Ti0.96)O3 (0.99NBT-0.01BZT) ceramics. High-density samples were obtained through the addition of Bi2O3 into 0.99NBT-0.01BZT ceramic. It was found that 0.99NBT-0.01BZT with the addition of 0-4.0 wt% Bi2O3 exhibit relatively good piezoelectric properties. For 0.99NBT-0.01BZT ceramic with the addition of 0.5 wt% Bi2O3, the electromechanical coupling coefficients of the planar mode kp and the thickness mode kt reach 0.15 and 0.55, respectively, at the sintering of 1100°C for 2 h. The ratio of thickness coupling coefficient to planar coupling coefficient is 3.6. It is obvious that 0.99NBT-0.01BZT solid solution ceramic by adding low quantities of Bi2O3 is one of the promising lead-free ceramics for high frequency electromechanical transducer applications.

Piezoelectric Properties of (Bi1/2Na1/2)TiO3-Based Solid Solution for Lead-Free High-Power Applications

Lead-free piezoelectric ceramics based on x(Bi1/2Na1/2)TiO3–y(Bi1/2Li1/2)TiO3–z(Bi1/2K1/2)TiO3 [x + y + z = 1] (abbreviated as BNLKT100y-100z) were prepared by conventional ceramic fabrication process. In this study, we clarified that the mechanical quality factor Qm of the rhombohedral side of the MPB composition is rather superior to that of the tetragonal side, although the piezoelectric constant d33 of the rhombohedral side is lower than that of the tetragonal side and MPB composition. As a second work, the effects of Mn doping on the variations in Td and piezoelectric properties including high-power characteristics were investigated using BNLKT4-8, which is a rhombohedral composition. The Qm of w wt % MnCO3-doped BNLKT4-8 (abbreviated as BNLKT4-8Mnw) markedly increased with increasing Mn concentration w, while Td, coupling factor k33, and d33 slightly decreased. The high-power characteristics of BNLKT4-8Mn0.6 were superior to those of hard PZT at a vibration velocity v0–p > 0.6 m/s. Therefore, a Mn-doped BNT-based solid solution with rhombohedral symmetry is a promising candidate for lead-free high-power applications.

The dependence of the piezoelectric properties on the differences of the A-site and B-site ions for (Bi 1− xNa x)TiO 3-based ceramics

The effect of the differences of the ionic size R, atomic weight M, and electric negative X of the A-site and B-site ions of the ABO 3 perovskite (Bi 1− x Na x )TiO 3(BNT)-based solid solutions (where the complex of Bi and Na ions occupy the A-site and Ti ion is in the B-site) on the electromechanical coupling factors ( k 33, k p) of the piezoelectric ceramics was investigated. It was found that the coupling factors (k 33, k p) of the ceramics have little dependence on the parameters of ∣ M∣, ∣ R∣ and ∣ X∣, respectively. However, if a comprehensive weight factor F( w) is defined as F( w) = ∣ M∣ + ∣ R∣ + 100∣ X∣, which is a dimentionless number containing M, R and X, and can be regarded as the comprehensive factor related to the spontaneous polarization of a unit cell in a given ceramic system, one can fined that F( w) has good correspondence with the coupling factors k 33 and k p. With increasing of the value of F( w), the k 33 and k p increase consequently. From this viewpoint, new BNT-solid solution with larger electromechanical coupling factors would be predicted, and a new system of (Bi 1− x Na x )TiO 3-based solid solutions was invented in our group by using this method.