BiPO4 Phase Research Articles

High total Li-ion conductivity of LiTa2PO8 ceramics sintered using Bi2O3 as an additive

Lithium tantalum phosphate LiTa2PO8 ceramics have attracted significant attention as solid electrolytes in oxide-based all-solid-state batteries owing to their superior bulk conductivity of more than 1 mS cm−1 at room temperature. However, high-temperature sintering at 1050 °C, which is required to achieve a dense morphology, results in a high interfacial resistance at the grain boundaries. In this study, dense LiTa2PO8 ceramics were successfully synthesized via a conventional solid-state method at a low sintering temperature of 900 °C using Bi2O3 as the additive. A total lithium-ion conductivity of 1.41 × 10−3 S cm−1 at 25 °C was achieved. The microstructures of the sintered LiTa2PO8 ceramics were analyzed by X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Large LiTa2PO8 grains grew in the dense solid-electrolyte body together with the interfacial BiPO4 phase, which acted as a sintering flux material, at a low sintering temperature of 900 °C. Thus, these LiTa2PO8 ceramics can serve as oxide solid electrolytes for all-solid-state lithium batteries owing to their high total Li-ion conductivity.

Low-temperature hydrothermal synthesis of BiPO4 for Rhodamine B removal

The synthesis and Rhodamine B removal efficiency of monazite monoclinic BiPO4 by hydrothermal route using Bi(NO3)3·5H2O, K2HPO4·3H2O and HNO3 as staring materials were presented in this work. The obtained samples were characterized by X-ray powder diffraction, high-resolution transmission field-emission scanning electron microscopy and diffuse reflectance UV-Vis spectrometry. The results showed that, by selecting suitable reaction parameters, the pure monazite monoclinic phase of BiPO4 was received readily at hydrothermal temperature as low as 130 oC, considerably lower than that reported previously. The obtained monazite monoclinic phase of BiPO4 powders exhibited a high removal efficiency of 96% for 150 min under 365nm-UV irradiation. The mechanism of the Rhodamine B photodegradation reaction over the synthesized monazite monoclinic BiPO4 was also proposed.

Superior atomic coherence time controlled by crystal phase transition and optical dressing.

We compare the atomic coherence time of doped ion crystals, i.e., BiPO4: Eu3+, YPO4: Eu3+, YPO4: Pr3+, and Y2SiO5: Pr3 + crystals. Such atomic coherence time is controlled by crystal field splitting (CF-splitting) and optical (photon and phonon) dressing. Compared with the other doped ion crystals, BiPO4: Eu3+ exhibits the longest coherence time. By controlling thermal phonon, phase-transition phonon, broadband or narrowband excitation, and fluorescence (FL) or spontaneous four-wave-mixing ratio (S-FWM), a superior atomic coherence time of up to 10 ± 0.6 ms is achieved in the pure hexagonal (0.5:1) phase of BiPO4: Eu3+. Furthermore, the relationship between TAT-splitting and spectral Autler-Townes (SAT)-splitting was investigated. This superior atomic coherence time has potential applications in quantum memory devices.

Probing into structural and spectroscopic properties of Dy3+ doped and Eu3+/Dy3+ co-doped bismuth phosphate (BiPO4) glass ceramics with different modifier fluorides

In the present work, the synthesis of BiPO4 phase resided in transparent bismuth phosphate glass ceramics has been accomplished by regular melt quenching route. Impact of modifier fluorides on structural and spectroscopic properties of Dy3+ doped and Eu3+/Dy3+ co doped different bismuth phosphate glass ceramics via PXRD, FTIR, XPS, SEM, optical absorption, emission, excitation and decay measurements has been thoroughly examined. Various spectroscopic parameters were calculated from the absorption spectra using Judd-Ofelt (J-O) theory and analyzed the parameters. From the emission spectra, emission characteristics were studied via optical band gains (σe × τR), gain bandwidths (σe × Δλeff), Y/B ratios and lifetimes (τ) from decay curves. The effect of Eu3+/Dy3+ co-doping on emission properties has been studied in these glass ceramics where energy transfer was observed. Color coordinates for all the studied systems also inferred. Among various multi component glass ceramics studied in the present work, NaF2 system could be suitable for laser and white light applications.

BiPO4:Ln3+ (Ln = Eu, Tb, Eu/Tb) nanorods: Room-temperature synthesis, reaction mechanism, and color-tunable emission

Ln3+ (LnEu, Tb, Eu/Tb) doping hexagonal BiPO4 nanorods were synthesized by a room-temperature co-precipitation method using ethylene glycol as solvent. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), thermal gravimetric (TG), and photoluminescence spectroscopy (PL) were utilized to investigate the structure, morphology, surface chemistry, and fluorescence performance of the obtained phosphors, respectively. The results showed that hexagonal phase of BiPO4 formed at room temperature, which consisted almost entirely of nanorods with an average diameter of 70 nm and an average length of 292 nm. The chemical reactions mechanism was well elucidated. Under short-wavelength UV light excitation, the as-obtained BiPO4:Eu3+ and BiPO4:Tb3+ samples exhibited strong orange-red and green emissions, respectively. Moreover, the photoluminescence color could be tuned from red, orange, yellow, and green-yellow, to green by simply adjusting the relative doping concentrations of Tb3+ and Eu3+ ions. The room-temperature synthesis reported in the present study could be extended to prepare other rare-earth doped inorganic luminescent materials.

Phase Transformation, Photocatalytic and Photoluminescent Properties of BiPO4 Catalysts Prepared by Solid-State Reaction: Degradation of Rhodamine B

Polycrystalline bismuth phosphate BiPO4 was synthesized by solid-state reaction at different temperatures varying from 500 to 900 °C. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and Raman spectroscopy. The low-temperature phase of BiPO4 has monoclinic structure with a space group P21/n, and was transformed into the monoclinic phase P21/m with a slight distortion of monoclinic lattice when it was heated above 500 °C. The effect of the transformation on the structure, morphology and photocatalytic properties was examined. The photocatalytic activity of each sample, in presence of Rhodamine B (RhB) in aqueous solution, was carried out and analyzed under UV light irradiation. Photoexperiments showed that the material prepared at 500 °C is the best catalyst with degradation efficiency of the order of 96% after 12 min of reaction time under UV light irradiation. This high photocatalytic efficiency could be due to their structural and morphological changes. The photocatalytic degradation mechanism of RhB in the presence of the best photocatalyst BiP-500 °C is proposed. The stability of the catalyst was also examined by carrying out four successive tests of the degradation in the presence of BiP-500 °C. Total organic carbon (TOC) was used to further estimate the rate of mineralization in the presence of BiP-500 °C (83% TOC removal). Photoluminescence experiments performed under UV-laser light irradiation revealed emissions in the green-orange range, with optimal intensities for the mix systems observed at 550 °C.

Influence of alkali and alkaline earths on structural and luminescence properties of Sm3+ doped lithium fluoro phosphate glass and different (Na, Mg, K, Ca and Sr) glass ceramics

Transparent glass ceramics comprising of BiPO4 nanocrystals in bismuth phosphate glass ceramics (59.5P2O5+15Bi2O3+10BaF2+10AF+05TeO2+0.5Sm2O3 where AF= alkali and alkaline earth fluorides) doped with Sm3+ ions were synthesized by typical melt quenching route. On the basis of data obtained from differential thermal analysis (DTA), prepared samples were analyzed for their thermal stability. Further powder X-Ray diffraction (PXRD) analysis has been done for all the samples to confirm the crystalline phase of BiPO4 and short-range order i.e., isotropic. Validations of various structural units were done with the help of FTIR. Spectral intensities were obtained using Judd-Ofelt (JO) theory for various absorption bands of Sm3+ ions using least square fit method for all the studied glass and glass ceramics. Various optical parameters of Sm3+ doped lithium phosphate glass and various glass ceramics were obtained from emission and absorption spectra studied in the present work. Theses optical parameters include JO intensity parameters (Ω2, Ω4 andΩ6), radiative transition probabilites (Aed), branching ratios (β), emission cross sections (σe), absorption cross sections (∑),gain bandwidths and optical gains (σe × Δλeff and σe × τR respectively). Influence of alkali and alkaline earths metals on radiation properties of various excited levels of Sm3+ has been investigated. In relation to the other glass networks and ceramics, SrF2 glass ceramics studied in the present work exhibited productive properties and could be useful in development of optical devices for visible laser applications.

Impact of phase segregation on optical and electrochemical property of BiPO4 nanostructures for energy storage applications

In the present paper, we report the influence of phase segregation (hexagonal and monoclinic phase) of facile microwave-assisted BPO (BiPO4) nanostructures on optical and electrochemical properties for supercapacitor applications. The XRD patterns reveal pure phase formation of both the samples of BiPO4 synthesized at 300 °C and 600 °C (JCPDS #15-0766 and JCPDS #43-0637). Phase transition of BiPO4 from hexagonal to monoclinic phase obtained by sintering the sample (BP600) at 600 °C. The FWHM values of the X-ray diffraction peaks observed to decrease with an increase in sintering temperature, which can be ascribed to the enhancement of the crystallite size. The synthesized samples of BiPO4 are in the nanometer dimension, which also revealed through FESEM examination. FTIR, Raman, and PL spectroscopy also revealed the crystal structure symmetry distinction among the hexagonal and monoclinic BiPO4 phase. Specific capacity calculated from GCD (galvanostatic charge and discharge) analysis for BP300 and BP600 samples is 1074 Cg−1 and 451 Cg−1, correspondingly, at the current density of 1 Ag−1. The investigation divulges that the phase segregation plays a considerable utility in tuning the electrochemical performance of BiPO4 nanostructures as active electrode material for next-generation electrochemical capacitors application.

Preparation of BiPO4/graphene photoelectrode and its photoelectrocatalyitic performance

In this work, a two-step electrodeposition method was employed to prepare BiPO4 nanorod/reduced graphene oxide/FTO composite electrodes (BiPO4/rGO/FTO). The BiPO4/rGO/FTO composite electrode showed the higher photoelectrocatalytic (PEC) activity for the removal of methyl orange than pure BiPO4, which was 2.8 times higher than that of BiPO4/FTO electrode. The effects of working voltage and BiPO4 deposition time on the degradation efficiency of methyl orange were investigated. The optimum BiPO4 deposition time was 45 min and the optimum working voltage was 1.2 V. The trapping experiments showed that hydroxyl radicals (•OH) and superoxide radicals (•O2) were the major reactive species in PEC degradation process. The BiPO4/rGO/FTO composite electrode showed the high stability and its methyl orange removal efficiency remained unchanged after four testing cycles. The reasons for the enhanced PEC efficiency of the BiPO4/rGO/FTO composite electrode was ascribed to the broad visible-light absorption range, the rapid transmission of photogenerated charges, and the mixed BiPO4 phase by the introduction of rGO in the composite electrode films.

One-pot fabrication of BiPO4/Bi2S3 hybrid structures for visible-light driven reduction of hazardous Cr(VI)

For the first time, a novel BiPO4/Bi2S3 heterostructures with different morphologies have been fabricated through a facile and rapid one pot precipitation route followed by anion-exchange strategy for the photoreduction of toxic Cr(VI) to harmless Cr (III). The hybrid structures systematically investigated using XRD, FE-SEM, EDS, TEM, HRTEM, XPS, FT-IR, UV–vis DRS, and PL. Changing the solvent type has a significant role for controllable morphologies of BiPO4/Bi2S3 hybrid as well as the catalytic activity. The BiPO4/Bi2S3 hybrid synthesized in diethylene glycol (DEG) performed the highest reduction efficiency of Cr(VI) within 20 min, compared with pure hexagonal phase of BiPO4 under visible light. The rate constant for BiPO4/Bi2S3 synthesized in DEG found to be 20.3 times larger than that for pure BiPO4. In addition, the presence of tartaric acid as hole scavenger could enhance the Cr(VI) reduction efficiency to 97.9%. No significant decrease in the catalytic efficiency after recycling up to four cycles. This promising study could present a significant approach towards Cr(VI) photoreduction from water through the novel BiPO4/Bi2S3 photocatalyst.

Influenced of Hydrothermal- and High temperature-Treatment on Luminescence Properties of BiPO4: Tb3+ Nanocrystals

Nanocrystals of BiPO4 and BiPO4: Tb were prepared by a room-temperature co-precipitation method, and then followed by post hydrothermaland high temperature-treatment. X-ray diffraction (XRD) analyses indicated that all the prepared samples are crystalline as a pure low-temperature monoclinic phase of BiPO4. The spectra of BiPO4: Tb powders showed the characteristics of Tb emission at 544 nm corresponding to the transition of 5D4→7F5 under irradiation of 370 nm light. Finally, the processing parameters were further optimized to acquire the BiPO4: Tb + to possess proper crystallinity, surface hydration layers and ethanol species, and thereby to get optimal luminescence performance for the BiPO4: Tb powders.

Hexamethylenetetramine assisted hydrothermal synthesis of BiPO4 and its electrochemical properties for supercapacitors

The well defined microstructures of BiPO4 were successfully synthesized by the facile hexamethylenetetramine (HMT) assisted hydrothermal method. The low temperature monoclinic BiPO4 structure with space group P21/n, were obtained from X-ray diffraction (XRD) for the pristine and HMT-assisted BiPO4 with 1, 3, 5 and 10 mmole concentration. A transformation from low temperature monazite-type phase to the high temperature SbPO4-type phase of BiPO4 was observed at the 10mmole concentration. There was a variation in the morphology from polyhedron to octahedra-like and finally into cube shape upon an increase in concentration of HMT. The role of reaction time in the morphology of BiPO4 particles was investigated. The selected area electron diffraction (SAED) pattern elucidated the ordered dot pattern and the calculated d-spacing revealed the formation of BiPO4. An increased specific capacitance of HMT assisted materials (202F/g) compared with pristine BiPO4 (89F/g) at 5mA/cm2 was observed upon morphological variation due to HMT addition.

Effects of aging time on phase, morphology, and luminescence by two-photon processes of BiPO4:Er3+, Yb3+ in the solvothermal synthesis

BiPO4:Er3+, Yb3+ phosphors were synthesized by the solvothermal process. The phase transformation, morphology, and UC luminescent property were characterized by different analytical techniques. The aging time has obvious influence on the phase, morphology, and luminescence of the samples. With the extension of aging time, the phase of BiPO4:Er3+, Yb3+ phosphors changes from hexagon to monocline. The morphology changes from nanorods through nanorugbies to microoctahedra. Under the excitation at 980nm, BiPO4:Er3+, Yb3+ phosphors show green and red UC emissions, which originate from the (2H11/2, 4S3/2)→4I15/2 and 4F9/2→4I15/2 transitions of Er3+ ions. The green and red UC emission intensities increase gradually with the increase of pumping power. On the basis of the luminescent properties, one can conclude that the two-photon process is involved in green and red UC emissions.

Phase and shape dependent electrochemical properties of BiPO4by PVP assisted hydrothermal method for pseudocapacitors

BiPO4 materials with different shapes are obtained under hydrothermal conditions by simply varying the concentration of PVP (polyvinylpyrrolidone). The prepared materials are characterized using various techniques such as X-Ray Diffraction (XRD), Thermo Gravimetric/Differential Scanning Calorimetry (TG/DSC), Fourier Transform Infrared (FT-IR) spectra, Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). The XRD with Rietveld analysis infers the formation of a monazite-type monoclinic BiPO4 structure. A transformation from monazite-type into trigonal BiPO4 phase is observed upon increasing the PVP concentration. The FE-SEM images reveal the change of shape from irregular cubic structure to octahedral to spindle upon increasing the concentration of PVP from 0.25 g to 1.0 g and thereafter the shape begins to disintegrate (1.25 g). Similarly, the effect of reaction time on the shape of BiPO4 is also studied. The electrochemical performance of pristine BiPO4 electrode is studied in various aqueous electrolytes such as 1 M LiOH, 1 M NaOH, 1 M KOH, 0.5 M K2SO4 and 1 M KNO3. Overall, the pristine BiPO4 provides a maximum specific capacitance in 1 M KOH electrolyte and a specific capacitance of 89 F g−1 is obtained at 5 mA cm−2. At low PVP concentration, there is an increase in specific capacitance whereas it decreases at high concentrations (1.0 g and 1.25 g). The monazite-type monoclinic structure with rod shape particles exhibits a high specific capacitance (167 F g−1 at 5 mA cm−2) and cycle life compared with other morphologies. The effective role of crystal phase and shape on the electrochemical performance of BiPO4 is elucidated.

Lipophilic bismuth phosphates: a molecular tetradecanuclear cage and a 1D-coordination polymer. Synthesis, structure and conversion to BiPO4

The reaction of the phosphate monoester {(ArO)PO(OH)2} (Ar = 2,6-i-Pr2C6H3) with BiPh3 in a 1 : 1 ratio in refluxing toluene afforded a tetradecabismuth-oxo-phosphate cage [{(ArO)PO3}10{(ArO)PO2OH}2(Bi14O10)·2(CH3OH)]·3C6H12·3CH3OH·2H2O (Ar = 2,6-i-Pr2C6H3) (1). On the other hand the reaction of the phosphate diester {((t)BuO)2PO(OH)} with BiPh3 in a 1 : 1 ratio at room temperature in ethanol afforded the 1D-coordination polymer [Bi(C6H5)2((t)BuO)2PO2]n (2). The molecular structure of 1 reveals that the cage is comprised of a central planar Bi6 rim and two Bi4 poles. The entire aggregate is held together by multiple coordination of O(2-), [(ArO)P(O)(OH)](-), [(ArO)PO3](2-) and methanol ligands. 2 is a 1D-coordination polymer where adjacent bismuth is bridged by isobidentate [((t)BuO)2PO2](-) ligands. In solution, however, 2 decomposes into the monomeric repeat unit [Ph2Bi{((t)BuO)2PO2}] which is indicated by ESI-MS studies. Thermolysis of 1 and 2 at 700 °C affords a pure phase of BiPO4.

BiPO4: A better host for doping lanthanide ions

In the present manuscript it is demonstrated that BiPO(4) is a better alternative to lanthanide phosphate host for making lanthanide ion-based luminescent materials. Hexagonal and monoclinic forms of BiPO(4) phase were prepared based on the reaction of Bi(3+) and PO(4)(3-) ions in ethylene glycol medium at 100 and 185 °C, respectively. From the differential thermal analysis (DTA) studies it is confirmed that the difference in the nucleation mechanism rather than the phase transition is responsible for the monoclinic phase formation at low temperatures (125 °C). Monoclinic BiPO(4) is quite stable and forms random solid solutions with lanthanide phosphates having both monoclinic (monazite) and tetragonal (xenotime) structures, as confirmed by XRD, FTIR and (31)P solid state nuclear magnetic resonance studies. On excitation corresponding to the (1)S(0)→(3)P(1) transition of Bi(3+) in BiPO(4):Ln samples, energy transfer from host to lanthanide ions takes place. The studies are quite relevant as there is a growing interest all over the world in replacing lanthanide based host used for different applications with easily available, easily purifiable and cheap main group elements (like Sb, Bi etc.) based hosts.

Effects of distortion of PO4 tetrahedron on the photocatalytic performances of BiPO4

Three kinds of crystal phase BiPO4 (HBIP, nMBIP and mMBIP) were selectively synthesized by a hydrothermal method. The governed factors for the formation of three crystal phase of BiPO4 were both on the acidity of the solution and reaction temperature. The BiPO4 with nMBIP phase structure showed higher activity for degradation of MB solution under UV irradiation than HBIP and mMBIP. The catalytic activity per surface area activity of nMBIP (3.8×105 h−1 m−2) was about ten times higher than that of P25(1.4×104 h−1 m−2). The BiPO4 with nMBIP structure exhibited the highest activity due to the most distorted PO4 tetrahedron. The induce effect of the dipole moment derived from the distorted PO4 tetrahedron promoting the separation of e−/h+ pairs and further benefited for the photocatalytic reaction. This correlation may help to design and develop other oxoacid salt photocatalysts with high activity.

Phase transformation and microwave dielectric properties of BiPO4 ceramics

Monazite-type compounds, BiPO4 polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO4 has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950∘C has good microwave dielectric properties; the relative dielectric constant (e r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ f ) = − 79 ppm/ ∘C.

Catalytic behavior of BiPO4 in the multicomponent bismuth phosphate system on the propylene ammoxidation

We found that the multicomponent bismuth phosphate (MBP) with multiphase activates catalytically the ammoxidation reaction of propylene and consists of mainly BiPO4 and metal molybdates, etc. The MBP has been characterized by several techniques such as DTA, XRD, and BET surface area and total pore volume measurements. The DTA curve clearly shows that there are phase transitions with sharp breaks of the curve. The specific surface area and total pore volume decrease with increasing of the BiPO4 phase content, showing that the BiPO4 phase remains essentially on the catalyst surface and blocks the active sites and catalyst pores. It would mean that the catalytic behavior in the MBP depends on the catalyst surface covered with the BiPO4 phase adequately. The pathway of the selective oxidation due to the controlled amounts of the BiPO4 phase favors the formation of acrylonitrile. The improvement of catalytic performances of the mixture of phases is explained by the synergy effect.