Sm-doped BiFeO3 Research Articles

Non-volatile memory characteristics of flexible ferroelectric field-effect transistors consisting of Sm-doped BiFeO3 thin films

This study investigates the impact of Sm doping on the structural, electrical, and functional properties of BiFeO3 (BFO) thin films. The aim is to improve their non-volatile memory characteristics for use in flexible ferroelectric field-effect transistors (FeFETs). We fabricated Sm-doped BFO (SBFO) thin films on flexible mica substrates with Sm concentrations ranging from 0 to 15 %. The FeFET device structures, which include MoS2 monolayer channels and SBFO thin films with Pt bottom electrodes, were analyzed. The SBFO thin films displayed a (111) preferential orientation due to the influence of underlying Pt electrodes. Notably, the SBFO thin film doped with a 10 % Sm concentration showed optimal enhancements, including a reduction in leakage current density and an increase in remanent polarization to 55.8 μC/cm2, compared to undoped thin film (35.5 μC/cm2). Furthermore, the thin film exhibited superior fatigue resistance for up to 1012 switching cycles and maintained stable values under significant bending stress for ferroelectric polarizations. On the other hand, SBFO thin film with 15 % Sm doping displayed relaxor antiferroelectric behavior, highlighting the importance of doping concentration. Therefore, for non-volatile memory application reliability, the FeFET device featuring a 10 % Sm-doped SBFO thin film not only enhanced the memory window but also showed superior fatigue characteristics over 1012 switching cycles, compared to its undoped counterpart. These findings demonstrate the effect of Sm doping in customizing the properties of BFO thin films for advanced, flexible non-volatile memory devices, offering a novel insight to optimize ferroelectric field-effect transistor performance.

Rhombohedral distortion induced structural, magnetic, optical phase transitions and photocatalytic activity in Sm and Sm-Cr co-substituted bismuth ferrite nanoparticles

Rhombohedral distortion induced structural, magnetic, optical phase transitions and photocatalytic activity of BiFeO3 (BFO), samarium (Sm)-substituted and Sm-Cr co-substituted bismuth iron oxide nanoparticles were prepared using the tartaric acid modified wet chemical sol–gel route. XRD and FESEM techniques confirmed the pristine phase and nanocrystalline property of BFO, Bi0.85Sm0.15FeO3 and BSFCO5 samples. XRD as well as Raman spectra confirmed structural phase transformations from the rhombohedral (pristine BFO) to rhombohedral (Bi0.85Sm0.15FeO3 and Bi0.85Sm0.15Fe0.95Cr0.05O3), in case of Sm-Cr co-doping there is indication of more change of crystal structure than single Sm-doped. Sm-Cr co-doped into BFO could enhance magnetism, more interestingly; M−H loops reveal the highest saturation magnetization value compared to Sm-doped and BFO. An obvious blue shift is noted in the substituted samples as well as the reduction of bandgap compared to pristine BFO. The co-substitution enhanced the photocatalytic degradation activity as compared to Sm-doped and pure BiFeO3.

The role of samarium (Sm) dopant on structural, magnetic and ferroelectric properties of BiFeO3 for magnetic data storage

We report the role of novel samarium (Sm3+) doping on the structural, thermal, magnetic, and ferroelectric properties of BiFeO3. Polycrystalline Sm-doped BiFeO3 samples were synthesized using a conventional solid-state reaction route. Bi1-xSmxFeO3 (x = 0.02–0.08) samples crystallize in rhombohedral structure (R3c). With the increase of Sm3+ content, the decrease in crystal size is attributed to the change in lattice parameters, since the ionic radius of Sm3+ (0.95 Å) is smaller than that of Bi+3 (1.03 Å). A clear magnetic transition temperature (TN) peak was obtained by DSC measurements. With the increase of Sm3+ content, the peak temperature gradually decreased. Sm-doped BiFeO3 samples exhibit ferromagnetic and antiferromagnetic behaviors. Magnetism is strongly influenced by the substitution of Sm3+ ions in BiFeO3, and thus the magnetism of the synthesized samples is greatly changed compared to that of pure BiFeO3. Bi1-xSmxFeO3 (x = 0.02–0.06) samples have weak pointed hysteresis loops. While the BSFO-0.08 sample exhibit unsaturated rounded hysteresis loops possibly due to the large electrical leakage. Overall, we observed enhanced magnetic and ferroelectric properties by varying the Sm3+ content in BiFeO3. Therefore, the Sm3+ doping in BiFeO3 makes it a very prospective material for applications in spintronic devices, data storage devices, and sensors.

Morphotropic Phase Boundary Enhanced Photocatalysis in Sm Doped BiFeO3.

This paper presents the results of the synthesis of samarium-doped bismuth ferrite (BFO) nanoparticles by the solution combustion method. The dependence of BFO properties on the amount of the samarium (Sm) in the composition was studied. The synthesized nanocomposites were characterized by scanning electron microscopy SEM), X-ray diffractometry (XRD), Raman, Electron Diffuse Reflectance Spectroscopy (EDRS) and Electron Magnetic Resonance (EMR). The photocatalytic (PC) measurements showed the absence of a strict correlation between the PC activity and the crystallite size and band gap. An increase in the PC activity of BFO samples with 10 and 15% doping was observed and it was concluded that in controlling the PC properties in doped BFO, the processes of interfacial polarization at the boundaries of the morphotropic phase transition are of decisive importance. It was supposed that the internal electric field formed at these boundaries contributes to the efficient separation of photogenerated charge carriers.

High and temperature-insensitive piezoelectric performance in the lead-free Sm-doped BiFeO3–BaTiO3 ceramics with high Curie temperature

Large sensor piezoelectric constant (d33 = 334 pC/N) and superior actuator piezoelectric constant (d33* = 552 pm/V) as well as a high Curie temperature (TC = 454 °C) were obtained simultaneously in the lead-free 0.67Bi1.03FeO3-0.33Ba1-xSmxTiO3 ceramics. Such an excellent and temperature-insensitive piezoelectric performance with only 10% temperature variation of piezoelectric strain at the range of 25–125 °C is highly desirable for real applications. The structural origin of the enhanced piezoelectric performance is mainly attributed to the morphotropic phase boundary and the highest known tetragonality (cT/aT = 1.02) in such materials. Transmission electron microscopy and electro-mechanical phenomenological theory demonstrate that the superior d33 and d33* are associated with the hybrids nanodomains (60–90 nm) and flattened thermodynamic energy profile owing to the local structure heterogeneity. These results are superior as the piezoelectric properties are temperature-independent and the material has large d33*, and high TC compared to other lead-free piezoelectric ceramics.

Morphotropic Phase Boundary Enhanced Photocatalysis in Sm Doped BiFeO3

Morphotropic Phase Boundary Enhanced Photocatalysis in Sm Doped BiFeO3

Pressure induced phase transitions in Sm-doped BiFeO3 in the morphotropic phase boundary

Sm-doped BiFeO3 compacted powders with composition across the morphotropic phase boundary region were prepared by sol-gel method. Crystal structure, morphology and magnetic state of the compounds were analyzed as a function of dopant concentration, temperature and external pressure using synchrotron and laboratory X-ray diffraction, electron microscopy, Raman and Mössbauer spectroscopy. Application of external pressure shifts the phase transition from the rhombohedral structure to the nonpolar orthorhombic structure towards lower concentration of the dopant content, wherein the amount of the anti-polar orthorhombic phase notably decreases. Raman and Mössbauer spectroscopy data provides additional information about the structural distortion on local scale level which testifies faster formation of nonpolar orthorhombic phase and associated modification in the magnetic state in the compounds subjected to high pressure. Temperature increase leads to the structural transition to the nonpolar orthorhombic phase regardless the structural state at room temperature; furthermore, application of external pressure decreases the phase transition temperature.

Optical and magnetic properties of Sm-doped BiFeO3 nanoparticles around the morphotropic phase boundary region

The crystal structure, photocatalytic activity, and ferromagnetic properties of Sm-substituted (Bi1−xSmxFeO3, x = 0.05, 0.10, 0.15, 0.20) nanoparticles were systematically investigated within the entire Sm substitution region. The morphotropic phase boundary (MPB) consisting of a rhombohedral phase, orthorhombic interim phase (Pna21), and orthorhombic phase with 0.1 ≤ x ≤ 0.2 is constructed and confirmed by x-ray diffraction and Raman spectra with new vibration modes at ∼310 cm−1. The photocatalytic activity and ferromagnetism are improved around the MPB region (x = 0.10). Meanwhile, the wasp-waisted hysteresis loops are present around the MPB region. Wasp-waisted hysteresis loops have the features of low hysteresis loss in low magnetic fields and are helpful in designing some multiferroic devices.

Predictability as a probe of manifest and latent physics: The case of atomic scale structural, chemical, and polarization behaviors in multiferroic Sm-doped BiFeO3

The predictability of a certain effect or phenomenon is often equated with the knowledge of relevant physical laws, typically understood as a functional or numerically derived relationship between the observations and known states of the system. Correspondingly, observations inconsistent with prior knowledge can be used to derive new knowledge on the nature of the system or indicate the presence of yet unknown mechanisms. Here, we explore the applicability of Gaussian processes (GP) to establish predictability and uncertainty of local behaviors from multimodal observations, providing an alternative to this classical paradigm. Using atomic resolution scanning transmission electron microscopy (STEM) of multiferroic Sm-doped BiFeO3 across a broad composition range, we directly visualize the atomic structure and structural, physical, and chemical order parameter fields for the material. GP regression is used to establish the predictability of the local polarization field from different groups of parameters, including the adjacent polarization values and several combinations of physical and chemical descriptors, including lattice parameters, column intensities, etc. We observe that certain elements of microstructure, including charged and uncharged domain walls and interfaces with the substrate, are best predicted with specific combinations of descriptors, and this predictability and associated uncertainties are consistent across the composition series. The associated generative physical mechanisms are discussed. It is also found that certain parameter combinations tend to predict the orthorhombic phase in the cases where rhombohedral phase is observed, suggesting a potential role of clamping and confinement phenomena in phase equilibrium in Sm-BiFeO3 system close to morphotropic phase boundary. We argue that predictability and uncertainty in observational data offer a new pathway to probe the physics of condensed matter systems from multimodal local observations.

Evolution of the crystal structure and magnetic properties of Sm-doped BiFeO3 ceramics across the phase boundary region

Samarium doped BiFeO3 compounds having nano-size crystallites were prepared by the ethylene glycol assisted sol-gel synthesis method. X-ray diffraction and SEM measurements as well as Raman spectroscopy and FTIR experiments were used to clarify an evolution of the crystal structure on microscopic and local scale levels in the compounds having formula Bi1-xSmxFeO3, where 0 = x ≤ 1. Magnetization measurements along with the structural data were used to determine a correlation between magnetic properties and crystal structure of the compounds. The compounds with 0.1 = x ≤ 0.2 are characterized by the sequence of the structural transitions driven by the dopant increase, viz. from the polar rhombohedral phase to the non-polar orthorhombic phase via two-phase regions characterized by the presence of the anti-polar orthorhombic phase. The concentration regions ascribed to a coexistence of the rhombohedral and the anti-polar orthorhombic phases as well as the anti-polar orthorhombic and the non-polar orthorhombic phases are observed in the ranges 0.12 = x ≤ 0.15 and 0.15 < x < 0.18 respectively. The compounds having single phase rhombohedral structure are characterized by a release of remnant magnetization as compared to ceramics with similar chemical compositions but synthesized by the solid-state reaction method and having microscopic size crystallites. A correlation between the type of structural distortion, morphology of crystallites and an onset of remnant magnetization is discussed highlighting a difference in the evolution of crystal structure and magnetization observed for the Sm-doped ceramics prepared by modified sol-gel method and conventional solid-state reaction technique.

Causal analysis of competing atomistic mechanisms in ferroelectric materials from high-resolution scanning transmission electron microscopy data

Machine learning has emerged as a powerful tool for the analysis of mesoscopic and atomically resolved images and spectroscopy in electron and scanning probe microscopy, with the applications ranging from feature extraction to information compression and elucidation of relevant order parameters to inversion of imaging data to reconstruct structural models. However, the fundamental limitation of machine learning methods is their correlative nature, leading to extreme susceptibility to confounding factors. Here, we implement the workflow for causal analysis of structural scanning transmission electron microscopy (STEM) data and explore the interplay between physical and chemical effects in a ferroelectric perovskite across the ferroelectric–antiferroelectric phase transitions. The combinatorial library of the Sm-doped BiFeO3 is grown to cover the composition range from pure ferroelectric BFO to orthorhombic 20% Sm-doped BFO. Atomically resolved STEM images are acquired for selected compositions and are used to create a set of local compositional, structural, and polarization field descriptors. The information-geometric causal inference (IGCI) and additive noise model (ANM) analysis are used to establish the pairwise causal directions between the descriptors, ordering the data set in the causal direction. The causal chain for IGCI and ANM across the composition is compared and suggests the presence of common causal mechanisms across the composition series. Ultimately, we believe that the causal analysis of the multimodal data will allow exploring the causal links between multiple competing mechanisms that control the emergence of unique functionalities of morphotropic materials and ferroelectric relaxors.

Effect of rare-earth Nd/Sm doping on the structural and multiferroic properties of BiFeO3 ceramics prepared by spark plasma sintering

Multiferroic Nd/Sm-doped BiFeO3 ceramics synthesized at 700 °C by spark plasma sintering in conjunction with sol-gel precursor powders are investigated by X-ray diffraction, scanning electron microscopy, dielectric, ferroelectric and magnetic measurements. With the doping content of Nd/Sm beyond 10 mol%, the crystal structure changes from R3c to coexistence of Pbam and R3c. It is also revealed that the grain size for all samples greatly decreases and the dielectric, ferroelectric and magnetic properties are obviously improved with Nd/Sm doping. The optimized remanent polarization are about 1.451 μC/cm2 and 3.448 μC/cm2 for the 10 mol% Nd-doped and 15 mol% Sm-doped BiFeO3 ceramics, respectively. Because of the reduced concentration of oxygen vacancies, the leakage current density of Nd/Sm-doped ceramics decreases more than two orders of magnitude compared to the pure BiFeO3 sample. The maximum remanent magnetization for the Sm-doped ceramics is approximately 0.279 emu/g, which is higher than that for the Nd-doped samples (0.263 emu/g).

Enhancement of dielectric, ferromagnetic and electrochemical properties of BiFeO3 nanostructured films through rare earth metal doping

In this present work first assessment of enhanced electrochemical properties of Bismuth Ferrite (BiFeO3)thin films through Samarium(Sm) doping are delivered. Apart from this enhancement of structural, dielectric and magnetic properties with increasing samarium concentration is discussed. The pure phase BiFeO3 films and Sm-doped BiFeO3(Bi1-xSmxFeO3 where x = 0.05 & x = 0.1) films were synthesized using 2methoxy aided sol-gel process and were deposited on platinum substrates through spin coating technique. X-ray diffraction confirmed the formation of pure phase BiFeO3 with Rhombohedral (R3c) structure. Morphological characterization through SEM presented the formation of nanostructures and its structural transformation through doping variant. AFM confirmed the smoothness of the film with a maximum grain size of 172.72 nm for the measured films. The elemental analysis and elemental purity was confirmed through EDAX. Mechanistic aspects of the prepared films were analyzed through Thermogravimetric, Differential Thermal Analysis and Fourier Transform Infrared spectroscopy. The variation of dielectric constant with frequency was measured until 1 MHz and remains almost constant due to the independent nature of polarization with frequency. The magnetic coercivity of the film improved from 77.7G to 240G with samarium doping. The Bi0.9Sm0.1FeO3 films deposited on platinum substrates enhanced the specific capacity to about 184Fg-1 along with its retention capability enabling it to be used as electrode material for supercapacitors.

Antiferroelectricity and weak ferromagnetism in rare earth doped multiferroic BiFeO3

The remanent polarization Pr and remanent magnetization Mr for different Sm-concentrations x in Sm-doped BiFeO3 is investigated using a microscopic model and the Green's function technique. For pure BiFeO3 with a rhombohedral symmetry we obtain a hysteresis loop P(E) which is typical for a ferroelectric material. Further increase of x (x = 0.16) leads to a double hysteresis loop, which is typical for an antiferroelectric substance. Sm substitution induces a weak ferromagnetic moment at room-temperature. Pr and Mr versus x show a maximum at x = 0.05. The ferroelectric phase transition temperature TC decreases strongly whereas the magnetic phase transition temperature TN increases slightly with increasing the Sm concentration x.

Microscopic origin of the high piezoelectric response of Sm-doped BiFeO3 near the morphotropic phase boundary

Rare-earth element-doped BiFeO3 has an ultrahigh piezoelectric response near the morphotropic phase boundary (MPB), making it a promising substitute for toxic lead-based piezoelectric materials. As a ferroelectric–antiferroelectric MPB, its microscopic mechanism, especially the contribution of each phase to the piezoelectric performance, is still unclear. In this work, the origin of the giant piezoelectric response of Sm-doped BiFeO3 thin films was studied by combining nanoscale in situ electric field experiments and atomic-resolution electron microscopy. Two independent reversible phase transitions were found under an external electric field: a phase transition between the polar and nonpolar phases and a phase transition between the polar and antipolar phases. Calculations indicated that the enhancement of the piezoelectric response at the MPB originated from these two reversible phase transitions, which were realized via the nucleation of the nanoscale new phase and the motion of the phase boundary under the external electric field. The above results provide deeper insight into the mechanism of the electromechanical response near the ferroelectric–antiferroelectric MPB in rare-earth element-doped BiFeO3 thin films.

Dielectric, Ferroelectric, and Magnetic Properties of Sm-Doped BiFeO₃ Ceramics Prepared by a Modified Solid-State-Reaction Method.

Sm-doped BiFeO3 (BFO) material was prepared using a modified solid-state-reaction method, which used fast heating and cooling during the sintering process. The Sm doping level varied between 1 mol % to 8 mol %. Processing parameters, such as sintering temperature and annealing temperature, were optimized to obtain high-quality samples. Based on their dielectric properties, the optimum sintering and annealing temperatures were found to be 300 °C and 825 °C, respectively. Leakage-free square-shaped ferroelectric hysteresis loops were observed in all samples. The remnant polarization was maximized in the 5 mol %-doped sample (~35 μC/cm2). Furthermore, remnant magnetization was increased after the Sm doping and the 8 mol%-doped sample possessed the largest remnant magnetization of 0.007 emu/g. Our results demonstrated how the modified solid-state-reaction method proved to be an effective method for preparing high-quality BiFeO3 ceramics, as well as how the Sm dopant can efficiently improve ferroelectric and magnetic properties.

Structure and piezoelectric properties of Sm-doped BiFeO3 ceramics near the morphotropic phase boundary

The evolution of crystal structure and piezoelectric properties of the Bi1-xSmxFeO3 ceramics with compositions corresponding to the phase boundary region between the polar rhombohedral and anti-polar orthorhombic phases have been studied. The materials have been investigated using X-ray diffraction, transmission electron microscopy and piezoresponse force microscopy techniques. The diffraction measurements have allowed studying the crystal structure transformations depending on the dopant concentration and temperature. Similar to the compounds with x > 0.18, the lightly-doped samples have been found to adopt the non-polar orthorhombic structure at elevated temperatures. The research has clarified the correlation between the structural state and piezoelectric behavior. Substantial increase in piezoresponse observed for the phase-separated compounds having a dominant fraction of the rhombohedral phase has been discussed assuming significant extrinsic contribution associated with a metastable structural state changing under external electric field.

Enhanced magnetization and bias voltage-dependent dielectric properties of Sm-doped BiFeO3 multiferroic nanofibers

The simultaneous enhancement of magnetic and ferroelectric properties of one-dimensional nanostructured bismuth ferrite (BiFeO3) is highly desired due to their potential applications in nanoscale devices, such as multistate memory device and micro-magnetoelectric sensor. Sm-doped BiFeO3 nanofibers were synthesized by a sol–gel-based electrospinning process. The as-fabricated nanofibers show significantly enhanced magnetization due to the suppressed periodic spin cycloid and the uncompensated surface spins. The magnetization of Bi0.90Sm0.10FeO3 nanofibers is nearly twice as much as that of the nanoparticles at the same doping level. More importantly, Sm-doped BiFeO3 nanofibers hold the higher dielectric constant and stronger DC bias-dependent dielectric constant due to the enhanced polarization by Sm doping. Temperature-dependent dielectric constant and dissipation factor suggest that the dielectric properties of Sm-doped BiFeO3 nanofibers remain stable below 250 °C, providing a wide temperature range for applications in memory devices or sensors. The tuning of magnetic and ferroelectric properties of the Sm-doped BiFeO3 nanofibers appears to be very promising for achieving multifunctionality in a single material.

Ferroelectric domains and phase transition of sol-gel processed epitaxial Sm-doped BiFeO3 (001) thin films

BiFeO3, a room-temperature multiferroic material, has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping. In this work, 12% Sm-doped BiFeO3 epitaxial thin films were fabricated on Nb-doped SrTiO3 (001) single crystal substrates via sol-gel method. The epitaxy was verified by reciprocal space mapping (RSM) and transmission electron microscope (TEM). The TEM results indicated the coexistence of R3c and Pbam phases in the film. The domains and piezoelectric properties from room temperature to 200 °C were characterized by piezoresponse force microscopy (PFM). Domains became active from 110 °C to 170 °C, and domain configurations changed obviously. A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam. The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion. Switching spectroscopy PFM (SS-PFM) was further conducted to investigate the piezoresponse during the phase transition. Anomalous responses were found in both ON and OFF states at 170 °C, and the film exhibits typical antiferroelectric behavior at 200 °C, implying that the completion of phase transition and structure turned to the Pbam phase. This work revealed the origin of the high piezoresponse of Sm-doped BiFeO3 thin films at the morphotropic phase boundary (MPB).

Synthesis and characterization of multiferroic Sm-doped BiFeO3 nanopowders and their bulk dielectric properties

Multiferroic Bi1−xSmxFeO3 (x=0, 0.05, 0.1, 0.2, and 0.3) nanopowders with particle sizes of 69–22.6nm were prepared by a simple co-precipitation method. The structure and morphology of the samples were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns confirmed the phase transition from rhombohedral to orthorhombic phases. The results of X-ray absorption spectroscopy (XAS) data indicate that the oxidation state of Fe in the sample was Fe3+. The results of magnetic properties revealed the enhancement of weak ferromagnetic property with increasing Sm doping in BFO nanopowders. SEM images revealed that the average grain size decreased with an increase in Sm concentration. Undoped BFO ceramics exhibited a high dielectric constant ε′ ∼1.1×104 and a low loss tangent of tan δ ∼0.5 at room temperature for 1kHz. The room temperature dielectric constant decreased with increasing concentration of Sm doping and the dielectric relaxation peaks were observed at x≤0.1. The dielectric relaxation peaks which were observed at all frequency ranges were x≤0.1 samples which were attributed to Maxwell-Wagner relaxation. As the temperature increased, great increases in dielectric permittivity were observed in all the Bi1−xSmxFeO3 samples. The effects of grain boundaries on the dielectric properties of Sm-doped BFO ceramics were investigated by measuring the dielectric responds in the frequencies of 100Hz–1MHz at room temperature under applied dc bias of 0–20V. It was found that, with an increase in applied dc bias voltage from 0 to 20V, the dielectric constant decreases at frequencies below 104Hz. However, the dielectric properties in the high-frequency region remained unchanged.