Sujata Sanghi

Rietveld analysis, dielectric and magnetic properties of Sr and Ti codoped BiFeO3 multiferroic

Polycrystalline Bi0.8Sr0.2Fe1 − xTixO3 (x = 0.0, 0.1, 0.2) multiferroics were synthesized via the conventional solid state reaction method. The structure, dielectric relaxation, and magnetic properties of as prepared samples were investigated. The crystal structure examined via XRD and Rietveld analysis confirmed a single phase rhombohedral (space group R3c no. 161) structure. In the Rietveld refinement, good agreement between the observed and calculated pattern was observed. The dielectric response of these multiferroics was analyzed in the frequency range of 10 Hz to 5 MHz at different temperatures. All the samples showed dispersion in dielectric constant (έ) and dielectric loss factor (tan δ) values. The temperature dependence of έ and tan δ showed broad peaks. A reduction in the values of έ and tan δ was observed upon the incorporation of Ti. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic hysteresis loops revealed a significant increase in magnetization wi...

Phase transformation, dielectric and magnetic properties of Nb doped Bi0.8Sr0.2FeO3 multiferroics

Bi0.8Sr0.2Fe1−xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent “s” of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in magnetization for x = 0.10 sample is due to the structural phase transition from rhombohedral to triclinic caused by Nb substitution. For this sample, values of remnant magnetization (Mr) and coercive field (Hc) are 0.155 emu/g and 2.695 kOe, respectively.Bi0.8Sr0.2Fe1−xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent “s” of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in ...

Study of optical band gap and FTIR spectroscopy of Li2O.Bi2O3.P2O5 glasses.

Glasses having composition (25+x)Li(2)O.(65-x)P(2)O(5).10Bi(2)O(3) (0< or =x< or =25 mol%) were prepared by normal melt quenching technique. The optical absorption spectra of the polished samples were recorded in spectral range from 200 to 3300 nm at room temperature. The optical absorption edge (lambda(cutoff)), optical band gap (E(g)) and Urbach energy (DeltaE) were determined from the absorption spectra. Variation in these optical parameters has been associated with the structural changes occurring in these glasses with increase in Li(2)O:P(2)O(5) ratio. Variation in density (D), molar volume (V(M)) and glass transition temperature (T(g)) has also been correlated with structural changes in the glass samples. The FTIR spectra have been recorded in the spectral range from 400 to 1400 cm(-1). The FTIR spectra show the rapid depolymerization of phosphate chains with increase in Li(2)O content and P-O-Bi bonds are formed.

Structural transformation and improved dielectric and magnetic properties in Ti-substituted Bi0.8La0.2FeO3 multiferroics

Ti-substituted BiLaFeO3 ceramics having compositions Bi0.8La0.2Fe1?xTixO3 (x?=?0.0, 0.05, 0.1, 0.15) were synthesized by the conventional solid-state reaction method. Powder x-ray diffraction investigations performed at room temperature show that the crystal structure is rhombohedral for x?=?0.0, 0.05; tetragonal for x?=?0.15; and a phase boundary occurs at x?=?0.1. In the Rietveld refinement good agreement between the observed and calculated pattern was observed. Dielectric response of these samples was analysed in the frequency range 1?kHz?5?MHz at different temperatures. A decrease in the values of real (??) and imaginary (??) parts of dielectric constant with Ti substitution indicates reduced conductivity and hence enhanced resistivity in doped samples. Stability of dielectric constant and conductivity with temperature is considerably improved with Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20?kOe. Magnetic properties of Bi0.8La0.2FeO3 ceramics are considerably improved on Ti substitution along with a significant opening in the room temperature M?H hysteresis loop. Higher values of remanent magnetization (Mr) 0.1373 and 0.1487?emu?g?1; coercivity (Hc) 4.856 and 5.904?kOe are observed for samples with x?=?0.1 and 0.15, respectively. This is due to the structural phase transition from rhombohedral to tetragonal.

Improved dielectric and magnetic properties of Ti modified BiCaFeO3 multiferroic ceramics

Ti substituted BiCaFeO3 ceramics having compositions Bi0.8Ca0.2Fe1−xTixO3 (x = 0.0, 0.1, 0.2) were synthesized by the conventional solid state reaction method. Powder X-ray diffraction investigations performed at room temperature show that all samples possess a rhombohedrally distorted perovskite structure described by the space group R3c. Rietveld refinement presented a good agreement between the observed and calculated patterns. Dielectric response of these samples was analyzed in the frequency range 1 kHz–5 MHz at different temperatures. Dispersion in dielectric constant (έ) and dielectric loss factor (tanδ) values decreases with Ti substitution. έ increases and tanδ decreases significantly by Ti substitution. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic properties of Bi0.8Ca0.2FeO3 ceramic are greatly improved on Ti substitution along with a significant opening in the room temperature M-H hysteresis loop. The values of remnant magnetization (Mr) 0.08 and...

Crystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O...

Spectroscopic properties of Sm3+ doped lead bismosilicate glasses using Judd–Ofelt theory

The spectroscopic properties of Sm(3+) ions in lead bismosilicate glasses (PBSS) as a function of bismuth oxide were investigated using optical absorption and fluorescence spectra. These glasses have shown strong absorption and emission bands in the near infrared and visible region respectively. From the measured absorption spectra, Judd-Ofelt intensity parameters Ω2, Ω4 and Ω6 were determined by applying least square analysis method. The variation of Ω2 and Ω6 with Bi2O3 content has been attributed to changes in the asymmetry of the ligand field at the rare earth ion site and to the changes in the rare earth oxygen (RE-O) covalency. The variation of Ω4 with Bi2O3 content has been attributed to rigidity of the samples. Using the Judd Ofelt intensity parameters the other radiative properties like radiative transition probability, radiative life time, branching ratio and the stimulated emission cross-sections of prepared PBSS glasses have been calculated. The values of radiative properties indicate that Sm(3+) ions emit intense reddish-orange emission ((4)G5/2→(6)H7/2) under excitation at 450 nm wavelength.

Investigation of spectroscopic properties, structure and luminescence spectra of Sm3+ doped zinc bismuth silicate glasses

The glasses with compositions 20ZnO·(79.5-x)Bi2O3·xSiO2·0.5Sm2O3 (10≤x≤50, mol%) have been synthesized using normal melt-quench technique. Optical absorption and fluorescence spectra of the glasses were recorded at ambient temperature. Judd-Ofelt (J-O) theory has been successfully applied to characterize the absorption and luminescence spectra of these glasses. From the measured intensities of absorption bands of these glasses, the Judd-Ofelt parameters, Ωλ (λ=2, 4, 6) have been evaluated. The variation of Ω2 with Bi2O3 content has been attributed to changes in the asymmetry of the ligand field at the rare earth (RE) ion site (due to structural change) and to changes in RE-O covalency, whereas the variation of Ω6 is found to be strongly dependent on nephlauxetic effect. The shift of the hypersensitive band shows that the covalency of the RE-O decreases with decrease in Bi2O3 content in the host glass. Also, using J-O theory various radiative properties like spontaneous emission probability (Arad), radiative life time (τr), fluorescence branching ratio (βr) and stimulated emission cross-section (σ) for various emission bands of these glasses in the visible spectral region have been determined. A close correlation is observed between the Bi2O3 content and the spectroscopic, radiative and structural properties of the prepared glasses. The values of radiative properties indicated that 4G5/2→6H7/2 and 4G5/2→6H9/2 transitions responsible for orange luminescence might be used in the development of materials for LEDs and other optical devices in the visible region.

Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferrites

M-type hexaferrites with compositions BaFe12O19 (BFO), SrFe12O19 (SFO), Ba0.5Sr0.5Fe12O19 (BSFO), and Ba0.5Pb0.5Fe12O19 (BPFO) were synthesized by commercial solid state reaction method. The Rietveld refinement of x-ray powder diffraction revealed a single hexagonal phase with space group P63/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite (α-Fe2O3) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant (ɛ′) and dielectric loss (tan δ) values with frequency. The values of ɛ′ and tan δ increase with increase in temperature due to increase in the number of charge carriers and their mobilities, which are thermally activated. The reciprocal temperature dependence of conductivity (σac) and the most probable relaxation time (τM″) satisfies the Arrhenius relation. A perfect overlapping of the normalized plots of modulus isotherms on a single “super curve” for all the studied temperatures reveals a temperature independence of d...

Effect of Bi2O3 on spectroscopic and structural properties of Er3+ doped cadmium bismuth borate glasses

Glasses with composition 20CdO·xBi(2)O(3)·(79.5-x)B(2)O(3) (15≤x≤35, x in mol%) containing 0.5 mol% of Er(3+) ions were prepared by melt-quench technique (1150°C in air). The amorphous nature of the glasses was confirmed by X-ray diffraction. The spectroscopic properties of the glasses were investigated using optical absorption spectra and fluorescence spectra. The phenomenological Judd-Ofelt intensity parameters Ω(λ) (λ=2, 4, 6) were determined from the spectral intensities of absorption bands in order to calculate the radiative transition probability (A(R)), radiative life time (τ(R)), branching ratios (β(R)) for various excited luminescent states. Using the near infrared emission spectra, full width at half maxima (FWHM), stimulated emission cross-section (σ(e)) and figure of merit (FOM) were evaluated and compared with other hosts. Especially, the numerical values of these parameters indicate that the emission transition (4)I(13/2)→(4)I(15/2) at 1.506 μm in Er(3+)-doped cadmium bismuth borate glasses may be useful in optical communication.