SrBi4Ti4O15 Ceramics Research Articles

Structural and electrical investigation of rare-earth doped lead-free SrBi4Ti4O15 ceramics

Structural and electrical investigation of rare-earth doped lead-free SrBi4Ti4O15 ceramics

Effect of ZnSnO3 on dielectric and ferroelectric properties of Sr2Bi4Ti5O18 ceramics

AbstractSr2Bi4Ti5O18 is one of the promising candidates for ferroelectric nonvolatile random access memory device applications. Albeit, this ceramic material is not suitable for certain ferroelectric device applications because of the merits and demerits associated with this material. Solid‐solution or composite ceramics in bulk configuration is the better choice to overcome the drawbacks associated with the individual compounds. Concurrently, solid‐solution of functional electro‐ceramics comprising Aurivillius family‐based lead‐free bismuth‐layered structured ceramics (1 − x) Sr2Bi4Ti5O18 (SBT) and x mol% of ilmenite structured ZnSnO3 (ZS) (where x = 0, 5, 10, and 20 mol%) were synthesized via conventional solid‐state reaction route to investigate the effect of ZS on the physical properties of SBT. X‐ray diffraction diffractograms revealed that a single phase was formed maximum up to 5 mol% of ZS in SBT and scanning electron microscopy studies suggested platelike microstructure of the samples. Intriguingly, positive‐up and negative‐down results indicated that the true switchable polarization for the 10 mol% ZS in SBT (10.87 μC/cm2), 33% higher than that of pure SBT ceramics in addition to the lower leakage current density and enhanced dielectric response in the SBT–ZS samples. The observed enhancement in electrical characteristics of SBT–ZS composite ceramics compared to pure SBT highlights the decisive role played by the ZS in lowering the thermodynamic barrier resulting in ease of polarization switching and mitigating the leakage current of SBT ceramics.

Structural and dielectric investigation of rare earth modified SrBi4Ti4O15 ceramics synthesized by high energy ball milling method

Lead free ferroelectric ceramics are under active research due to their nontoxic nature. Bismuth layered structure ferroelectric materials have engrossed a lot of consideration in research community due to its versatile applications and tunable electrical properties. In this research work, structural, morphological and electrical properties of rare-earth (Ho3+) modified SrBi4Ti4O15 (SBT) samples are investigated. The ceramic pellets were synthesized by solid state route using high energy ball milling. XRD studies indicated a single phase orthorhombic structure and the morphological investigation revealed formation of grain like features with marginal decrease in average grain size with Ho incorporation. Enhancement in Curie temperature is observed in the modified system. The dielectric constant for pristine SBT and SBHT sample were calculated as 1880 and 1389 at their transition temperature measured at 100 kHz frequency. An abrupt surge in loss at higher temperature can be related to enhancement in conductivity at elevated temperature. The modified sample have shown improved thermal stability making it a suitable candidate for application in high temperature sensors, transducer and actuator application.

Structural, Dielectric Properties and Conduction Mechanism of SrBi4Ti4O15 Ceramics

Objectives: 1. To prepare SrBi4Ti4O15 ceramics via solid-state reaction method. 2. To make a systematic investigations on structural and dielectric properties of SBT ceramics. Methods: The structural information of Strontium Bismuth Titanate (SBT) ceramics is examined by X-ray diffraction and Raman spectroscopy techniques. The surface morphology and elemental analysis of SBT ceramic is employed by scanning electron microscope attached with energydispersive X-ray spectroscopy. The dielectric measurements of SBT ceramics were performed using the impedance analyzer HIOKI-3532 LCR meter. Findings: From the X-ray diffraction studies, SBT exhibits a strongest diffraction peak (1 1 9) with the lattice parameters a = 5.428 Å, b = 5.423 Å, and c = 42.146 Å. The diffraction patterns were indexed to the orthorhombic phase. The surface morphology of the samples shows plate-like morphology with a grain size of ~1mm. The temperature-dependent ac conductivity confirms the thermally activated conduction mechanism. The ac conductivity of SBT ceramic was increased from 2.25  10-5 to 7.16  10-4 Ω.m-1 with an increase of frequency from 10 kHz to 1 MHz. The high curie temperature at ~540 ◦C, and low dielectric loss of ~0.031 for SBT ceramics can be appropriate for high-temperature electronic applications. Novelty: SBT ceramic exhibits enhanced electrical conductivity value (7.16  10-4 Ω.m-1)and makes it suitable for electronic device applications. Keywords: Scanning electron microscope; Dielectric constant; Dielectric loss; Conduction mechanism 1; X-ray diffraction

Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi4Ti4O15 High-Temperature Piezoelectric Ceramics.

In this work, SrBi4Ti4O15 (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd2O3, CeO2, MnO2 and Cr2O3) were fabricated by a conventional solid-state reaction route. The effects of oxide additives on the phase structures and electrical properties of the SBT ceramics were investigated. Firstly, X-ray diffraction analysis revealed that all these oxides-modified SBT ceramics prepared presented a single SrBi4Ti4O15 phase with orthorhombic symmetry and space group of Bb21m, the change in cell parameters indicated that these oxide additives had diffused into the crystalline lattice of SBT and formed solid solutions with it. The SBT ceramics with the addition of MnO2 achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd2O3 could increase the TC of SBT. At a low frequency of 100 Hz, those dielectric loss peaks appearing around 500 °C were attributed to the space-charge relaxation as an extrinsic dielectric response. The synergetic doping of CeO2 and Cr2O3 could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr2O3 can significantly enhance both d33 and kp of SBT, and produce a higher phase-angle maximum at resonance. Such an enhanced piezoelectricity was attributed to the further increased orthorhombic distortion after Ti4+ at B-site was substituted by Cr3+. Among these compositions, Sr0.92Gd0.053Bi4Ti4O15 + 0.2 wt% Cr2O3 (SGBT-Cr) presented the best electrical properties including TC = 555 °C, tan δ = 0.4%, kp = 6.35% and d33 = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d33 was decreased by only 3.6% after being annealed at 500 °C for 4 h. Such advantages provided this material with potential applications in the high-stability piezoelectric sensors operated below 500 °C.

Observation of magnetoelectric effect in CuO-doped SrBi4Ti4O15 ceramics

Room temperature magnetoelectric coupling effect was observed in CuO-doped SrBi4Ti4O15 lead-free ferroelectric ceramics. Interstitial doping of CuO resulted in the formation of secondary phases at lower angles, which was confirmed from X-ray diffraction studies. Due to the strong magnetic superexchange interactions of CuO, weak room temperature ferromagnetic hysteresis curve was observed. The highest saturation magnetization of 1.61 memu/g and remnant polarization of 6.21 µC/cm2 was achieved for x = 1 mol% of CuO-doped ceramic. Further, the existence of weak magnetoelectric effect (χE = 0.1352 mVcm-1Oe-1) was also achieved. The obtained weak magnetoelectric effect is due to the presence of spontaneous magnetization and oxygen deficiency in the prepared samples.

Tunable upconversion luminescence in new Ho3+/Yb3+‐doped SrBi4Ti4O15 photochromic ceramics for switching application

AbstractUpconversion (UC) luminescence modulation is quite important in controlling and processing light for active components of light sources, photoswitches, optical memories, and optical sensing devices. In this work, we reported one kind of novel phosphor, Ho3+/Yb3+‐doped SrBi4Ti4O15 ceramics, which displayed both strong UC luminescence and obvious photochromic (PC) reaction. The UC luminescence, PC effect, and the modulation of UC performance based on PC behavior were investigated in detail. By alternating visible light irradiation and thermal stimulus, the UC luminescence could be reversibly regulated. Meanwhile, the modulation was unveiled to tightly rely on the irradiation time and thermal treatment processes. Excellent reproducibility was also achieved. In addition, as an alternative method to thermal treatment, the manipulation of luminescence by electric field was also explored. Finally, the mechanism related to the UC luminescence manipulation was illustrated. The results indicate that these samples could be potentially utilized in optical data storage and anti‐counterfeiting security fields.

Impact of Sm-substitution and microwave sintering on dielectric and mechanical properties of SrBi4Ti4O15 ceramics

In quest of finding an alternative for lead-based materials, ferroelectric materials with Bi-layered structure have attracted great attention due to their potential applications in non-volatile memory, electro-optic devices, and microelectromechanical systems. In this work, samarium (Sm)-substituted SrBi4Ti4O15 (SBTi) ceramics have been prepared by solid-state reaction method and sintered using microwave, as well as conventional heating. XRD phase analysis reveals the formation of single phase compound, and there is no effect of Sm-substitution on basic crystal structure. SEM micrographs showed the plate-like structure of grains both in microwave and conventional furnace. Temperature-dependent dielectric properties were investigated in the temperature range 40–600 °C and frequency range 10 kHz–1 MHz. Sm-substitution increases dielectric constant upto Sm ~ 0.75 and also introduces small relaxor behavior. Hardness and Young’s modulus of SrBi4-xSmxTi4O15 ceramics were measured by nanoindentation. The structural, morphology, dielectric, and mechanical properties of pure and substituted SrBi4Ti4O15 ceramics along with sintering methods have been investigated in detail.

Effect of CuO modification on dielectric, ferroelectric and piezoelectric properties of lead-free SrBi4Ti4O15 ceramics

We report a systematic investigation of the structure, micro-structure, dielectric, ferroelectric and piezoelectric properties of CuO added SrBi4Ti4O15 ceramics. All the samples were prepared by solid state reaction technique, where the wt% of CuO in SrBi4Ti4O15 was varied as x = 0, 0.05, 0.2, 0.5. The addition of CuO increased the density of SrBi4Ti4O15 ceramics which in turn resulted in the improvement of dielectric, ferroelectric as well as piezoelectric properties. However, no change either in the crystal structure or lattice parameter was observed with CuO addition. Further a dense micro-structure with improved electrical properties is expected to be due to liquid phase sintering. Raman spectra and specific heat measurements were also performed for getting further insight into the properties.

Strong red emission and enhanced electrical properties in Pr-doped SrBi4Ti4O15 multifunctional ceramics

Pr3+-modified SrBi4Ti4O15 ceramics were prepared using a conventional solid-state reaction method. The modified ceramics simultaneously exhibited both visible photoluminescence and enhanced electrical properties. In visible light, ceramics exhibited a strong red emission peak at 610 nm corresponding to the inter-4f transition 1D2 → 3H4 due to the absence of inversion symmetry at Pr3+ sites. This red luminescence is greatly potential in various display devices. Meanwhile, samples modified by Pr3+ in x = 0.002 showed a large piezoelectric constant of 20pC/N and a remnant polarization of 22.78 μC/cm2, as well as a high Curie temperature value of 511 °C and excellent piezoelectric temperature stability. Moreover, the Pr3+-modified SrBi4Ti4O15 ceramics show a fatigue-free polarization behavior. All these advantages may expand the application fields of the materials as multifunctional devices by integrating their luminescent and piezoelectric properties.

Spark plasma sintering of grain-oriented Sr2Bi4Ti5O18 aurivillius phase ceramics

To improve dielectric, piezoelectric and ferroelectric properties of Sr2Bi4Ti5O18 ceramics, highly textured, dense ceramics are required. Highly grain-oriented Sr2Bi4Ti5O18 textured ceramics were prepared by pressure-assisted spark plasma sintering. The textured ceramics exhibited crystallographic anisotropy with c-axis oriented grains (Lotgering factor of 71%). The dielectric permittivity, piezoelectric constant and ferroelectric remnant polarization measured on the ceramics in the direction perpendicular to the pressure applied during sintering are higher than those along the parallel direction. These improved properties are related to the preferred polarization rotation in the textured microstructures prepared during spark plasma sintering.

Correlation between orthorhombic distortion with relaxation and Conduction mechanism of Gd3+ modified SrBi4Ti4O15 ceramics

Aurivillius single-phase ceramics of Gd3+ substituted SrBi4Ti4O15 with nominal formula of Sr1-xGd2×/3Bi4Ti4O15 (where x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.1) herein denoted as SGBT-x have been prepared by using mixed oxide technique. The primary structural analysis from XRD study confirms that orthorhombic distortion to increase with increase in Gd-content, which was strongly supported by Raman spectroscopy. Two of the relaxation mechanisms were clearly identified from cole-cole plot and modulus spectroscopy analysis, which could be discerned to both grain and grain boundary contributions effect. The kinetic study of frequency dependent AC conductivity at various temperature was investigated by using Jonscher's power law equation, σtot(ω)=A(T) ωs + σDC(T); where 0 < s < 1. Close resemblance of obtained activation energy from relaxation mechanism, DC conductivity as well as hopping conduction below transition temperature (TC) suggested that the transport behavior is to originate from oxygen vacancy related hopping mechanism in SGBT-0.08 specimen. In order to further confirm the possible conduction mechanisms in the system the 's' exponent has also been analyzed detail at different temperature regions. Overall we examine that CBH (correlated barrier hopping) and NSPT (non-overlapping small polaron) are two of the appropriate models for conduction process in ferroelectric and paraelectric region respectively. Also the orthorhombic distortion (b/a) of SGBT system plays a major role in the conduction and relaxation process.

Study of the properties of SBT ceramics doped with different concentrations of Ca

This study investigated how Ca doping affects the electrical properties of Sr2Bi4Ti5O18 (SBT) ceramics. Among the samples tested, a sample with a substitution level of 0.15 showed the highest a-axis orientation and the largest lattice distortion. Through XPS analysis, it was found that the formation of oxygen vacancies is suppressed by Ca substitution in SBT. A large remnant polarization (2Pr) of 17.7 μC/cm2 and small coercive field (2Ec) of 91 kV/cm was observed for the Ca0.15Sr1.85Bi4Ti5O18 (CSBT-0.15) ceramic, which indicated that this sample possessed the best ferroelectric properties. As the substitution level increased, the variation of the leakage current density first decreased and then increased, and the sample with the substitution level of 0.15 showed the smallest leakage current density of J= 1.1 × 10−6A/cm2 at ~80 kV/cm. For the investigated CaxSr2-xBi4Ti5O18 (CSBT) ceramic samples, space-charge-limited conduction (SCLC) was determined to be the main conduction mechanism.

Structural and electrical properties of the SrBi4Ti4O15: V2O5 matrix in the microwave frequency range

In this present work, material has been developed to have thermal stability over microwave range. The SrBi4Ti4O15 ceramics are perovskite material from Aurivillius family and were produced by solid state reaction method with temperatures lower than other recent works reported. X-ray diffraction patterns have confirmed single phase and afterward the sample data were refined by using Rietveld method. V2O5 was added to the pure specimen with different amounts (5, 10 and 15 wt.%) to possibly enhance electrical and dielectric properties of SrBi4Ti4O15. An impedance analyzer and a network analyzer were used to obtain electrical measurements in the range of microwave. Thermal stability measures over a microwave range were used as well as numerical simulations of dielectric resonator antenna (DRA) using the HFSS software. The obtained results have shown an efficient synthesis, and the dielectric constants indicate a real possibility of miniaturization. It was also found that the specimen for 6 wt.% of V2O5 presented temperature coefficient (τf) near zero at microwave region. The bandwidths measured from the specimens were classified as S-type with wide bandwidth and it can be applied for meteorological radars and satellite communications.

Microstructure evolution and dielectric properties of Ce-doped SrBi4Ti4O15 ceramics synthesized via glycine-nitrate process

Ce-doped strontium bismuth titanate (SrBi4Ti4O15, SBT) powders were prepared by glycine-nitrate process at 400-500?C and the ceramics were sintered at 980?C. The phase composition, morphology and electric properties were investigated. It was found that the calcined powders consist of a single phase SBT and the calcination temperature is lower than that for the conventional solid state method. The morphology of Cedoped SBT is flake-like and the layer size decreases with Ce-addition from 12 to 2?m confirming that the addition of Ce3+ inhibits grain growth. The Curie temperature of Ce-doped SBT increased for about 20?C compared to the pure SBT. The tan ? was ~0.005 at 35?C and even below 0.05 up to 400?C. The temperature coefficient of dielectric constant was ~0.012 and the rate of frequency change was 0.01-0.04, which indicated the high stability of dielectric properties of the Ce-doped SBT. Impedance analysis revealed that the conduction mechanism of the Ce-doped SrBi4Ti4O15 ceramics is mainly grain conduction.

Bright green emission and enhanced electrical properties in SrBi4-xHoxTi4O15 multifunctional ceramics

Ho3+-modified SrBi4Ti4O15 ceramics with bright green light emission and enhanced electrical properties were fabricated by a conventional solid-state reaction method. Upon visible light irradiation, samples exhibit a strong green emission located at 546 nm and a weak red emission at 653 nm. These two emissions corresponding to the intra f-f transition from the excited state 5S2 to the ground state 5I8 and the 5F5→5I8 transition of Ho3+, respectively. The relative intensity of green and red emissions is related to the Ho3+ contents closely, due to the concentration quenching effect. Moreover, it is also found that Ho3+ doping significantly enhanced the electrical properties. At x = 0.008, samples exhibit optimal electrical properties and excellent piezoelectric temperature stability for the SBT-xHo system. These results reveal that these materials have good application prospect in future optical temperature sensors by integrating its luminescent and piezoelectric properties.

Optimization of calcination and sintering temperature of Sol-gel synthesised Ba2Bi4Ti5O18, Pb2Bi4Ti5O18 and Sr2Bi4Ti5O18 ceramics

Abstract In the present work, s intering characteristics of polycrystalline A 2 Bi 4 Ti 5 O 18 (A = Ba, Pb, Sr) ceramics prepared using sol gel synthesis route has been studied. The effect of sintering temperature on the phase formation, electrical and ferroelectric properties of these five layered Aurivillius oxides is investigated. Density and grain size of the sintered pellets increases with rise in sintering temperature. Dielectric constant and remanent polarization were found to increase while the conductivity decreased with increasing sintering temperature. Mechanism of grain boundary conduction was analyzed by Nyquist plots for the samples sintered at different temperatures. Activation energy was calculated using Arrhenius plots and it was found to increase with temperature.

Grain size-dependent dielectric, piezoelectric and ferroelectric properties of Sr2Bi4Ti5O18 ceramics

Fine powders comprising nano-crystallites of Sr2Bi4Ti5O18 (SBT) were synthesized via citrate-assisted sol–gel route. Different ceramics of SBT with different grain sizes (93 nm–1.42 μm) were fabricated by varying sintering temperatures and durations. The usage of nano-crystalline powders for fabricating ceramics facilitated lower sintering temperatures. The grain growth in these powder compacts was found to be controlled by the grain boundary curvature mechanism, associated with the activation energy of 181.9 kJ/mol. Interestingly, with a decrease in grain size there was an increase in structural distortion which resulted in a shift of Curie temperature (phase transition) toward higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the spherical ferroelectric particles was invoked to explain experimentally observed size-dependent phase transition temperature, and the critical size for SBT is predicted to be 11.3 nm. Grain size-dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2Pr) = 16.4 μC cm−2, coercive field (Ec) = 38 kV cm−1, piezoelectric coefficient (d33) = 22 pC N−1 and planar electromechanical coupling coefficient (kp) = 14.8 %.

Effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 lead-free ferroelectric ceramics

The effect of CuO addition on magnetic and electrical properties of Sr2Bi4Ti5O18 (SBT) lead-free bismuth layered structure ferroelectric ceramics have been studied and reported. Interestingly, the prepared samples exhibit multiferroic behavior with the coexistence of magnetic and ferroelectric phase transition temperature. Magnetic phase transition with Neel׳s temperature (TN) of 657K is observed at 0.75mol% of CuO added SBT ceramics, which is higher than the well known multiferroic BiFeO3 (643K) and the ferroelectric phase transition with Curie temperature (TC) of 587K is observed at 1mol% of CuO added SBT ceramics, which is relatively higher than the reported pure SBT ceramics (558K). Further, the electrical properties such as dielectric, ferroelectric, piezoelectric, leakage current density characteristics and optical properties were investigated as a function of x (x=0, 0.25, 0.5, 0.75 and 1mol%). Presence of strong magnetic super-exchange interactions in CuO and the creation of oxygen vacancies play a vital role in the enhancement of magnetic and electrical properties of CuO doped SBT ceramics. Moreover, the present results indicate that, small amount (0.25mol%) of CuO addition in SBT ceramics enhances the electrical properties significantly and vice versa, large amount (0.75mol%) of CuO addition enhances the magnetic properties. Thus, the presence of magneto-electric coupling effect was observed in CuO doped Sr2Bi4Ti5O18 ferroelectric ceramics.

Effect of increasing lanthanum substitution and the sintering procedures on the properties of SrBi4Ti4O15 ceramics

Lanthanum-substituted SrBi4Ti4O15 (SBTi) ceramic, that is SrBi4−x La x Ti4O15 (SBLTi), samples were calcined by solid-state reaction and densified using the microwave sintering and conventional sintering techniques. Their structural, morphological and mechanical properties were investigated. The microwave sintered samples showed high densities like 95% of the theoretical density with short duration exposures. Compared with SBTi ceramics and other lanthanide-substituted compositions, the incorporation of La 3+ results in clear improvement in properties for SBLT (x ∼0.75) with respect to the values of hardness and Young’s modulus of the microwave sintered samples (8.8–12.5 and 160–180 GPa) are higher than that for conventional sintered (8–10 and 135–155 GPa) samples.