Phase Transition In Bi Research Articles

Ag-induced Phase Transition of Bi2 O3 Nanofibers for Enhanced Energy Conversion Efficiency towards Formate in CO2 Electroreduction.

Bi-based electrocatalysts have been widely investigated in the CO2 reduction reaction (CO2 RR) for the formation of formate. However, it remains a challenge to achieve high Faradaic efficiency (FE) and industrial current densities at low overpotentials for obtaining both high formate productivity and energy efficiency (EE). Herein, we report an Ag-Bi2 O3 hybrid nanofiber (Ag-Bi2 O3 ) for highly efficient electrochemical reduction of CO2 to formate. Ag-Bi2 O3 exhibits a formate FE of >90% for current densities from -10 to -250 mA ⋅ cm-2 and attains a yield rate of 11.7 mmol ⋅ s-1 ⋅ m-2 at -250 mA ⋅ cm-2 . Moreover, Ag-Bi2 O3 increased the EE (52.7%) by nearly 10% compared to a Bi2 O3 only counterpart. Structural characterization and in-situ Raman results suggest that the presence of Ag induced the conversion of Bi2 O3 from a monoclinic phase (α-Bi2 O3 ) to a metastable tetragonal phase (β-Bi2 O3 ) and accelerated the formation of active metallic Bi at low overpotentials (at > -0.3 V), which together contributes to the highly efficient formate formation.

Dynamics of the phase transition in Bi0.5Na0.5TiO3 based on in situ Raman spectroscopy

Phase transition dynamics of Bi0.5Na0.5TiO3 is analyzed using in situ Raman technique with varying temperature. Complex polarization properties are also revealed, such as ferroelectric origin and the thermal hysteresis behavior.

The phase regulation of Bi4O5I2 nanosheets through the controlled hydrolysis in polyhydric alcohol for the enhanced photocatalytic performances of BPA

• Bi 4 O 5 I 2 were regulated via controlled hydrolysis of urea in polyhydric alcohol. • Polyhydric alcohol with proper viscosity is the key role of controlled hydrolysis. • Bi 4 O 5 I 2 with tuned band structure showed superior photodegradation activity. • The reaction rate constant of Bi 4 O 5 I 2 is almost 3 times than that of BiOI. In this study, the phase transition of Bi 4 O 5 I 2 was regulated via the controlled hydrolysis of urea in polyhydric alcohol. The systematic conditions of the controlled hydrolysis for Bi 4 O 5 I 2 phase transition were examined. Polyhydric alcohol solution with proper viscosity (such as EG, and mixture of EG and G), temperature over 180 °C, over 3 h, and tetrabutylammonium iodide (TBAI) over 4 mmol could contribute to the controlled hydrolysis of urea (1.0 g) for Bi 4 O 5 I 2 . The band structure of resulted Bi 4 O 5 I 2 was altered, resulting in superior photodegradation performances of BPA removal due to the efficient charge separation and transfer.

Compression-rate dependence of pressure-induced phase transitions in Bi

It is qualitatively well known that kinetics related to nucleation and growth can shift apparent phase boundaries from their equilibrium value. In this work, we have measured this effect in Bi using time-resolved X-ray diffraction with unprecedented 0.25 ms time resolution, accurately determining phase transition pressures at compression rates spanning five orders of magnitude (10–2–103 GPa/s) using the dynamic diamond anvil cell. An over-pressurization of the Bi-III/Bi-V phase boundary is observed at fast compression rates for different sample types and stress states, and the largest over-pressurization that is observed is ΔP = 2.5 GPa. The work presented here paves the way for future studies of transition kinetics at previously inaccessible compression rates.

Doping-induced topological phase transition in Bi: The role of quantum electronic stress

Charge doping is an essential means to tailor a materials' properties. However, besides moving the Fermi level, charge doping is generally not expected to induce topological phase transition (TPT). Here, using first-principles calculations, we demonstrate an electron doping-induced TPT in bulk Bi from a higher-order topological insulator (HOTI) to a TI. The underlying mechanism is revealed to be driven by an electron doping-induced quantum electronic stress (QES), which in turn induces a highly anisotropic lattice expansion to close/reopen the small energy gap in Bi band structure. Our finding significantly resolves an outstanding controversy concerning the topological characterization of bulk Bi among existing experiments and theories, and explains the physical origin of the topological order in Bi (111) thin films. It sheds new light on the fundamental understanding of topological properties of small band gap materials in relation to doping and QES.

Unusual grain coarsening behavior of bismuth under high pressure

It is well known the atomic diffusion caused by high temperature leads to conspicuous grain coarsening, which is of crucial importance to the properties of materials. High pressure usually slows down the diffusion rate of atoms and refines the grain size. In this study, using synchrotron angle dispersive x-ray diffraction (ADXRD) techniques, we observed an abnormal grain coarsening behavior of bismuth (Bi) stemming from the high pressure phase transition at room temperature, demonstrating that the grain coarsening can also be triggered by pressure. Two factors mainly give raise to this unusual coarsening behavior of Bi: (1) the nucleation rate of new phase is very slow during transformation according to the kinetics study of the phase transition in Bi, which inhibits the grain refinement; (2) the liquid interphase in the phase transition process enables the recrystallization of Bi under high pressure. Our experiment results are consistent with the previous theoretical calculations, which is crucial for describing the nucleation and growth process and clarifying the phase transition mechanisms in Bi.

Correlation of Electrical Response and Structural Phase Transitions in Bi2O3 Nanowires

The electric response of Bi2O3 nanowires is studied by means of impedance spectroscopy at high temperatures and compared to a reference bulk Bi2O3 ceramic. Nanowires present the α to δ phase transition at a similar temperature than the ceramic (1007 vs. 1010 K), showing an increase of over two orders of magnitude in the conductance. On cooling, nanowires change directly to the α phase instead of presenting metastable phases, like the bulk sample. Both samples present a dominant ionic contribution in the δ phase which is also present in the α phase at the highest temperatures. X‐ray absorption spectroscopy (XAS) measurements reveal no differences in the short range structural order of both kinds of samples at room temperature, while a detailed analysis by high temperature X‐ray diffraction (HTXRD) confirms the transitions observed in the conductance measurements. The authors relate the direct phase transition δ → α in nanowires to a lower thermal conductivity in these nanostructures.

Force analysis and pressure quantitative measurement for the high pressure cubic cell

Large volume cubic press is one of the most popular high pressure devices which can produce pressures up to about 7 GPa. It is well known experimentally that the enhancing of the maximum pressure generated in the large volume cubic press has attracted wide attention among scientists and engineers because the higher pressure is capable of synthesizing some materials with interesting properties. In the large volume cubic press, pyrophyllite is typically used as a pressure-transmitting medium. A specimen immersed in such a solid experiences a generalized stress state. The pressure distribution in pyrophyllite is an important parameter for characterizing the sample environment and designing the experiments at high pressure. There is a need for the quantitative measurement of pressure gradients in the pyrophyllite pressure medium, so that the accurate experimental data under high pressure can be obtained. In the large volume cubic apparatus (68 MN), we put a circuit into the high pressure cubic cell, so that the pressures at various positions can be measured by using the phase transitions in Bi, Tl and Ba. In the present work, the relationship between the total press load and the press load allocated to the anvil face, and the relationship between the total press load and the press load allocated to gaskets are established at room temperature. The results show that with the increase of the total press load, the load allocated to the gaskets is increased sharply, while the curve of load allocated to the anvil face versus total press load reaches a plateau, which results in the cell pressure reaching upper limit when the cell pressure reaches up to about 5 GPa. According to the experimental results, the stress state of the cubic cell under high pressure is analyzed and the reason why the pressure generated in the large volume cubic chamber is difficult to exceed 7 GPa is explained. Based on the geometrical structure of the cubic cell, the scheme to increase the upper pressure limit for cubic cell by using the material with high bulk modulus as the pressure transmitting medium and the material with low bulk modulus as the gasket, is proposed. Additionally, the method of calculating the pressure values at different positions along the axis of symmetry in the cubic cell is given through the quantitative calibration of the pressure gradient in the axial direction of the cubic cell. This method can provide more accurate pressure data for high pressure experiments.

Negative pressure effect on the electrical conductivity of San Carlos olivine and its implication to the electrical structure in the upper mantle

Pressure effect on the electrical conductivity of San Carlos olivine was investigated by the newly installed electrical conductivity measurement system at China University of Geosciences. Electrical conductivity of San Carlos olivine aggregates was measured up to 12 GPa and 1475 K using the Walker-type multi-anvil apparatus equipped with eight WC cubes as the second-stage anvils. The pressure generation against applied load for the experimental assemblage was examined by phase transition of Bi, quartz, forsterite under different P - T conditions. To check the data validity of this new system, electrical conductivities of the serpentinites and talc samples were measured. The results are consistent with the published data of the same samples. Electrical conductivity ( σ ) of the San Carlos olivine aggregates and temperature ( T ) satisfy the Arrhenian formula: σ = σ 0 exp[−(Δ E+P Δ V)/kT ]. The pre-exponential factor ( σ 0 ), activation energy (Δ E ) and activation volume (Δ V ) yield value of 7.74 S/m, 0.85 eV and 0.94 cm 3 /mol, respectively. Electrical conductivities of the San Carlos olivine aggregates decline with increasing pressure at same temperatures. The negative pressure effect can be interpreted by strain energy model of defect energy together with the lattice deformation. In addition, the electrical conductivity-depth 1-D profile of the upper mantle was constructed based on our results and some assumptions. The calculated profile is concordant with the geophysical observation at the depth of 180–350 km beneath Europe, which indicates that the upper mantle beneath Europe might be dry.

The inelastic thermal spike model applied to metal/insulator interfaces

AbstractRecently, inter‐diffusion induced by 200 MeV Xe ion irradiation in metal‐insulator interfaces (Bi/Al2O3and Au/Al2O3) was investigated experimentally via in‐situ RBS measurements using 16 MeV C ions. In this work, the experimental results were tried to be explained by the inelastic thermal spike model (ITSM). Although these results explained qualitatively the inter‐diffusion, the experimentally observed diffusion length (∼800 nm) at a fluence value of 7 x 1013cm‐2was much larger than the estimated maximum value within the ITSM (∼80 nm). It was found that the Bi concentration profiles measured via in‐situ RBS could not be fitted by simple diffusional ones. We suggested that the main responsible of the huge atomic diffusion exhibited by Bi in Al2O3could be the directional motion of Bi atoms in molten Al2O3triggered off by the pressure due to liquid‐vapor phase transition of Bi near the interface. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compressibility determination by electrical resistance measurement: a universal method for both crystalline and amorphous solids

A new method is introduced for investigating the compressibility of solids under high pressure by in situ electrical resistance measurement of a manganin wire, which is wrapped around the sample. This method does not rely on the lattice parameters measurement, and the continuous volume change of the sample versus pressure can be obtained. Therefore, it is convenient to look at the compressibility of solids, especially for the X-ray diffraction amorphous materials. The I–II and II–III phase transition of Bi accompanying with volume change of 4.5% and 3.5% has been detected using the method, respectively, while the volume change for the phase transition of Tl occurring at 3.67 GPa is determined as 0.5%. The fit of the third-order Birch–Murnaghan equation of state to our data yields a zero-pressure bulk modulus K 0=28.98±0.03 GPa for NaCl and 6.97±0.02 GPa for amorphous red phosphorus.

What is the structure of liquid Bismuth?

The structure of liquid Bismuth is probably the best-studied among elemental liquid metals because of a combination of the interesting physical properties of Bismuth and its excellent neutron scattering properties. Over the last six decades there have been more than 10 independent studies of the structure of liquid Bi, near the melting temperature. This remarkable number of measurements provides an opportunity to compare these results and to analyze the different sources of error contributing to the calculated pair distribution function. In the present contribution we analyze possible sources of error by varying the analysis procedure for a given measurement. By repeating a previous measurement in a new experimental configuration we demonstrate that an invariant (i.e. up to an absolute error) structure factor can be obtained. Transforming the structure factor into the radial distribution introduces new sources of error which causes the scatter to be greater than that required to resolve issues such as the existence of liquid-liquid phase transitions in Bi and to obtain correlation between thermo-physical properties and structure. We consider the contribution of different parameters when transforming the structure factor to the radial distribution function.

Influence of mechanical configuration and hardness of last stage anvil on high pressure producing efficiency for octahedral cell

We analyse the loading force transmissions for two kinds of loading structures directed at multistage octahedral cell of high pressure device, and build a mechanical relationship for high pressure producing efficiency. The relationship between cell pressure and hydraulic load is calibrated at room temperature for 14/8, 12/6 and 10/4 cell assemblies using the phase transitions of Bi, ZnTe, ZnS and GaAs under high pressure. Also we discuss qualitatively the influences of both mechanical configuration and hardness of last stage anvil on high pressure producing efficiency of octahedral cell. The experimental results show that both mechanical configuration and hardness of last stage anvil are key factors for affecting high pressure producing efficiency, what is more, the mechanical configuration is more important. The larger the geometry configuration of octahedral cell, the higher the high pressure producing efficiency is; high pressure producing efficiency of 6-8 type loading configuration is higher than that of 2-6-8 type loading configuration; when the pressure of octahedral cell approaches to Vickers hardness of last stage anvil, the harder the last stage anvil, the higher the high pressure producing efficiency and the higher cell pressure is.

Study on Pressure-induced Ferroelectric Phase Transition in Bi<SUB>4</SUB>Ti<SUB>3</SUB>O<SUB>12</SUB> by Molecular Dynamics Simulation

在壳模型的基础上, 通过分子动力学方法模拟了压强对Bi 4 Ti 3 O 12 (BIT)铁电相变行为的影响. 为了提高模拟的准确性, 在原有势参数的基础上增加了Ti-Ti短程相互作用势. 计算得出了温度为300K时BIT单晶的铁电正交B2cb相在 x 方向和 z 方向的自发极化强度分别为39.4μC/cm 2 和0, 与实验结果较好的吻合. 然后模拟了压强对BIT相变行为的影响. 模拟结果表明: BIT单晶在压强从-2 GPa到24 GPa范围内, 经历了两次结构相变, 分别发生在 6 GPa和20 GPa处. 这种对称性的改变类似于在环境压力条件下温度导致BIT单晶对称性的改变. 因而模拟结果为研究压强引起BIT的相变行为提供了理论依据.

Field-induced phase transition in Bi1/2Na1/2TiO3-based lead-free piezoelectric ceramics

The origin of the electric field-induced strain in the polycrystalline ceramic 0.92Bi1/2Na1/2TiO3–0.06BaTiO3–0.02K1/2Na1/2NbO3was investigated usingin situhigh-resolution X-ray and neutron diffraction techniques. The initially existing tetragonal phase with pseudocubic lattice undergoes a reversible phase transition to a significantly distorted rhombohedral phase under electric field, accompanied by a change in the oxygen octahedral tilting froma0a0c+toa−a−a−and in the tilting angle. The polarization values for the tetragonal and rhombohedral phases were calculated based on the structural information from Rietveld refinements. The large recoverable electric field-induced strain is a consequence of a reversible electric field-induced phase transition from an almost nonpolar tetragonal phase to a ferroelectrically active rhombohedral phase.

La content and size effects on crystal structure and phase transition of Bi 4−xLa xTi 3O 12 nanocrystals

Crystal structure and phase transition of Bi 4− x La x Ti 3O 12 nanocrystals with x=0−1.25 and grain sizes of 23, 42 and 53 nm were investigated in detail by X-ray diffraction and Raman scattering. The results showed that La atoms substitution for Bi atoms in Bi 4Ti 3O 12 nanocrystal strengthens the short-range interaction between atoms and leads to a ferroelectric–paraelectric phase transition at a critical La content x c. The critical x c decreases as the grain size d decreases. The relationship between x c and 1/ d can be described by a linear equation.

Pulsed Photoacoustic: A Reliable Technique to Investigate Diffuse Phase Transitions and Associated Phenomena in Ferroelectrics

Often permittivity against T curves do not provide a conclusive characterisation of dielectric features of ferroelectric materials. Particularly, when permittivity is obtained from impedance measurements, where to experimental data is gradually lost at high frequencies when the temperature rises. Here we show how a combination of permittivity measurements and photoacoustic experiments can give a much more complete characterization of the ferro-paraelectric phase transitions and associated phenomena than those obtained from permittivity data alone. Peaked correlation curves, obtained from photoacoustic experiments were interpreted to be a manifestation of large enough microscopic variations of the compressibility as the temperature changed. On one hand, using a classical ferroelectric (BaTiO 3 ) and a well-recognized relaxor (Ba(Ti 0.65 Zr 0.35 )O 3 ) the main differences between their photoacoustic response are established. On the other hand, dielectric and photoacoustic results from the compounds Bi 2 WO 6 and Bi 2 [Ta 0.1 W 0.9 ]O 6 − δ , were combined to characterize the temperature dependence of their dielectric behavior. Results provide evidence of the presence of a diffuse phase transition in Bi 2 WO 6 at 660°C similar to that corresponding to relaxor behavior. Additionally the occurrence of a classical ferro-paraelectric phase transition above 900°C was found. This last phenomenon is detectable only by photoacoustic experiments. In Bi 2 [Ta 0.1 W 0.9 ]O 6 − δ the presence of a well defined transition was not detected. Dielectric determinations throughout ac measurements were carried out in the frequency interval 5 Hz-13 MHz. A pulsed Nd:YAG laser (10 Hz, 5 ns pulse width) was used to perform the photoacoustic experiments, where the out-coming signal was detected by a piezoelectric transducer. Dielectric and photoacoustic experiments were performed in a temperature interval from 250°C up to 1000°C.

A slide-type multianvil ultrahigh pressure apparatus and calibrations of its pressure and temperature

A slide-type ultrahigh pressure apparatus with 6/8 anvils is described. The three-supporting pillars of the main framework and the slide-type multi-anvils have conformable mechanical symmetry. Under the loading uniaxial pressure, the first-stage anvils can be self-corrected and run with excellent synchronicity and reproducibility. In the present experiments, the edge length of pyrophyllite octahedron is 125 mm and the truncation edge length of tungsten carbide anvil is 8 mm. The cell pressure was calibrated at room temperature by means of the known pressure-induced phase transitions of Bi and ZnTe at 255, 77, 96 and 120 GPa. The cell temperature under 10 GPa was measured up to 1560 ℃ by WRe3-WRe25 thermocouple. The temperature calibration was reconfirmed and extended to the higher range by observation of diamond formation on the interface between graphite heater and steel plug, and by comparison of the variational details of recorded data and the Fe—C phase diagram, and then the axial temperature gradient was estimated to be about 21 ℃/mm.

Design and assembly of split-sphere high pressure apparatus based on the hinge-type cubic-anvil press

A new split-sphere large-volume high pressure apparatus has been developed to generate high pressure above 10 GPa. The apparatus is based on a domestic hinge-type cubic-anvil press known as the DS6×800T press. In this work, the split-sphere parts are directly placed in the cubic-anvil cell, and the effect of the gasket dimension and phyrophyllite density on pressure transmitting efficiency has been investigated. The relationship of cell pressure versus press load was calibrated at room temperature for the 14/8 (octahedral edge-length/anvil truncation edge-length, in millimeters) cell assembly using the phase transitions of Bi Ⅰ-Ⅱ(2.55 GPa), Ⅲ-Ⅴ(7.7 GPa), and SnⅠ-Ⅱ(9.4 GPa).The experimental results show that the cell pressure can reach about 10 GPa with a sample volume of 3—4 mm3 under an applied load of 290 ton.

Phase Diagram in Bi4 − x La x Ti3O12

Synopsis: Phase transitions in Bi 4 − x La x Ti 3 O 12 (BiLT-x) mixed crystals with the low La concentration (x < 0.5) were investigated. It was found that the dielectric anomaly showing the phase transition appears below 675°C where the transition temperature depends on the concentration x, while the transition at 675°C remains in the concentration range of 0 ≤ x ≤ 0.5. The spontaneous polarization along the c-axis at room temperature was found to decrease as the La concentration increases and to disappear at about x = 0.2. New phase transition from the orthorhombic to the monoclinic phase in the BiLT-x was experimentally confirmed. The phase transition and its symmetry change were discussed on the basis of the Landau theory.