Room Temperature Raman Spectroscopy Research Articles

Structural phase transition, relaxor behavior, and ultra-low strain hysteresis in BaTiO3 ceramics modified by BiYO3

In this study, the structural properties, phase transition, relaxor behavior, and strain properties of (1−x)BaTiO3‒xBiYO3 (x= 0.02‒0.15 mol) ceramics were investigated. The room temperature x-ray diffraction and Raman spectroscopy results reveal that (1−x)BaTiO3‒xBiYO3 ceramics undergo phase transition from tetragonal to pseudo-cubic structure with x increasing. The curves of dielectric constant and loss tangent as a function of temperature and frequency show that the dielectric constant was changing from being dependent on temperature to being independent of it upon increasing BiYO3 amount, which is induced obvious dielectric relaxation behavior. Slimmer polarization–electric field (P–E) loops and lower remnant polarization (Pr ) were observed for samples with x ⩾ 0.08. The transition between the ferroelectric and relaxor states leads to the narrow strain–electric field (S–E) loops, which exhibit a high electric field-induced strain of 0.192% and an ultra-low strain hysteresis of 10.4% at an electric field of 70 kV cm−1 for x= 0.04. This excellent performance indicates that 0.96BaTiO3‒0.04BiYO3 ceramic may be promising lead-free materials for high-precision displacement actuators applications.

Experimental conditions for room temperature ferromagnetism in Fe-doped SnO2 via mechanochemical milling and thermal treatment

Identifying optimal experimental conditions, preferably through a simple and cost-effective method, for the fabrication of oxide-diluted magnetic semiconductors, such as Fe-doped SnO2, holds great significance in the quest for spintronic materials operating at room temperature (RT). While mechanochemical milling is a well-established technique meeting these requirements, its numerous milling variables necessitate careful consideration of restricted experimental conditions. In this study, we present some experimental mechanochemical milling conditions to prepare impurity-free iron-doped tin dioxide nanoparticles exhibiting RT ferromagnetic signal. To achieve this, we investigated the effects of milling time, the choice of the starting Sn reactant, and iron concentration on the purity of Sn1−xFexO2 (x = 0, 0.03, and 0.05) nanopowders obtained through mechanochemical milling followed by thermal treatment. Characterization through XRD, XANES, and EXAFS at the Fe K-edge, RT Raman spectroscopy, 119Sn and 57Fe Mössbauer spectroscopies, and magnetic measurements was conducted. Among the experimental techniques, micro-Raman spectroscopy proved the most effective in detecting the formation of hematite as an impurity phase. Our results indicate that extending the milling time to 12 h, as opposed to 3 h, employing anhydrous SnCl2, instead of SnCl2·2H2O and using the low iron concentration of x = 0.03, results in proper conditions for producing impurity-free samples with a robust RT ferromagnetic signal. The oxidation states for iron and tin ions were determined to be 3+ and 4+, respectively, with both occupying octahedral sites, suggesting iron’s replacement of tin. Our findings propose that both the bound magnetic polaron and RKKY models offer potential explanations for the origin of the ferromagnetic signal observed at room temperature in Sn0.97Fe0.03O2 sample milled for 12 h.

Investigating cerium redox changes between aluminosilicate glass and melt: A multispectroscopic approach.

Redox control of glasses is paramount both to their fusion process and to obtaining the desired properties of high technological glasses. However, the link between melting parameters, such as temperature, furnace atmosphere, or quenching rate, and the redox state of the final products is poorly understood. In this work, in situ x-ray absorption near-edge structure (XANES) data at Ce L3-edge data were acquired at high temperatures on cerium-containing sodium aluminosilicate glasses, allowing the determination of thermodynamic constants necessary to predict the cerium redox state over a wide temperature range (900-1500 °C). The results obtained were compared to the Raman spectra of samples quenched at different temperatures. Our findings demonstrate that the quench performed was fast enough to block the cerium oxidation state, meaning the redox measured at room temperature is representative of a high temperature state. This was further verified by room temperature Raman spectroscopy, where a relationship was found between the spectra and melting conditions. Wet chemical analysis, XANES at Ce L3-edge, Raman spectroscopy, and optical absorption spectroscopy were successfully used to determine the redox state of cerium in aluminosilicates.

Sol-gel synthesis and Opto-electrical properties study of double perovskite oxide Dy2NiMnO6 thin film

Thin film of double perovskite oxide Dy2NiMnO6 (DNMO) has been synthesised by the simple and cost-effective chemical solution deposition technique. The room temperature X-ray diffraction pattern and Raman spectroscopy confirm the monoclinic (space group - P21/n) crystal structure of polycrystalline DNMO thin film. The optical and electrical properties of DNMO thin film are investigated to study the detailed photo physical properties of DNMO thin film. The direct band gap and temperature dependant impedance spectroscopy confirm its semiconductor behaviour. Impedance spectroscopy also shows two types of dielectric relaxation behaviour and the nature of conductivity reveals the electron hopping conduction mechanism. Moreover, the chemical solution deposited DNMO film shows promising photo response under white light.

Nickel doped bismuth sulfide nanomaterials: Synthesis, characterization, and enhancement of anti-microbial activity

This study aims to evaluate the minimum inhibitory concentration (MIC) of pristine Bi2S3 and Ni-doped Bi2S3 nanostructures for their anti-microbial study. The nanostructures were synthesized by the reverse micelle method using the AOT/Water/Cyclohexane ternary system. As per our knowledge, the current study shows the lowest value of MIC compared to reported work for pristine Bi2S3 against Staphylococcus Aureus and Bacillus Subtilis pathogens. The compositional, structural, morphological, optical, and vibrational properties of synthesized Bi2S3 and Ni-doped Bi2S3 nanomaterials were investigated using EDAX, X-ray diffraction, HR-TEM, DLS, diffuse UV–Vis reflectance spectroscopy, room temperature, and low-temperature Raman spectroscopy, respectively. Finally, the anti-microbial activity of synthesized nanostructures against four different pathogens was examined using the broth dilution method in terms of MIC value. The result of MIC reports that pristine Bi2S3 and Ni-doped Bi2S3 nanomaterials have a strong anti-microbial effect for two Gram-negative Serratia Marcescens and Pseudomonas Aeruginosa compared to two Gram-positive Staphylococcus Aureus and Bacillus Subtilis micro-organisms.

Photocatalytic activity of GeSbSeEr quaternary chalcogenide for efficient methylene blue degradation in visible light

For the first time, simple and robust melt quench synthesis based pure and doped quaternary Ge17Sb8Se75−xErx (Er; x = 0, 0.6, 1) chalcogenides have been used to demonstrate photo-catalytic dye degradation under green light (560 nm) illumination. Inspired by the excellent optoelectronic and thermal properties of the studied composition, rare earth element doped chalcogenide was found to show variation in band gap from 1.88 eV (for pure) to ∼1.78 eV (for highest amount of dopant Erbium). We found an enhanced thaizene dye (methylene blue) degradation up to 96% in 160 min for Er; x = 0.6 sample. SEM-EDX, UV–Vis (Tauc Plots), Room temperature Raman spectroscopy measurements are supplemented to discuss the visible light driven catalytic properties. These pure and Er doped GeSbSe chalcogenides are found to have low cost synthesis, scalability and environmental friendly response which suggests its potential in many optoelectronic application.

Observation of well-defined Kohn-anomaly in high-quality graphene devices at room temperature

Due to its ultra-thin nature, the study of graphene quantum optoelectronics, like gate-dependent graphene Raman properties, is obscured by interactions with substrates and surroundings. For instance, the use of doped silicon with a capping thermal oxide layer limited the observation to low temperatures of a well-defined Kohn-anomaly behavior, related to the breakdown of the adiabatic Born–Oppenheimer approximation. Here, we design an optoelectronic device consisting of single-layer graphene electrically contacted with thin graphite leads, seated on an atomically flat hexagonal boron nitride substrate and gated with an ultra-thin gold layer. We show that this device is optically transparent, has no background optical peaks and photoluminescence from the device components, and no generation of laser-induced electrostatic doping (photodoping). This allows for room-temperature gate-dependent Raman spectroscopy effects that have only been observed at cryogenic temperatures so far, above all the Kohn-anomaly phonon energy normalization. The new device architecture, by decoupling graphene optoelectronic properties from the substrate effects, allows for observing quantum phenomena at room temperature.

Structural, electrical, and magnetic properties of Ce and Fe doped SrTiO3

Here, we report on the structural, vibrational phonon, electrical, and magnetic properties of undoped strontium titanate SrTiO3, Ce doped Sr1−xCexTiO3, and (Ce, Fe) co-doped Sr1−xCexTi1−yFeyO3 samples synthesized through solid state reaction route. The Rietveld refined powder x-ray diffraction analysis confirmed the cubic Pm-3m phase in our as-synthesized samples. We observed grain size reduction in SrTiO3 from scanning electron micrographs due to the incorporation of Ce and Fe dopants. The sample purity in terms of chemical species identification has been confirmed from energy-dispersive x-ray spectroscopy. The characteristic phonon modes in our samples are identified using room temperature Raman spectroscopy and benchmarked against existing relevant experimental observations. The incorporation of Ce and Fe as substitutional dopants in SrTiO3 unit cell was confirmed from the absence of absorption at 480, 555, 580, and 1635 cm−1 band in Fourier transform infrared spectra. The 3% Ce doping in Sr0.97Ce0.03TiO3 sample may have induced ferroelectric order, whereas the undoped SrTiO3 (STO) revealed lossy paraelectric nature. In the case of (Ce = 3%, Fe = 10%) co-doped Sr0.97Ce0.03Ti0.90Fe0.10O3 sample, we observed ferromagnetic hysteresis with orders of magnitude enhancement in remnant magnetization and coercivity as compared to undoped STO sample. This long range robust ferromagnetic order may have originated from F-center mediated magnetic interaction.

Room temperature Raman spectroscopy and 29Si MAS NMR combined with high temperature Raman spectroscopy and DFT calculation of xMgO-(1-x)CaO–SiO2 glasses and melts

In order to study the effect of MgO on the microstructure and macroscopic thermos-physical properties of calcium silicate melt, quantitative analysis of the various silicon-oxygen Q i species in magnesium-calcium silicate glasses and melts at a constant alkalinity has been performed by in-situ high temperature Raman spectroscopy, 29 Si MAS NMR and DFT (Density Functional Theory) calculation. Several cluster models, probably existed in magnesium-calcium silicate glasses and melts, modified by Ca 2+ or Mg 2+ have been designed, their Raman vibrational modes and scattering activities were thus simulated and calculated. A function correlating the wavenumbers of Si-O nb (non-bridge oxygen) of various SiOTs (silicon-oxygen tetrahedrons) with their RSCS (Raman scattering cross sections) was constructed and used to calibrate the experimental Raman spectra. The abundance of each primary Q i species of various magnesium-calcium silicate glasses can be composed by all the deconvoluted hyperfine peaks within the same Q i species. The quantitative description for glasses was proven to be consistent with the result from 29 Si MAS NMR. Thus, Q i species distributions for melts were also quantitatively derived. It demonstrated that the abundances of Q 1 and Q 3 species increased while Q 2 species decreased with the increasing replacing amount of MgO. The relationship between the viscosity and Q i species distributions as well as different cations has been investigated and correlated. Q 3 species was predominantly responsible for the contribution of viscosity of melt.

A DFT+U look into experimentally synthesized monoclinic scheelite BiVO4

We present a combined experimental and Hubbard interaction corrected density functional theory (DFT+U) based study of monoclinic scheelite (ms) bismuth vanadate BiVO4 (BVO). The ms-BVO samples were synthesized using the standard solid state reaction technique. The ms phase of the synthesized BVO samples has been confirmed from Rietveld analysis of the powder x-ray diffraction pattern and room temperature Raman spectroscopy. Both experimentally obtained crystal parameters and Raman peak positions were benchmarked against the DFT+U simulations. The variations in morphology and chemical concentrations due to different sintering temperatures and milling times were analyzed using field emission scanning electron microscopy and energy dispersive x-ray spectroscopy. The measured energy bandgap in the range of 2.38–2.58 eV from UV-Vis-NIR diffuse reflection spectroscopy was explained within the context of grain size variations in combination with bismuth and oxygen vacancies from DFT+U simulations.

Study of temperature dependent phonon properties of SbxGe1-xSe (x = 0.00 and 0.15) crystals

A detailed study of phonon properties of SbxGe1-xSe (x = 0.00 and 0.15) crystals is demonstrated here. DVT technique was employed for crystal growth. Powder XRD confirmed the phase-singularity and revealed the structural minutiae of the grown materials. The surface morphology of the crystals was studied under a high-resolution microscope. Room temperature Raman spectroscopy revealed a blue shift in the out-of-plane mode (B3g) and in-plane modes (Ag(1) and Ag(2)) of GeSe with Sb mixing. Further, the temperature-dependent Raman spectroscopy showed a monotonous red-shift and softening of modes as the temperature increases from 103 K to 298 K. The first order temperature coefficients for peaks B3g and Ag(2) are calculated. Shifting of modes pertaining to laser-power is also recorded for room temperature, and thermal conductivity of the crystals is determined. A strong anisotropy is found in the thermal conductivity for out-of-plane and in-plane modes for both crystals.

Structural, dielectric and energy storage properties of Neodymium niobate with tetragonal tungsten bronze structure

The present work reports the effect of Nd3+ substitution on the structural, dielectric and energy storage properties of the polycrystalline Ba2NaNb5O15(BNN) ceramics. The ferroelectric lead-free Ba2Na1-xNdx/3Nb5O15 ceramics were prepared by conventional solid-state reaction technique. The room temperature X-ray study and Raman spectroscopy investigations have allowed evidencing the stabilization of a tetragonal tungsten bronze structure with P4bm space group for all the studied compounds. Dielectric study carried out on the prepared ceramics has permitted to determine the temperature of phase transitions (Tc). It was found that the dielectric constant increased with increasing the amount of Nd in BNN matrix. Room temperature energy storage property was determined using P-E hysteresis loops. The optimum discharge density was found for the composition x = 0.7 with Wrec = 18.1 mJ cm−3) at 1 Hz. Finally, the dynamic of phase transition was approached using thermal Raman spectroscopy investigations.

Laser‐induced phonon and magnon properties of NiO nanoparticles: A Raman study

AbstractIn the present study, the influence of laser intensity on phonon and magnon properties of nickel oxide (NiO) nanoparticles were extensively studied using room temperature Raman spectroscopy. The required NiO nanoparticles were synthesized using a simple sol–gel method. The structural and morphological properties were characterized using powder X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), and transmission electron microscopy (TEM) techniques. The rarely reported surface optical (SO) phonon modes of NiO nanoparticles were observed and well‐studied using the dielectric continuum (DC) model. A mismatch between the experimental and DC model SO phonon wavenumbers were observed and is attributed to one magnon‐induced first order phonon shift. The difference between the experimental and DC model SO phonon wavenumbers were reduced with increase in laser power, which indicates the diminishing behavior of magnon excitations. The laser power dependency of highly distinguishable two magnon (2 M) excitation of NiO nanoparticles were well studied. The 2 M modes were experienced a red shift and decrease in intensity with increase in laser power.

Polymorphism characterization of segesterone acetate: A comprehensive study using XRPD, FT-IR and Raman spectroscopy

Segesterone acetate (SA) is a promising and recently approved drug substance used as a contraceptive. SA has two major polymorphic forms, Form I and II. We have shown through indirect analysis that Form I is the more thermodynamically stable polymorphic form at room temperature, however, during the manufacturing process of SA drug products the solid-state stability must be shown to be under control. In the present work, a systematic study has been done using X-ray powder diffraction (XRPD), Fourier Transformed Infrared spectroscopy (FT-IR), and room temperature Raman spectroscopy on both micronized and non-micronized SA powder samples. XRPD showed a crystalline structure in both powder samples with a distinct coexistence of the polymorphic Forms I and II which was confirmed by FT-IR and Raman spectroscopy. The study showed that after thermal annealing a noticeable reduction of the amount of polymorphic Form II was found in both samples. Our results suggest the possibility of reducing the amount of SA Form II by thermal treatment inducing an irreversible solid-state transition to yield the thermodynamically more stable polymorphic Form I. To quantify the ratio of polymorphs I and II we have implemented a method that can be used as a routine analysis step in the manufacturing process of SA.

Phase evolution, microstructure and dielectric properties of electrospun Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3

Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 or simply BZT-0.5BCT has attracted increasing attention due to its excellent ferroelectric properties and lack of lead. BZT-0.5BCT nanofibers were fabricated by sol–gel assisted electrospinning and post-calcination process. Different types of analysis were utilized to study phase evolutions and characterization of calcined fibers. TGA indicated three stages of polymer decomposition at temperatures below 500 °C. FTIR spectroscopy revealed the presence of acetate salts of inorganic precursors in electrospun fibers. Also, it was determined that the formation of oxides started at temperatures around 300 °C and intensified with a rise in temperature. In keeping with DSC and FTIR results, XRD analysis revealed a low crystallization temperature of 550 °C for the perovskite phase. The room-temperature Raman spectroscopy demonstrated the coexistence of both orthorhombic and tetragonal phases at 900 °C and higher temperatures. SEM images illustrated the stability of fibrous morphology up to 1000 °C. High-temperature XRD showed that the curie temperature of nanofibers is between 120 and 150 °C. The dielectric constant of calcined fibers at 900 °C was measured to be 2283.

A Study on the Optical Behavior of Dyx3+ ion Activated Sr(1‐X)Y2O4 Nanophosphors

AbstractWhite light emitting voluminous powder of Sr(1‐x)Y2O4:Dyx3+ nanophosphors (NPPs) is synthesized through solution combustion method using organic fuel as glycine. The doping agent Dy3+ ion is incorporated in the form of dysprosium nitrate hexahydrate and Dy3+ ion varied as 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, and 0.11%. Further, the sample is calcinated at a temperature of 1300 °C for 3 h. The structural and optical properties are investigated using X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), high‐resolution transmission electron microscopy (HR‐TEM), photoluminescence (PL), Fourier transform infrared (FTIR), and Raman spectroscopic techniques. XRD spectra confirm the orthorhombic structure of SrY2O4: Dyx3+ with Pnam space group and cell parameters of a = 10.07 Å, b = 11.91 Å, c = 3.41 Å, the particle size is about 40 nm estimated from the Debye–Scherer method. The morphology and particles size is further confirmed by FE‐SEM and HR‐TEM. The PL emission spectra obtained at an 354 nm excitation wavelength and corresponding PL emission spectra indicate two distinctive peaks, that is, blue (4F9/2 → 6H15/2) and yellow (4F9/2→ 6H13/2). FTIR and room temperature Raman spectroscopy confirms the presence of various bonds. PL emission, correspondingly, is confirmed by the CIE diagram. All these analysis reveal Sr(1‐x)Y2O4:Dyx3+ NPP may be potential candidates for white light‐emitting diodes.

Raman Spectral Probe on Size-Dependent Surface Optical Phonon Modes and Magnon Properties of NiO Nanoparticles

The particle size-dependent surface optical (SO) phonon and magnon modes of NiO nanoparticles were extensively studied using room-temperature confocal Raman spectroscopy. The required nanoparticles...

Improved ferroelectric response of pulsed laser deposited BiFeO3-PbTiO3 thin films around morphotropic phase boundary with interfacial PbTiO3 buffer layer

(1 − x)BiFeO3-xPbTiO3 (BF-xPT) is an interesting material for sensing and actuating devices with large polarization near the morphotropic phase boundary (MPB) (x = 0.30) in the bulk form. However, pulsed laser deposition (PLD) grown (BF-xPT) thin films usually show high electrical leakage and, hence, saturated ferroelectric hysteresis loops are only obtained at subzero temperatures. In this article, we report on high room temperature ferroelectric polarization with saturated hysteresis loops in pulsed laser deposited (BF-xPT) polycrystalline thin films of compositions near the MPB with the use of a thin buffer layer of PbTiO3 (PT). The thin films possessed a perovskite structure with excellent crystallinity and exhibit the presence of a monoclinic (Cm) phase (MA-type) for x = 0.20–0.25 and a mixture of a monoclinic (Cm) phase and a tetragonal (P4mm) phase for x = 0.30–0.35 compositions. The thin films with composition x = 0.25 exhibit a monoclinic phase and yield very large room temperature ferroelectric polarization (2Pr > 80μC/cm2), perhaps the highest room temperature ferroelectric polarization and excellent piezoelectric properties in PLD deposited (BF-xPT) thin films of near-MPB composition. Furthermore, the evolution of ferroelectricity with PT content, studied using room temperature Raman spectroscopy, reveals a correlation with lattice dynamics and stereochemical activity of Bi. Piezoforce domain analysis of the thin films reveals that ferroelectric polarization and electrical leakage in the thin films are intricately related to the type of domains present in the samples, viz., 180°, 109°, 90°, and 71° due to differences in the nature of the domain walls.

Plasmon induced enhancement of surface optical phonon modes and magnon properties of NiO nanoparticles: Raman spectral probe.

In the present work, the influence of Ag-induced plasmons on the surface optical (SO) phonon modes of NiO nanoparticles was extensively studied using room temperature Raman spectroscopy. Remarkable intensity enhancements were observed for the rarely reported SO phonon modes compared to the other first-order phonon modes of NiO nanoparticles. The occurrence of SO modes was further studied using an approximate dielectric continuum (DC) model and a difference between the calculated and experimental SO frequencies was observed, which can be attributed to the presence of one magnon background over the first order phonon modes. The experimental and theoretical SO frequencies became closer at higher Ag concentration and the second-order magnon (2M) and phonon bands disappeared in the NiO:Ag samples. The absence of magnon and higher order phonon modes in the NiO:Ag samples indicates changes in the magnetic properties of the nanomaterials, which has been further supported by the vibrating-sample magnetometer (VSM) measurements.

Temperature-dependent band gap characteristics of Bi12SiO20 single crystals

Bi12SiO20 single crystals have attracted interest due to their remarkable photorefractive characteristics. Since bandgap and refractive index are related theoretically to each other, it takes much attention to investigate temperature dependency of bandgap energy to understand the behavior of photorefractive crystals. The present study aims at investigating structural and optical characteristics of photorefractive Bi12SiO20 single crystals grown by the Czochralski method. The structural characterization methods indicated that atomic composition ratios of constituent elements were well-matched with the chemical compound Bi12SiO20, and grown crystals have a cubic crystalline structure. Optical properties of crystals were investigated by room temperature Raman spectroscopy and temperature-dependent transmission measurements between 10 and 300 K. The analyses of transmittance spectra by absorption coefficient and derivative spectrophotometry techniques resulted in energy bandgaps decreasing from 2.61 to 2.48 eV and 2.64 to 2.53 eV as temperature was increased from 10 to 300 K. The Varshni model was applied to analyze temperature-bandgap energy dependency.