Sodium Bismuth Titanate Research Articles

Acoustic and electrical properties of 1–3 connectivity bismuth sodium titanate–Portland cement composites

In this study, bismuth sodium titanate (BNT)–Portland cement (PC) composites with 1–3 connectivity pattern were fabricated by the dice-and-fill technique with different BNT ceramic content ranging from 30 to 70vol%. The acoustic impedance (Zc) and electrical properties of the composites were studied. When the BNT content varies from 30 to 70vol%, Zc value increases from 8.95 to 14.79×106kg/m2s. At BNT ceramic content of 70vol%, dielectric constant (ϵr), electromechanical coupling coefficients (Kt) and piezoelectric coefficient (d33) are 346, 21.28% and 70pC/N, respectively. Interestingly, the piezoelectric voltage coefficient (g33) values exhibited an opposite trend, that is, the g33 value decreases as the BNT content increases. Therefore, 1–3 connectivity of bismuth sodium titanate–Portland cement composites can be tailored by adjusting the piezoelectric ceramic content in composite; the developed composites have potential to be used as sensors for structural health monitoring applications in smart structures.

Phonon modes and central peaks in anA-site relaxor: A low-frequency Raman study of sodium bismuth titanate

Raman spectroscopic measurements of sodium bismuth titanate $({\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}{\mathrm{TiO}}_{3}$ or NBT) were carried out upon cooling from 1000 to 80 K to study its two phase transitions. Full spectral deconvolution was performed, comparing the results from several fitting models, with a particular emphasis on the evolution of the central peak and low-frequency phonon modes. The central intensity profile is found to be composed of two well-defined Lorentzian peaks, the temperature dependence of which suggests the presence of fluctuations in $M$-point and $R$-point rotations of the oxygen octahedra as well as cation displacements related to polar nanodomains. The temperature behavior of both central peaks is discussed in relation to the (tilting or shifting) transition behavior in similar perovskite systems. The four observed low-frequency phonon modes indicate a different symmetry assignment than the commonly assigned $R3c$ for the low-temperature phase.

Neutron diffraction on functional materials under electric field or mech. load

In this contribution neutron diffraction studies on functional materials under special environmenal conditions will be presented. In particular, studies of ferroelectric ceramics under high electric fields as well as shape memory alloys under mechanical load will be highlighted. The investigations were carried out at the high-resolution neutron powder diffractometer SPODI (FRM II / Garching n. Munich) which offers special sample environmenal tools for electric fields, mechanical load etc. In-situ studies on ferroelectrics under the influence of high electric fields enable to establish correlations between the macroscopic poling behaviour and corresponding structural changes. The investigations were carried out on technologically applied lead zirconate titanate based samples and on a bismuth sodium titanate based system. A self-designed device allows the investigation of large bulk samples under different orientations of the electric field. This method allows to analyze the poling mechanisms in technical ferroelectrics, such as piezoelectric effect, domain reorientation and phase transformations. In the system Bi0.5Na0.5TiO3 - BaTiO3 – K0.5Na0.5NbO3 the large recoverable field-induced strain could be attributed to a reversible field-induced phase transition from an almost non-polar, pseudocubic tetragonal phase to a distorted, ferroelectric active phase [1]. Polycristalline monoclinic nickel-titanium shape memory alloys have been investigated under mechanical load to analyze their stress-strain behaviour and to derive the elastic constants. A novel tensile rig allows to orient the load axis in a Eulerian cradle like manner. The elastic constants tensor could be calculated based on a series of diffraction patterns under different sample orientations in the initial state and under 0.6 % strain. Furthermore the contributions of elastic deformation (lattice dilatation) and inelastic deformation (orentation of twins) to the total strain could be separated.

Effect of poling on piezoelectric and ferroelectric properties of Bi0.5Na0.5Ti1-xZrxO3 ceramics

Lead-free bismuth sodium titanate zirconate powders with the stoichiometric formula of Bi0.5Na0.5Ti1 − xZrxO3 (where x = 0, 0.20, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80 mol fraction) were prepared by solid state reaction method. Based on XRD pattern from phase analysis of Bi0.5Na0.5Ti1-xZrxO3 powders, the quantitative profile fitting analysis was carried out. Phase characterization of the powders showed that at x = 0–0.65 mol fraction, only rhombohedral phase existed. With x = 0.68–0.75 mol fraction, the coexistence of rhombohedral and orthorhombic phases occurred. Orthorhombic phase completely formed with x = 0.80 mol fraction. Small addition of Zr into BNT caused dielectric constant to increase. High Zr concentration induced more unit cell distortion which caused the degradation of dielectric properties. Poling also had some effects on ferroelectric behavior of BNTZ ceramics particularly in the rhombohedral phase region in terms of improved breakdown strength.

Bismuth sodium titanate based lead-free ceramic/epoxy 1–3 composites: fabrication and electromechanical properties

The 1–3 piezocomposites based on 0.96Bi0.5(Na0.84K0.16)0.5TiO3–0.04SrTiO3 (BNKT–ST) were fabricated by a modified dice-fill method. Electro-mechanical properties of the composites as a function of the ceramic volume fraction (v) were measured and compared with theoretical values as well as with those of monolithic ceramics. The as-prepared piezocomposite with v = 0.276 showed a clear single thickness mode with a relatively high resonance frequency of more than 2 MHz, together with a relatively high piezoelectric strain constant (d 33 ~ 104 pC/N), a high thickness coupling coefficient (k t ~ 0.547), low acoustic impedance (Z ~ 9 Mrayls) and a large piezoelectric voltage coefficient (g 33 ~ 91.5 × 10−3 m2/C). From the practical application point of view, these promising results indicate that the BNKT–ST ceramic/epoxy 1–3 composite has great potential to be used in biomedical ultrasonic transducers as well as nondestructive evaluations.

Development of lead free magnetoelectric laminates of Na0.5Bi0.5TiO3–Tb0.3Dy0.7Fe1.95 for power generation

Lead free magnetoelectric laminates has been prepared by sandwiching Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) between two Tb0.3Dy0.7Fe1.95 (TDF) by epoxy bonding. The piezoelectric material Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) has been prepared by conventional solid state double sintering method and the magnetostrictive material, Tb0.3Dy0.7Fe1.95 (TDF) by vacuum induction melting process. NBT showed a saturated ferroelectric hysteresis behavior with the values of Ps=22.24μC/cm2, Ec=41kV/cm and Pr=27μC/cm2. The piezoelectric charge coefficient (d33) measured for NBT was 102pC/N. Magnetization versus magnetic field measurements were performed in longitudinal (L) and transverse (T) modes of TDF specimen that showed ferromagnetic hysteresis behavior. The magnetostriction of 950ppm at 4kOe and static strain coefficient of 0.37×10−6kOe−1 at 1kOe magnetic field were recorded for Tb0.3Dy0.7Fe1.95. The magnetoelectric output was measured in L and T modes for the different NBT thickness of 1.0, 1.5 and 2mm with TDF thickness of 1.5mm. The high magnetoelectric coefficient (α) was found to be 0.08mV/cmOe (L mode) and 0.13mV/cmOe (T mode) for the NBT/TDF laminates with 1.0mm thick NBT.

Load Characteristics of Lead‐Free Ceramic Multilayer Actuators Based on Bismuth–Sodium–Titanate

The electromechanical behavior of a lead‐free ceramic multilayer actuator is described. The actuator is made of an Nd‐doped [Bi0.500Na0.335K0.125Li0.040]TiO3 ceramic with inner electrodes of an Ag/Pd‐alloy. For electromechanical characterization, the actuator is under constant mechanical stress, and the strain over the applied electric field is recorded. The mechanical stress ranges from 0.1 to 80 MPa. The maximum applied electric field is 8 kV/mm. Starting with 0.1 MPa mechanical stress, the actuator exhibits a maximum strain of <0.1%. With increasing stress, the strain increases up to 0.17% at 5 MPa. With higher stress, the strain decreases and reaches 0.125% at 80 MPa. Reducing the mechanical stress leads to a steady increase in strain, which results in a doubling of the strain at 0.1 MPa compared with the initial value. The strain characteristic contains an electrostrictive part, a linear piezoelectric regime, and some creep behavior.

Dielectric and Pyroelectric Properties of Lead-Free Sodium Bismuth Titanate Thin Films Due to Excess Sodium and Bismuth Addition

Pb-free ferroelectric (Na0.5Bi0.5)TiO3 (NBT) thin films were prepared by a modified sol-gel process. Their structural, dielectric and pyroelectric properties were investigated as a function of the excess Na/Bi ratio and the annealing temperature. In the case of thin films containing no excess Na and Bi, only partial amounts of the perovskite NBT were crystallized, where the films consisted mainly of the pyrochlore phase of Bi2Ti2O7 for annealing conditions of 600~800 o C. With increasing excess Na/Bi ratio, the proportion of the perovskite phase effectively increased due to the compensation of the volatile Na and Bi components. For a Na/Bi ratio of 2.0, the thin film with single NBT perovskite phase was obtained within XRD detection limit after annealing at 700 o C for 10 min and it showed the excellent dielectric properties, er of ~550 and tan δ of 0.03. While these properties were degraded for Na/Bi ratio of 2.5 despite the existence of pure perovskite phase. The NBT thin film with Na/Bi ratio of 2.0 are also promising candidates for applications requiring pyroelectric devices because it was found to have pyroelectric coefficients of 1.3~7 nC/cm 2 K in the temperature range of 30~100 o C.

Flux growth and characterization of lead-free Sodium Bismuth Titanate–Barium Titanate single crystals

Polycrystalline material of Na0.5Bi0.5TiO3– BaTiO3 (abbreviated as NBBT) was synthesised by solid state reaction technique. NBBT single crystal with reasonable size has been successfully grown by spontaneous nucleation technique. The X-ray diffraction results confirmed that the crystal system of as grown NBBT was cubic at room temperature. The unit cell parameters of as-grown NBBT crystal are a=b=c=4.07Å; V=68Å3. The composition of as-grown NBBT was analyzed by Energy Dispersive X-ray analysis (EDS). Differential Scanning Calorimetry (DSC) revealed the thermal behavior of the grown NBBT crystal. The temperature dependence of dielectric constant was measured and the Curie temperature was found to be 310°C for NBBT crystal. The dielectric data fitted with Curie–Weiss law shows that the gamma value of the as-grown NBBT crystal is 1.46, which also confirms the relaxor behavior.

Fabrication of [100]-oriented bismuth sodium titanate ceramics with small grain size and high density for piezoelectric materials

Abstract A layered titanate H1.07Ti1.73O4·nH2O (HTO) with a plate-like particle morphology was used as a template for the fabrication of [1 0 0]-oriented bismuth sodium titanate (Na0.5Bi0.5TiO3, or BNT) ceramics by a reactive-templated grain growth (RTGG) method. The oriented BNT ceramic with a high degree of orientation (95%), high density (98%), and small grain size (2 μm) was fabricated for the first time by the RTGG method using a HTO-TiO2-Bi2O3-Na2CO3 reaction system. The oriented BNT ceramic is formed by a topotactic transformation reaction of plate-like HTO template particles to plate-like BNT mesocrystal particles, and then epitaxial crystal growth of BNT on the BNT mesocrystal particles. The epitaxial crystal growth reaction is affected by TiO2/HTO mole ratio, chemical component of the starting material, and calcination temperature program. The fabricated oriented BNT ceramic shows a higher d33* value than the non-oriented BNT ceramic, suggesting the promising application to high performance Pb-free piezoelectric materials.

Thermally-induced loss of piezoelectricity in ferroelectric Na0.5Bi0.5TiO3–BaTiO3

The loss of piezoelectricity in ferroelectric sodium bismuth titanate (NBT) in solid solution with barium titanate ((1−x)NBT−xBT) is studied by means of thermal depoling and Raman spectroscopy. In the range 0≤x≤13%, the highest thermal stability of the piezoelectric coefficients is found in x=13%, for which a longitudinal piezoelectric coefficient of 118pC/N was nearly temperature-independent up to a maximum temperature of 165°C. The composition nearest the morphotropic phase boundary, x=6%, exhibited the lowest thermal depoling temperature of 107°C. Depoling of this composition is suggested to arise from a second order phase transition evidenced in the temperature-dependent Raman spectra.

Correlations between mechanical and photoluminescence properties in Eu doped sodium bismuth titanate

Nanoindentation technique is utilized to examine mechanical property variation in Eu doped Na0.5Bi0.5TiO3 (NBT). Doping levels of Eu in NBT is systematically varied. Dilute doping results in a linear reduction in both modulus and hardness. At higher concentrations, a recovery of the mechanical properties (to undoped NBT values) is observed. These experimental trends mirror variations in the optical emission intensities with Eu concentration. Observed trends are rationalized on the basis of a model, which hypothesizes phase segregation beyond a critical Eu doping level. Such segregation leads to the formation of pure NBT, nano-Eu saturated NBT, and nano-mixed Eu oxides in the microstructure. Pure NBT is optically inactive, while saturated Eu:NBT is a much better emitter when compared to europium oxide. Hence beyond the critical concentration, luminescence signal comes primarily from the saturated Eu:NBT phase. The model presented is supported by nanoindentation, and spectroscopic results.

Characterization and Piezoelectric Properties of Bismuth Sodium Titanate Prepared by the Hydrothermal Synthesis Method

Bismuth sodium titanate (Na1/2Bi1/2)TiO3 powders were prepared by the hydrothermal route with starting chemicals containing Ti (OC4H9)4, Bi (NO3)35H2O as Bi and Ti sources at 180°C for 48 h in a PTFE-lined autoclave. XRD result confirms the formation of a pure pervoskite structure for the synthesized powders. SEM observation shows that the powders consist of spherical particles in the range of 0.2~1.0 μm, exhibiting a mean particle size of 0.5 μm. Compared with (Na1/2Bi1/2)TiO3 ceramics made by the conventional solid state reaction method, the specimen made by the hydrothermal synthesis method has superior piezoelectric properties with its piezoelectric constant d33 attaining a relatively high value of 78 pC/N.

Ferroelectric Mesocrystals of Bismuth Sodium Titanate: Formation Mechanism, Nanostructure, and Application to Piezoelectric Materials

Ferroelectric mesocrystals of Bi0.5Na0.5TiO3 (BNT) with [100]-crystal-axis orientation were successfully prepared using a topotactic structural transformation process from a layered titanate H1.07Ti1.73O4·nH2O (HTO). The formation reactions of BNT mesocrystals in HTO-Bi2O3-Na2CO3 and HTO-TiO2-Bi2O3-Na2CO3 reaction systems and their nanostructures were studied by XRD, FE-SEM, TEM, SAED, and EDS, and the reaction mechanisms were given. The BNT mesocrystals are formed by a topotactic structural transformation mechanism in the HTO-Bi2O3-Na2CO3 reaction system and by a combination mechanism of the topotactic structural transformation and epitaxial crystal growth in the HTO-TiO2-Bi2O3-Na2CO3 reaction system, respectively. The BNT mesocrystals prepared by these methods are constructed from [100]-oriented BNT nanocrystals. Furthermore, these reaction systems were successfully applied to the fabrication of [100]-oriented BNT ferroelectric ceramic materials. A BNT ceramic material with a high degree of orientation, high relative density, and small grain size was achieved.

A neutron diffraction study of the ergodic transition in sodium bismuth titanate

A neutron diffraction study of the ergodic transition in sodium bismuth titanate

Effect of cobalt doping on the sintering mechanisms of the lead-free piezoceramic (Bi0.5Na0.5)TiO3

Abstract In the search for lead-free piezoelectric ceramics, such as potassium sodium niobate, (K0.5Na0.5)NbO3 (KNN), and bismuth sodium titanate (Bi0.5Na0.5)TiO3 (BNT), high sintering temperatures and the associated volatilization of cations represent a major obstacle to achieve well performing materials. In this study, we investigated the effect of cobalt on the sintering behavior of BNT using in situ thermo-optical dilatometry. The addition of cobalt significantly reduced the sintering temperature at which fully dense ceramic bodies are obtained. This is accomplished by a dual effect of the dopant which facilitates oxygen diffusion: a fraction of the available Ti forms a secondary cobaltous phase. Instead of Ti, some Co is incorporated into BNT at the Ti site, causing oxygen vacancies for charge balancing. To a small degree, the dopant induces liquid phase sintering. At high sintering temperatures, swelling was observed, which was attributed to oxygen release caused by the valence transition from Co3+ to Co2+.

Structural and electrical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3) thin films optimized using the Taguchi approach

Controllable Pulsed Laser Deposition (PLD) parameters have been optimized to grow sodium bismuth titanate (Na0.5Bi0.5TiO3) (NBT) thin films. Target to substrate distance, background gas pressure, substrate temperature, laser fluence, laser rate of repetition, annealing time and NBT targets with and without excess Bi have been chosen as the parameters using a Taguchi L18 orthogonal array. Taguchi's Signal-to-Noise (S/N) ratios and analysis of variance (ANOVA) tools highlight the relevance of each parameter, and also yield the optimal setting of the parameters. The dominant parameters affecting dielectric properties are oxygen gas pressure and substrate temperature, whereas the distance between target to substrate and laser fluence appear as significant parameters. Fine tuning experiments and a subsequent verification experiment using the dominant and significant parameters result in the best values for the dielectric constant of 735, dielectric loss of 0.07 at 1kHz and remnant polarization of 21.42µC/cm2.

Effect of BaTiO3 additive on the electrical properties of Na0.50Bi0.50TiO3 lead free ceramics

The near morphotropic phase boundary (MPB) compositions of lead-free piezoelectric ceramics based on sodium bismuth titanate (Na0.50Bi0.50TiO3: NBT) and barium titanate (BaTiO3: BT) were carefully investigated by conventional high temperature mixed-oxide method. All the ceramics exhibit single phase rhombohedral symmetry. The frequency (100 Hz to 1 MHz) and temperature (Room temperature–500 °C) dependence of impedance spectroscopy of (1 − x)Na0.50Bi0.50TiO3–xBaTiO3 (x = 0.0, 0.06, 0.07 and 0.08) ceramics were investigated by impedance analyzer. The frequency explicit plots of Z″ versus frequency at various temperatures show peaks in the higher temperature range (>400 °C). The compounds show dielectric relaxation, which is found to be of non-Debye type and the relaxation frequency shifted to higher side with increase in temperature. The activation energy values obtained for different BT content suggest that the electrical conduction in NBT is mainly due to the mobility of the ionized oxygen defects.

Electrical and optical properties of Nd3+-doped Na0.5Bi0.5TiO3 ferroelectric single crystal

Sodium bismuth titanate Na0.5Bi0.5TiO3 (NBT) single crystal doped with Nd3+ was grown by a top-seeded solution growth method. Powder x-ray diffraction revealed a pure perovskite structure with the rhombohedral phase. We found that the dielectric and ferroelectric properties were enhanced by the Nd3+ dopant. After poling along the [1 1 1] direction, transmittance was enhanced dramatically. The Sellmeier dispersion equation and energy band gaps were obtained. The absorption band around 808 nm has high full-width at half-maximum and large absorption cross-section, which is suitable for AlGaAs diode-laser pumping. A strong emission transition band of Nd3+ at around 1066 nm was observed; a long radiation lifetime 324 µs shows a low quenching effect. These results indicate that Nd3+-doped NBT crystal could be applied in photonic or integrated optoelectronic devices as a multi-functional crystal.

Dielectric relaxation in NBT–ST ceramic composite materials

Lead-free piezoelectric ceramic composites (1-x) Na0.5Bi0.5TiO3-xSrTiO3, where x = 0.05, 0.10, 0.15 and 0.2, are prepared by mixing independently-prepared individual phases through sol–gel method. X-ray diffraction revealed the coexistence of rhombohedral and cubic phases. Surface morphology of the composites is observed using SEM, and both the phases are observed in the samples. Spectroscopic studies of the composites are characterized based on Fourier transform infrared, and vibration bands are analyzed at room temperature in the wave number region 500–3,000 cm−1. Dielectric properties of these composites are measured from room temperature to 400 °C in the frequency range 1–10 kHz, and these studies indicate the presence of defect clusters within the composite materials. P–E hysteresis loops of these samples were measured as a function of temperature and observed large anomalies in the behavior compared to pure sodium bismuth titanate (NBT) (the host material). Unlike NBT, all the composites exhibited excellent P–E loops. In addition, decrease in remanence polarization is observed, with increase of SrTiO3 at room temperature. Piezoelectric parameter d33 is measured on poled composites.