Rhombohedral R3c Research Articles

Elucidating the Mn-Doping Induced Phase Transition from Orthorhombic Pnma to Rhombohedral R3c in LaFeO3: Insights from Mössbauer Spectroscopy

LaFe1-xMnxO3 (0≤x≤0.9) samples were synthesized through the sol-gel method. According to X-ray diffraction (XRD) results, with the increase of Mn doping, the crystal structure of the sample changes from orthogonal Pnma structure to rhombohedral R3c structure, and a two-phase coexistence phenomenon exists within the range of 0.4≤x≤0.7. Using Mössbauer spectroscopy, the coexistence range of the two phases and the iron content in each phase were identified. At x=0.4, the Pnma phase contribution (91.1%) dominates, with only a slight R3c phase contribution (8.9%). As the amount of Mn doping gradually increases, the R3c phase becomes dominant at x=0.6 (74.6%), and the Pnma phase completely disappears at x=0.8. This work will provide an important perspective for future researchers studying similar phase coexistence systems.

Effect of excess Bi2O3/PbO on the structural and electrical properties of ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 ceramics

The ternary 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3:x(Bi2O3/PbO) [x = 0, 1, and 2 wt%] ceramics were synthesized via solid-state sintering technique. The impact of excess addition on structural and electrical properties was investigated. PXRD results confirmed the diffusion of excess addition in the 0.39Bi(Ni1/2Ti1/2)O3–0.20PbZrO3–0.41PbTiO3 (BNPZT) lattice, exhibiting the perovskite structure with major rhombohedral (R3c) and minor tetragonal (P4mm) phases. The microstructure of the samples exhibits average grain size distribution (<8 μm). The temperature and frequency-dependent dielectric measurement revealed the relaxor-like ferroelectric behaviour and curie temperature (Tc∼290 °C) observed in BNPZT:1 Pb ceramics. The improved remnant polarization (Pr∼23.47 μC/cm2) and coercive field (Ec∼16.13 kV/cm) were obtained in BNPZT:2 Pb ceramics. The enhanced piezoelectric charge coefficient (d33∼ 496 pC/N) and maximum strain (Smax∼0.12 %) were obtained for BNPZT. The least asymmetric factor (γs) illustrates the lower concentration of inherent defects in BNPZT:1(Bi/Pb) ceramics. This study provides insight into microstructural and electrical properties tuning and paves the way for designing piezoelectric materials.

Large electrostrictive response via tailoring ergodic relaxor state in Bi1/2Na1/2TiO3-based ceramics with Bi(Mn1/2Ce1/2)O3 end-member

Lead-free Bi1/2Na1/2TiO3 (BNT)-based relaxor ferroelectric ceramics with superior electrostrictive coefficient features have recently gained a lot of attention due to their application in high-precision displacement actuators. In this work, we propose an effective approach to enhance the electrostrictive effect via tuning the phase transition temperature around ambient temperature in BNT-based ceramics. Herein, a novel Bi(Mn1/2Ce1/2)O3 (BMnCe) modifier was adopted as an activator into 0.935Bi1/2Na1/2TiO3-0.065BaTiO3 (0.935BNT-0.065BT) for modifying the phase boundary (TF-R) around the ambient temperature. The compositional and temperature-dependent dielectric, ferroelectric, and electrostrain were systematically investigated. All samples exhibit a pure perovskite structure. Rietveld refinement revealed that the 0.935BNT-0.065BT ceramic presents a coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases. As the BMnCe content increases, the tetragonal (P4bm) phase becomes more prevalent and eventually shifts into a pseudocubic phase. It was found that the addition of BMnCe can effectively tune the TF-R below ambient temperature and enhance the relaxor behavior. The polarization and electrostrain analysis revealed that the ferroelectric long-range order decreases with increasing BMnCe; specifically, a unique region emerges where remnant polarization, quasistatic d33, and negative strain abruptly drop. As a result, a high electrostrain (S) of 0.43 % with a normalized strain (Smax/Emax) of 716 pm/V was achieved at the critical composition (0.01 M concentration of BMnCe). More importantly, (0.935-x)BNT-0.065BT-xBMnCe (x = 0.01) shows a large electrostrictive coefficient (Q33) of 0.032 m4/C2 with a giant normalized electrostrictive coefficient (Q33/E) of 5.33ｘ10−9 m5/C2V at room temperature. Furthermore, the Q33 and Q33/E values show temperature insensitivity up to 120 °C, rendering the compound suitable for actuation-based devices. These results offer an effective avenue for designing high-performance BNT-based materials with giant electrostrictive coefficients.

Structural analysis, ferroic properties with enhanced magnetoelectric coupling in novel (1-x)BiFeO3-(x)GdFeO3 nanocomposites

Multiferroic composites exhibit substantially greater magnetoelectric interaction among order variables as compared to single-phase multiferroics, making them particularly attractive for futuristic multi-state RAM and spintronic gadgets. The multiferroic nanocomposites (1-x)BiFeO3-xGdFeO3 (x = 0.05, 0.10, 0.15, & 0.20) are synthesized by using solid-state route. The crystallographic and profile parameters are extracted from the dual-phase refinement of the rhombohedral (R3c) and orthorhombic (Pbnm) crystal structures. The optimized density, crystallite size and homogenous microstructure may be responsible for the improved dielectric and ferroic properties. TEM images reveal a reduction in the particle size (67–59 nm) upon GdFeO3 (GFO) loading. The HRTEM images unravel the interplanar spacing and associated Bragg planes, while the SAED rings validate the polycrystalline features of the samples. The high Curie temperature (Tc ̴ 643 °C) with enhanced specific heat (Cp ̴ 29.5 J/g°C) in x= 0.10 sample ensures its stable operation, efficient heat dissipation, minimal overheating, and greater thermal stability for reliable performance in demanding conditions. The surface and finite-size effects enhanced the magnetization (MS=1.04emu/g) in nanostructured ferromagnetic nanocomposite, making it a promising candidate for high-density magnetic storage devices and sensors. The high polarization (Pmax=8.39µC/cm2) and ME-coupling coefficient (αE=0.16mVcm−1Oe−1) observed in the most dense nanocomposite make it a potential candidate for magnetoelectric applications.

Significantly enhancing piezoelectric temperature stability of BNT-based ceramics by constructing the successive ferroelectric-relaxor phase transition

Bi0.5Na0.5TiO3 (BNT)-based piezoceramics with the morphotropic phase boundary MPB are confronted with some critical challenges for practical applications, such as the low depolarization temperature Td, the poor thermal shock resistance and the high fluctuation of the real-time piezoelectric coefficient d33. Herein, an ingenious strategy that integrating quenching process and successive ferroelectric-relaxor phase transition is proposed to enhance piezoelectric temperature stability of BNT-based ceramics. The multilayer ceramic composites (0.93Bi0.5Na0.5TiO3-0.07BaTiO3/0.89Bi0.5Na0.5TiO3-0.11BaTiO3/0.85Bi0.5Na0.5TiO3-0.15BaTiO3-0.2 g/0.25 g/0.15 g-Q, abbreviated as BNT-7/11/15BT-0.2 g/0.25 g/0.15 g-Q, the Q refer the quenching process and the 0.2 g/0.25 g/0.15 g refers the mass of each layer) feature the relatively large d33 (130pC/N) and near the Curie point Td (244℃), which jumps out of the d33-Td trade-off boundary of BNT-based ceramics. Besides, the BNT-7/11/15BT-0.2 g/0.25 g/0.15 g-Q ceramic composite also shows the superior thermal shock resistance and decent temperature stability of real-time d33 over the temperature region from 25℃ to 235℃. Enhanced piezoelectric temperature stability should be attributed to the development of tetragonal P4mm and P4bm phase gradients caused by the successive ferroelectric-relaxor phase transition and the development of bamboo-shaped domain based on Ba2+ diffusion layer. In addition, the relatively large d33 stems from the coexistence of rhombohedral R3c phase and tetragonal P4bm and P4mm phases and the formation of lamellar domain. Therefore, this strategy provides a good design methodology for the practical application of BNT-based materials.

High Energy Storage and Excellent Thermal Stability in Ternary (1−x)[0.94(Bi0.5Na0.5)TiO3‐0.06BaTiO3]‐xCa(Mg1/3Nb2/3)O3 Lead‐Free Ferroelectric Ceramics

AbstractIn this work, a new type of ternary lead‐free ferroelectric ceramics (1−x)[0.94(Bi0.5Na0.5)TiO3‐0.06BaTiO3]‐xCa(Mg1/3Nb2/3)O3 is synthesized by traditional solid‐state reaction method (x = 0.02, 0.04, 0.06, 0.07, 0.08, 0.10, and 0.15). No phase transition is detected and all ceramics exhibited the perovskite structure consisting of the rhombohedral (R3c) and tetragonal (P4bm) phases. By increasing the Ca(Mg1/3Nb2/3)O3(CMN) content, the average grain size shows a slight change. More specifically, the grain size is 1.00 µm when x &lt; 0.10 and then increases to 1.20 µm in x = 0.10 and 0.15. When x = 0.07, an optimum energy storage performance with recoverable energy density (Wrec) of 4.13 J cm−3 is achieved under an electric field of 340 kV cm−1. At the same time, it exhibits excellent pulse performance at 25 °C, with an effective discharging time (t0.9) of 3.2 ns and a discharge energy density (WD) of 0.61 J cm−3, suggesting a fast charging–discharging rate. In addition, the current density (CD) and power density (PD) are 92.31 A cm−2 and 6.46 MW cm−3, respectively. Overall, the 0.93[0.94(Bi0.5Na0.5)TiO3‐0.06BaTiO3]‐0.07Ca(Mg1/3Nb2/3)O3 ceramics is considered a competitive candidate for the development of high‐energy storage capacitors and pulse‐power devices.

Quenching-driven advancements in functional properties of high-temperature lead-free Sc, Ga modified 0.67BiFeO3-0.33BaTiO3 relaxor ceramics

The processing method is one of the most important deciding factors in the fabrication of BiFeO3–BaTiO3 (BF-BT) based piezoceramics because of the Bi2O3 volatization. It significantly influences the functional properties, including the piezoelectric coefficients, dielectric properties, and microstructure. This study presents a significant advancement in the realm of high-temperature lead-free piezoelectric ceramics in terms of understanding effects of processing method on functional properties. In this light, a novel ceramic solid-solution, 0.67{Bi(Fe0.97Ga0.03)1-xScxO3}-0.33(BaTiO3) with x ≤ 0.07, incorporating Scandium (Sc) and Gallium (Ga) modifications, was meticulously designed and synthesized. Impact of two distinct sintering methods, namely air quenching (AQ) and closed sintering (CS) on the structure and properties of the developed materials are investigated. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analysis verified the formation of pure perovskite phases with successful incorporation of Sc and Ga into the 0.67BF-0.33BT lattice. The FTIR analysis revealed a sharp absorptive band in the 590-604 cm−1 range, corresponding to the signature of stretching and bending vibrations of (Ti/Fe)O6 octahedra. Rietveld structure refinement confirmed the coexistence of pseudocubic (Pm-3m) and rhombohedral (R3c) phases in AQ samples, with predominantly pseudocubic phase, while CS samples closely approximated the pseudocubic phase. The microstructure of the samples exhibits small average grain size distribution (<2 μm). Temperature-dependent dielectric measurements show strong frequency dispersion in the dielectric permittivity with broadened transition peaks. The ferroelectric studies reveal low Pr and Ec values. These observations suggest a ferroelectric relaxor-like behavior of the developed materials. Moreover, the permittivity peaks maxima (Tm) temperature corresponding to CS samples for 0.04<x < 0.07 is less than 390 °C at 10 Hz while it is above 400 °C for AQ samples. The results of our study reveal that AQ samples exhibit superior electrical and ferroelectric properties as compared to the CS samples. The AQ samples demonstrate improvements in Tm (>400 °C), d33(∼35 pC/N), Pr (∼4–11 μC/cm2), PS (∼8–21 μC/cm2), Ec (∼13–25 kV/cm) with reduced dielectric loss, and a better dielectric constant over a wide temperature range.

Influence of A‐Site Doping on the Local Structure and Magnetic Behavior of BiFeO3 Nanoparticles Investigated by X‐Ray Absorption Fine Structure Spectroscopy

Structural transformation and magnetic change of pure and 1% La/Nd‐doped multiferroic BiFeO3 (BFO) nanoparticles are presented to study the influence of introducing rare‐earth elements at the A‐site in BFO. All samples are successfully produced by the conventional hydrothermal method. Scanning electron microscopy picture demonstrates that doping has an impact on the surface and size of particles, and the magnetic properties of BFO also are improved, even significant ferromagnetism is observed in the Nd‐doped sample. Though the room‐temperature X‐ray diffraction patterns reveal the rhombohedral R3c symmetry for all samples, further identified by the Bi L3‐edge and Fe K‐edge X‐ray absorption fine structure (XAFS) spectra, the nanoscale secondary orthorhombic phase is only detected in Bi0.99Nd0.01FeO3 when analyzing the doped elements according to the La and Nd L3‐edge XAFS spectra. The different magnetic behavior is speculated to be in connection with the orthorhombic symmetry around the Nd atom.

Phase structure, dielectric and energy storage properties of Na0.5Bi0.5TiO3-BaTiO3 ceramics with Bi(Mg2/3Nb1/3)O3 modification

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications owing to their individual crystal structure and phase transition information. However, the high coercive field (EC) and large remnant polarization (Pr) are detrimental for practical applications. In this work, the composition-dependent phase structure, micromorphology, dielectric and energy storage properties of (1-x)(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-xBi(Mg2/3Nb1/3)O3 (NBBT-100xBMN, x = 0.18, 0.20, 0.22 and 0.25) ternary ceramics were hereby investigated. The addition of BMN facilitates the phase transformation from rhombohedral (R3c) to tetragonal (P4bm), which is beneficial for the enhancement of relaxation behavior, and meanwhile impels the grain growth. Combined with the influence of grain size on breakdown field strength, an optimal recoverable energy storage density (Wrec) of 1.88 J/cm3 with a high energy storage efficiency (η) of 82.15% was achieved in the NBBT-20BMN ceramic composition under the dielectric breakdown strength (DBS) of 150 kV/cm, accompanied by the excellent temperature stability from room temperature to 200 °C. All these manifest that the NBBT-20BMN ceramics have an attractive application prospect in the energy storage field.

Room temperature polar and weak-ferromagnetic oxide with low dielectric loss

Single-phase materials that are simultaneously ferroelectric and ferromagnetic at room temperature are promising for devices such as non-volatile random-access memory. Perovskite BiFeO3 which crystallizes in the polar rhombohedral structure (R3c) is ferroelectric and antiferromagnetic at room temperature. Here, we report a family of perovskite oxides in the BiFeO3 – Bi2/3TiO3 – ATiO3 (where A2+ is divalent alkaline earth metal ions e.g., Ca2+, Sr2+, Ba2+) ternary phase diagram that is polar as well as weak ferromagnetic above room temperature. The composition (Bi0.9167A0.075)(Fe0.9Ti0.1)O3 crystallizes in the polar rhombohedral structure space group R3c as corroborated by powder X-ray and neutron diffraction analysis. The nearly pure A-site perovskite possesses a long-range magnetic ordering above room temperature. These perovskites show a low dielectric loss, and the electrical response is dominated by grain contributions below 723 K.

Effect of bismuth deficiency with K substitution for Na on piezoelectric properties and crystal structure of Bi0.5−x(Na0.8−yK0.2+y)0.5TiO3–3x/2 (0 ≤ x ≤ 0.015, 0 ≤ y ≤ 0.1) ceramics

The piezoelectric properties and crystal structure of Bi0.5−x(Na0.8−yK0.2+y)0.5TiO3–3x/2 (0 ≤ x ≤ 0.015, 0 ≤ y ≤ 0.1) ceramics were characterized in this study. The crystal-structure refinement for Bi0.5−x(Na0.8K0.2)0.5TiO3–3x/2 was carried out using synchrotron X-ray diffraction data and Rietveld analysis and revealed the coexistence of rhombohedral (R3c) and tetragonal (P4mm) phases for the compositions with 0 ≤ x ≤ 0.015, although the fraction of these phases was almost independent of the composition x (49% for the rhombohedral phase and 51% for the tetragonal phase at x = 0.015). The Bi deficiency led to an increase in the lattice distortion of rhombohedral phase and a decrease in the that of tetragonal phase. The piezoelectric constant (d33) value decreased from 151.5 to 120.6 pC/N as x was increased from 0 to 0.015, and a shift of the depolarization temperature to higher temperatures was also confirmed by in situ d33 measurements. These results are attributed to an increase in the lattice distortion of rhombohedral phase enhanced by the Bi deficiency. The K substitution for Na in Bi0.485(Na0.8−yK0.2+y)0.5TiO2.9775 led to the formation of a morphotropic phase boundary (MPB) in the composition range 0 ≤ y ≤ 0.06, resulting in an increase in the fraction of the tetragonal phase. Although a decrease in the mechanical quality factor (Qm) was observed for K-rich compositions, the highest d33 value of 195.4 pC/N with a mechanical coupling factor of 32.9% was obtained for the Bi0.485(Na0.76K0.24)0.5TiO2.9775 (y = 0.04) ceramic because of the enhancement of the tetragonality in the MPB region, resulting in the onset of depolarization at ∼170 °C.

Crystal and magnetic structures of solid solutions based on BiFeO3

The correlation between the multiphase state of the system and its magnetic properties was studied on Bi1–xEuxFeO3 ceramic samples in the range 0.12 ≤ x ≤ 0.18. The X-ray diffraction results indicate that, with an increase in the concentration of Eu ions, a structural transition from the rhombohedral (R3c) to nonpolar orthorhombic (Pnma) phase is observed through the partial formation of an antipolar orthorhombic structure (Pbam). The mixed phase state in the obtained compounds is observed in the range 0.12 ≤ x ≤ 0.16. Magnetic measurements in a strong magnetic field indicate a weak ferromagnetic interaction. The magnetic response in a strong field is explained by the location of the spins at the phase boundary, as well as by the presence of intrinsic antiferromagnetic spins.

Outstanding Energy Storage Performance of NBT-Based Ceramics under Moderate Electric Field Achieved via Antiferroelectric Engineering.

Ultrahigh energy-storage performance of dielectric ceramic capacitors is generally achieved under high electric fields (HEFs). However, the HEFs strongly limit the miniaturization, integration, and lifetime of the dielectric energy-storage capacitors. Thus, it is necessary to develop new energy-storage materials with excellent energy-storage densities under moderate electric fields (MEFs). Herein, the antiferroelectric material Ag0.9Ca0.05NbO3 (ACN) was used to modify the relaxor ferroelectric material 0.6Na0.5Bi0.5TiO3-0.4Sr0.7Bi0.2TiO3 (NBT-SBT). The introduction of ACN results in high polarization strength, regulated composition of rhombohedral (R3c) and tetragonal (P4bm), nanodomains, and refined grain size. An outstanding recoverable energy density (Wrec = 4.6 J/cm3) and high efficiency (η = 82%) were realized under an MEF of 260 kV/cm in 4 mol % ACN-modified NBT-SBT ceramic. The first-principles calculation reveals that the interaction between Bi and O is the intrinsic mechanism of the increased polarization. A new parameter ΔP/Eb was proposed to be used as the figure of merit to measure the energy-storage performance under MEFs (∼200-300 kV/cm). This work paves a new way to explore energy-storage materials with excellent-performance MEFs.

Achieving superb electric energy storage in relaxor ferroelectric BiFeO3-BaTiO3-NaNbO3 ceramics via O2 atmosphere

Lead-free perovskite dielectric materials for storing electrical energy have been widely investigated due to their high polarization and reversible phase. However, their low electric resistivity limits the energy density and stability. In this study, the (1-x)(0.7BiFeO3-0.3BaTiO3)-xNaNbO3 ceramics (x = 0 – 0.2) were prepared using two sintering atmospheres (air and oxygen). A superb recoverable energy-stored density (Wrec) of 8.2 J/cm3 and efficiency (η) of 70% was achieved at x = 0.15 sintered in O2 atmosphere. The superior Wrec is due to the structural coexistence of ferroelectric rhombohedral (R3c), nonpolar cubic (Pm-3m), and antiferroelectric orthorhombic (Pbam) symmetries, tailored via antiferroelectric NaNbO3 addition. The improved breakdown strengths (up to 325 kV/cm) are due to the increased interatomic bonding linked to the BO6 octahedron and lattice network. Altogether, NaNbO3-substitution and O2 sintering synergistically resulted in excellent energy storage and pave a scheme of antiferroelectric-tailoring BiFeO3-BaTiO3–NaNbO3 relaxor ferroelectrics for dielectric capacitor.

Synergistic effect of multi-phase and multi-domain structures induced high energy storage performances under low electric fields in Na0.5Bi0.5TiO3-based lead-free ceramics

Lead-free dielectric ceramics with ultrahigh-power density, fatigue properties, and excellent thermal stability are regarded as potential dielectric energy storage materials for the next-generation advanced pulse power capacitors. However, the large energy storage density (Wrec) and high discharging efficiency (η) of dielectric capacitors are generally achieved under ultrahigh electric fields. Developing dielectric capacitors with high energy storage performances under low electric fields is of great significance. Herein, we utilized a synergistic design strategy of multi-phase and multi-domain structures to successfully synthesize the (0.65-x)(Na0.5Bi0.5)TiO3-0.35(Sr0.7Bi0.2)TiO3-xAg0.97Nd0.01Ta0.2Nb0.8O3 ((0.65-x)BNT-0.35SBT-xANTN) ceramics suitable for the low electric field situation. The formed multi-phase coexistence structure of the Rhombohedral (R3c) and Tetragonal (P4bm) phases and the elevated concentration of Bi3+ at A site in BNT-SBT-ANTN ceramics are beneficial to obtain the high maximum polarization (Pmax). Meanwhile, the introduction of ANTN in the BNT-SBT matrix can disrupt the long-range order ferroelectric domain structures and also form the local polar nanoregions (PNRs), leading to the small remnant polarization (Pr) and the improvement of the relaxation behavior. Encouragingly, the optimized 0.63BNT-0.35SBT-0.02ANTN composition exhibits excellent energy storage performances with a large Wrec of 3.61 J/cm3 and relatively high η of 80.6% at a low electric field of 200 kV/cm. In addition, this 0.63BNT-0.35SBT-0.02ANTN sample presents better thermal stability (20–120 ℃) and frequency stability (10–1000 Hz). Moreover, the high charge power density (PD) of 69.42 MW/cm3, the rapid discharge speed rate (τ0.9) of 0.22 μs, and the good fatigue endurance are also achieved in the 0.63BNT-0.35SBT-0.02ANTN sample. This work may provide an effective method for designing dielectric ceramics with remarkable comprehensive energy storage performances at low electric fields to meet the requirements of advanced energy storage capacitors under extreme conditions.

Enhanced dielectric and magnetic properties of magnetodielectric La2−xPrxCoMnO6 for spintronic applications

La2−xPrxCoMnO6 (x = 0.5, 1.0, 1.5 and 2.0) double perovskites were prepared via sol gel method. X-ray diffraction peak profile inveterate the nonexistence of impurity phases in the prepared system. Rietveld refinement suggested that ordered monoclinic (P21/n) phase exist along with disordered orthorhombic (Pbnm) and rhombohedral (R3c) structural phases. A decrease in unit cell volume and lattice parameters is observed with increase in Pr content which is in agreement with the difference in ionic radii of La and Pr ions. Morphological and compositional study using FESEM with EDX suggested that grain size lies in micrometer range and signifies the purity of developed samples. Dielectric constant as well as tangent loss exhibit dispersive behavior at lower frequencies and higher temperatures. The strong effect of bond angle, anti-site disorder and grain size is observed on dielectric properties. Due to large bond angle and large antisite disorder, LPCMO2 exhibited largest value of dielectric constant among all developed compositions. Cole-Cole plots proposed a non-Debye type relaxation and indicated NTCR (negative temperature coefficient of resistance) behavior for the synthesized compositions. Ac conductivity showed increasing tendency with rise in both frequency as well as temperature. Increase in dc conductivity with temperature proposed semiconducting behavior of prepared samples that can be explained on the basis of Thermal activation (TA) and Variable range hopping (VRH) models. The saturation magnetization (Ms) showed a strong correlation with bond angle, tilting of CoO6/MnO6 octahedra and grain size i.e. LPCMO2 is having largest Ms whereas lowest Ms is exhibited by LPCMO3 which may be due to variation in exchange interaction which strictly depends on bond angle and tilting of MO6 octahedra. Enhanced magnetic properties make these materials useful for spintronic devices and magnetic storage. Dielectric and magnetic properties of the prepared samples depend strongly on ˂Co-O-Mn˃ bond angle and have same variation tendency with Pr substitution which indicates coupling between these properties.

Effect of La doping on the structure and cycloidal spin ordering in multiferroic BiFeO3.

A series of Bi1-xLaxFeO3 samples with 0.00 ≤ x ≤ 0.30 was synthesized by the sol-gel method. The effects of lanthanum concentration on the phase formation, microstructure and cycloidal spin ordering were studied using X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy. The crystal structure of the La-doped bismuth ferrite transformed from rhombohedral R3c (x ≤ 0.05) to a mixture of R3c and cubic Pm3m (0.07 ≤ x ≤ 0.15) and finally to a mixture of R3c, Pm3m and orthorhombic Pbam (0.20 ≤ x ≤ 0.30). The Pbam phase, with characteristic porous microstructure shown by microscopy images, was observed in Bi1-xLaxFeO3 compounds for the first time. Based on the Mössbauer spectroscopy, it was found that the cycloidal spin ordering started to disappear at x = 0.07. With increasing La concentration the share of the cycloid decreased from 100% at 0.00 ≤ x ≤ 0.05 to 0% at x = 0.30. At the beginning, for x ≤ 0.02, the anharmonicity parameter, m, of the cycloidal spin ordering was about 0.5, which is typical of a pure BiFeO3 compound. In the range 0.05 ≤ x ≤ 0.25, the m parameter was of the order of 0.1, which indicated the practically harmonic character of the cycloid. The structural transition at x = 0.07 was accompanied by a substantial increase in magnetization.

Structural evaluation in vicinity of composition induced non-ergodic to ergodic crossover in niobium doped (Na0.41K0.09Bi0.5)TiO3

A structural crossover from non-ergodic to ergodic phase in niobium doped (Na0.41K0.09Bi0.5)TiO3, i.e., (Na0.41K0.09Bi0.50)1−x/2(Ti1−xNbx)O3 was investigated using high resolution x-ray diffraction and Raman spectroscopy. The diffraction studies reveal the co-existence of cubic (Pm3m), rhombohedral (R3c), and tetragonal (P4bm) phases for lower concentrations of niobium, i.e., for x ≤ 0.005 and the emergence of the pseudo-cubic (Pm3m) structure for higher niobium contents (for x ≥ 0.0075). On the other hand, Raman spectroscopy reveals the augmentation of the tetragonal phase with niobium content. These observations advocate the crossover from the non-ergodic to ergodic phase with niobium content. The presence of the pseudo-cubic phase (Pm3m), especially for x ≥ 0.0075, does not indicate the existence of the long-range cubic phase; rather, it models the contribution of nano-regions with the tetragonal symmetry as indicated in the Raman measurements. It further suggests that, with the incorporation of niobium, the size polar nano-regions diminish that leads to the crossover from the non-ergodic to ergodic phase.

Structural mechanisms of large piezoelectric responses in BiFeO3-PbTiO3 based solid-solution ceramics

Achieving large piezoelectric response and high Curie temperature, simultaneously, are of great demand but have been rarely achieved in BiFeO3-PbTiO3 (BF-PT) based morphotropic phase boundary (MPB) systems. In this work, in-situ synchrotron x-ray diffraction and transmission electron microscopy were carried out in BF-PT-0.19Ba(Zr,Ti)O3 high-temperature piezoceramic, a recently reported MPB composition with high piezoelectric coefficient, to elucidate the underlying structural mechanism. A field induced irreversible transition from tetragonal (T) P4mm phase to rhombohedral (R) R3c phase is identified although R and T phases are still coexisted after poling. This induces the significantly enhanced irreversible domain switching of both R and T phases and the reversible domain switching of R phase but only a slightly enhanced reversible switching of T phase of as compared with other BF-PT-x Ba(Zr,Ti)O3 MPB compositions, leading to the significant increase of lattice strain up to ∼0.15% but only a slightly increase of strain from extrinsic domain switching due to the strong coupling between lattice strain and domain switching in both R and T phases, although the strain contribution seems to be composition independent after the field induced irreversible phase transition. The present study demonstrates a new performance enhancement mechanism to design the high-performance BF-PT based high-temperature piezoelectric ceramics in terms of the different roles of R and T phases within MPB.

The Influence of BaTiO3 Content on the Energy Storage Properties of Bi0.5Na0.5TiO3-Bi(Mg2/3Nb1/3)O3 Lead-Free Ceramics

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications due to their outstanding dielectric and ferroelectric properties derived from large polarization. However, the high coercive field and large remnant polarization are unfavorable for practical applications, and thus NBT-based ceramics with relaxation behavior via doping/forming solid solutions with other elements/components have been widely studied. In this work, BaTiO3 (BT) was introduced to the 0.94Na0.5Bi0.5TiO3-0.06Bi(Mg2/3Nb1/3)O3 system by a conventional solid-state reaction to form a homogeneous solid solution of 0.94[(1−x)Na0.5Bi0.51TiO3-xBaTiO3]-0.06Bi(Mg2/3Nb1/3)O3 (BNT-100xBT-BMN). As the BT content increased, the proportion of the rhombohedral R3c phase increased while that of the tetragonal P4bm phase decreased, leading to the maximum Pmax (38.29 μC/cm2) and Eb (80 kV/cm) obtained in BNT-7BT-BMN (x = 0.07) composition. Specifically, the optimal energy storage properties of Wrec ~ 1.02 J/cm3 and η ~ 62.91% under 80 kV/cm were obtained in BNT-7BT-BMN ceramics, along with good temperature stability up to 200 °C, which are promising factors for future pulse power applications.