High pressure in-situ X-ray diffraction study on Zn-doped magnetite nanoparticles

We have performed high pressure synchrotron X-ray powder diffraction experiments on two different samples of Zn-doped magnetite nanoparticles (formula Fe_(3-x)Zn_xO₄; x = 0.2, 0.5). The structural behavior of then a noparticles was studied up to 13.5 GPa for x = 0.2, and up to 17.4 GPa for x = 0.5. We have found that both systems remain in the cubic spinel structure as expected for this range of applied pressures. The analysis of the unit cell volume vs. pressure results in bulk modulus values lower than in both end-members, magnetite (Fe₃O₄) and zinc ferrite (ZnFe₂O₄), suggesting that chemical disorder may favor compressibility, which is expected to improve the increase of the Neel temperature under compression.     

Compressibility and structural behavior of pure and Fe-doped SnO2 nanocrystals

We have performed high-pressure synchrotron X-ray diffraction experiments on nanoparticles of pure tin dioxide (particle size ∼30 nm) and 10 mol % Fe-doped tin dioxide (particle size ∼18 nm). The structural behavior of undoped tin dioxide nanoparticles has been studied up to 32 GPa, while the Fe-doped tin dioxide nanoparticles have been studied only up to 19 GPa. We have found that both samples present at ∼13 GPa a second-order structural phase transition from the ambient pressure tetragonal rutile-type structure (P4₂/mnm) to an orthorhombic CaCl₂-type structure (space group Pnnm). No phase coexistence was observed for this transition. Additionally, pure SnO₂ presents a phase transition to a cubic structure at ∼24 GPa. The evolution of the lattice parameters with pressure and the room-temperature equations of state are reported for the different phases. The reported results suggest that the partial substitution of Sn by Fe induces an enhancement of the bulk modulus of SnO₂. Results are compared with previous studies on bulk and nanocrystalline SnO₂. The effects of pressure on Sn-O bonds are also analyzed.     

Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa

We have studied CaWO₄ under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO₄ beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure–volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of the fergusonite phase and a different transition pressure. These facts suggest that deviatoric stresses influence on the high-pressure structural behavior of CaWO₄ as previously found in related compounds. The reported experiments also provide information on the pressure dependence of interatomic bond distances, shedding light on the transition mechanisms.     

Lithium storage in hollow spherical ZnFe2O4 as anode materials for lithium ion batteries

Hollow microspheres composed of phase-pure ZnFe₂O₄ nanoparticles (hierarchically structured) have been prepared by hydrothermal reaction. The unique hollow spherical structure significantly increases the specific capacity and improves capacity retention of this material. The product of each phase transition during initial discharge (ZnFe₂O₄ ? Li_0.5ZnFe₂O₄ ? Li₂ZnFe₂O₄ → Li₂O + Li–Zn + Fe) and their structural reversibility are recognized by X-ray diffraction and electrochemical characterization. The products of the deeply discharged (Li–Zn alloy and Fe) and recharged materials (Fe₂O₃) were clarified based on high resolution transmission electron microscopic technique and first-principle calculations.     

Graphene anchored with ZnFe2O4 nanoparticles as a high-capacity anode material for lithium-ion batteries

Heterostructured ZnFe₂O₄–graphene nanocomposites are synthesized by a facile hydrothermal method. The as-prepared ZnFe₂O₄–graphene nanocomposites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and galvanostatic charge and discharge measurements. Compared with the pure ZnFe₂O₄ nanoparticles, the ZnFe₂O₄–graphene nanocomposites exhibit much larger reversible capacity up to 980 mAh g⁻¹, greatly improved cycling stability, and excellent rate capability. The superior electrochemical performance of the ZnFe₂O₄–graphene nanocomposites could be attributed to the synergetic effect between the conducting graphene nanosheets and the ZnFe₂O₄ nanoparticles.     

Reactivity of nanoparticles; interaction between zinc and copper oxide nanoparticles and iron ions in an alkaline medium

The reactivity of zinc and copper oxide nanoparticles was investigated upon their interaction with iron oxides. It was ascertained that, depending on the reaction conditions, nanoparticles of zinc and copper ferrites (ZnFe₂O₄ and CuFe₂O₄) or core/shell nanoparticles (Fe₃O₄/ZnO) are produced. Size, composition, and structure of the resulting nanoparticles were determined by transmission electron microscopy and X-ray diffraction analysis. The average size of zinc and copper ferrite nanoparticles was ascertained to be 9–10 and 2–3 nm, respectively. For core/shell Fe₃O₄/ZnO nanoparticles, the average size is 20 nm. It was experimentally proved that the photoluminescence radiative characteristics of ZnO nanoparticles are retained in core/shell Fe₃O₄/ZnO nanoparticles.     

Structural transitions under high-pressure in a langasite-type multiferroic Ba3TaFe3Si2O14

The iron containing langasite family compound Ba₃Ta⁵⁷Fe₃Si₂O₁₄ was studied at high pressure up to 30 GPa at room temperature by means of in situ X-ray diffraction, Raman and Mössbauer spectroscopies in diamond anvil cell. Two structural transitions at pressures ∼5 and ∼20 GPa are observed. At ∼5 GPa, the low-pressure trigonal P321 phase undergoes phase transition to the most likely P3 structure as manifested by slight increase in the c/a ratio and by anomalies of the Mössbauer and Raman spectra parameters. At ∼20 GPa, the first order phase transition to monoclinic structure occurred with a drop of unit cell volume by 9%. The appearance of the ferroelectric state at such transitions is discussed in connection with the multiferroic properties.     

Pressure-induced phase transition of Fe2TiO4: X-ray diffraction and Mössbauer spectroscopy

X-ray diffraction and Mössbauer spectroscopy were employed to investigate structural stability of Fe₂TiO₄ under high pressure. Measurements were performed up to about 24 GPa at room temperature using diamond anvil cell. Experimental results demonstrate that Fe₂TiO₄ undergoes a series of phase transitions from cubic (Fd3?m) to tetragonal (I4₁/amd) at 8.7 GPa, and then to orthorhombic structure (Cmcm) at 16.0 GPa. The high-pressure phase (Cmcm) of Fe₂TiO₄ is kept on decompression to ambient pressure. In all polymorphs of Fe₂TiO₄, iron cations present a high-spin ferrous property without electric charge exchange with titanium cations at high pressure supported by Mössbauer evidences.     

Polymorphs of the Gadolinite-Type Borates ZrB2O5 and HfB2O5 Under Extreme Pressure

Based on the results from previous high-pressure experiments on the gadolinite-type mineral datolite, CaBSiO₄(OH), the behavior of the isostructural borates β-HfB₂O₅ and β-ZrB₂O₅ have been studied by synchrotron-based in situ high-pressure single-crystal X-ray diffraction experiments. On compression to 120 GPa, both borate layer-structures are preserved. Additionally, at ≈114 GPa, the formation of a second phase can be observed in both compounds. The new high-pressure modification γ-ZrB₂O₅ features a rearrangement of the corner-sharing BO₄ tetrahedra, while still maintaining the four- and eight-membered rings. The new phase γ-HfB₂O₅ contains ten-membered rings including the rare structural motif of edge-sharing BO₄ tetrahedra with exceptionally short B−O and B⋅⋅⋅B distances. For both structures, unusually high coordination numbers are found for the transition metal cations, with ninefold coordinated Hf⁴⁺, and tenfold coordinated Zr⁴⁺, respectively. These findings remarkably show the potential of cold compression as a low-energy pathway to discover metastable structures that exhibit new coordinations and structural motifs.     

The influence of extraframework cations on the behavior of K-exchanged gonnardite at high pressure

The behavior of K-exchanged gonnardite K_2.18Na_0.04Ca_0.02(H₂O)_2.2[Al_2.26Si_2.74O₁₀] at compression in penetrating water-containing medium was studied by synchrotron powder diffraction in diamond anvil cell. In contrast to the initial gonnardite, which exhibits the transition to high-hydrated paranatrolite at elevated humidity, its K-exchanged form is not capable of over-hydration even at high pressure. Within the whole studied pressure range (up to 4.8 GPa) the sample experiences the compression. At 3.5-4 GPa the compression anomaly is observed, which is interpreted as a phase transition accompanied by the symmetry lowering from tetragonal to monoclinic. The high-pressure structure evolution of K-exchanged forms of gonnardite and natrolite is compared; the difference in their behavior is explained by distinct configuration of the framework water-cation subsystem.     

Facile synthesis and properties of ZnFe2O4 and ZnFe2O4/polypyrrole core-shell nanoparticles

We demonstrated that ZnFe₂O₄/polypyrrole core-shell nanoparticles could be facilely synthesized via in situ chemical oxidative polymerization of pyrrole monomers on the surface of ZnFe₂O₄ nanoparticles. The shell thickness of core-shell nanoparticles could be easily controlled by adjusting the amount of pyrrole monomers. The phase structures, morphologies and properties of the as-prepared products were investigated by XRD, TEM, SEM, VSM, and FTIR spectra. Magnetic studies revealed that the saturation magnetization (M_s) and coercivity (H_c) of ZnFe₂O₄/PPy core-shell nanoparticles is 17.8 emu/g and 130 Oe, respectively. The electromagnetic characteristics of products showed that ZnFe₂O₄/PPy core-shell nanoparticles exhibit excellent microwave absorption performance than ZnFe₂O₄ nanoparticles, such as more powerful absorbing property and wider electromagnetic wave absorbing frequency band due to the proper matching of the permittivity and the permeability of ZnFe₂O₄/PPy core-shell nanoparticles.     

Study of nano-sized (ZnFe2O4)y particles/CuTl-1223 superconductor composites

Zinc ferrite (ZnFe₂O₄)_y nanoparticles/Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ (CuTl-1223) superconductor composites with y = 0–2 wt.% were prepared by adding ZnFe₂O₄ nanoparticles into CuTl-1223 superconductor matrix and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Fourier transforms infrared (FTIR) spectroscopy and dc-resistivity (ρ) measurements. The bulk CuTl-1223 superconductor matrix was synthesized by solid-state reaction and Zinc ferrite (ZnFe₂O₄) nanoparticles were separately prepared by sol–gel method. XRD analysis revealed the tetragonal and spinel structure of CuTl-1223 superconductor and ZnFe₂O₄ nanoparticles, respectively. The XRD analysis showed that increased concentration of ZnFe₂O₄ nanoparticles doesn't disturb the tetragonal structure of host CuTl-1223 superconductor matrix and has no appreciable effect on its lattice parameters. The SEM images confirm the granular structure of the host superconductor matrix. The presence of ZnFe₂O₄ nanoparticles in host superconductor matrix is confirmed by using FTIR study. Variation of zero resistivity critical temperature {T_c (0)} depends upon the concentration of the nanoparticles in the host superconductor matrix. The overall suppression of T_c (0) and diamagnetism with increasing nanoparticles concentration is most probably due to trapping of mobile free carriers and reflection of spin charge due to presence of paramagnetic ZnFe₂O₄ nanoparticles. There is possibility for the incorporation of Fe and Zn in the lattice sites during the synthesis process, which may also cause the reduction of T_c (0) of the final composites.     

Synthesis,magnetic and ethanol gas sensing properties of semiconducting magnetite nanoparticles

The superparamagnetic magnetite (Fe₃O₄) nanoparticles with an average size of 7 nm were synthesized using a rapid and facile microwave hydrothermal technique. The structure of the magnetite nanoparticles was characterized by X-ray diffraction (X-ray), field effect scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The prepared Fe₃O₄ was shown to have a cubic phase of pure magnetite. Magnetization hysteresis loop shows that the synthesized magnetite exhibits no hysteretic features with a superparamagnetic behavior. The ethanol gas sensing properties of the synthesized magnetite were investigated, and it was found that the responsibility time is less than 10 s with good reproducibility for ethanol sensor. Accordingly, it is evaluated that the magnetite nanoparticles can be effectively used as a solid state ethanol sensor in industrial commercial product applications.     

Structural change of layered perovskite La2Ti2O7 at high pressures

The perovskite-related layered structure of La₂Ti₂O₇ has been studied at pressures up to 30 GPa using synchrotron radiation powder X-ray diffraction (XRD) and Raman scattering. The XRD results indicate a pronounced anisotropy for the compressibility of the monoclinic unit cell. The ratio of the relative compressibilities along the [100], [010] and [001] directions is ∼1:3:5. The greatest compressibility is along the [001] direction, perpendicular to the interlayer. A pressure-induced phase transition occurs at 16.7 GPa. Both Raman and XRD measurements reveal that the pressure-induced phase transition is reversible. The high-pressure phase has a close structural relation to the low-pressure monoclinic phase and the phase transition may be due to the tilting of TiO₆ octahedra at high pressures.     

Hydrothermal synthesis of monodisperse Fe3O4 nanoparticles based on modulation of tartaric acid

In this paper, monodisperse Fe₃O₄ nanoparticles with single crystalline structure were synthesized via a facile environment-friendly method. And the size of the nanoparticles ranges from 10 nm to 15 nm. As-synthesized Fe₃O₄ were characterized by X-ray diffraction instrument (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectrometer and field emission transmission electron microscope (FE-TEM). The effect of tartaric acid (TA) amount on products was investigated by XRD and TEM. The results indicated that TA could commendably modulate the crystalline phase, morphology and size of nanometer Fe₃O_4. A possible generated mechanism of Fe₃O₄ crystals was proposed in virtue of UV–vis absorption spectra. Besides, the magnetic properties of as-synthesized Fe₃O₄ were detected.     

Facile synthesis of Fe3O4 nanoparticles by reduction phase transformation from γ-Fe2O3 nanoparticles in organic solvent

A phase transformation induced by the reduction of as-synthesized γ-maghemite (γ-Fe₂O₃) nanoparticles was performed in solution by exploiting the reservoir of reduction gas (CO) generated from the incomplete combustion reaction of organic substances in the reactor. Results from X-ray diffraction, color indicator, and magnetic analysis using a SQUID strongly support this phase transformation. Based on this route, monodisperse magnetite (Fe₃O₄) nanoparticles were simply produced in the range from 260 to 300 °C. Almost all aspects of the original γ-Fe₂O₃ nanoparticles, such as shape, size, and monodispersity, were maintained in the produced Fe₃O₄ nanoparticles.     

High-pressure diffraction study of zeolites stilbite and stellerite

The high-pressure behavior of zeolites of the stilbite-stellerite isomorphous series is studied by X-ray powder diffraction using synchrotron radiation in the penetrating (water-containing) medium in a high-pressure cell. At the initial stage (< 2 GPa), orthorhombic stellerite |Ca_3.77(H₂O)₂₈| [Al_7.54Si_28.46O₇₂] shows lower compressibility than monoclinic stilbite |Ca_4.00Na_1.7(H₂O)₃₀| [Al_9.7Si_26.3O₇₂]. Single crystal XRD does not display any significant differences in the behavior of stellerite in the penetrating and nominally non-penetrating media. At the first stage of the compression, the number of H₂O molecules increases from 28 to 32 due to the filling of statistically occupied positions. With further compression no changes are observed. At around 1 GPa stellerite undergoes a second-order phase transition with a decrease in symmetry from Fmmm to F2/m. The compressibility of the powder sample of stellerite is considerably lower than that of the single crystal. These differences may be attributed to kinetic effects of additional hydration induced by the pressure.     

High-pressure X-ray diffraction study of SrMoO4 and pressure-induced structural changes

SrMoO₄ was studied under compression up to 25 GPa by angle-dispersive X-ray diffraction. A phase transition was observed from the scheelite-structured ambient phase (space group I4₁/a) to a monoclinic fergusonite phase (space group I2/a) at 12.2(9) GPa. The unit-cell parameters of the high-pressure phase are a=5.265(9) Å, b=11.191(9) Å, c=5.195 (5) Å, and β=90.9(1)°, Z=4 at 13.1 GPa. There is no significant volume collapse at the phase transition. No additional phase transitions were observed and on release of pressure the initial phase is recovered, implying that the observed structural modifications are reversible. The reported transition appeared to be a ferroelastic second-order transformation producing a structure that is a monoclinic distortion of the low-pressure phase and was previously observed in compounds isostructural to SrMoO₄. A possible mechanism for the transition is proposed and its character is discussed in terms of the present data and the Landau theory. Finally, the room temperature equation of states is reported and the anisotropic compressibility of the studied crystal is discussed in terms of the compression of the Sr-O and Mo-O bonds.     

Pressure induced phase transformation in U2O(PO4)2

The high pressure behavior of U₂O(PO₄)₂ has been investigated with the help of Raman scattering and X-ray diffraction measurements up to ∼14 and 6.5 GPa, respectively. The observed changes in the Raman spectra as well as the X-ray diffraction patterns suggest that U₂O(PO₄)₂ undergoes a phase transition at ∼6 GPa to a mixture of a disordered ambient pressure phase and a new high pressure phase. The new phase resembles the triclinic mixed-valence phase of uranium orthophosphate (U(UO₂)(PO₄)₂). On release of pressure the initial phase is not retrieved.     

Pressure-induced transition in Tl2MoO4

Tl₂MoO₄ has been studied under high-pressure by X-ray diffraction, Raman spectroscopy, and optical absorption measurements. A first-order phase transition is observed at 3.5±0.5 GPa. The nature (ordered vs. disordered) of the high-pressure phase strongly depends on the local hydrostatic conditions. Optical absorption measurements tend to show that this transition is concomitant with an electronic structure transformation. Prior to the transition, single crystal X-ray diffraction shows that pressure induces interactions between MoO₄ fragments and the Mo coordination number tends to increase. In addition, the stereoactivity of the lone-pair electrons on the three symmetrically independent Tl-sites is not uniform; while for two sites the stereoactivity decreases with increasing pressures for the third site the stereoactivity increases.