PO4 Phase Research Articles

Comparative Study of Cu Ion Adsorption by Nano-Hydroxyapatite Powder Synthesized from Chemical Reagents and Clam Shell-Derived Calcium Sources.

The increasing contamination of water sources by heavy metals necessitates the development of efficient and sustainable adsorption materials. This study evaluates the potential of nano-hydroxyapatite (HA) powders synthesized from chemical reagents (Chem-HA) and clam shells (Bio-HA) as adsorbents for Cu ions in aqueous solutions. Both powders were synthesized using microwave irradiation at 700 W for 5 min, resulting in nano-sized rod-like particles confirmed as HA by X-ray diffraction (XRD). Bio-HA exhibited higher crystallinity (67.5%) compared to Chem-HA (34.9%), which contributed to Bio-HA's superior adsorption performance. The maximum adsorption capacities were 436.8 mg/g for Bio-HA and 426.7 mg/g for Chem-HA, as determined by the Langmuir isotherm model. Kinetic studies showed that the Cu ion adsorption followed the pseudo-second-order model, with Bio-HA achieving equilibrium faster and displaying a higher rate constant (6.39 × 10⁻4 g/mg·min) than Chem-HA (5.16 × 10⁻4 g/mg·min). Thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic, with Bio-HA requiring less energy (ΔH° = 39.00 kJ/mol) compared to Chem-HA (ΔH° = 43.77 kJ/mol). Additionally, the activation energy for Bio-HA was lower (41.62 kJ/mol) than that for Chem-HA (46.39 kJ/mol), suggesting better energy efficiency. The formation of a new Cu2(OH)PO4 phase after adsorption, as evidenced by XRD, confirmed that the Cu ions replaced the Ca ions in the HA lattice. These findings demonstrate that Bio-HA, derived from natural sources, offers environmental benefits as a recyclable material, enhancing heavy metal removal efficiency while contributing to sustainability by utilizing waste materials and reducing an environmental impact.

Temperature dependences of phase composition, densification, and thermal/chemical stability of Sr0.5Zr2(PO4)3-Nd0.5Sm0.5PO4 composite ceramics for nuclear waste form

A kind of Sr0.5Zr2(PO4)3-Nd0.5Sm0.5PO4 (hereinafter SrZP-Nd0.5Sm0.5PO4) composite ceramics was prepared through a one-step microwave sintering technique, where Sr, Nd, Sm were simulated for fission products and minor actinides (MA). The crystal structure and morphology of constituent phases were systematically characterized by XRD, TEM, and SEM techniques. The temperature dependent phase analysis results of SrZP-Nd0.5Sm0.5PO4 composite ceramics illustrate that with evaluating temperature monazite structure formed primarily, and the SrZP phase formed subsequently. With the temperature rising further, the monazite phase finally transformed into Nd0.5Sm0.5PO4 monazite solid solution. XRD refinement and TEM measurements are used to verify the crystal structures of the as-prepared SrZP and Nd0.5Sm0.5PO4 phases in the composite ceramics. The dependence of densification behaviors on temperature shows that the distinct densification of the SrZP-Nd0.5Sm0.5PO4 composite ceramics occurs in the temperature range of 950 °C to 1000 °C, and the relative density reaches 97.7 % at 1050 °C. TG-DSC tests show that the SrZP-Nd0.5Sm0.5PO4 composite ceramics exhibit excellent thermal stability at high temperatures. And SrZP-Nd0.5Sm0.5PO4 composite ceramics possess outstanding chemical stability, whose normalized leaching rate of Sr, Nd, and Sm is 10−4 g·m−2·d−1, 10−7 g·m−2·d−1, and 10−7 g·m−2·d−1 order of magnitude, respectively.

Transition mechanism and thermokinetic analysis of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics for nuclear waste forms based on in-situ synthesis

In this study, the novelly designed Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics were utilized as nuclear waste form to simultaneously immobilize simulated fission products Sr and actinide nuclides. The phase transition mechanism, thermokinetics and densification behavior of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics based on in-situ synthesis were systemically analyzed by XRD, in-situ XPS, TG-DSC, SEM and density measurements. The results demonstrate that the formation of Ce0.5Sm0.5PO4 solid solution phase preceded that of Sr0.5Zr2(PO4)3 phase, of which there is a valence change of Ce from Ce4+ to Ce3+ before 1023 K. Additionally, as for the exothermic crystallization enthalpy, change of exothermic crystallization enthalpy and activation energy, the values of Sr0.5Zr2(PO4)3 and Ce0.5Sm0.5PO4 phases in composite ceramics are 286.17 – 515.61 mJ, 19.11 – 35.38 J/g, 702.45 kJ/mol and 145.21 – 232.44 mJ, 9.26 – 15.44 J/g, 450.04 kJ/mol, respectively. It is then indicated that the formation of Ce0.5Sm0.5PO4 phase is definitely more favorable than that of Sr0.5Zr2(PO4)3 phase. Simultaneously, the relative densities of Sr0.5Zr2(PO4)3–Ce0.5Sm0.5PO4 composite ceramics are more than 95 % when the sintering temperature exceeds 1273 K.

Microstructural and dielectric properties of LiNi0.5Co0.45Zn0.05PO4 cathode material

LiNiPO4 has been the focus of research in developing environmentally friendly, low cost and high performance cathode materials for lithium-ion batteries. The aim of this work is to synthesize LiNi0.5Co0.45Zn0.05PO4 cathode material using solid-state reaction method at 850 °C for 20 hours and all the parameters compared with LiNiPO4. The X-ray diffraction (XRD) analysis confirmed that LiNi0.5Co0.45Zn0.05PO4 phase is well crystallized with olivine structure indexed by orthorhombic symmetry with Pnma space group. The phase purity supported by energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM). Local structure of the LiNi0.5Co0.45Zn0.05PO4 phospho-olivine material has been investigated by Fourier transforms infrared spectra (FTIR). All the parameters of LiNi0.5Co0.45Zn0.05PO4 are found in good agreement with XRD, FTIR results of LiNiPO4. Impedance spectroscopy technique has been used to study the cathode materials because it can reveal the relationship between the crystal lattice with the electrochemical properties.

Performance of Coconut Shell Activated Carbon in LiMn<sub>0.7</sub>Fe<sub>0.3</sub>PO<sub>4</sub>/CNT/C Composite for Lithium Ion Battery Cathode

Synthesis and characterization of LiMn0.7Fe0.3PO4/CNT/C composite used as lithium ion battery cathode has been carried out. The active materials of LiMn0.7Fe0.3PO4 was synthesized via hydrothermal method from the precursors of LiOH, NH4H2PO4, FeSO4.7H2O and MnSO4.7H2O. The activated carbon was pyrolyzed from coconut shell whereas the carbon nanotube (CNT) was commercially available in the market. The composite was prepared using a ball-mill to mix the components homogeneously. Simultaneous thermal analysis STA was used to determine the formation temperature of LiMn0.7Fe0.3PO4 to which the sintering process was conducted at 700 °C. After sintering, the materials in powder forms were characterized using scanning electron microscope (SEM) to examine the morphology, whereas X-ray diffraction (XRD) was used to identify the phases formed. The performance of the composite as lithium ion battery cathode was characterized using electrochemical impedance spectroscopy (EIS) and battery analyzer. Secondary electron image from SEM showed that the samples have homogeneous particle distribution. Examination result from X-ray diffraction indicated that LiMn0.7Fe0.3PO4 phase has been successfully synthesized with small impurities from a secondary phase. Performance analysis showed that the presence of activated carbon and CNTs in LiMn0.7Fe0.3PO4 to form LiMn0.7Fe0.3PO4/CNTs/C gives significant improvement in the conductivity; however, some more improvement is still needed for the capacity.

Immobilization of a simulated HLW in phosphate based glasses/glass-ceramics by melt-quenching process

In this paper, monazite-iron phosphate based glass-ceramics for immobilization of a simulated high-level nuclear waste (HLW) derived from the composition of a nuclear waste in China were prepared through a melt-quenching process. The effect of HLW incorporation on phases, structural features, aqueous durability and properties of the as-prepared wasteforms were investigated in detail. The results show that the waste loading can be significantly elevated by forming monazite (Ce, La, Nd)PO4 containing glass-ceramic wasteforms through the melt-quenching process. The obtained glass/glass-ceramic wasteforms show good aqueous durability (∼10−4 g m−2 d−1) and thermal stability. Moreover, the formation of monazite (Ce, La, Nd)PO4 phase in the wasteforms is discussed. The conclusions suggest that it is feasible to synthesize (Ce, La, Nd)PO4-phosphate glass-ceramic wasteforms through melt-quenching process and monazite-iron phosphate based glass-ceramics are potential candidates for immobilization of the HLW.

Structural evidence for Mg-doped LiFePO4 electrode polarisation in commercial Li-ion batteries

The reaction evolution and kinetics of the LiFePO4 positive electrode material is dependent on the synthesis method and cycling conditions. In operando neutron powder diffraction is used investigate the structure-electrochemistry relationship of the electrode materials in a Valence Technology Inc. 18650 Energy cell (IFR18650EC) containing a graphite negative electrode and a Mg-doped LiFePO4 (Li(MgFe)PO4) positive electrode. Two cells were studied at ambient (298 K) and elevated (323 K) temperature, and higher temperatures were found to improve reaction kinetics and hence capacity. Rietveld refinement of structural models against the diffraction data revealed information about the nucleation of the lithiated and delithiated phases in the Li(MgFe)PO4 positive electrode material as a function of each cell's state of charge. Polarisation was indicated by a shift in the potential at which the lithiated and delithiated (MgFe)PO4 phases nucleate during cycling, the extent of which was found to be linearly proportional to the applied current. This work provides new evidence for polarisation of the positive electrode material in a Li-ion battery system.

Resorption of Ca3 – xM2x(PO4)2 (M = Na, K) Calcium Phosphate Bioceramics in Model Solutions

The resorbability of bioceramics in the Ca3(PO4)2–CaNaPO4–CaKPO4 system is evaluated in an approach involving thermodynamic assessment of solubility and investigation of the dissolution kinetics in model media, in particular in citric acid solutions. Thermodynamic calculation indicates high solubility of the Ca5Na2(PO4)4, α-CaМPO4, β-CaKPO4, and β-СаK0.6Na0.4PO4 phases. Investigation of the dissolution kinetics of ceramics has made it possible to identify two distinct types of behavior of resorbable materials in weakly acidic solutions: with fast resorption kinetics in the case of the phases based on nagelschmidtite solid solutions and α-CaМPO4 disordered high-temperature solid solutions, and with a nearly constant, relatively low dissolution rate and a high solubility limit in the case of β-СaK1 – xNa x -based phases.

Visible‐Light Photocatalytic Activity of Ionic Liquid TiO2 Spheres: Effect of the Ionic Liquid's Anion Structure

AbstractThe effect of the ionic liquid's (IL) anion type ([BMIM][X], where BMIM=1‐butyl‐3‐methylimidazolium and X=[Br], [PF6], or octylsulfonate [OctSO4]) and IL content on the morphology, surface properties, and photoactivity of TiO2 obtained by the solvothermal method has been systematically investigated. Our results revealed that the presence of [Br] and [OctSO4] anions favor the formation of anatase phase, whereas the presence of [PF6] causes formation of anatase and Ti(OH)PO4 phase mixtures. The highest photocatalytic activity under visible radiation (approximately four times higher than pristine TiO2) was observed for the TiO2 sample grown in the presence of 1‐butyl‐3‐methylimidazolium bromide for ionic liquid to TiO2 precursor molar ratio 1:2. Visible‐light‐induced phenol degradation was found to be realized mainly by oxygen radical anions, whereas the contributions of the other processes involving reactions with trapped electrons, holes, and hydroxyl radical, are limited in the overall reaction mechanism. Quantum chemical calculations on a model of anatase vacancy suggest that the charge transfer between the bromide anion and molecular oxygen interacting with the vacancy is a source of photoactivity induced by visible photons.

Co11Li[(OH)5O][(PO3OH)(PO4)5], a Lithium-Stabilized, Mixed-Valent Cobalt(II,III) Hydroxide Phosphate Framework.

A new metastable phase, featuring a lithium-stabilized mixed-valence cobalt(II,III) hydroxide phosphate framework, Co11.0(1)Li1.0(2)[(OH)5O][(PO3OH)(PO4)5], corresponding to the simplified composition Co1.84(2)Li0.16(3)(OH)PO4, is prepared by hydrothermal synthesis. Because the pH-dependent formation of other phases such as Co3(OH)2(PO3OH)2 and olivine-type LiCoPO4 competes in the process, a pH value of 5.0 is crucial for obtaining a single-phase material. The crystals with dimensions of 15 μm × 30 μm exhibit a unique elongated triangular pyramid morphology with a lamellar fine structure. Powder X-ray diffraction experiments reveal that the phase is isostructural with the natural phosphate minerals holtedahlite and satterlyite, and crystallizes in the trigonal space group P31m (a = 11.2533(4) Å, c = 4.9940(2) Å, V = 547.70(3) Å3, Z = 1). The three-dimensional network structure is characterized by partially Li-substituted, octahedral [M2O8(OH)] (M = Co, Li) dimer units which form double chains that run along the [001] direction and are connected by [PO4] and [PO3(OH)] tetrahedra. Because no Li-free P31m-type Co2(OH)PO4 phase could be prepared, it can be assumed that the Li ions are crucial for the stabilization of the framework. Co L-edge X-ray absorption spectroscopy demonstrates that the cobalt ions adopt the oxidation states +2 and +3 and hence provides further evidence for the incorporation of Li in the charge-balanced framework. The presence of three independent hydroxyl groups is further confirmed by infrared spectroscopy. Magnetization measurements imply a paramagnetic to antiferromagnetic transition at around T = 25 K as well as a second transition at around 9-12 K with a ferromagnetic component below this temperature. The metastable character of the phase is demonstrated by thermogravimetric analysis and differential scanning calorimetry, which above 558 °C reveal a two-step decomposition to CoO, Co3(PO4)2, and olivine-type LiCoPO4 with release of water and oxygen.

An FTIR and ESR study of iron doped calcium borophosphate glass-ceramics

A series of glasses in the xFe2O3-(100-x) [42B2O3–24CaO–34P2O5] system has been prepared for x = 0–10. Structure of as casted glasses and their heat treated counterparts have been studied by X-ray diffraction, infrared and electron spin resonance spectroscopies. Amorphous nature of all of the compositions studied is confirmed by the XRPD spectra. After the heat treatment, besides the main BPO4 phase, CaBPO5 and Ca(PO3) crystalline phases were identified in the iron free glass while B0.57Fe0.43PO4 phase was also observed in the XRD pattern of iron containing samples. FTIR spectra indicate changes in the glass network upon iron addition. X-band ESR spectra exhibits resonance signals at g ∼ 2.0 and g ∼ 4.3 for all analyzed samples. A supplementary line centered at g ∼ 6 appears after the thermal treatment. The nature of ESR absorption signals and influence of iron content on the evolution of ESR parameters are discussed.

Low‐Temperature Sinterable (1−x)Ba3(VO4)2–xLiMg0.9Zn0.1PO4 Microwave Dielectric Ceramics

The novel low‐temperature sinterable (1 − x)Ba3(VO4)2–xLiMg0.9Zn0.1PO4 microwave dielectric ceramics were prepared by cofiring the mixtures of pure‐phase Ba3(VO4)2 and LiMg0.9Zn0.1PO4. The phase structure and grain morphology of the ceramics were evaluated using X‐ray diffraction, Raman spectra, and scanning electron microscopy. The results indicated that Ba3(VO4)2 and LiMg0.9Zn0.1PO4 phases can well coexist in the sintered body. Nevertheless, a small amount of LiZnPO4 and some vanadate phases with low melting points were observed, which not only can influence the microwave dielectric properties of the ceramic but also can obviously improve the densification behavior at a relatively low sintering temperature. The near‐zero temperature coefficients of the resonant frequency (τf) could be achieved by adjusting the relative content of the two phases owing to their opposite τf values and simultaneously a desirable quality factor Q × f value can be maintained. No chemical reaction between the matrix ceramic phase and Ag took place after sintering at 800°C for 4 h. The ceramics with 45 vol% LiMg0.9Zn0.1PO4 can be well sintered at only 800°C and exhibit excellent microwave dielectric properties of εr ~ 10, Q × f ~ 64 500 GHz, and τf ~ −2.1 ppm/°C, thus showing a great potential as a low‐permittivity low‐temperature cofired microwave dielectric material.

Operando57Fe Mössbauer and XRD investigation of LixMnyFe1−yPO4/C composites (y = 0; 0.25)

LiMn0.25Fe0.75PO4 and LiFePO4 powders have been synthesized by a ceramic route. A comparative investigation of their electrochemical behaviour using operando57Fe Mössbauer and X-ray diffraction is reported. The partial substitution of Fe by Mn atoms enhances the energy density of the olivine phase since the average potential of cycling is increased. The complementarity of the operando techniques used in this study allows the monitoring of changes in the local electronic environment and the lattice modifications that are directly linked to the redox reaction mechanisms. The lithium deintercalation/intercalation mechanism in LiMn0.25Fe0.75PO4 has been found to be completely different from LiFePO4. During the charge, the LiMn0.25Fe0.75PO4 phase has been found to undergo three well defined and reversible reactions; (i) a biphasic reaction at 3.46 V corresponding to a partial oxidation of FeII into FeIII, (ii) the remaining FeII is oxidized in a monophasic reaction between 3.46 and 4.1 V. Finally, (iii) MnII is converted to MnIII by mean of biphasic reaction at 4.2 V. Interestingly, the FeIII Mössbauer signature has been found to be sensitive to the oxidation of MnII since this oxidation is accompanied with a significant increase in the quadrupole splitting. The non-optimized LiMn0.25Fe0.75PO4electrode has been successfully cycled with constant capacity (120 mAh.g−1) for more than 40 cycles at room temperature.

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.

Insertion properties of LiFe0.5Mn0.5PO4 electrode materials for Li-ion batteries

This paper addresses the synthesis structural and electrochemical properties of LiFe0.5Mn0.5PO4 electrode materials for Li-ion batteries. The charge–discharge reaction of Li/LiPF6-EC–DEC/LiFe0.5Mn0.5PO4 cell carried out at the 1-C rate shows a capacity retention of 128 mAh/g. The local structure of the delithiated LixFe0.5Mn0.5PO4 phases have been studied by Fourier transform infrared spectroscopy and magnetometry. Spectral features indicate that the structure of the delithiated phase remains in the orthorhombic system. The compositional dependence of the magnetic moment is found to be in quantitative agreement with the theoretical value predicted for oxidation of M2+ ions in the high spin state.

Spectroscopic and Magnetic Properties of Co1.7Mn0.3(OH)PO4.

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Spectroscopic and Magnetic Properties of Co1.7Mn0.3(OH)PO4

AbstractCo1.7Mn0.3(OH)PO4 has been prepared under mild hydrothermal conditions and characterized from powder X‐ray diffraction. IR data are characteristic of three distinct features corresponding principally to the vibrations of the hydroxide and [PO4]3− anions. UV‐Visible studies show the existence of bands ascribed to the chromophores of Co ions in two coordination polyhedra, octahedral and trigonal bipyramidal. The magnetic behaviour indicates the existence of antiferromagnetic interactions as predominant. Magnetization measurements show the presence of two maxima at 65 K and 9 K, respectively. The first peak was attributed to a three‐dimensional antiferromagnetic ordering and the second one reveals the possible existence of a spin‐glass like state. The substitution of Co2+ (S = 3/2) by Mn2+ (S = 5/2) ions at about 15 % keeps the two magnetic transitions observed in the non‐substituted phase. ZFC‐FC curves show magnetic irreversibility at temperatures just below TN due to the spin decompensations in Co1.7Mn0.3(OH)PO4. The remanent magnetization indicates higher ferromagnetic interactions at lower temperatures than that observed in the ordered Co2(OH)PO4 phase. These results could be attributed to the existence of a spin‐glass state similar to that exhibited by the Co2(OH)PO4 and substituted Co2−xMx(OH)PO4 (M = Ni, Cu; x = 0.1−0.3) compounds. A comparative magnetic study with the analogous Ni2+ (S = 1) and Cu2+ (S = 1/2) phases is carried out.

Magnetic evolution of the antiferromagnetic Co2–xCux(OH)PO4 (0 ≤x≤ 2) solid solution. A neutron diffraction study

The Co2−xCux(OH)PO4 (0 ≤ x ≤ 2) solid solution was prepared from hydrothermal synthesis. Neutron powder diffraction patterns show that the Co2+ and Cu2+ ions are simultaneously present in both the [MO4(OH)2] octahedra and the [MO4(OH)] distorted trigonal bipyramid topologies. The evolution of the lattice parameters follows Vegard’s law in the whole range of substitution. This study allowed us to determine correctly the a and b crystallographic parameters of the Cu2(OH)PO4 phase which were interchanged in the literature. The magnetic behaviour in the cobalt–copper compounds indicates the existence of overall antiferromagnetic interactions as predominant. Three-dimensional magnetic ordering with critical temperatures of 69, 64, 60 and 47 K for x = 0.1, 0.3, 0.5 and 1 respectively is observed. The magnetic study of Co1.9Cu0.1(OH)PO4 suggests a spin-glass like state below 10 K. AC measurements obtained at different frequencies and applied fields confirm the freezing process in Co1.9Cu0.1 and the long range interactions in the Co2−xCux(OH)PO4 (x ≤ 1) phases. For x > 1, the magnetic dimensionality decreases with the increase of Cu(II) amount being of short range for x = 2. These results are attributed to the presence of the unpaired electron in the dx2−y2 orbital and the absence of overlap between neighbour ions. Specific-heat measurements confirm the evolution to a short range magnetic system with the Cu(II) amount. From low-temperature neutron diffraction data, it can be observed that the existence of antiferromagnetic order for x ≤ 1 is originated by the antiparallel ordering of both ferromagnetic linear octahedral chains and trigonal bipyramidal dimers. The propagation vector is k = [0,0,0] and the magnetic moments are aligned in the z direction. The values of the main magnetic exchange pathways [M–O–M] are characteristic of ferro- and antiferromagnetic couplings with a superexchange ferromagnetic angle, M(1)–O(3)–M(2) of 107–109°, which plays an important role in the competition of the freezing process. These results are explained on the basis of both the electronic configuration and the correlations between structural and magnetic properties.

Nano-Raman mapping of porous glass ceramics with a scanning near-field optical microscope in collection mode

A nano-Raman setup using the optical fiber of a scanning near-field optical microscope, working in collection mode, is described and applied to mapping of TiO2∕PO4 phase distribution in glass ceramics. This material is extremely important as a surface-enhanced raman scattering substrate for biological and chemical analyses. The collected Raman signal in this near-field geometry reaches spatial resolutions better than 100nm, well below the diffraction limit.

Effect of Ni2+(S = 1) and Cu2+(S = ½) substitution on the antiferromagnetic ordered phase Co2(OH)PO4with spin glass behaviour

The hydroxyphosphates with formula Co1.7M0.3(OH)PO4 (M = Ni, Cu) have been prepared from hydrothermal synthesis. The compounds have been characterized by X-ray powder diffraction and spectroscopic measurements. Diffuse reflectance data of both phases show bands belonging to the two chromophores, octahedral and trigonal bipyramidal, of the Co(II) ions together with others associated to the chromophores of nickel(II) and copper(II) ions. Magnetization measurements of Co1.7Ni0.3(OH)PO4 show the presence of two maxima at ca. 62 and 5 K, respectively. The first peak was attributed to a three-dimensional antiferromagnetic ordering and the second one reveals the existence of a spin glass-like state. This behaviour was confirmed from the ac measurements obtained at different frequencies and applied fields. The Co1.7Cu0.3(OH)PO4 phase exhibits only one maximum at 65 K in both χm and ac measurements associated to the three-dimensional antiferromagnetic interactions; however, the existence of spin glass behaviour is not observed. ZFC-FC curves for the cobalt–nickel and cobalt–copper compounds show irreversibility just below TN indicating the existence of higher spin decompensations than in the Co2(OH)PO4 phase. This difference and its influence in the magnetic anomalies observed at low temperatures is the more important effect in the magnetic measurements of the ordered Co2(OH)PO4 phase substituted at about 15% of the Co2+ (S = ) by Ni2+ (S = 1) or Cu2+ (S = ½) ions. The origin of the frustration, which is necessary to achieve a disordered ground state, is investigated in these kinds of spin glass compounds. Taking into account the possible magnetic exchange pathways, which are essential to install competition and ensure cooperativeness of the freezing process, correlations between structural and magnetic properties have been performed.