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Carvedilol is a poorly water-soluble drug employed to treat chronic heart failure. In this study, we synthesize new carvedilol-etched halloysite nanotubes (HNTs) composites to enhance solubility and dissolution rate. The simple and feasible impregnation method is used for carvedilol loading (30–37% weight). Both the etched HNTs (acidic HCl and H2SO4 and alkaline NaOH treatments) and the carvedilol-loaded samples are characterized by various techniques (XRPD, FT-IR, solid-state NMR, SEM, TEM, DSC, and specific surface area). The etching and loading processes do not induce structural changes. The drug and carrier particles are in intimate contact and their morphology is preserved, as demonstrated by TEM images. The 27Al and 13C solid-state NMR and FT-IR findings show that carvedilol interactions involve the external siloxane surface, especially the aliphatic carbons, the functional groups, and, by inductive effect, the adjacent aromatic carbons. All the carvedilol–halloysite composites display enhanced dissolution rate, wettability, and solubility, as compared to carvedilol. The best performances are obtained for the carvedilol–halloysite system based on HNTs etched with HCl 8M, which exhibits the highest value of specific surface area (91 m2 g−1). The composites make the drug dissolution independent of the environmental conditions of the gastrointestinal tract and its absorption less variable, more predictable, and independent from the pH of the medium.

The eco-friendly method of kneading was here used to synthesize a cocrystal of probenecid, an uricosuric drug used in treating gout and hyperuricemia, with the aim to improve its pharmaceutical behavior. Benzamide was selected as a co-former showing functional groups favorable to the formation of supramolecular synthons with the active principle. The kneading product was characterized by a range of experimental techniques (microscopic, spectroscopic, thermal and diffractometric) all proving the formation of the new multicomponent crystal. In particular, the FT-IR and NMR techniques showed that an important change of hydrogen bonds network takes place in the kneading product and that the acid–acid interaction in the pristine drug is replaced with the related acid-amide one in the cocrystal. The cocrystal solubility and dissolution rate measured in several biorelevant fluids showed an actual improvement with respect to the pure drug.

The present work is a concrete example of how physico-chemical studies, if performed in depth, are crucial to understand the behavior of pharmaceutical solids and constitute a solid basis for the control of the reproducibility of the industrial batches. In particular, a deep study of the thermal behavior of glipizide, a hypoglycemic drug, was carried out with the aim of clarifying whether the recognition of its polymorphic forms can really be done on the basis of the endothermic peak that the literature studies attribute to the melting of the compound. A number of analytical techniques were used: thermal techniques (DSC, TGA), X-ray powder diffraction (XRPD), FT-IR spectroscopy and scanning electron microscopy (SEM). Great attention was paid to the experimental design and to the interpretation of the combined results obtained by all these techniques. We proved that the attribution of the endothermic peak shown by glipizide to its melting was actually wrong. The DSC peak is no doubt triggered by a decomposition process that involves gas evolution (cyclohexanamine and carbon dioxide) and formation of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which remains as decomposition residue. Thermal treatments properly designed and the combined use of DSC with FT-IR and XRPD led to identifying a new polymorphic form of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which is obtained by crystallization from the melt. Hence, our results put into evidence that the check of the polymorphic form of glipizide cannot be based on the temperature values of the DSC peak, since such a peak is due to a decomposition process whose Tonset value is strongly affected by the particle size. Kinetic studies of the decomposition process show the high stability of solid glipizide at room temperature.

The aim of this work was to search for new polymorphic forms of febantel, an anthelminthic drug of great present interest for the veterinary industry. Solvent-based recrystallization, thermal and mechanical treatments and spray drying were chosen to discover new solid forms. The solids obtained were physicochemically characterized by thermal techniques (DSC and TG), FTIR spectroscopy, laboratory and synchrotron X-ray powder diffraction and scanning electron microscopy. Our work leads to obtain a new solid form never described in the literature. In particular, the new polymorph was obtained by the anti-solvent method and the crystallization from isopropanol. The experimental conditions of crystallization favorable to the formation of the highest amount of the new solid phase were selected. The new phase shows a thermal, spectroscopic and diffractometric behavior unique. Furthermore, the preliminary structure investigation suggests two possible crystal systems: an orthorhombic or a monoclinic one, with really comparable lattice parameters and cell volume. Measurements put into evidence that the new phase is a metastable polymorph that is in monotropic relationship with the stable and known form.

A detailed characterization of the polymorphs constituting cathode materials, both before and after cell cycling, is mandatory to develop more stable and powerful lithium batteries. In many cases, e.g., for transition metal lithium silicates, standard diffraction techniques cannot give a clear-cut response. Here we show that broadband adiabatic fast MAS NMR can give unique information in the case of model Li2(Mn,Fe)SiO4 high-capacity cathode materials. By coupling 7Li and 29Si 1D and 2D spectra, we are able to address polymorphs speciation also in the mixed Mn/Fe compositions, which is a nearly impossible task for X-rays and neutrons diffraction. We finally discuss the conditions under which this approach is useful when applied to rare nuclei such as 29Si.

Lithium metal orthosilicates are attracting a lot of attention owing to their promising prospects as potential high capacity cathode materials for Li-ion batteries. Currently, great efforts are being made in order to achieve the full theoretical specific capacity of 330 mA h g(-1), but many issues remain unsolved (e.g., poor structural and cycling stability), which limit their practical application. The present perspective highlights the importance of assessing the electrochemical behaviour of Li2(Fe,Mn)SiO4 by combining an arsenal of characterization techniques both spectroscopic and structural, in and ex situ. Here, we review the most recent achievements in the investigation of the electrochemical performance of lithium metal orthosilicate cathodes and, through some of our recent results, we attempt to clarify the relationship between the structure and electrochemistry of these compounds.

The global energy demand calls for more efficient storage systems. In this review, the state of the art of Li/air and Li/O 2 batteries is discussed with particular attention on the more recent findings regarding all the battery compartments. Both aqueous and non-aqueous systems are considered, and the most critical issues for better battery design are addressed. Whereas the predicted charge/discharge values for these devices do justify the intense research efforts performed nowadays, great problems are still present which must be overcome in order to make Li/air and Li/O 2 a reality for future large-scale applications.

The role of lithium excess and Mn doping on lithium titanium phosphate properties is studied by structural (X-ray and neutron diffraction) and spectroscopic (electron paramagnetic resonance and impedance) techniques. The dopant cation is present with 2+, 3+, and 4+ oxidation states in both the lithium and titanium sublattices: Mn2+ is preferentially located on Li sites and Mn4+ on Ti ones, and Mn3+ can occupy both the sites. The refinement of neutron diffraction patterns allowed us to identify the 18e crystallographic site as the preferred location of the excess Li ions. Cationic distribution and valence state are mainly related to sol–gel or solid-state synthesis routes. Consequently, the complex behavior of the bulk conductivity can be explained by the presence of Mn on the Li site and the amount of Li excess, while the effect of the sintering degree is comparable in all the samples as revealed by scanning electron microscopy.

Mo{sub 1-x}W{sub x}O{sub 3} oxides with different cationic fraction (x=0.2, 0.5 and 0.8) and, for comparison purposes, pure MoO{sub 3} and WO{sub 3} were prepared. Along with textural and structural characterizations, absorbance FT-IR, diffuse reflectance UV-vis-NIR and EPR spectroscopies were employed to study the changes in the electronic properties of these materials passing from Mo{sub 1-x}W{sub x}O{sub 3} in oxidizing atmosphere to Mo{sub 1-x}W{sub x}O{sub 3-{delta}} in reducing conditions. XRD analysis showed that the Mo-W mixed oxides are constituted by two or three crystalline phases, whose abundance and composition are well characterized by structural refinement with the Rietveld method. Only the sample with the highest Mo content (x=0.2) shows a predominant mixed phase and also a superior ability to lose oxygen with respect to the other mixed oxides. The oxygen loss in the reduced oxides induces the formation of defects with electronic levels in the band gap of the material, in particular, electrons trapped in oxygen vacancies and/or at cationic sites (polarons). While the nature of defect sites induced in the mixed and in the pure oxides is similar, the photo-ionization energies, the ratio between surface and bulk defects and the stability of the defects in oxygen at increasing temperaturemore » are peculiar of each mixed oxide. - Graphical abstract: The combined use of different techniques provides new insight into structural, optical and electronic properties of semiconductor Mo{sub 1-x}W{sub x}O{sub 3-{delta}} mixed oxides.« less

Structural, microstructural, and spectroscopic properties of Ba6Zr2Ta8O30 (BZT) and Ba6Zr1.94M0.06Ta8O30 (M = Ni, Co, Fe, Mn, Cr) related doped compounds are reported. The distribution of Zr, Ta, and M dopant ions on the cationic sites and the M valence states are discussed on the basis of the results obtained by the application of the Rietveld method on X-ray powder diffraction (XRPD) patterns and by electron paramagnetic resonance. The micro-Raman spectra of pure and doped BZT, reported and discussed for the first time, confirm the capability of the lattice to host transition cations in a glasslike matrix. The particle size effects of the samples are investigated by analyzing XRPD line broadening and scanning electron microscopy observations. Comparisons with the isostructural pure and doped Ba6Ti2Nb8O30 compounds are also reported.

Pure and doped Ba 6 Ti 2 Nb 8 O 30 (BTN), obtained by substituting M = Cr, Mn, or Fe on the Ti site (Ba 6 Ti 2-x M x Nb 8 O 30 , x = 0.06 and 0.18) and Y and Fe on the Ba and Ti sites, respectively (Ba 6-x Y x Ti 2-x Fe x Nb 8 O 30 , x = 0.18), are synthesized. The influence of cation doping on the local structure, the cation oxidation state, and the possible defect formation able to maintain the charge neutrality are investigated by spectroscopic (electron paramagnetic resonance (EPR) and micro-Raman), structural (X-ray powder diffraction) and transport (impedance spectroscopy, thermoelectric power) measurements, in the temperature range of 300-1200 K in air and N 2 flow. Starting from the valence state of the doping ions (Fe 3+ , Cr 3+ , and Mn 2+ ), determined by EPR, and from thermoelectric power measurements, evidencing a negative charge transport, different charge-compensating defect equilibria, based on the creation of positive electron holes or oxygen vacancies and electrons, are discussed to interpret the conductivity results.

The synthesis of pure and Cr-doped nanosized LiMn 2 O 4 particles has been carried out by solid-state process on high-energy ground mixtures. In situ X-ray analysis demonstrates the spinel forms as single phase at 623 K passing through the Mn 3 O 4 precursor at temperatures as low as 573 K. In the doped high-energy ground mixture Li-rich spinel phase forms at 623 K and Cr ions insert in the spinel octahedral site only at 723 K. A mean particle size value of 60 A, quite independent of the reaction time, is obtained for T

The dopant role on the electric and dielectric properties of the perovskite-type CaCu3Ti4O12 (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1–2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90 e r 180 . Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07 eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76 eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.

Two metastable polymorphs of paracetamol (forms II and III) were prepared by appropriate thermal methods from binary mixtures containing 10% (w/w) of hydroxypropylmethylcellulose. By controlling the reheating step, it was possible to address the recrystallization of the drug either into form II or III. Moreover, it was observed that form III transforms either into form II or I depending on the preparation method. The physical characterization of the polymorphs was performed by means of micro-Fourier transform infrared spectroscopy (MFTIR) and powder X-ray diffractometry (PXRD), both temperature controlled.

Ga-doped Li−Mn-spinels Li1.02GaxMn1.98-xO4 with 0.00 ≤ x ≤ 0.20 are investigated to verify the lattice capability to allocate the Ga3+ ions on both tetrahedral and octahedral sites and to determine the lowest amount of dopant that prevents the occurrence of the Jahn−Teller (J−T) transition observed near room temperature in LiMn2O4. XRPD, NMR, and EPR spectra and static magnetic susceptibility and conductivity data are related to the site occupancy, the Mn valence state and the homogeneous distribution of the dopant. The electronic and magnetic features of the spinel framework are strongly dependent on substitution in its cationic sublattice: dopant amounts as low as 1% significantly modify the temperature of the conductivity drop associated with the J−T distortion. Ga3+ ions substitute chiefly in the octahedral sites, Mn4+ ions occupy regular and distorted octahedral sites and, at the same time, the value of lattice parameter remains unchanged. Mn2+ ions are present in the tetrahedral site and Li+ increa...

In this work we reported, for the first time, the preparation by radio frequency sputtering and the electrochemical characterization of Li/M/Si/O thin films (M = Fe, Mn), as positive electrodes for lithium microbatteries. The deposited films were amorphous both in case of pure iron and mixed iron/manganese compositions. The electrochemical performances, in terms of capacity values and coulombic efficiency, were comparable to those currently reported for the corresponding crystalline bulk materials. In particular, capacities of the order of 50 mAh g −1 were obtained at 2.5 C with coulombic efficiency near 90% by using a standard liquid electrolyte. Our preliminary electrochemical results, together with the easiness of preparation, suggested that Li/M/Si/O thin films could be interesting candidates as cathodes in lithium microbatteries.

The aim of this study is to determine the minimum amount of dopant that prevents the occurrence, near room temperature, of a Jahn–Teller (J–T) transition in the M-doped lithium manganese spinel of composition Li1.02MxMn1.98−xO4 with 0.00

The electrical conductivity of lithium-manganese spinels is analyzed in samples with different starting Li cationic fraction x. Li-rich spinels, resulting from Li-Mn substitution around the stoi-chiometric value (x= 0.333), show conductivity values higher than that observed in stoichiometric LiMn2O4 . Besides, a conductivity drop, associated with a structural phase transition at about 290 K in LiMn2O4 , progressively disappears by decreasing x, while it is absent in Li-rich samples. Stoi-chiometry effects on the concentration of charge carriers and on the available sites for the hopping transport process are evaluated, as well as the effects due to coexisting insulating phases. The role of the Jahn-Teller effect on the conductivity behaviour of stoichiometric and Li-poor spinels is also considered.

A thermoanalytical (TGA/DSC) and diffractometric (XRD) study has been performed on the solid state reaction system Li2CO3 -Fe2O3 in the x Li range 0.10±0.50. A detailed analysis of the results shows that the data are in agreement with a reaction model where the carbonate decomposition is regulated by the formation of both LiFeO2 and LiFe5O8 , and the relative amount of the two phases depends on the initial composition. The DSC evidence offers the possibility to directly quantify the LiFe5Ox phase. Furthermore it allows one to obtain the enthalpies of formation of both LiFeO2 and LiFe5O8 .

The coexistence of LiMn 2 O 4 and Li 2 MnO 3 phases from MnO/Li 2 CO 3 mixtures with lithium cationic fraction 0.33≤ x ≤0.53 was studied by X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) measurements. XRD quantitative phase analysis was carried out using the Rietveld profile refinement procedure, while the Li 2 MnO 3 percentage was determined directly by comparing the EPR intensities with the intensity of the pure Li 2 MnO 3 spectrum. The experimental results show the presence of an Li-rich spinel phase and allow an estimation of the lithium excess, since the structural analysis of pure Li 2 MnO 3 samples evidenced a nearly stoichiometric composition ( x =0.663) with very limited cationic disorder.

Transition metal lithium orthosilicates are promising cathode materials for lithium-ion batteries. Here we report a combined experimental (in situ X-ray diffraction) and computational (static lattice and molecular dynamics) study of the thermal behavior of the Li 2 Fe 0.5 Mn 0.5 SiO 4 orthosilicate from room temperature to 950 °C. Our X-ray results showed that Pmnb polymorph is the most stable all over the explored temperature range. A significant cation disorder up to 80%, based on the anti-site defect, was found. The defect concentration depends on the synthesis route and temperature, and is completely reversible after the thermal treatments. Moreover, a careful analysis of the impurity phases allowed us to identify Li 2 SiO 3 , Fe 3 O 4 and Li 3 Fe 5 O 8 , the last one never reported before. The minimization of defects by opportunely tuning the synthetic parameters would be of great importance in view of potential applications of these materials in lithium batteries.

The LiMn2O4 formation from MnO and Li2CO3 mixtures with lithium cationic fraction 0.31 ̲ 0.37. In the former range only the stoichiometric spinel phase was obtained, in the latter, in addition to the Li2MnO3 compound, two spinel phases could be considered: I) LiMn2O4 stoichiometric spinel; II) Li1 + yMn2-yO4 (0.11

Co and Li{sub 2}CO{sub 3} were used as starting materials to obtain cobalt-based plaques of potential use in molten carbonate fuel cell technology. Samples were prepared by thermal treatments in the temperature range 800-1300{degrees}C. Their composition and microstructure have been investigated at room temperature by X-ray diffraction analysis (Rietveld refinement), weight change and density data, porosimetry, and scanning electron microscopy. It is shown that a highly nonstoichiometric Co{sub 3}O{sub 4} forms on lithium-containing samples in the entire temperature range investigated, while a stoichiometric Co{sub 3}O{sub 4} is always obtained in the absence of Li. Moreover, clear evidence has been obtained that sinterization starts at lower temperatures on lithiated samples than on pure Co ones and that it causes the formation of consistent amounts of stoichiometric CoO in both types of sample. It is argued that the increased sinterization rate shown by Li-containing samples is due to the highly defective structure of their Co{sub 3}O{sub 4} phase.

The stability of ordered solid solutions (OSS) with LiNiO2 structure has been studied in a wide range of the lithium cationic fraction (0.22< xt < 0.42). The OSS is obtained from the reactive system Ni0/Li2CO3 at 800 °C starting with high nominal lithium content (xt = 0.5). By analysis of the decrease of x, observed after annealing, during which evaporation and a contact reaction occurs, structure-composition relationships can be obtained. The transformation of the ordered phase, due to a cation exchange process, is observed for xt < 0.31 by accurate X-Ray powder pattern analysis (Rietveld method). By increasing the annealing time (decreasing lithium content), the data can be explained on the basis of progressive formation of the simple solid solution (SSS) with only one cation site and halved c axis value. The variations of structural parameters during the transformation are compared with those reported in the literature. The coherence domains of the OSS become smaller and the phase percentage decreases, while the SSS percentage increases. The rate of such a process can be well described on the basis of a two dimensional diffusion mechanism.

DSC measurements in the 25–240°C temperature range have been performed on sulphur—selenium physical mixtures (1.99–95.06 mass% of Se) in order to clarify the interaction mechanism. The experimental results can be interpreted on the basis of an interaction model according to which a S/Se copolymerization process takes place in mixtures with Se contents up to 55 mass%. Beyond the 55 mass% Se content the interaction mechanism appears to shift towards an “anomalous melting” behaviour of the two components.

The study of the ionic conducting material LiTi2(PO 4)3 and of its Mn-substituted derivate reveals that the Mn distribution is strictly related to the synthetic method. The results of the structural refinement of X-ray and neutron (ToF) powder diffraction data and of XPS analysis demonstrate that Mn2+ ions are located on the lithium octahedral site, while Mn3+ and Mn4+ ions occupy the titanium ones. The Mn2+ amount on the lithium site seems to be the main factor responsible for the conductivity decrease observed in doped samples. The EPR spectra evidence clustering effects of Mn on both Li and Ti sites and the presence of more insulated Mn2+ ions. The effect of the major Mn amount on Ti site in the case of the sol-gel synthesis is consistent with the different EPR line shape of the related sample. The neutron diffraction and 7Li MAS NMR results do reveal that lithium occupies the M1 site of the rhombohedral LiTi2(PO4)3 structure.

We investigate the influence of particle size and crystal orientation on the electrochemical behavior of carbon-coated LiFePO4 prepared by a hydrothermal synthesis in the presence of a polymeric surfactant and a source of carbon. We evaluated the charge/discharge profiles of two samples, one constituted by particles in the micrometer range with a platelet-like shape (large ac facet and (020) crystal orientation) and another made of sub-micrometer-rounded particles with a random crystal orientation. At low current rates the crystal orientation seems to be the prevailing factor, whereas at high current rates smaller particles can allow a shorter electronic conduction path, so reducing the resistance experienced by Li ions during diffusion.

Bioactive glasses and glass-ceramics of the system SiO2-P2O5-CaO with and without zinc were synthesized by sol-gel with the aim to address the influence of both the chemical composition and the microstructure on the growth of hydroxycarbonate apatite (HCA) following soaking in simulated body fluid (SBF). In the standard compositions 58S, 70S, and 80S the silica precursor was also partially replaced with a nanoscale silica powder (HiSil) in order to separate the contributions of porosity and composition. The combined use of XRPD, N2 absorption measurements, and SEM allowed us to establish quantitative correlations among the above-mentioned quantities. We found that the HCA formation rate increases with the silica content and that an important role is played by the specific surface area of the samples. Notably, the addition of even small quantities (0.4 wt%) of ZnO at the expenses of both CaO and P2O5 in the 58S glass leads to the increase, with respect to the 58S sample, of both the HCA formation rate and the HCA content after 8 days of treatment in SBF. A preliminary result revealed that sample with 0.4 wt % ZnO displayed good in vitro biocompatibility as shown by LDH assay

Cr- and Ni-doped Li4Ti5O12 compound has been characterized through the combined use of X-ray powder diffraction, electron paramagnetic resonance (EPR), 7Li nuclear magnetic resonance magic-angle spinning (NMR-MAS), micro-Raman, and magnetization measurements. The doping, occurring on the octahedral site of the cubic Li4Ti5O12 spinel lattice, strongly affects both the local and the average structural properties. The glassy character of the observed EPR signals suggests structural disorder in the stable Li4Ti5O12 matrix and the presence of clustering phenomena or nonhomogeneous distribution of the dopant ion, as also supported by 7Li NMR-MAS, micro-Raman, and magnetization results. The computation by numerical method of the complex EPR signal of the Cr-doped sample suggests that both CrTi and CrLi substitutions occur, giving rise to two distinct EPR components, corresponding to opposite axial distortion of the relative octahedral environments. On the basis of the compositional data, defect models involving oxygen or cation vacancies are proposed to explain the conductivity of the doped material

It is known from the literature that a slight distortion of the ideal cubic cell is present in the NiO structure. This work shows that such a distortion can be accurately evaluated by means of a refinement of the structural and profile parameters of X-ray powder diffraction data. Moreover, since only small amounts of products are sometimes at disposal to perform structural characterizations, it was thought useful to extend the refinement procedure to X-ray data collected on NiO samples of much lower mass (15-60 mg) than those usually utilized in X-ray diffractometric studies. The results obtained show that reliable structural parameters can be obtained from low mass samples too

A DSC characterization of the sulfur-tetracyanoethylene (TCE) system was performed, and the thermal traces obtained quantitatively analyzed. It was shown that (a) some type of solid state interaction takes place between sulfur and TCE, which forces part of the sulfur to be “frozen” into its rhombic form; (b) variable amounts of sulfur and TCE fail to melt at their expected melting temperatures; and (c) a much higher than expected enthalpy change is associated with sulfur polymerization. A phenomenological model is proposed according to which the sulfur and TCE that fail to melt at their melting temperatures undergo fusion in the wake of the liquid-phase sulfur polymerization process. It is shown that the model proposed is valid in the entire composition range studied.

The Rietveld profile refinement has been applied to X-ray powder diffraction data on Naß''-gallate, a solid electrolyte isostructural with Naß''-alumina and characterized by different types of lattice defect. Several structural models have been refined and discussed in order to understand if a statistical comparison of the structure discrepancy factors can be used as a reliable criterion to retain or reject structural changes from one model to the other. It is shown that, due to the correlation between structural parameters and to the poor sensitivity of the structure discrepancy factors to chemical composition, some care is necessary to direct correctly the refinement and to obtain a reliable structural model

The room temperature cation occupancy in LiMgVO(4) and LiZnVO(4) crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), (7)Li and (51)V magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO(4) Cmcm orthorhombic structure, the 4c (C(2)(v) symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C(2)(h) symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO(4): the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li(+) displays a slightly preferred occupation of the T1 position (approximately 55%) and Zn(2+) of the T2 position (approximately 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li(3)VO(4). High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds.

This study deals with the effects of 5 and 10% chromium additions on the transport and structural properties of Li3VO4. The Cr substitution is easily obtained without impurity phases and does not affect the room- and high-temperature host crystal structure, as evidenced by X-ray powder diffraction and micro-Raman analysis. The EPR signals are interpreted in terms of quantified amounts of Cr ions in 5+ and 3+ valence states. Suitable 7Li and 51V MAS NMR spectra simulations agree with the EPR results about the relative amount of Cr5+ and Cr3+ ions substituted in V5+ and Li+ sites, respectively. The Cr3+ presence on Li site, also suggested by Raman results and Rietveld refinements, requires Li vacancies to maintain the charge neutrality. The p-type conductivity, suggested by the positive thermoelectric power coefficients, significantly increases by the cation doping up to an order of magnitude.

Lithium manganese spinel Li1+yMn2-yO4 (0.0 less than or equal to y less than or equal to 0.07) synthesized by the sol-gel process is studied with a focus on the effects of the changes of formation conditions which can sensibly determine the mean crystallite size from a few nanometers to several hundred nanometers. Changes of stoichiometry and abundance of the spinel phase can be observed in the 573 less than or equal to T-A (K) less than or equal to 1073 range of annealing temperature (T-A). Comparing spinel phases obtained by sol-gel and solid state synthesis evidences the correlation among composition, structure, and electric and magnetic properties. (C) 1999 Academic Press.

Magnetic susceptibility measurements and electron paramagnetic resonance spectra of samples prepared from the reactive system MnO/Li2CO3 with different starting Li cationic fraction x are analyzed, taking into account the structural and compositional information provided by x-ray diffraction. Parent phases, as Mn2O3 , Mn3O4 and Li2 MnO3 , arise together with the lithium-manganese spinel as a result of Li-deficiency or Li-excess with respect to the x = 0.33 composition pertinent to the stoichiometric LiMn2O4 spinel. The data show that the spinel phase can sustain a partial Li-Mn substitution in the cation sites, according to compositional models described, for x > 0.33, by Li1+y Mn3+ 1-3y Mn4+ 1+2y O4 (Li-rich spinel) and, for x< 0.33, by Li1-|y| Mn2+ |y| Mn3+ 1+|y| Mn4+ 1-|y| O4 (Li-poor spinel). Paramagnetic resonance data of the Li-poor spinel phase are analyzed to discuss the possible oxidation state of Mn in the tetrahedral site.

XRD measurements proved the coexistence of spinel, lithium-rich spinel, and rock-salt phases in the Li-Mn-O system. An investigation of the electrical properties, carried out on polycrystalline samples, shows that Li{sub 2}MnO{sub 3} has insulating behavior while the spinel phases provide an example of hopping conduction mechanism. The negative Seebeck coefficient suggests that electrons constitute the charge carriers and their number is consistent with the fraction of Mn{sup 3+} over the total number of Mn{sup 3+} and Mn{sup 4+} sites in the spinel structure. The static magnetic susceptibility results agree with the presence of the Mn{sup 3+} ions in high spin configuration.

Li2MSiO4 (M = Fe, Mn, etc.) are promising cathode materials for Li-ion batteries. One appealing strategy for improving their cathode properties is to develop mixed transition metal compounds. Density Functional Theory calculations were performed to evaluate the structural, magnetic and electrochemical properties of Li2M0.5N0.5SiO4 compounds. Our theoretical study allows us to individuate the most promising candidates for practical applications in lithium batteries.