BaTiO3 Matrix Research Articles

Colossal Dielectric Constant of Nanocrystalline/Amorphous Homo-Composite BaTiO3 Films Deposited via Pulsed Laser Deposition Technique.

We report the pulsed laser deposition (PLD) of nanocrystalline/amorphous homo-composite BaTiO3 (BTO) films exhibiting an unprecedented combination of a colossal dielectric constant (εr) and extremely low dielectric loss (tan δ). By varying the substrate deposition temperature (Td) over a wide range (300-800 °C), we identified Td = 550 °C as the optimal temperature for growing BTO films with an εr as high as ~3060 and a tan δ as low as 0.04 (at 20 kHz). High-resolution transmission electron microscopy revealed that the PLD-BTO films consist of BTO nanocrystals (~20-30 nm size) embedded within an otherwise amorphous BTO matrix. The impressive dielectric behavior is attributed to the combination of highly crystallized small BTO nanograins, which amplify interfacial polarization, and the surrounding amorphous matrix, which effectively isolates the nanograins from charge carrier transport. Our findings could facilitate the development of next-generation integrated dielectric devices.

A study on BaTiO3 – NiFe2O4 composite; microstructure, multiferroic and magnetodielectric properties

The lead-free x NiFe2O4 – (1-x) BaTiO3 (x = 0, 0.05, 0.1, 0.15) multiferroic composites were prepared via the solid-state sintering technique. Microstructure, multiferroic, and magnetodielectric properties of composites were investigated. According to the XRD data (from x = 5 to 15 wt%), the tetragonality factor (cT/aT) and unit cell volume of the BaTiO3 (BTO) crystal system diminished. Based on SEM images, ferromagnetic NiFe2O4 (NFO) grains are uniformly dispersed in the ferroelectric BTO matrix without additional reaction in the interfaces of two phases. The highest values of dielectric (dielectric constant (εr) ∼ 1905 and dielectric loss factor (tan δ) ∼ 0.049) and ferroelectric properties (saturation polarization (PS) ∼ 13 μC/cm2 and remnant polarization (Pr) ∼ 10 μC/cm2) are attained for x = 5 wt% due to the lowest NFO (non-ferroelectric) concentration. Also, with increasing ferrite concentration (up to 15 wt%), the ferroelectric properties of the composites show a gradual decrease. The saturation magnetization (MS) values rise due to increasing ferrite concentration (from 2 to 5 emu/g for x = 5 to 15 wt%). Moreover, coercivity (HC) drops from 150 to 110 Oe. The simultaneous observation of the ferroelectric and ferromagnetic characteristic hysteresis loops confirmed the multiferroic effect for x = 5, 10, and 15 wt%. The highest magnetodielectric constant (3 %) is obtained for x = 15 wt% multiferroic composite at the applied magnetic field of 6 kOe.

On the Lanthanide Effect on Functional Properties of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 Ceramic.

The beneficial effects of lanthanide incorporation into 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (BNT-BT) matrix on its functional properties were investigated. The conventional solid-state method was used for synthesizing samples. The structural refinement revealed that all samples crystallized in R3c rhombohedral symmetry. Raman spectroscopy study was carried out using green laser excitation and revealed that no clear perceptible variation in frequency is observed. Dielectric measurements unveiled that the introduction of rare earth obstructed the depolarization temperature promoted in BNT-BT, the diffusive phase transition decreasing with increasing lanthanide size. Only dysprosium addition showed comparable diffusion constant and dielectric behavior as the unmodified composition. Further, the comparison of the obtained ferroelectric hysteresis and strain-electric field loops revealed that only Dy-phase exhibited interesting properties comparing parent composition. In addition, the incorporation of lanthanides Ln3+ into the BNT-BT matrix led to the development of luminescence characteristics in the visible and near infrared regions, depending on the excitation wavelengths. The simultaneous occurrence of photoluminescence and ferroelectric/piezoelectric properties opens up possibilities for BNT-BT-Ln to exhibit multifunctionality in a wide range of applications.

Investigation of negative permittivity in BaTiO3/TiN metacomposites at the radio frequency region

The intriguing and unexpected properties of metacomposites have attracted significant attention, especially in terms of tuning their negative permittivity. In this study, we fabricated percolative BaTiO3/TiN (BTN) metacomposites employing mesoporous BaTiO3 nanoparticles synthesized via a novel solvothermal method as the matrix, combined with varying concentrations of TiN as the filler. Dielectric properties investigated in the frequency range of 100 Hz to 100 kHz unveiled a transition in the permittivity, shifting from positive to negative as the TiN content increased (primarily noticeable at frequencies above 10 kHz). The initial permittivity shifting is associated with an enhanced interfacial polarization, commonly recognized as Maxwell-Wagner-Sillars effect observed below the percolation threshold. Further, Lorentz model is attributed to induce dielectric resonance in the BaTiO3 matrix triggered by the Ti4+ ions in Ti–O octahedral sites leading to negative permittivity in conjunction with increase in TiN particles above the percolation threshold. Interestingly, AC conductivity exhibited an increase with increasing frequency when TiN content was lower. However, intriguingly, this frequency-dependence in the conductivity of BTN metacomposites did not hold as TiN content increased. Moreover, the investigation of reactance revealed the inductive character derived from the conductive network, a conclusion further confirmed through equivalent circuit analysis. The findings presented in this study are poised to unlock new possibilities in the design and development of metacomposites, ultimately facilitating practical applications of epsilon-negative materials in electromagnetic devices.

Driving magnetic oscillation by electric flip in Permalloy/BaTiO3 composite

In this work, the Permalloy/BaTiO3 composite with granule/matrix structure is designed. The theoretical calculation reveals coupling between electric polarization and magnetic anisotropy. As electric polarization is downward and upward in BaTiO3 matrix, the magnetizing orientation tends to be parallel and perpendicular in Permalloy granule respectively. The Landau-Lifshitz-Gilberts model further predicts magnetic oscillation driven by electric flip. Explicitly, as electric polarization flips with low frequency in BaTiO3 matrix, the magnetic moment oscillates with high frequency in Permalloy granule. It results from the anisotropy field altered periodically by polarization flip. Based on the magnetic tunneling model, the moment oscillation can output periodical voltage signal. With the Square-Root circuit, the oscillating amplitude of output voltage becomes stable. Through 4-level connection of this design, the 1.0 MHz input can drive 3.5 GHz output. This work gives a novel strategy for spin torque nano-oscillator. Compared to the spin-transfer torque method, this avenue could avoid the heat influence of current.

Construction of sandwich‐layered polyimide hybrid films containing double core–shell structured fillers for high energy storage density

AbstractThe inherent low dielectric constant of polyimide (PI) dielectrics restricts their applications to become a component of high energy density film capacitors. In this work, double core–shell structured barium titanate@magnesium oxide@polydopamine (BaTiO3@MgO@PDA) nanoparticles were synthesized successfully and utilized as high dielectric constant functional fillers for PIs, in which the insulating MgO layer meliorated dielectric constant difference between BaTiO3 and PI matrix, and the organic PDA layer improved the compatibility between the inorganic fillers and PI matrices. Then, a series of sandwich‐structured PI‐based hybrid films was prepared through a layer‐by‐layer solution casting method. The middle layer of pure PI with excellent insulating properties effectively suppressed charge injection. With the combination of sandwich structure and the BaTiO3@MgO@PDA nanoparticles, the PI hybrid film containing 15 wt% fillers in the outer layers achieved the maximum breakdown strength of 425.68 kV/mm and the maximum energy density of 5.132 J/cm3, which was 68.3% and 413% higher than those of pure PI film, respectively, meanwhile maintained a low dielectric loss value of 0.0083 at 1 kHz. The introduction of BaTiO3@MgO@PDA enhanced the interfacial polarization due to the high barrier energy between adjacent layers preventing the transfer of electrons and weakening the leakage current in the sandwich‐structured composite film. This work demonstrates that an appropriate combination of high dielectric hybrid fillers and multilayer structure can effectively increase the energy storage density of PI substrate for high‐temperature energy storage applications.Highlights The double core–shell structured BaTiO3@MgO@PDA was synthesized successfully. The sandwich‐structured hybrid films were prepared by layer‐by‐layer method. The energy density of hybrid films reached a high value of 5.132 J/cm3.

Microstructural and physical characterizations of (1-x)(0.67BiFeO3+ 0.33BaTiO3+ 1%MnO2)− x(CoFe2O4+ 3%ZnO) magnetoelectric composites

BiFeO3 (BFO) was mixed with BaTiO3 (BTO) to form a solid solution of large piezoelectric coefficient (d33) for the fabrication of magnetoelectric (ME) composites with the Zn-doped CoFeO4 (CFO). The 0.67BFO+0.33BTO solid solution, which was doped with 1 at% MnO2 for lowering leakage current, showed a high d33 of 121 pC/N. However, in the composites made with CFO, a much lower d33 (<42 pC/N) was retained. The microstructure of the composites was featured by the large CFO grains (∼5 μm) embedded in the 0.67BFO+0.33BTO matrix of much finer grains (∼0.5 μm). The CFO grains each had a well-defined morphology with clear boundary discriminating them from the neighboring piezoelectric phase. Both the CFO and piezoelectric grains showed a high crystallinity as indicated by the appearance of clear Kikuchi patterns in electron backscattered diffraction. After reducing DC conductivity of CFO by Zn-doping and the optimization of fractional ratio of the Zn-doped CFO in the composites, a ME voltage coefficient of 81.8 mV/cm-Oe was achieved, which was high among the lead-free particulate ME composites prepared by the conventional solid-state sintering.

Self-Assembled Au Nanoelectrodes: Enabling Low-Threshold-Voltage HfO2-Based Artificial Neurons.

Filamentary-type resistive switching devices, such as conductive bridge random-access memory and valence change memory, have diverse applications in memory and neuromorphic computing. However, the randomness in filament formation poses challenges to device reliability and uniformity. To overcome this issue, various defect engineering methods have been explored, including doping, metal nanoparticle embedding, and extended defect utilization. In this study, we present a simple and effective approach using self-assembled uniform Au nanoelectrodes to controll filament formation in HfO2 resistive switching devices. By concentrating the electric field near the Au nanoelectrodes within the BaTiO3 matrix, we significantly enhanced the device stability and reduced the threshold voltage by up to 45% in HfO2-based artificial neurons compared to the control devices. The threshold voltage reduction is attributed to the uniformly distributed Au nanoelectrodes in the insulating matrix, as confirmed by COMSOL simulation. Our findings highlight the potential of nanostructure design for precise control of filamentary-type resistive switching devices.

Controlled Growth of Vertically Aligned Nanocomposites through a Au Seeding-Assisted Method.

Heteroepitaxial metal-oxide vertically aligned nanocomposites (VAN) have piqued significant interest due to their remarkable vertical interfacial coupling effects, strong structural and property anisotropy, and potential applications in magnetoelectrics, photocatalysts, and optical metamaterials. VANs present a unique pillar-in-matrix structure with uniform but rather random pillar distributions. Achieving a well-controlled pillar growth remains a major challenge in this field. Here, we use BaTiO3 (BTO)-Au as a model VAN system to demonstrate the effects of Au seedings on achieving such pillar-growth control with enhanced ordering and morphology tuning. The Au seedings are introduced using an anodic aluminum oxide (AAO) template through pulsed laser deposition (PLD). TEM characterization reveals that the Au seedings result in straighter and more evenly distributed Au pillars in the BTO matrix compared to those without seeding, with the diameter of the Au seedings increasing with the number of pulses. Additionally, spectroscopic ellipsometry demonstrates distinct permittivity dispersion for all samples. This demonstration lays a foundation for future controlled and selective growth of VAN systems for on-chip integration.

Simultaneously realizing ultrahigh energy storage density and efficiency in BaTiO3-based dielectric ceramics by creating highly dynamic polar nanoregions and intrinsic conduction

Nowadays, it is urgent to explore advanced and eco-friendly energy storage capacitors based on lead-free relaxor ferroelectric (RFE) ceramics in order to meet the ever-increasing requirements in pulsed power systems. BaTiO3 (BT)-based RFE ceramics are considered as ones of the best high-temperature energy storage materials due to their good thermal stability. However, relatively low recoverable energy storage density (Wrec<5 J/cm3) has been a key bottleneck restricting the practical applications of them. Here, a novel strategy is proposed to create highly dynamic PNRs and the intrinsic conduction by introducing Bi(M1-0.015xTa0.015x)O3+0.015x (BMO-Ta, M=Mg2/3Ta1/3) to BT matrix. As a consequence, the designed (1-x)BT-x(BMO-Ta) ceramics exhibit dramatically enhanced energy storage properties including ultrahigh Wrec and efficiency (η), because of the coexistence of very slim polarization hysteresis (P-E) loops, large polarization difference (ΔP) and giant dielectric breakdown electric strength (Eb). Wrec and η of the x=0.25 ceramic reach up to 9.03 J/cm3 and 95.2% under 720 kV/cm, respectively. Furthermore, it shows excellent temperature/frequency/cycling stability over a wide range of 20−200 °C, 1−500 Hz and 1−3.3 × 105 cycles, respectively (the variations of Wrec and η are < 3% and < 4%, respectively). The findings in this paper not only indicate excellent comprehensive properties achieved in the novel (1-x)BT-x(BMO-Ta) system, but also provide an effective approach to explore advanced energy storage capacitors in other lead-free ceramic systems.

Perovskite/metal (Bi0.5Na0.5TiO3-BaTiO3/Ag) lead-free composite ceramics featuring enhanced depolarization temperature

The thermal stability of Bi0.5Na0.5TiO3-based piezoelectrics is one of the most critical metrics for practical applications. Finite element method (FEM) calculations estimate that incorporating Ag into the perovskite 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 (BNT-6BT) matrix will generate increased tensile stress during the cooling process from sintering temperatures due to the large mismatch in the thermal expansion coefficient. Thus, we propose a strategy to improve the depolarization temperature (Td) by introducing Ag into the representative BNT-6BT and forming perovskite/metal (BNT-6BT/100xAg) composite ceramics. Td of the composite with x = 0.06 is improved to 145 °C without the degradation of piezoelectric response, which is approximately 45 °C higher than the prototype BNT-6BT. Comparative experiments demonstrate that the increase in Td stems from the synergistic effect of residual thermal stress, colossal grain size (above 200 μm), and oxygen vacancies. The present study provides an effective method to improve the thermal stability of BNT-based ceramics and can be also extended to other systems.

Achieving excellent energy storage performances and eminent charging-discharging capability in donor (1-x)BT-x(BZN-Nb) relaxor ferroelectric ceramics

Prodigious efforts have been paid to explore excellent dielectric energy storage capacitors based on lead-free relaxor ferroelectric (RFE) ceramics in the last decades. However, there are rare candidates among them simultaneously possessing high energy storage density (Wrec), high efficiency (η), wide work temperature range and stable charge–discharge ability, etc. In this work, excellent energy storage performances are achieved in donor doped BaTiO3 (BT)-based RFE ceramics by adopting two effective strategies of domain engineering and defect engineering. By introducing Bi(Zn2/3-0.01xNb1/3+0.01x)O3+δ (BZN-Nb) into BT matrix, firstly, long-range ferroelectric polarization is broken to form polar nanoregions (PNRs) via domain engineering. Subsequently, Nb donor substitution results in a dramatic increase in bulk resistivity (ρb) accompanied by a significant increase in dielectric breakdown electric strength (EDBS) via defect engineering. Finally, a combination of relative high Pmax, much low Pr and giant EDBS ensures that the optimum composition x = 0.3 in (1-x)BT-x(BZN-Nb) system exhibits high Wrec of 5.96 J/cm3 and high η of 89.5 %. Such properties together with good thermal stability (up to 220 °C), good fatigue endurance (for 106 cycles) and eminent charging-discharging capability (e.g., discharge time t0.9 ∼ 50 ns, current density CD ∼ 1.17 kA/cm2 and power density PD ∼ 175.38 MW/cm3 at 300 kV/cm) suggest that the 0.7BT-0.3(BZN-Nb) ceramic is a very promising candidate among lead-free dielectric capacitors for energy storage applications.

A novel approach to fabricate load-bearing Ti6Al4V-Barium titanate piezoelectric bone scaffolds by coupling electron beam melting and field-assisted sintering

A critical-size bone defect in load-bearing areas is a challenging clinical problem in orthopaedic surgery. Titanium alloy (Ti6Al4V) scaffolds have advantages because of their biomechanical stability but lack electrical activity, which hinders their further use. This work is focused on the fabrication of Ti6Al4V-Barium Titanate (BaTiO3) bulk composite scaffolds to combine the biomechanical stability of Ti6Al4V with electrical activity through BaTiO3. For the first time, a hollow cylindrical Ti6Al4V is additively manufactured by electron beam melting and combined with piezoelectric BaTiO3 powder for joint processing in field-assisted sintering. Scanning electron microscope images on the interface of the Ti6Al4V-BaTiO3 composite scaffold showed that after sintering, the Ti6Al4V lattice structure bounded with BaTiO3 matrix without its major deformation. The Ti6Al4V-BaTiO3 scaffold had average piezoelectric constants of (0.63 ± 0.12) pC/N directly after sintering due to partial dipole alignment of the BaTiO3 tetragonal phase, which increased to (4.92 ± 0.75) pC/N after a successful corona poling. Moreover, the nanoindentation values of Ti6Al4V exhibited an average hardness and Young’s modulus of (5.9 ± 0.9) GPa and (130 ± 14) GPa, and BaTiO3 showed (4.0 ± 0.6) GPa and (106 ± 10) GPa, respectively. It reveals that the Ti6Al4V is the harder and stiffer part in the Ti6Al4V-BaTiO3 composite scaffold. Such a scaffold has the potential to treat critical-size bone defects in load-bearing areas and guide tissue regeneration by physical stimulation.

Single-Step Fabrication of Au-Fe-BaTiO3 Nanocomposite Thin Films Embedded with Non-Equilibrium Au-Fe Alloyed Nanostructures.

Nanocomposite thin film materials present great opportunities in coupling materials and functionalities in unique nanostructures including nanoparticles-in-matrix, vertically aligned nanocomposites (VANs), and nanolayers. Interestingly the nanocomposites processed through a non-equilibrium processing method, e.g., pulsed laser deposition (PLD), often possess unique metastable phases and microstructures that could not achieve using equilibrium techniques, and thus lead to novel physical properties. In this work, a unique three-phase system composed of BaTiO3 (BTO), with two immiscible metals, Au and Fe, is demonstrated. By adjusting the deposition laser frequency from 2 Hz to 10 Hz, the phase and morphology of Au and Fe nanoparticles in BTO matrix vary from separated Au and Fe nanoparticles to well-mixed Au-Fe alloy pillars. This is attributed to the non-equilibrium process of PLD and the limited diffusion under high laser frequency (e.g., 10 Hz). The magnetic and optical properties are effectively tuned based on the morphology variation. This work demonstrates the stabilization of non-equilibrium alloy structures in the VAN form and allows for the exploration of new non-equilibrium materials systems and their properties that could not be easily achieved through traditional equilibrium methods.

Enhancing the dielectric properties of poly (arylene ether nitrile) by introducing co-modified BaTiO3

In this study, a facile co-modification of dopamine (DA) and methylphenyldimethoxysilane (MPDS) was utilized to functionalize barium titanate (BaTiO3) nanoparticles with organic functional film. With the organic film coated on surface of BaTiO3, the compatibility between BaTiO3 and PEN matrix was greatly enhanced, which led to the promotion in thermal and dielectric properties. Results indicated that the glass transition temperature (Tg) of BaTiO3@(MPDS+PDA)/PEN composite showed increment from 171.9°C to 181.2°C. Besides, the dielectric constant of PEN composite containing 20 wt.% of BaTiO3@(MPDS+PDA) improved to 9.32 with a relative low dielectric loss compared to BaTiO3/PEN under the same additive ratio.

Microstructure and magnetoresistance driven magnetocapacitance in ex-situ combustion derived BaTiO3-CoFe2O4 bulk magnetodielectric composites

Enhanced magnetodielectric properties including magnetocapacitance have been observed in the BaTiO3-CoFe2O4 composites due to the microstructural interactions between the dielectric and magnetic phases. Based on this concept, this research work explores the frequency and field dependent magnetocapacitance and magnetoresistance of 70 wt% BaTiO3 – 30 wt% CoFe2O4 composites. Ex-situ synthesis method is adopted to form a partial 0–3 microstructure and this composite is sintered at 900 °C and 1000 °C. Phases such as pseudo-cubic BaTiO3 and cubic CoFe2O4 have been observed in both composites. Secondary phase of barium hexaferrite is observed at 1000 °C. Based on FESEM, CoFe2O4 phase is found to be embedded in the BaTiO3 matrix at 900 °C, however interconnected CoFe2O4 along with partially shrunk BaTiO3 has been observed at 1000 °C. The permittivity of composite is found to be ∼ 317 and ∼ 451 at 900 °C and 1000 °C, respectively, and the Maxwell-Wagner polarization is tuned by the microstructure. The effect of space charge is found to be relatively larger at 1000 °C. Magnetic nature is altered due to the connectivity of ferrite phases. Magnetocapacitance values are mostly analogues to the magnetoresistance behavior in both composites. The percentage of magnetocapacitance is found to be increased nearly 5 times due to the microstructural variations. Field and frequency-dependent magnetocapacitance responses along with Cole-Cole plots of composite confirmed the role of microstructural interactions and magnetoresistance.

Investigation of the structural, optical and dielectric properties of La-doped BaTi0.97Y0.03O3 ceramic

A series of Lanthanum (La)-doped BaTi0.97Y0.03O3 ceramics were successfully prepared using the sol gel process and their structural, microstructural, optical and dielectric properties investigated. The X-ray diffraction (XRD) patterns of all the as-prepared samples showed a tetragonal phase without the presence of any secondary phase which was also confirmed by Rietveld refinement. Raman spectroscopy analysis revealed the appearance of the A1g mode, which can be considered as the signature of the co-doping with La at the Ba-sites and Y at the Ti-sites in the BaTiO3 matrix. Scanning electron microscopy (SEM) analysis revealed a decrease in grain size with the incorporation of La into the BaTi0.97Y0.03O3 matrix. Ultraviolet–Visible (UV–Vis) spectroscopy results showed that La did not significantly influence the band gap energy of the BaTi0.97Y0.03O3 matrix and therefore it preserved its insulating character in contrast to other dopants (Iron, Samarium) as reported in the literature. Dielectric measurements showed that doping with La lowered both the temperature value of the maximum of the permittivity (Tm = 44 °C for x = 5% at 10 kHz) and of the dielectric losses (tan δ < 0.02 for x = 3% at 10 kHz). Moreover, a weak positive temperature coefficient of resistivity (PTCR) effect was observed on the Lanthanum doped samples for the two compositions x = 1% and 3%.

Synchrotron based x-ray absorption spectroscopy investigation and temperature dependent ferroelectric properties of Ni doped BaTiO3 nanostructures

In this report, the local structure geometry of BaTi1-xNixO3 (0.0 ≤ x ≤ 0.06) ceramics has been studied through synchrotron based x-ray-absorption spectroscopy, measured at the Ti K, Ba L3 and Ni K-edges at room temperature. The x-ray absorption near edge spectroscopy (XANES) at Ti K-edge confirms the TiO6 octahedron geometry of Ti atom due hybridization between Ti(3d)-O(2p) orbitals and signifies the non-centrosymmetric nature of BaTiO3 samples. However, Ti–O off-center displacement (non-centrosymmetric) is disturbed under the effect of Ni doping as a result of oxygen vacancies formation. More interestingly, XANES studies at Ni K-edge ensure successful substitution of Ni in BaTiO3 as Ni2+ ions. Extended x-ray absorption fine structure (EXAFS) data at Ni K-edge have been fitted to estimate pertinent local structural parameters of the Ni–O, Ni–Ba, Ni–Ti and Ni–Ni shells (viz. bond lengths and disorder parameters) and it also reveal that the structural disorders around the Ti sites in the doped BaTiO3 expand with Ni doping. The mixed-valence states of titanium ion, i.e., Ti4+ and Ti3+ in the doped samples were established with the x-ray photoelectron spectroscopy (XPS). Moreover, XPS divulges the creation of oxygen vacancies due to Ni doping in BaTiO3 matrix. The complementary information about the lattice vibration is analyzed through Raman studies that approve the softening of the transverse optical (TO) mode present at 515 cm−1. The temperature dependent ferroelectric studies affirm that the ferroelectricity vanishes in the doped samples due to the decrement in the off-center displacement between the Ti4+ and O2− ions in the TiO6 octahedral geometry. Differential thermal analysis (DTA) exhibits a ferroelectric tetragonal to para-electric cubic phase transition in the pristine as well as Ni doped BaTiO3 samples.

Effect of Sm2O3 addition on the dielectric behaviour of BaTiO3

BaTiO3 is a widely used ferroelectric ceramic having applications in transducers, capacitors, thermistors, non linear optics etc. BaTiO3 exhibits Curie temperature (Tc) of 120 °C. Recent research in BaTiO3 based thin films has resulted in a significant rise in their Tc. The most prominent increase in Tc has been reported in BaTiO3 – Sm2O3 system in which Sm2O3 nanorods were incorporated in BaTiO3 matrix resulting in the Tc ∼ 800 °C. Such a remarkable increase in the Tc was attributed to the high elastic modulus of Sm2O3 (E = 125 GPa) w.r.t. that of BaTiO3 (E = 67 GPa). Higher elastic modulus of the second phase resulted in the generation of strain in the matrix thereby delaying the onset of tetragonal – cubic transition. The improvement in the Tc of BaTiO3 thus opened possibilities of use of BaTiO3 based systems for high temperature piezoelectric applications. Since BaTiO3 based thin films exhibited a remarkable increase in the Tc, it needed to be studied if such a phenomenon could be replicated in bulk ceramics. Hence, BaTiO3 – Sm2O3 ceramics were prepared by the conventional ceramics processing route. Submicron-sized BaTiO3 and Sm2O3 powders were used as starting materials and compositions with Sm2O3 content varying between 5 and 30 wt% were prepared. BaTiO3 and Sm2O3 powders were milled using a jar mill for 48 h in ethanol followed by drying of slurries and room temperature uniaxial pellet pressing. Green pellets were sintered by pressureless sintering at 1350 °C for 4 h. X-ray diffraction (XRD) analysis of BaTiO3 and BaTiO3 – 5 wt% Sm2O3 ceramics confirmed the presence of tetragonal phase. However, further increase in Sm2O3 content resulted in the transformation of tetragonal BaTiO3 to cubic BaTiO3. Since cubic phase is centrosymmetric and cannot exhibit ferroelectricity, compositions with Sm2O3 > 5 wt% became redundant for any ferroelectric application. Moreover, BaTiO3 – 5 wt% Sm2O3 exhibited Tc of just 100 °C with lower dielectric constant thereby making this composition ineffective for high temperature piezoelectric application. While it had been anticipated that incorporation of Sm2O3 in bulk BaTiO3 ceramics would increase their Tc as in thin films, none of these compositions exhibited the anticipated behaviour. This paper discusses why BaTiO3 – Sm2O3 bulk ceramics failed to exhibit similar dielectric behaviour to their thin film counterparts in light of the phase formation, microstructure and dielectric behaviour.

Highly Flexible Freestanding BaTiO3 -CoFe2 O4 Heteroepitaxial Nanostructure Self-Assembled with Room-Temperature Multiferroicity.

Multiferroics with simultaneous electric and magnetic orderings are highly desirable for sensing, actuation, data storage, and bio-inspired systems, yet developing flexible materials with robust multiferroic properties at room temperature is a long-term challenge. Utilizing water-soluble Sr3 Al2 O6 as a sacrificial layer, the authors have successfully self-assembled a freestanding BaTiO3 -CoFe2 O4 heteroepitaxial nanostructure via pulse laser deposition, and confirmed its epitaxial growth in both out-of-plane and in-plane directions, with highly ordered CoFe2 O4 nanopillars embedded in a single crystalline BaTiO3 matrix free of substrate constraint. The freestanding nanostructure enjoys super flexibility and mechanical integrity, not only capable of spontaneously curving into a roll, but can also be bent with a radius as small as 4.23µm. Moreover, piezoelectricity and ferromagnetism are demonstrated at both microscopic and macroscopic scales, confirming its robust multiferroicity at room temperature. This work establishes an effective route for flexible multiferroic materials, which have the potential for various practical applications.