Phase transitions and ionic mobility in hydrogen zirconium phosphates with the NASICON structure, H1±XZr2−XMX(PO4)3·H2O, M = Nb, Y

Phase transitions and the mobility of proton-containing groups in hydrogen zirconium phosphate HZr₂(PO₄)₃·nH₂O with the NASICON structure were studied by X-ray powder diffraction, ¹H, ³¹P NMR, IR spectroscopy and TG analysis. Heating HZr₂(PO₄)₃·H₂O above 420 K results in dehydration and in a rhombohedral-triclinic phase transition. Continued heating to about 490 K results in the thermal activation of cation disordering and phase transition of HZr₂(PO₄)₃ from triclinic to rhombohedral phase. Parameter “a” of HZr₂(PO₄)₃ lattice decreases during the heating. It is shown that oxonium ions in HZr₂(PO₄)₃·H₂O are characterized by high rotation and translation mobility. Rotation mobility of oxonium ions can be increased by the substitution of zirconium by yttrium or niobium.     

Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases: Crystal structure of Co0.4Ni0.6(SeO3)·2H2O

The Co_xNi_1−x(SeO₃)·2H₂O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co_0.4Ni_0.6(SeO₃)·2H₂O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO₃)·2H₂O (M = Co and Ni) minerals and crystallizes in the P2₁/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO₃)²⁻ selenite oxoanions and edge-sharing M₂O₁₀ dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d⁷ and 3d⁸ cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO₃)²⁻ anions which are linked to the M₂O₁₀ polyhedra in three dimensions.     

Reinvestigation of the binary diagram Na3PO4-FePO4 and crystal structure of a new iron phosphate Na3Fe3(PO4)4

A new iron(III) phosphate Na₃Fe₃(PO₄)₄ has been synthesized and characterized. It decomposes before melting at 860°C into FePO₄ and Na₃Fe₂(PO₄)₃. The structure of the compound was determined by single-crystal X-ray diffraction. The unit cell is monoclinic with the following parameters: a=19.601(8) Å, b=6.387(1) Å, c=10.575(6) Å and β=91.81(4)°; Z=4; space group: C2/c. Na₃Fe₃(PO₄)₄ exhibits a layered structure involving corner-linkage between FeO₆ octahedra, and corner- and edge-sharing between FeO₆ octahedra and PO₄ tetrahedra. The Na⁺ cations occupying the interlayer space are six- and seven-fold coordinated by oxygen atoms. The relationship between the structure of Na₃Fe₃(PO₄)₄ and the previous reported hydrate K₃Fe₃(PO₄)₄·H₂O will be discussed.     

2D-network of inorganic-organic hybrid material built on Keggin type polyoxometallate and amino acid: [L-C2H6NO2]3[(PO4)Mo12O36]·5H2O

A new inorganic-organic hybrid material based on polyoxometallate, [L-C₂H₆NO₂]₃[(PO₄)Mo₁₂O₃₆]·5H₂O, has been successfully synthesized and characterized by single-crystal X-ray analysis, elemental analysis, infrared and ultraviolet spectroscopy, proton nuclear magnetic resonance and differential thermal analysis techniques. The title compound crystallizes in the monoclinic space group, P2₁/c_, with a = 12.4938 (8) Å, b = 19.9326 (12) Å, c = 17.9270 (11) Å, β = 102.129 (1)°, V = 4364.8 (5) Å³, Z = 4 and R₁(wR₂) = 0.0513, 0.0877. The most remarkable structural feature of this hybrid can be described as two-dimensional inorganic infinite plane-like (2D/∞ [(PO₄)Mo₁₂O₃₆]³⁻) which forming via weak Van der Waals interactions along the z axis. The characteristic band of the Keggin anion [(PO₄)Mo₁₂O₃₆]³⁻ appears at 210 nm in the UV spectrum. Thermal analysis indicates that the Keggin anion skeleton begins to decompose at 520 °C.     

A new borophosphate chain anion in an organo-templated iron(III) borophosphate: Synthesis, crystal structure and magnetic properties of (C4H12N2)3Fe6(H2O)4[B6P12O50(OH)2]·2H2O

The organo-templated iron(III) borophosphate (C₄H₁₂N₂)₃Fe^III₆(H₂O)₄[B₆P₁₂O₅₀(OH)₂]·2H₂O was prepared under mild hydrothermal conditions (443 K). The crystal structure was determined from single-crystal X-ray data at 295 K (orthorhombic, Pbca (No. 61), Z=4, a=17.8023(7) Å, b=16.1037(5) Å, c=19.1232(6) Å, V=5482.3(3) Å³, R1=0.055, wR2=0.104, 6576 observed reflections with I>2σ(I)) and contains a new type of borophosphate anion: a mixed open- and loop-branched zehner single chain, , built from heptamers [B₂P₅O₂₁] interconnected by BO₃(OH) tetrahedra sharing their third oxygen corners with additional (terminal) PO₄ tetrahedra to form open branchings. The mixed open- and loop-branched single chains running along [0 0 1] are interconnected by three crystallographically independent iron coordination octahedra to form a 3D framework structure containing eight-membered ring channels running along [0 1 0] and cages, which are occupied by two crystallographically independent piperazine cations and H₂O molecules. The displacement parameters of C and N atoms in the piperazine cations are dramatically influenced by the strength of the hydrogen bond reflecting the shape of the cavities. The magnetic investigations indicate the existence of antiferromagnetic interactions as the major components. A narrow hysteresis at low temperatures indicates a weak ferromagnetic component, due to a non-cancellation of spins.     

Structural, thermal, magnetic and electrical studies of the iron oxophosphate Rb7Fe7(PO4)8O2·2H2O

A new iron oxophosphate of composition Rb₇Fe₇(PO₄)₈O₂·2H₂O has been synthesized and studied by X-ray diffraction, TG and DTA analysis, magnetic susceptibility, neutron diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic system with the P2₁/c space group and the unit cell parameters a = 8.224(8) Å, b = 22.162(6) Å, c = 9.962(6) Å and β = 109.41(8)°. Its structure is built up from Fe₇O₃₂ clusters of edge- and corner-sharing FeO₅ and FeO₆ polyhedra. Neighboring clusters are connected by the phosphate tetrahedra to form a three-dimensional framework. The Rb⁺ cations and the water molecules are occupying intersecting tunnels parallel to a and c. The presence of water molecules was confirmed by TG and DTA analysis. The magnetic susceptibility measurements have shown the existence of antiferromagnetic ordering below 22 K with a weak ferromagnetic component. Additionally, these measurements show evidence for a strong magnetic frustration characterized by |θ/T_N| ≈ 12. Powder neutron diffraction study confirms the presence of a long range antiferromagnetic order coupled to a weak ferromagnetic component along the b-axis. The strongly reduced magnetic moments extracted from the refinement support the existence of a magnetically frustrated ground state. The Mössbauer spectroscopy results confirmed the presence of only Fe³⁺ ions in both five and six coordination. The ionic conductivity measurements led to activation energy of 0.81 eV, a value that agrees with the obtained for other rubidium phosphates.     

Composition dependent phase connectivity, dielectric and magnetoelectric properties of magnetoelectric composites with Pb(Mg1/3Nb2/3)0.67Ti0.33O3 as piezoelectric phase

Ferrite (Ni_0.6Co_0.4Fe₂O₄) phase, ferroelectric (Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃) phase and magnetoelectric composites of (x)Ni_0.6Co_0.4Fe₂O₄ + (1 − x)Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ with x = 0.15, 0.30 and 0.45 were prepared using solid-state reaction technique. Presence of Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ was confirmed using X-ray diffraction technique. The scanning electron microscopic images were used to study the microstructure of the composites. Connectivity scheme present in the magnetoelectric (ME) composites are discussed from the microscopic images. Variation of dielectric constant and dielectric loss with temperature for all the composites was studied. Here we report the effect of Ni_0.6Co_0.4Fe₂O₄ mole fraction on connectivity schemes between Ni_0.6Co_0.4Fe₂O₄ and Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composite. The variation of magnetoelectric voltage coefficient with dc magnetic field shows peak behaviour. The maximum value of magnetoelectric voltage coefficient of 9.47 mV/cm Oe was obtained for 0.15Ni_0.6Co_0.4Fe₂O₄ + 0.85Pb(Mg_1/3Nb_2/3)_0.67Ti_0.33O₃ composites. Finally we have co-related the effect of Ni_0.6Co_0.4Fe₂O₄ content and dielectric properties on magnetoelectric voltage coefficient.     

Phase transitions, structure and ion conductivity of zirconium hydrogen phosphates, H1±XZr2−XMX(PO4)3·H2O (M = Nb, Y)

Structure transformations and proton conductivity of hydrogen zirconium phosphates with the NASICON structure, H_1±XZr_2−XM_X(PO₄)₃·H₂O (X = 0, 0.02 and 0.1, M = Nb, Y), were studied by X-ray powder diffraction, calorimetry, IR- and impedance spectroscopy. Substitution of zirconium by niobium leads to decrease of the lattice parameters, while yttrium doping leads to their increase. H_0.9Zr_1.9Nb_0.1(PO₄)₃ structure was determined at 493 and 733 K. This phase crystallizes in rhombohedral space group with lattice parameters a = 8.8564(5) Å, c = 22.700(1) Å at 493 K and a = 8.8470(2) Å, c = 22.7141(9) Å at 733 K. The a parameter and lattice volume were found to decrease with temperature increasing. Structure transformations upon heating are caused mainly by the decrease of the M1 site and C cavities. Ion conductivity of obtained materials was found to increase in humid atmosphere. Activation energies of conductivity were calculated. Rhombohedral-triclinic phase transition found by X-ray powder diffraction was proved by calorimetry data. According to XRD and IR spectroscopy data hydrogen bond in HZr₂(PO₄)₃ was found to be weaker than in hydrated material.     

Hydrothermal synthesis, characterization and magnetic properties of (N4C6H21)·(Co(H2PO4)(HPO4)2)

The title compound, (N₄C₆H₂₁)·(Co(H₂PO₄)(HPO₄)₂), was prepared hydrothermally (473 K, 10 days, autogenous pressure), in the presence of the tris(2-aminoethyl)amine as organic template. Its structure is built up from a network of four membered-rings, formed by the vertex linkages between [CoO₄] and [H₂PO₄] tetrahedra with [HPO₄] moieties hanging from the Co center. Hydrogen bonds involving the cobalt phosphate units and the triply protonated amine molecule, contribute to the stability of the structure. The IR spectrum shows bands characteristic of the (N₄C₆H₂₁)³⁺ cations and the (H₂PO₄)⁻ and (HPO₄)²⁻ phosphate anions. The UV-Visible-NIR spectrum confirms the tetrahedral coordination of Co²⁺ ions. The TGA analysis indicates that the dehydration of (N₄C₆H₂₁)·(Co(H₂PO₄)(HPO₄)₂) occurs in one step. Magnetic measurements from 4.5 to 305 K show a weak antiferromagnetic character of this compound.     

Structural characterization, thermal, spectroscopic and magnetic studies of the (C3H12N2)0.75[Mn1.50Fe1.50(AsO4)F6] and (C3H12N2)0.75[Co1.50Fe1.50(AsO4)F6] compounds

The (C₃H₁₂N₂)_0.94[Mn_1.50Fe_1.50^III(AsO₄)F₆] and (C₃H₁₂N₂)_0.75[Co_1.50Fe_1.50^III(AsO₄)F₆] compounds 1 and 2 have been synthesized using mild hydrothermal conditions. These phases are isostructural with (C₃H₁₂N₂)_0.75[Fe_1.5^IIFe_1.5^III(AsO₄)F₆]. The compounds crystallize in the orthorhombic Imam space group. The unit cell parameters calculated by using the patterns matching routine of the FULPROOF program, starting from the cell parameters of the iron(II),(III) phase, are: a = 7.727(1) Å, b = 11.047(1) Å, c = 13.412(1) Å for 1 and a = 7.560(1) Å, b = 11.012(1) Å, c = 13.206(1) Å for 2, being Z = 8 in both compounds. The crystal structure consists of a three-dimensional framework constructed from edge-sharing [M^II(1)₂O₂F₈] (M = Mn, Co) dimeric octahedra linked to [Fe^III(2)O₂F₄] octahedra through the F(1) anions and to the [AsO₄] tetrahedra by the O(1) vertex. This network gives rise two kinds of chains, which are extended in perpendicular directions. Chain 1 is extended along the a-axis and chain 2 runs along the c-axis. These chains are linked by the F(1) and O(1) atoms and establish cavities delimited by eight or six polyhedra along the [1 0 0] and [0 0 1] directions, respectively. The propanediammonium cations are located inside these cavities. The thermal study indicates that the structures collapse with the calcination of the organic dication at 255 and 285 °C for 1 and 2, respectively. The Mössbauer spectra in the paramagnetic state indicate the existence of two crystallographically independent positions for the iron(III) cations and a small proportion of this cation in the positions of the divalent Mn(II) and Co(II) ones. The IR spectrum shows the protonated bands of the H₂N- groups of the propanediamine molecule and the characteristic bands of the [AsO₄]³⁻ arsenate oxoanions. In the diffuse reflectance spectra, it can be observed the bands characteristic of trivalent iron(III) cation and divalent Mn(II) and Co(II) ones in a distorted octahedral symmetry. The calculated Dq and B-Racah parameters for the cobalt(II) phase are 710 and 925 cm⁻¹, respectively. The ESR spectra of compound 1 maintain isotropic with variation in temperature, being g = 1.99. Magnetic measurements for both compounds indicate that the main magnetic interactions are antiferromagnetic in nature. However, at low temperatures small ferromagnetic components are detected, which are probably due to a spin decompensation of the two different metallic cations. The hysteresis loops give values of the remnant magnetization and coercive field of 84.5, 255 emu/mol and 0.01, 0.225 T for phases 1 and 2, respectively.     

Synthesis and characterization of the open-framework cobalt borophosphate: (C4N2H12)Co[B2P3O12(OH)]

A high yield hydrothermal synthesis of the open-framework cobalt borophosphate (C₄N₂H₁₂)Co[B₂P₃O₁₂(OH)], has been developed. The compound was characterized by single crystal X-ray diffraction methods, thermogravimetric analysis, vibrational (IR and Raman) spectroscopy and magnetic measurements. In the structure Co(II)O₆ octahedra, BO₄ and PO₄ tetrahedra form nine-member rings which in turn are linked to form CoBPO layers parallel to the bc plane. The layers are joined together by another set of PO₄ tetrahedra and the (piperazinium)²⁺ cations occupy the channels running along [1 0 0]. The structure is compared with that of (C₂N₂H₁₀)Co[B₂P₃O₁₂(OH)].     

Syntheses and structures of Ta2(WO2)0.87H0.26(PO4)4 and Ta2(MoO2)(PO4)4

Tantalum hydrogen phosphate, β-TaH(PO₄)₂, has a three-dimensional structure that is stable to remarkably high temperature (∼600 °C) presumably due to the presence of strong hydrogen bonds. Impedance measurements indicate a low conductivity, 2.0 × 10⁻⁶ S/cm at 200 °C in 5% H₂. In further studies aimed at enhancing the conductivity by aliovalent doping, we have investigated systematically the synthesis of compounds in the TaH(PO₄)₂-W₂P₂O₁₁ system at 380 °C. As a result, a new phase, Ta₂(WO₂)_0.87H_0.26(PO₄)₄, was identified and subsequently the molybdenum analog Ta₂(MoO₂)(PO₄)₄ was also prepared. The structures were determined by single crystal X-ray diffraction techniques. The structures of Ta₂(WO₂)_0.87H_0.26(PO₄)₄ and Ta₂(MoO₂)(PO₄)₄ can be formally derived from the structure of β-TaH(PO₄)₂ by the replacement of two P-OH protons with an MO₂²⁺ (M = Mo and W) group together with a change in the orientation of some phosphate tetrahedra.     

Chemical preparation, crystal structure and characterization of the new sodium ytterbium cyclotriphosphate Na3Yb(P3O9)2·9H2O

Chemical preparation and crystal structure are reported for a new lanthanide cyclotriphosphate Na₃Yb(P₃O₉)₂·9H₂O. This salt crystallizes in the trigonal system, space group with the following parameters: a = 30.933(2), c = 12.8282(5) Å. The crystal structure was refined to R₁ = 0.0432 using 1782 reflections with I > 2 σ(I). In the Na₃Yb(P₃O₉)₂·9H₂O structure, the phosphoric ring anions, located around the axis are interconnected by YbO₈ dodecahedra and NaO₆ and NaO₇ polyhedra to build, around the threefold axis, large channels parallel to the c axis. All the nine water molecules in the present arrangement participate in the coordination spheres of the associated cations. The thermogravimetric analysis shows that the removal of these water molecules occurs in three stages between 305 and 736 K.The vibrational study by IR absorption spectroscopy of Na₃Yb(P₃O₉)₂·9H₂O is also reported.     

Ion exchange and electrochemical evaluation of the microporous phosphate Li9Fe7(PO4)10

A new lithium iron(III) phosphate, Li₉Fe₇(PO₄)₁₀, has been synthesized and is currently under electrochemical evaluation as an anode material for rechargeable lithium-ion battery applications. The sample was prepared via the ion exchange reaction of Cs₅K₄Fe₇(PO₄)₁₀1 in the 1 M LiNO₃ solution under hydrothermal conditions at 200 °C. The fully Li⁺-exchanged sample Li₉Fe₇(PO₄)₁₀2 cannot yet be synthesized by conventional high-temperature, solid-state methods. The parent compound 1 is a member of the Cs_9−xK_xFe₇(PO₄)₁₀ series that was previously isolated from a high-temperature (750 °C) reaction employing the eutectic CsCl/KCl molten salt. The polycrystalline solid 1 was first prepared in a stoichiometric reaction via conventional solid-state method then followed by ion exchange giving rise to 2. Both compounds adopt three-dimensional structures that consist of orthogonally interconnected channels where electropositive ions reside. It has been demonstrated that the Cs_9−xK_xFe₇(PO₄)₁₀ series possesses versatile ion exchange capabilities with all the monovalent alkali metal and silver cations due to its facile pathways for ion transport. 1 and 2 were subject to electrochemical analysis and preliminary results suggest that the latter can be considered as an anode material. Electrochemical results indicate that Li₉Fe₇(PO₄)₁₀ is reduced below 1 V (vs. Li) to most likely form a Fe(0)/Li₃PO₄ composite material, which can subsequently be cycled reversibly at relatively low potential. An initial capacity of 250 mAh/g was measured, which is equivalent to the insertion of thirteen Li atoms per Li_9+xFe₇(PO₄)₁₀ (x = 13) during the charge/discharge process (Fe²⁺ + 2e → Fe⁰). Furthermore, 2 shows a lower reduction potential (0.9 V), by approximately 200 mV, and much better electrochemical reversibility than iron(III) phosphate, FePO₄, highlighting the value of improving the ionic conductivity of the sample.     

Improved microwave dielectric properties of B2O3-doped Nd(Co1/2Ti1/2)O3 ceramics with near zero temperature coefficient of resonant frequency

The microwave dielectric properties and the microstructures of Nd(Co_1/2Ti_1/2)O₃ ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co_1/2Ti_1/2)O₃ exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B₂O₃ (up to 0.75 wt.%) can significantly improve the density and dielectric properties of Nd(Co_1/2Ti_1/2)O₃ ceramics. Nd(Co_1/2Ti_1/2)O₃ ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320 °C. Second phases were not observed at the level of 0.25-0.75 wt.% B₂O₃ addition. The temperature coefficient of resonant frequency (τ_f) was not significantly affected, while the dielectric constants (?_r) and the unloaded quality factors Q were effectively promoted by B₂O₃ addition. At 1320 °C/4 h, Nd(Co_1/2Ti_1/2)O₃ ceramics with 0.75 wt.% B₂O₃ addition possesses a dielectric constant (?_r) of 27.2, a Q × f value of 153,000 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (τ_f) of 0 ppm/°C. The B₂O₃-doped Nd(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices requiring low sintering temperature.     

PEG-300 assisted hydrothermal synthesis of 4ZnO·B2O3·H2O nanorods

4ZnO·B₂O₃·H₂O is commonly used as a flame-retardant filler in composite materials. The microstructure of the powder is of importance in its applications. In our study, for the first time, one-dimensional (1D) nanostructure of 4ZnO·B₂O₃·H₂O with rectangle rod-like shape has been synthesized by a hydrothermal route in the presence of surfactant polyethylene glycol-300 (PEG-300). The nanorods have been characterized by X-ray powder diffraction (XRD), inductively coupled plasma with atomic emission spectroscopy (ICP-AES), thermogravimetry (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with selected area electron diffraction (SAED) as well as high-resolution transmission electron microscopy (HRTEM). These nanorods are about 70 nm in thickness, 150-800 nm in width and have lengths up to a few microns. 4ZnO·B₂O₃·H₂O nanorods crystallize in the monoclinic space group P2₁/m, a = 6.8871(19) Å, b = 4.9318(10) Å, c = 5.7137(16) Å, β = 98.81(21)° and V = 191.779(71) Å³.     

Synthesis, crystal structure and thermal decomposition of [La2(CH3CH2COO)6·(H2O)3]·3.5H2O precursor for high-k La2O3 thin films deposition

Lanthanum acetylacetonate La(C₅H₇O₂)₃·xH₂O has been used in the preparation of the precursor solution for the deposition of polycrystalline La₂O₃ thin films on Si(1 1 1) single crystalline substrates. The precursor chemistry of the as-prepared coating solution, precursor powder and precursor single crystal have been investigated by Fourier Transformed Infrared Spectroscopy (FTIR), differential thermal analysis coupled with quadrupole mass spectrometry (TG-DTA-QMS) and X-ray diffraction. The FTIR and X-ray diffraction analyses have revealed the complex nature of the coating solution due to the formation of a lanthanum propionate complex. The La₂O₃ thin films deposited by spin coating on Si(1 1 1) substrate exhibit good morphological and structural properties. The films heat treated at 800 °C crystallize in a hexagonal phase with the lattice parameters a = 3,89 Å and c = 6.33 Å, while at 900 °C the films contain both the hexagonal and cubic La₂O₃ phase.     

Synthesis and electromagnetic properties of microwave absorbing material: Cox(Cu0.5Zn0.5)1−xFe2O4 (0 < x < 1) nanoparticles

Spinel ferrite Co_x(Cu_0.5Zn_0.5)_1−xFe₂O₄ over a compositional range 0 < x < 1 was prepared using a simple hydrothermal method. Particle sizes could be varied from 14 to 25 nm by changing the x value. X-ray diffraction results confirmed that all the as-prepared nanoparticles revealed typical spinel structure and transmission electron microscopy images showed that the particle size of the samples increased with increasing x value. The magnetic properties of the as-prepared Co_x(Cu_0.5Zn_0.5)_1−xFe₂O₄ nanoparticles have been systematically examined. The maximum saturation magnetization existed at the highest Co content (x = 1). The electromagnetic properties of all the samples have been measured by an Agilent network analyzer and the results showed that Co_0.1(Cu_0.5Zn_0.5)_0.9Fe₂O₄ possessed the best microwave absorbing properties.     

Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

Mg_xCu_3−xV₂O₆(OH)₄·2H₂O (x ∼ 1), with similar crystal structure as volborthite Cu₃V₂O₇(OH)₂·2H₂O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V₂O₅ with few mL of 30 vol.% H₂O₂ followed by addition of distilled water). When ammonium hydroxide NH₄OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO₄ to trigonal bipyramidal VO₅, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu₃V₂O₈ phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu₃V₂O₈ phases.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.