Polycrystalline Ba0 Research Articles

In situ electric field-dependent structural changes in (Ba,Ca)(Zr,Ti)O3 with varying grain size

The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed.

Improved relaxor ferroelectrics and energy storage performance of polycrystalline Ba0.95Sr0.05Ti2O5 ceramics modified with La dopants

Lead-free relaxor ferroelectrics are useful in energy storage applications. In particular, BaTi2O5-based dielectric materials may have great potential for such applications. In this study, polycrystalline Ba0.95Sr0.05Ti2O5-xLa (BST2-xLa) ceramics were synthesized using a standard solid-state reaction method with as-prepared nanoparticles prepared via a modified Pechini polymeric precursor method. The structural and electrical properties of the BST2-xLa ceramics were systematically investigated using a series of measurements. The phase analysis results confirm that La3+ is a donor dopant that replaced Ba2+ sites in the structure, which results in a decrease in oxygen vacancies to maintain charge neutrality. The intrinsic electronic conduction mechanism for electrical conductivity was evaluated from the fitted activation energy based on the Arrhenius equation. The relaxor ferroelectric behaviour and energy storage density and efficiency are improved by the addition of a small amount of lanthanum (<3.6 mol%) because of the charge and ionic radius mismatch in the structure. These results suggest that lanthanum can effectively optimise the relaxor ferroelectrics of BST2-xLa ceramics, which have promising potential as energy storage materials.

Lead-free BaTiO3-based relaxor ferroelectric thin film rendering rapid discharge rate for pulsed power energy application

Ferroelectric thin film capacitors have large application potential in pulsed-power electronic and electrical systems due to their high-power density and rapid discharge capabilities. Although lead-based dielectrics are promising, the pursuit of eco-friendly, lead-free alternatives is gaining research attention. Here, the Bi and Li co-doped BaTiO3 thin film exhibiting relaxor ferroelectric properties was investigated for its energy storage properties. The fabricated polycrystalline Ba0.85(Bi0.5Li0.5)0.15TiO3 thin film by pulsed laser deposition revealed good breakdown strength (∼4 MV cm−1), a slim ferroelectric loop, and low leakage characteristics suitable for energy storage applications. The film exhibits a significant value of recoverable energy density (∼70 J cm−3) with better frequency and thermal stability. Notably, the better overall performance parameters of the film, including a sizable power density (261 MW cm−3) and a fast discharge rate (150 ns), along with good energy density and breakdown strength, make the material suitable for pulsed-power energy applications.

Tunable energy bandgap of Fe-doped (Bi, Li) co-substituted barium titanate

In this work, a polycrystalline Ba0.96(½ Bi, ½ Li)0.04Ti(1-x) FexO3; (0 ≤ x ≤ 0.08) ceramics have been synthesised using a solid-state reaction method. The prepared systems were explored to detect the impact of Fe substitution on the energy bandgap of the ceramics. XRD patterns confirmed that there is a structural phase transition from tetragonal (P4 mm) to hexagonal (P63/mmc) phase as the concentration of Fe increases. Rietveld refinement was performed to obtain the lattice information. Furthermore, Raman spectroscopic analysis confirmed the structural information obtained from XRD study. The average bond length variations, strain evolutions, crystallite size, and theoretical density have been calculated from the structural analysis. It is found that the lower Fe concentration with the tetragonal phase showed a strong Jahn-Teller effect. Meanwhile, the higher concentration of Fe led to phase transition to hexagonal phase with fewer structural distortions. The optical band gap species were investigated through UV-Vis. Following the onset of defects induced by acceptor ions, an exciting band gap reduction up to 2.09 eV for the sample with x = 0.08 was attained. ESR and PL spectroscopies analyses showed that in the hexagonal phase region more defects are formed giving rise to promoting band gap narrowing. Furthermore, the ac conductivity analysis indicates the appearance of defect levels due to the formation of oxygen vacancies. This study demonstrates that the right choice of Fe content in the host material can tune the energy band gap significantly in the BLBTF system and may be exploited in photovoltaics in the visible region.

Stress-induced tailoring of energy storage properties in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ferroelectric bulk ceramics

In this study, the stress-modulated energy storage properties of lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 was investigated as a function of temperature from 25 °C to 55 °C. The externally applied uniaxial compressive stress of −160 MPa increased the recoverable energy storage density by 226% to a maximum value of 274 mJ/cm3, in addition to enhancing the energy storage efficiency by approximately 10% to a value of 88.2%. The macroscopic mechanical constitutive behavior is presented as well as the stress-dependent dielectric and ferroelectric properties and the Rayleigh behavior in order to elucidate the effect of stress on the energy storage properties. Importantly, the stress-induced tailoring of energy storage performance can be utilized for other nonlinear dielectric ceramics to tune their extrinsic polarization mechanisms to significantly enhance the recoverable energy density and reduce the hysteretic losses.

Structural analysis of Ba0.8Sr0.2Ti0.6Zr0.3Mn0.1O3 ceramics

Polycrystalline Ba0.8Sr0.2Ti0.6Zr0.3Mn0.1O3 was synthesized by solid-state reaction at 1600°C. The single phase formation of the compound without any impurities was confirmed by the X-ray diffraction technique. The prepared compound crystallized to a cubic structure with a space group of Pm-3m and the refined lattice parameters were a = b = c = 4.0253 Ǻ, α = β = γ = 90°. Rietveld refinement was carried for the powder XRD data using GSAS software and the experimental data peaks were indexed by Powder X software.

Transport and magnetic properties in polycrystalline Ba(Mn[formula omitted]Cr[formula omitted])[formula omitted]As[formula omitted] and Ba[formula omitted]K[formula omitted](Mn[formula omitted]Cr[formula omitted])[formula omitted]As[formula omitted

Here we report the structure, electrical and magnetic properties of polycrystalline Ba(Mn1−xCrx)2As2 (x=0.0-0.1) and Ba0.8K0.2(Mn1−xCrx)2As2 (x=0.0-0.4). Upon the substitution of Cr for Mn in BaMn2As2 semiconductor, it is found that the resistivity can be substantially decreased by five orders in magnitude without changing the structural symmetry. The XPS and Hall measurements demonstrate that the valence of doped Cr is +3 instead of expected Cr2＋, which can effectively introduce electron carriers. Meanwhile, a magnetic transition shows up at ∼40 K with small saturated moment of Msat=0.02 μB/Mn(Cr) and a low coercive field of Hc=135 Oe. The transition may originate from the change in spin re-orientation from ideal AFM to canted AFM state. For p-type AFM metal Ba0.8K0.2Mn2As2, doping Cr3＋ equivalently provides electrons to compensate the holes, leading to a metal–semiconductor transition and a similar canted AFM state. Our results demonstrate that majority carriers, resistivity and magnetism in BaMn2As2 can be controlled through relatively low levels of Cr3＋ doping.

Electron density contour maps via Rietveld-MEM analysis using HR-XRD for the polycrystalline ferroelectric BCZT

The maximum entropy method in combination with the Rietveld refinement method applied to the analysis (Rietveld-MEM analysis) of high-resolution x-ray diffraction (HR-XRD) is an important tool to elucidate the electron density distribution and chemical bonding nature of materials. In this work, we present the comparison of electron density distribution obtained from the Rietveld-MEM analysis for polycrystalline perovskite BaTiO3 (reference sample) and Ba0.9Ca0.2Ti0.9Zr0.1O3 (BCZT). To perform this task, HR-XRD patterns using synchrotron radiation were acquired. Tetragonal phase with P4mm (No.99) space group and pseudo-Voigt function were considered to model the HR-XRD peaks by the Rietveld method using the profile fitting Fullprof suite program. VESTA software was used to visualize 3D, 2D electron density distribution maps and line profiled to monitor the chemical bonding nature between Ba-O and Ti-O interactions and to visualize the off-center displacement of Ti cations by the incorporation of Zr and Ca cations. The interaction between Ti contours with O contours in the electron density distribution and the minimum electron density values revealed the enhancement of covalent nature and predominant ionic nature between barium and oxygen ions in the BCZT. To monitor the ferroelectric hysteresis behavior, polarization versus electric field curves complement the characterization of these samples.&#x0D;

Electronic structure and multiferroic properties of (Y, Mn)-doped barium hexaferrite compounds

We have systematically studied the crystal and electronic structures and the magnetic and electrical polarization properties of polycrystalline Ba0.95Y0.05Fe12−xMnxO19 (denoted as BaYFe12−xMnxO19) compounds with x = 0–2. The analyzes of X-ray diffraction patterns and Raman scattering spectra indicated their single phase in the M-type hexaferrite structure. With increasing x, the lattice constant a slightly increased while c decreased, which related to the Jahn-Teller effect. Though an increase of x reduced gradually magnetization in a range of 23–32 emu/g, the coercive force increased from 3.3 kOe for x = 0 to about 4 kOe for x = 0.5–2. The study of the electrical polarization properties proved the dependence of the shape of electric hysteresis loops on x and applied electric field. The samples with x = 0 and 0.5 exhibit a weak ferroelectricity with the maximum polarization of ~0.11 μC/cm2 for x = 0, and of ~0.06 μC/cm2 for x = 0.5. Meanwhile, the other samples showed nearly circular hysteresis loops, which are characteristic of conductive materials. Detailed investigations indicated an increase in leakage current when x increased. All of such phenomena are tightly related to the chemical shift of Mn2+ → Mn3+ and the replacement of Mn2+,3+ for Fe3+ in BaYFe12−xMnxO19. These oxidation states and the chemical shift of Mn have been confirmed upon analyzing X-ray absorption spectra.

Cation distribution in Ni substituted Ba0.5Sr1.5Co2Fe12O22 Y-type hexagonal ferrites

The present work reports the study of cation distribution in Ni substituted polycrystalline Ba0.5Sr1.5Co2Fe12O22 (Co2Y-BSCFO) hexaferrite samples using complimentary experimental methods viz., in-field F57e Mössbauer and Raman spectroscopy. Combining the analysis of in-field F57e Mo¨ssbauer and Raman spectroscopy measurements it is shown that the substituted Ni in Co2Y-BSCFO preferentially occupies the octahedral site with spin-down configuration i.e., 6cVI. The obtained cation distribution data is found to qualitatively match the magnetization values as obtained from bulk magnetic measurements. Temperature dependent dielectric data reveals a significant dispersion in dielectric constant associated with loss peaks and the conduction-hopping mechanism explains such behavior.

Electrical conductivity and dielectric analysis of Ba0.9Ag0.1TiO3 compound

In this research paper, our central focus is upon investigating structural and electrical properties of polycrystalline Ba0.9Ag0.1TiO3 powder which was fabricated through standard solid-state reaction technique. X-ray diffraction analysis at room temperature confirmed that the component crystallizes in both tetragonal and orthorhombic structures. The electrical response was explored by complex impedance spectroscopy in the temperature range of 540 K–620 K and frequency from 67. 5 Hz to 1 MHz. The findings demonstrated that the variation of the imaginary part of impedance (Z'') as a function of the real one (Z') at various temperatures presented semicircle arcs. An electrical similar circuit was set forward to interpret the impedance data. The results obtained from the temperature dependence of the exponent s suggest that the transport process of the charge carriers in the compound Ba0.9Ag0.1TiO3 follows the correlated barrier hopping (CBH) model.

Chemically degraded grain boundaries in fine-grain Ba0.6K0.4Fe2As2 polycrystalline bulks

In this study, we investigated nanostructure and local compositional variations at grain boundaries (GBs) in polycrystalline Ba0.6K0.4Fe2As2 (K-Ba122) bulks. Analytical scanning transmission electron microscopy revealed that K-Ba122 bulks made in a regular glove box filled with 99.9% Ar show Ba–O segregation at the GBs, forming a network of insulated GBs. By significantly reducing the oxygen and water content in the glove box, K became preferential segregation at GBs. Our nanostructural study suggests that the K-Ba122 GBs are easily compromised by different kinds of chemistry variations that can be fully addressed only by synthesis in a very clean environment.

Effect of polar nano region dynamics on pyroelectric energy conversion efficiency of doped BaTiO3

Ferroelectrics, which exhibit spontaneous ordering of electrical dipoles below a certain critical temperature, are promising candidates in the field of green – solid state – refrigeration technology due to displaying significant thermal response against application/removal of the electric field, known as electrocaloric effect. Additionally, ferroelectric materials are also capable to convert heat energy into electric energy. This converse phenomenon, generation of electricity as a result of thermal fluctuation, is known as pyroelectric effect. We synthesize polycrystalline Ba0.9Pb0.1(Ti0.9Zr0.1)O3 ferroelectric using conventional solid state method. The Rietveld refined X-ray diffraction pattern shows that the synthesized compound crystallizes into tetragonal phase with P4mm space group. The temperature dependent dielectric permittivity (ε-T) shows plateau like broad anomaly near Tm ∼ 399 K. The ε-T profile suppresses with increase in frequency and peak position remain insensitive to frequency variation. The diffusion coefficient, γ ≈ 1.3, is estimated from modified Curie-Weiss fitting of ε-T curve, which suggests that occurring ferroelectric transition is of diffused type. This diffusive characteristics and slim and unsaturated ferroelectric hysteresis loop, determined from P-E loop measurement, occurs due to the existence of polar nano – regions (PNRs). Ferroelectric materials with PNRs are highly desirable in the field of waste thermal energy conversion rather than normal ferroelectric with γ = 1. Here, we report high pyroelectric energy conversion efficiency ∼97% for Ba0.9Pb0.1(Ti0.9Zr0.1)O3. Presently, for green technological aspect, this study is quite reasonable in the field of waste thermal energy management.

Influence of Mn2+ substitution on structural, morphological, electrical, and magnetic properties of Ba0.4Ca0.4Sr0.2MnxTi1−xO3 perovskites

In this research, we have explored the structural, morphological, electrical, and magnetic properties of Mn2+ substituted polycrystalline Ba0.4Ca0.4Sr0.2MnxTi1−xO3 (where x = 0.0, 0.05, 0.10, 0.15, and 0.20) ceramic samples prepared by the standard solid-state reaction system. The x-ray diffraction pattern of the 20% Mn-doped BCSMTO sample has confirmed a cubic to tetragonal structural phase transition. The lattice parameter is found to increase at 15% and 20% Mn concentrations, which is caused due to the inequality in ionic radii of cations. Scanning electron microscope analysis exhibited that, with the increase in Mn contents (x = 0.0–0.15), the average grain size of the samples gets bigger but then significantly decreased at 20% Mn substitution. Dielectric constants for all the samples are higher for lower frequency regions and remain independent at a higher frequency domain. The initial permeability remains almost constant at lower frequencies and then sharply falls at the cut-off frequency, which is in agreement with the Globus model. Among all the studied samples, the 10% Mn-doped ceramic sample shows the highest relative quality factor with significantly demolished loss (tan δM). At room temperature, the M–H loop for the 10% Mn-doped sample demonstrates a domination of diamagnetic nature at a higher magnetic field. The decrement in saturation magnetization with Mn addition suggests that the double-exchange interactions in tetragonal BaTiO3 may have been weakened. The outcome of this analysis emphasizes the impact of Mn as a doping element with 10% concentration in Ba0.4Ca0.4Sr0.2MnxTi1−xO3 that provides enhanced structural and electrical properties, which are associated with homogeneous grain size, reduced porosity, and lower tangent loss.

Study of conduction mechanism, electrical property, and nonlinear electrical behaviors of Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 perovskite

The conduction mechanism, electric properties, and I–V behavior of the polycrystalline Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 (BBTZN) ceramic analyzed as a function of frequency and temperature. The relaxation phenomena were studied with impedance and modulus formalism, while the conductivity mechanism was investigated using electrical conductivity. The thermal evolution of the electrical conduction was adjusted by Jonscher’s Law and explained in terms of the Correlated Barrier Hopping conduction mechanism. The nonlinear current–voltage confirmed the negative temperature coefficient of resistance comportment for our compound. The electrical behavior confirmed that the relaxation processes are of non-Debye type. The study of complex impedance suggests a poly-dispersive non-Debye-type relaxation occurring in the polycrystalline (BBTZN). The dielectric response confirmed the dominance of the Maxwell–Wagner (M–W) model effect in conduction phenomenon. The value of permittivity is highly around 103, and low dielectric loss and low electrical conductivity of around 10–4 S cm−1 for BBTZN were observed. These values make this composition interesting for microelectric applications. In the thermal study, the relaxation processes observed by electrical conductivity, impedance, and modulus are associated with singly and doubly ionized oxygen vacancies for the lower and higher temperature, respectively.

Synthesis and electrical properties of lead-free piezo electrics for magnetoelectric applications

The Lead-free piezoelectric polycrystalline materials, BaTiO3 (BTO) and Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramic are prepared by sol-gel synthesis method. The synthesis dynamics and the effect of sintering temperature on the purity and the formation of morphotropic phase boundaries in these samples are investigated. X-ray Diffraction studies show the cubic phase for the BTO at low temperature, whereas it transforms into the tetragonal for high-temperature synthesis. The BCZT exists in the mixed phases of tetragonal and orthorhombic structures. Formation of MPBs in BCZT are observed for the sintering temperature above 1350 °C. Polarization (P) versus electric field (E) measurement shows enhanced polarization values for the BCZT in comparison to the BTO.

Negative Capacitance Effect in the Low-Frequency Impedance of Barium Strontium Titanate Semiconductor Ceramics

Polycrystalline (Ba0.85Sr0.15)0.999Ce0.001TiO3 samples prepared by a standard ceramic processing technique for positive temperature coefficient of resistance materials have been characterized by impedance spectroscopy. Major attention has been paid to the inductive character of the impedance in the low-frequency range of the measuring signal. In the literature, such an impedance is interpreted in terms of a negative capacitance effect. Based on analysis of the existing notions of the structure of grain boundaries in ceramics, we have proposed an equivalent circuit that models frequency dependences of the immitance in good agreement with experimental data.

Large nonlinear refraction in pulsed laser deposited BCZT thin films on quartz substrates

Optical thin films based on ferroelectric materials are forerunners for novel optoelectronic and photonic applications due to their large inherent coupling between optical and electrical properties. We report here on the thickness dependence of linear and nonlinear optical properties of polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) thin films fabricated on quartz substrates by the pulsed laser deposition technique. In order to probe the linear optical properties of BCZT thin films, we have obtained optical transmission spectra from which the optical parameters like the refractive index and extinction coefficient were deduced using the Swanepoel method. Using the Sellemier relation, we have estimated the oscillator parameters like oscillator strength and oscillator energy from the refractive index dispersion data, which are indicative of the efficiency of the electro-optic coupling process. Further, the third-order optical nonlinearity of these thin films was measured by a closed-aperture Z-scan technique with a low-power, continuous-wave He–Ne laser as the excitation source. These films exhibited high optical nonlinearity, and the nonlinear refractive index was determined to be ∼5×10−7 m2/W. The enhanced nonlinear refraction in BCZT thin films at the low power regime could be attributed to both photothermal and photorefractive origin with a plausible larger contribution from the latter. Such a large nonlinear optical response exhibited at low optical powers in BCZT thin films is very promising technologically, as it may find applications in a number of photonic devices such as optical interconnects, optical processors, optical memories, and waveguide modulators.

Enhanced Curie temperature and piezoelectric properties of (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free ceramics after the addition of LiTaO3

Polycrystalline (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3–xLiTaO3 ceramics were designed and synthesized using a solid-state reaction to improve both the Curie temperature and the electrical properties of (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free piezoelectric ceramics. The effect that the addition of LiTaO3 has on the structure and electrical properties of BCZT ceramics was studied systemically. The results show that the Curie temperature and the piezoelectric properties of BCZT can be substantially enhanced by adding LiTaO3. The Curie temperature increased from 93 °C to 102 °C after adding LT of 0.3 mol.%. X-ray diffraction and Raman spectral analysis of the ceramics reveal the coexistence of orthorhombic (O) and tetragonal (T) phases. This coexistence of O and T phases at room temperature helps improve the ferroelectric and piezoelectric properties. The ceramic with x = 0.3 mol.% exhibits the highest values for d33 = 433 pC/N, d33* = 858 pm/V (at 1 kV/mm) and kp = 44.6%. Furthermore, giant electrostrictive coefficients (Q33 ≈ 0.040–0.050 m4/C2) were also obtained for these LT-doped BCZT ceramics. These properties confirm that BCZT-xLT is a promising candidate system for lead-free piezoelectric ceramic materials.

Magnetodielectric effect in (1 − x)(Ba0.88Ca0.12)(Ti0.88Zr0.12)O3 − xCoFe2O4

Magnetodielectric (MD) materials have attracted considerable attention due to their intriguing physics and potential future applications. In this work, polycrystalline (1 − x)(Ba0.88Ca0.12)(Ti0.88Zr0.12)O3 − xCoFe2O4 (x = 0.10, 0.20, 0.30, 0.40) ceramic have been prepared via sol-gel method. The room temperature magnetic and ferroelectric behaviors of the synthesized composites were investigated. For the composite with x = 0.40, a MD ratio of 5.37% was achieved under a magnetic field of 1.5 T at f = 1 kHz. The measured “butterfly hysteresis” MD curves exhibit an obvious dielectric anomaly. Theoretical analysis suggests that the observed magnetodielectric effect is attributed to the magnetoresistance effect and magnetoelectric coupling.