Bi Substitution Research Articles

In-situ optical and structural insight of reversible thermochromic materials of Sm3-xBixFe5O12 (x= 0, 0.1, 0.3, 0.5)

Reversible thermochromic inorganic materials of rare-earth iron garnets Sm3-xBixFe5O12 (x = 0, 0.1, 0.3, 0.5) with different ratio of doped Bi3+ were synthesized via high temperature solid state reaction and their structure and properties were investigated by powder x-ray diffraction (XRD), infrared spectroscopy (IR), Raman, and UV-vis-NIR spectroscopy. Refinement of the as-prepared powders XRD results indicates that the lattice constants decreased with the increasing of the doping amount of Bi3+. Thermochromism for all Sm3-xBixFe5O12 (x = 0, 0.1, 0.3, 0.5) samples showed the change in colour from yellow-green to brown and the substitution of Bi3+ ions also affect the colour of the samples. The initial colour of the samples is related to O2−→Fe3+ ligand-to-metal charge transfer at 2.54 eV and d-d transitions peaking at 1.38 and 2.03 eV. The macroscopic thermochromic is originated from charge transfer at lower energy, whereas the d−d is only very weakly affected. This family of materials could be applied as a thermal indicator pigments for cooking tools and hotplates.

Competing dopants grain boundary segregation and resultant seebeck coefficient and power factor enhancement of thermoelectric calcium cobaltite ceramics

The present work demonstrates the feasibility of increasing the values of Seebeck coefficient S and power factor of calcium cobaltite Ca3Co4O9 ceramics through competing dopant grain boundary segregation. The nominal chemistry of the polycrystalline material system investigated is Ca3−xBixBayCo4O9 with simultaneous stoichiometric substitution of Bi for Ca and non-stoichiometric addition of minute amounts of Ba. There is continuous increase of S due to Bi substitution and Ba addition. The electrical resistivity also changes upon doping. Overall, the power factor of best performing Bi and Ba co-doped sample is about 0.93 mW m−1 K−2, which is one of the highest power factor values ever reported for Ca3Co4O9, and corresponds to a factor of 3 increase compared to that of the baseline composition Ca3Co4O9. Systematic nanostructure and chemistry characterization was performed on the samples with different nominal compositions. When Bi is the only dopant in Ca3Co4O9, it can be found at both the grain interior and the grain boundaries GBs as a result of segregation. When Bi and Ba are added simultaneously as dopants, competing processes lead to the segregation of Ba and depletion of Bi at the GBs, with Bi present only in the grain interior. Bi substitution in the lattice increases the S at both the low and high temperature regimes, while the segregation of Ba at the GBs dramatically increase the S at low temperature regime.

Photoluminescence and electric properties of Pr/Nb codoped Bi4Ti3O12 bismuth layered-structure ceramics

Bi4Ti3O12 (BIT) belongs to bismuth-layer structure piezoelectric materials, along with high Curie temperature ( T c) and high resistivity. Pr/Nb co-doped BIT piezoelectric ceramics were synthesized by conventional solid-state reaction method and their structural, up-conversion luminescent and dielectric properties were investigated in this study. The substitution of Nb5+ ion was fixed as 0.08 mol and the amount of Pr3+ was 0≤ x ≤0.1. The X-ray diffraction data showed that the samples were single phase with orthorhombic unit cell, and SEM micrographs revealed that the samples have similar plate-like grain morphology. Raman spectroscopy revealed that Er3+ substitution for Bi3+ occured predominantly at the A-site in the perovskite blocks. The red emission was observed under the ultraviolet and blue light excitation at room temperature, which is adaptable to the emission band of commercial blue light-emitting diodes (LEDs) chips. With increasing Pr3+ content, the intensity of the photoluminescence increased initially and then decreased due to concentration quenching. The T c was slightly shifted to the lower temperature, the piezoelectric and ferroelectric properties was both enhanced by doping. These results indicated the Pr doped BITN ceramics were a kind of multifunctional materials with excellent optical performance.

Lillianite homologues from Kutná Hora ore district, Czech Republic: a case of large-scale Sb for Bi substitution

Lillianite homologues from Kutná Hora ore district, Czech Republic: a case of large-scale Sb for Bi substitution

Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics

To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+.

Bi Substitution Effects on Superconductivity of Valence-Skip Superconductor AgSnSe2

We have synthesized AgSn1-xBixSe2 polycrystalline samples to investigate the effect of partial substitution of mixed-valence Sn by Bi3+ to the superconductivity of the valence-skip superconductor AgSnSe2. The Bi-substituted AgSn1-xBixSe2 were obtained up to x = 0.2, but an insulating phase Ag2SnBi2Se5 with a NaCl-type structure showed up above x = 0.3. The superconducting transition temperature increased from 4.5 K (x = 0) to 5.0 K (x = 0.1) by Bi substitution. The enhancement of superconductivity by the suppression of the valence-skip states of Sn suggests that the valence-skip states of Sn are not positively linked to the pairing mechanisms of superconductivity in the AgSnSe2 system.

Structural and Magnetic Properties of Pure and Mn-Doped Bismuth Ferrite Powders

ABSTRACTMultiferroic materials are of great interest from the scientific and technological viewpoints based on their multifunctional behavior involving ferroelectricity, ferromagnetism, ferroelasticity and strong electromagnetic coupling properties. Among these materials, BiFeO3 (BFO), is a well-known multiferroic with simultaneous ferroelectricity (TC=1103K) and G-type antiferromagnetism (TN=643K). In this work, we doped BiFeO3 with Mn species and studied the doping effect on the corresponding magnetic properties, expected from the substitution of Bi3+ by Mn2+. Additionally, the optimum processing conditions to minimize the formation of any impurity phase were also identified. X-Ray Diffraction (XRD) characterization confirmed the formation of powdered impurity-free BFO in pure and 7 at.% Mn-BFO only after annealing of the precursor compounds at suitable temperatures and time (700°C, 15 minutes). Scanning Electron Microscopy (SEM) analyses were used to determine the size and morphology of synthetized powders. Vibrating sample magnetometry (VSM) measurements showed that maximum magnetization values increased with doping and reached a maximum value in the 7 at.% Mn-doped BFO annealed at 700°C for 15min; the corresponding magnetization in the non-saturated MH loops reached 0.68 emu/g. This behavior can be attributed to the actual incorporation of Mn species into the BFO lattice and the substitution of non-magnetic Bi species.

Role of trivalent bismuth ion substitution at Dy site on the physical properties of DyMnO3

Polycrystalline compounds of Dy1−xBixMnO3 (x = 0 & 0.1) synthesized by ceramic method were characterized by X-ray diffraction technique and their vibrational, transport and magnetic properties studied. Refinement of powder X-ray diffraction data showed that both materials exhibit orthorhombic structure with Pnma space group. Although Bismuth substitution retains the crystal structure, bond angles and bond lengths within MnO6 octahedra are altered as compared to the pristine compound, DyMnO3. While bond angle between manganese ions along the b-axis reduces slightly (1°), axial bond angle increased by ∼3° in the substituted compound. Raman bands arising from the atomic vibrations of rare earth dysprosium and oxygen ions have been identified from room temperature Raman spectra. For 10 at.% substitution of Bi3+, these modes are hardened. Transport measurement studies indicated that the materials are semiconducting in nature with small polaron hopping type of conduction. Hopping energy is decreased to 98.52 meV for Bi3+ substituted DyMnO3 (Dy0.9Bi0.1MnO3) from 103.85 meV for DyMnO3. Temperature dependence of dc magnetization studies revealed anomalies around 39 K, 12 K and 3.62 K corresponding to antiferromagnetic ordering involving Mn3+ and Dy3+ ions respectively. Temperature and frequency variation of ac susceptibility data corroborated the dc magnetization results. In both compounds, magnetization versus applied magnetic field curves measured at several temperatures from room temperature down to 10 K showed linear behavior revealing paramagnetic nature. This behavior indicates the absence of magnetic correlations which is in accordance with MT data. On the other hand, hysteresis loops were observed in M-H data registered ∼2 K with coercive fields of 1520 Oe and 1365 Oe for DMO and DBMO respectively. However, magnetization does not saturate even at 7 × 104 Oe field. The origin for the ferromagnetic coupling could be ascribed to the correlations between Dy3+ and Mn3+ ions through apical oxygen ions in the unit cell favoring superexchange interactions.

Magneto-optical properties of SrBixLaxFe12-2xO19 (0.0≤x≤0.5) hexaferrites by sol-gel auto-combustion technique

SrBixLaxFe12-2xO19 (0.0≤x≤0.5) hexaferrites were synthesized by sol-gel auto combustion technique. The influence of Bi and La substitutions on structural, magnetic and optical properties were investigated by X-ray diffraction (XRD), Furrier transformed infrared (FT-IR), Vibrating sample magnetometer (VSM) and Percent diffuse reflectance spectroscopy (DR %). XRD analysis confirmed the single phase formation for all the samples, the purity of the products was also confirmed by FT-IR. The specific magnetization (σ-H) curves revealed the ferromagnetic nature of the samples. The extrapolated specific saturation magnetization (σs) decreases from 63.45emu/g to 49.84emu/g with increasing Bi, La substitutions. Similar decrement is observed from 32.6emu/g to 25.8emu/g at remnant magnetization (σr). The average crystallite size varies in a range of (43.28–51.40)nm. The coercive fields are between 4682 and 5315Oe. Magnetic anisotropy was assigned as uniaxial and calculated effective anisotropy constants (Keff) are between 5.57×105 Ergs/g and 4.03×105 Ergs/g. The observed high magnitudes of intrinsic coercivity (Hci) above 16,000Oe confirm hard magnetic nature of the samples. The Tauc plots were used to extrapolate the direct optical energy band gap (Eg) of hexaferrites. The Eg values decreased from 1.81 to 1.68eV with increasing Bi, La contents.

Effects of Bi-Pb substitution in (Bi,Pb)2223 thin films fabricated by sputtering method

Superconducting Bi2-nPbnSr2Ca2Cu3Ox (2223) thin films were deposited by using a multi-target sputtering system. A multi-target system enables the fabrication of thin films with varying compositions. First, we tried to obtain 2223 single-phase films by using the as-grown method. However, it is difficult to remove the influence deficiency of Bi atoms at high temperatures, so only thin films with mixed crystals of Bi2Sr2Ca1Cu2Ox (2212) and 2223 were obtained. We next conducted post-annealing to improve the crystallinity of the thin films and studied the effects of substitution of Bi with Pb. As a result, single-phase 2223 thin films with a critical temperature of 108K were obtained by optimizing the annealing conditions and the thin film composition.

The effect of Bi substitution on the microstructure and magnetic properties of the Sr0.4Ba0.3La0.3Fe12−xBixO19 hexagonal ferrites

Bi3+ ions doped M-type hexaferrites, Sr0.4Ba0.3La0.3Fe12−xBixO19 (0≤x≤0.7), were prepared by the ceramic process. The phase components of the magnetic powders were investigated by X-ray diffraction. The results show that a single magnetoplumbite phase is obtained for the magnetic powders with x from 0 to 0.2, and BiFeO3 as a second phase appears when Bi content (x)≥0.3. The micrographs of the sintered magnets were observed by a field emission scanning electron microscopy. The sintered magnets are formed of hexagonal-shaped crystals. The magnetic properties of the sintered magnets were measured at room temperature by a permanent magnetic measuring system. The remanence (Br) first increases with x from 0 to 0.2, and then decreases when Bi content (x)≥0.2. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) firstly decrease quickly with x from 0 to 0.1, and then increase linearly when Bi content (x)≥0.1. The maximum energy product [(BH)max] increases with x from 0 to 0.3, and then decreases when Bi content (x)≥0.3. The ratio Hk/Hcj ratio first increases with Bi content (x) from 0 to 0.4. And the Hk/Hcj ratio decreases when x≥0.4.

β-RE1-xBixB3O6 (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, Y): Bi(3+) Substitution Induced Formation of Metastable Rare Earth Borates at Ambient Pressure.

There emerge great interests in the syntheses of metastable polyborates; however, most are involved with the high-pressure technique. A facile method to synthesize metastable rare earth borates at ambient pressure is eagerly required for the large-scale production and property investigation. Here we demonstrate the critical role of Bi(3+) substitutions in the stabilization of metastable β-REB3O6 (RE = Sm, Eu, Gd, Tb, Dy, Ho, Er, and Y) at ambient pressure, where the Bi(3+)-to-RE(3+) substitutions would efficiently reduce the synthetic temperatures to 735-820 °C, well below the upper limit of thermodynamically stable window (840-980 °C). Partial solid solutions of β-RE1-xBixB3O6 were prepared, and the ranges of the solution were also studied experimentally. The thermal behaviors of β-RE0.8Bi0.2B3O6 were investigated by differential thermal analyses and powder X-ray diffraction, and they were divided into two categories; that is, β-RE0.8Bi0.2B3O6 (RE = Sm, Eu, Gd) transfers to α-RE0.8Bi0.2B3O6 with further increasing the temperature to 950 °C, while β-RE0.8Bi0.2B3O6 (RE = Tb, Dy, Ho, Er, and Y) decomposes into hexagonal REBO3 and B2O3. In particular, the allowed concentration of Bi(3+) in β-Gd1-xBixB3O6 was 0.10 ≤ x ≤ 0.25, and these samples show bright blue emissions under UV excitation, which suggests the high efficiency of light absorption and high potential as phosphors with further doping of other activators.

Phonon spectra of eulytite crystals Bi4M3O12 (M = Ge,Si): ab initio study

In this paper we present the results of ab initio DFT calculation of phonon spectra for bismuth ortho-germanate Bi4Ge3O12 and bismuth ortho-silicate Bi4Si3O12 crystals, in the center of the first Brillouin zone. First, the geometry optimization was performed using the analytical energy gradients, with respect to atomic coordinates and unit cell parameters. Vibrational frequencies and normal modes were calculated within the harmonic approximation by diagonalizing the mass-weighted Hessian matrix. The IR and Raman spectra of both crystals were simulated with the periodic ab initio Crystal 09 code and B3LYP hybrid functional and the two sets of Transverse-Optical and Longitudinal-Optical frequencies are generated, together with their intensities. Also, the influence of isotopic substitution for Bi, Ge and O in phonon modes and the picture with values of frequencies shift in each mode by isotopic substitution were calculated. The obtained results are discussed and the comparision between the computed spectra and experimental data is quite satisfactory, which justifies the model and simulation scheme used for the title systems.

Fe/W Co-Doped BiVO4 Photoanodes with a Metal-Organic Framework Cocatalyst for Improved Photoelectrochemical Stability and Activity.

BiVO4 has been identified as one of the excellent visible light responsive photoanodes for use in photoelectrochemical (PEC) water splitting. However, pristine BiVO4 usually exhibits relative low photocatalytic properties owing to insufficient charge separation and transport characteristics. Although the marginal n-type doping of higher valence ions can obviously raise the photocurrent value, it by no means improves the PEC stability. In this work, we successfully enhanced the PEC stability of BiVO4 by doping Fe ions in substitution of Bi. Density functional theory calculations have illustrated that Fe-doping would result in an impurity band in the forbidden gap, and thus narrow its energy gap. More importantly, Fe-doping can synergize with other means to further improve the PEC activities of BiVO4 . Therefore, we fabricated a nanoporous Fe/W co-doped BiVO4 photoelectrode, and then loaded the metal-organic framework (MOF) MIL-100(Fe) as cocatalyst to further promote the separation of charge carriers. To the best of our knowledge, MOFs have not yet been utilized as a cocatalyst to facilitate the charge separation, which could increase the photocurrent density of Fe/W co-doped BiVO4 .

Phase evolution and microwave dielectric properties of (Bi1−xLnx)2MoO6 (Ln=Nd and La, x≤0.3) ceramics

(Bi1−xLnx)2MoO6 (Ln=Nd and La) ceramics were prepared by conventional solid state reaction method. Solid solutions crystallizing in a monoclinic structure with a space group P21/c were obtained in the (Bi1−xLax)2MoO6 (x≤0.3) ceramics. For the (Bi1−xNdx)2MoO6 ceramics, tetragonal Nd2MoO6 phase with a space group I41/acd was detected when x value reached 0.2 besides the Bi2MoO6 solid solution. Temperature stability and quality factor Qf value at microwave frequencies were improved by appropriate substitution for Bi3+ by Nd3+ and/or La3+ in Bi2MoO6 system. When x=0.2, for both (Bi1−xNdx)2MoO6 and (Bi1−xLax)2MoO6 ceramics, Qf values reached maximum about 30,200GHz and 32,900GHz, respectively. TCF value shifted towards zero with substitution of Bi3+ by Nd3+ and/or La3+. When x=0.3, TCF values of (Bi1−xNdx)2MoO6 and (Bi1−xLax)2MoO6 ceramics were −70 and −85ppm/°C, respectively. Relation between crystal structure, microstructure and microwave dielectric properties were discussed.

Point defect engineering of high temperature piezoelectric BiScO3-PbTiO3 for enhanced voltage response

BiScO3-PbTiO3 is the most promising system among high sensitivity piezoelectric BiMO3-PbTiO3 perovskite solid solutions with high Curie temperature, which are under extensive investigation for expanding the operation temperature of state of the art Pb(Zr,Ti)O3 (PZT) up to 400°C. The viability of these alternative materials requires the development of specific point defect engineering that allow a range of piezoelectric ceramics comparable to commercial PZTs to be obtained, optimized for the different applications. A distinctive feature of BiMO3-PbTiO3 systems is the simultaneous presence of both Bi3+ and Pb2+ at the A-site of the perovskite. This enables the possibility of introducing charged point defects without incorporating new chemical species, just by defining an A-site non–stoichiometry. In this work, we present a comprehensive study of the effects of Bi substitution for Pb, along with the formulation of Pb vacancies for charge compensation. Results indicate an overall lattice stiffening that yields reduced polarizability and compliance, and dominates over a limited enhancement of the ferroelectric domain wall dynamics, so as a largely enhanced voltage response is obtained. Specifically, BiScO3-PbTiO3 with the A-site non-stoichiometry is shown to be very suitable as the piezoelectric component of magnetoelectric composites for magnetic field sensing.

Magnetic inhomogeneity and Griffiths phase in Bi substituted La0.65−xBixCa0.35MnO3 manganites

In the present communication, we report the effect of Bi substitution on structural, magneto-transport, magnetic and thermal properties of La0.65−xBixCa0.35MnO3 (0≤x≤0.2) compounds. Rietveld refined XRD patterns confirm that all the samples are single phase and crystallize in rhombohedral symmetry with R-3C space group. It was observed from electrical and magnetic studies that with increasing Bi content both the metal-insulator transition temperature (TMI) and ferromagnetic–paramagnetic (FM–PM) transition temperature (TC) shift towards lower temperatures. Deviation of the temperature dependence of inverse susceptibility curves from the Curie–Weiss law suggests the existence of Griffiths-like phase. The electrical resistivity data were analyzed by utilizing various theoretical models. It is revealed that the electron–electron scattering is dominating in the metallic region, while the insulating region is well-described by the polaron hopping model. Analysis of thermoelectric power data further reveals that the small polaron hopping (SPH) mechanism is operative in the high-temperature insulating regime. The entropy change associated with the FM–PM transition is found to decrease with increasing x, which is presumably due to the increase in magnetic inhomogeneity with increasing Bi content.

On the electrical properties of the Bi2−ySryIr2O7 pyrochlore solid solution: Quantum ab initio and classic calculations

In this work, a theoretical study of the electrical properties of the Bi2−ySryIr2O7 (Bi2−ySryIr2O16O2) α-pyrochlore-type solid solution is presented. Quantum ab initio DFT(WIEN2k) calculations were performed in order to understand the electrical resistivity changes associated to the Bi substitution by Sr in this system. The main crystallographic modification associated to this substitution is the x position of the 48f oxygen (x, 18, 18) (O1); this substitution substantially modifies the Bi/Sr–O1 and Ir–O1 atomic distances, increasing the former and diminishing the latter. Experimentally, the Bi2−ySryIr2O7 samples are metallic and the electrical resistivity increases with the Sr content. Electronic structure calculations for Bi2Ir2O7 and BiSrIr2O7 show that, regardless of structural changes, there is only a small change of electrical conductivity with the Sr substitution, and the experimentally observed increase of the resistivity can be explained in terms of a larger impact on the electronic structure of both; the Sr ‘impurities’ as well as of the thermal Sr oscillations.

High-Temperature Dielectrics in BNT-BT-Based Solid Solution.

Bi0.5Na0.5TiO3-BaTiO3 (BNT-BT)-based ternary solid solutions were investigated for high-temperature capacitor applications. Through a comprehensive investigation of the (1 - x )(0.92Bi0.5Na0.5TiO3-0.08BaTiO3)- x NaNbO3 [(1 - x )(BNT-BT)- x NN, x = 0 -0.45] system, 0.85(BNT-BT)-0.15NN was selected as the parent matrix due to its relatively high permittivity (>1800) and favorable energy-storage density (0.56 J/cm3 at 7 kV/mm). The effect of bismuth substitution on the dielectric properties of the matrix was further characterized. The introduction of bismuth greatly broadened the operational temperature range of 0.85(BNT-BT)-0.15Na1-3yBiyNbO3 ceramics to over 327 °C for a ±15% tolerance. The dc resistivities were of the order of 108 - [Formula: see text] magnitude from room temperature to 300 °C. An activation energy of 1.1-1.2 eV in 200-350 °C was obtained from dc resistivity data, suggesting that the conduction process in this temperature range may be associated with oxygen vacancy migration. Furthermore, the energy-storage properties were largely improved by the addition of bismuth. When the substitution of Bi over Na achieved was up to 7%, the energy-storage density and efficiency reached 0.62 J/cm3 and 88% at 7 kV/mm, respectively. These results confirm that a BNT-BT-based solid solution is a promising candidate for lead-free high-temperature capacitor applications.

Optical and electrical characterization of BixSe1−x thin films

Abstract Bulk samples of the BixSe1-x system with (x = 0, 5, and 10) were prepared using conventional melt quenching technique. Thin films were then deposited by thermal evaporation technique under high vacuum conditions from the prepared bulk samples. Effect of Bi substitution on surface morphology, electrical and optical properties of BixSe1-x thin films was studied. X-ray diffraction studies showed the formation of nanocrystalline clusters at Bi concentration x = 10. Formation of these clusters resulted in a rough surface which was confirmed by AFM measurements. The film surface was smooth, with RMS roughness of 0.0124 nm for Bi5Se95. For Bi10Se90, the RMS roughness increased to 3.93 nm indicating the formation of Bi2Se3 clusters. A simple hot probe technique showed a transition from p-type to n-type due to Bi incorporation. Charge transport mechanisms were investigated by temperature dependent DC electrical conductivity measurements in the temperature range of 209 K to 313 K. Electrical activation energy (ΔE) of the films with different Bi concentrations was found to exhibit a notable change at the p to n transition. At low temperature, the conduction was in reasonable agreement with Mott’s condition of variable range hopping. Mott parameters and the density of localized states near Fermi level were evaluated and correlated with the structural changes resulting from Bi addition. In addition, a red shift of the optical absorption edge of the films under study caused by Bi-Se substitution was observed. Slight changes in the optical parameters were observed with the γ-irradiation. Addition of Bi atoms could be used to tailor the structural, electrical and optical properties of chalcogenide materials such as junctionless photovoltaic devices.