Nanocrystalline Samples Research Articles

Effect of tensile stress during ultra-rapid annealing on the soft magnetic properties of Fe-B based nanocrystalline alloys

The effect of applied stress during ultra-rapid annealing (URA) on the magnetic properties has been investigated for rapidly-solidified (Fe1-xCox)86B13Cu1 (x = 0–0.05) alloys. Nano-meter scale grains with an average size of about 15 nm and a small coercivity value of 5 ± 1 A/m are confirmed for all the alloys after URA at 763 K for 0.5 s. The saturation magnetic polarization (Js) of these nanocrystalline alloys shows a slight increase with Co content from 1.88 T at x = 0 to 1.94 T at x = 0.05. A clear creep-induced anisotropy (Ku) up to 460 ± 20 J/m3 is observed with a hard axis along the direction of applied tensile stress for x = 0–0.04 while an easy axis is confirmed in the same direction for x = 0.05. The saturation magnetostriction (λs) of nanocrystalline (Fe1-xCox)86B13Cu1 increases monotonously from + 13 ± 2 ppm to + 20 ± 2 ppm with an increase of x from 0 to 0.05 and the observed change in the anisotropy axis cannot be attributed to the bulk magnetoelastic effect. The magnetostriction was also measured for polycrystalline Fe1-xCox (x = 0–0.1) binary alloys prepared for comparison and λs of bcc-Fe is confirmed to change its sign from negative to positive by Co addition. A similar trend is confirmed for the local magnetostriction estimated for the bcc-Fe(Co) phase in the nanocrystalline samples by assuming the inverse effect of the local magnetostriction, suggesting that Ku in nanocrystalline (Fe1-xCox)86B13Cu1 (x = 0–0.05) alloys is due to the strain retained within the bcc-Fe(Co) nanocrystallites. Our results demonstrate that the shape of the hysteresis curve in the URA Fe-B based nanocrystalline alloys (HiB-Nanoperm) can be controlled by stress applied to the precursor amorphous ribbons during annealing.

Composition engineering of ultra-soft-magnetic Co-based alloys

In the present study, the liquidus temperature, mixing enthalpy, and atomic mismatch factor are used to predict and empirically evaluate the amorphisation capability of Co-Fe-B alloys fabricated by melt spinning. Based on this approach, five out of seven alloys have an amorphous structure, confirming the capability of the proposed model in predicting the alloy compositions with higher amorphisation ability in a ternary alloy system in the absence of any costly elements, such as Nb, Mo and Zr. X-ray diffraction, TEM and Mössbauer results show that the other two alloys exhibit different in-situ crystallisation behaviour. In one case, only the free-side crystallises, whereas the crystallisation occurs through the entire thickness of the ribbon in the other alloy. The lower amorphisation ability exhibited by these alloys in relation to the predictive parameters has been evaluated. Additionally, there is a strong correlation between amorphisation ability and crystallisation behaviour of alloys. Alloys, which crystallise through eutectic mode, are more likely to exhibit high amorphisation capability, whereas crystallisation via the primary mechanism can be the sign of lower amorphisation ability. The output of the alloy design process is five amorphous compositions, among which one is magnetically ultra-soft, Hc = 2.9 A/m; a surface crystalline alloy, with a low coercivity and higher value of anisotropy field compared to amorphous samples; and a nanocrystalline sample with a very high saturation flux density, Bs = 1.57 T. The surface crystallisation can eliminate the need for inducing transverse anisotropy by magnetic annealing. Therefore, optimising the alloy composition through this method can be a universal strategy of composition design for the fabrication of alloys with excellent properties, to be utilised in both high-Bs and low-Hc applications.

Negative Magnetization and Exchange Bias Behavior in Nanocrystalline Ho2CoMn1−xNixO6 (x=0‐0.4) Double Perovskite

A gel combustion method is opted to prepare nanocrystalline samples of Ho2CoMn1−xNixO6 (x = 0–0.4) (HCMNO) double perovskite. Structural studies reveal a formation of nanocrystalline samples, which crystallize into monoclinic structure with space group P21/n. A drop in the lattice parameters including unit cell volume are noticed with Ni substitution. Magnetization versus temperature (M-T) analysis shows a single FM transition in the parent compound at 83 K (TC1) and it is ascribed to the super exchange interaction in Co2+ - O2- - Mn4+ networks. However, it is turned into two FM transitions (TC1, TC2) after Ni substitution, where TC2 arises due to possible super exchange interaction in Co2+ - O2- - Ni4+ networks. The transition temperature TC1, is decreasing from 83 to 76 K for x = 0.0–0.4 sample, whereas TC2 increases up to 88 K for x = 0.4 sample. A magnetization reversal (MR) has been observed in higher Ni concentration (x = 0.3 and 0.4) samples in the field cooled state with a compensation temperature (Tcomp) of 4.4 K and 10 K respectively. This MR is attributed to the competition between the ferromagnetic (FM) moment of the transition metal (TM) ions and the polarization of magnetic moments of rare-earth (RE) ions at low temperatures. A typical bipolar switching of magnetization has been demonstrated for x = 0.3 and 0.4 sample. At 5 K, the hysteresis (M-H) loops demonstrate a decrease in saturation magnetization (MS) and coercivity (Hc) value after Ni substitution. However, the observed MS of the order of 11.60–10.27 µB/f.u. (for x = 0.0–0.4) at 5 K is attributed to some visible contribution related to the polarization/ordering of Ho moment with the net magnetic moment of TM ions. A maximum exchange bias field value of 230 Oe has been observed at 5 K for x = 0.4 sample. It is due to the competition between the spin canted magnetic moments of RE ions and the FM moments of TM ions.

Influence of phase boundary on magnetic and magnetocaloric properties of nanocrystalline La0.17Ca0.83MnO[formula omitted] sample

In this present study we report the Magnetic properties and magnetocaloric effect of two nanocrystalline La0.17Ca0.83MnO3 samples with average particle size ∼40 nm and ∼70 nm. According to the reported phase diagram, the bulk compound lies near the phase boundary between charge ordered antiferromagnetic and canted antiferromagnetic state. In contrast to the bulk counterpart, the significant effect of the phase boundary was observed on the physical properties of nanocrystalline compounds. Moreover, the signature of canted magnetic phase in nanocrystalline sample was probed through magnetocaloric effect study.

Impact of Nd3+ and Ni2+ dopants on the structural, electrical and dielectric behaviour of PbZrO3 nanocrystalline material

Pb1−4.75x Nd0.5x Ni4x ZrO3 (where x = 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) nanocrystals were synthesized through the micro-emulsion, a wet chemical route. The prepared samples were annealed at 700°C for 3 h. Nanocrystalline samples were characterized by various techniques like XRD (X-rays diffraction), FTIR (Fourier transform infrared spectroscopy), SEM (Scanning electron microscopy), dielectric properties, and dc-electrical resistivity. XRD analysis of synthesized nanocrystals confirmed the phase development of orthorhombic perovskite structure. The average measured size of nanocrystals was about 21 nm. Some other parameters like densities (bulk and X-rays) and porosity of the nanomaterials were also calculated from obtained XRD data. The obtained results showed the effect of dopant materials (Nd3+ and Ni2+ metal ions) incorporation. The FTIR spectra elucidated the intrinsic cations vibrations in the characteristic perovskite orthorhombic structure. The SEM results revealed that nano-grains were synthesized successfully and their average observed size was 60 nm. It was observed that with the addition of dopant material, the dielectric parameters like dielectric constant, loss factor, and conductivity were showed an overall decreasing trend. The average calculated value of the ac conductivity at the frequency of 3 GHz was observed as 1.45 × 10−2 (Ω-cm)−1. By using the current–voltage (I–V) characteristics, the dc-electrical resistivity was calculated in the range between 2.68 × 1010 and 4.82 × 1010 Ω-cm. The dc-electrical resistivity was increased with the increase of doping contents.

Wear properties of a bulk nanocrystalline Fe-1at% Zr alloy

In this work, a bulk nanocrystalline Fe-1 at% Zr alloy was prepared by combining mechanical alloying and spark plasma sintering techniques. Sliding wear experiments were conducted to investigate wear behaviors of the bulk nanocrystalline samples under different testing conditions. The results show that the bulk nanocrystalline Fe-1 at% Zr alloy exhibits a superior wear resistance. Taking Si3N4 and Al2O3 spheres with a diameter of 3 mm as the counterfaces, under a load of 1 N, a displacement amplitude of 1 mm, and a sliding frequency of 0.5 Hz, the specific wear rate of the bulk NC Fe-1 at% Zr alloy is determined to be in the order of 10−7 mm3 N−1 m−1. When the counterface, the displacement amplitude, and the sliding frequency are a Al2O3 sphere with a diameter of 3 mm, 1 mm and 0.5 Hz, respectively, the main wear mechanism of bulk NC Fe-1 at% Zr alloy corresponds to the abrasive wear under the loads of 1 and 5 N. Under the same testing conditions, taking the Si3N4 sphere with a diameter of 3 mm as the counterface, the main wear mechanism of the alloy is attributed to the abrasive wear under the load of 1 N; while the load is increased to 5 N, the main wear mechanism of the alloy becomes the delamination of the interfacial layer.

In-situ STEM study on thermally induced phase transformation of magnetic (Nd0.75Ce0.25)2Fe14B ribbons

Studying the phase transformation and microstructure evolution of magnetic Nd-Ce-Fe-B nanocrystalline melt-spun ribbon is of paramount significance in developing this important class of magnetic materials. In this work, the thermal-induced phase transformation of (Nd0.75Ce0.25)2Fe14B nanocrystalline sample was revealed via in-situ heating scanning transmission electron microscopy (STEM) experiment (RT-750 ℃). Starting from a single-phase (Nd0.75Ce0.25)2Fe14B nanocrystalline matrix at room temperature (RT), grain boundary (GB) diffusion behavior was investigated at an atomic scale. Our result shows that the rare earth elements accumulate at GB area from 200 °C and form a uniform thin amorphous layer between grains. The decomposition of the primary phase was observed at about 350 ℃ and crystalized as BCC-Fe, Fe2B, and (Nd0.75Ce0.25)2O3 phases driven by thermal activation at a higher temperature. This work provides the essential information of phase transformation and microstructure evolution of NdCeFeB-based magnets at high temperatures and new insights into thermal treatment designing and thermal stability considerations.

Charge Transport in Organic Semiconductors: The Perspective from Nonadiabatic Molecular Dynamics.

ConspectusOrganic semiconductors (OSs) are an exciting class of materials that have enabled disruptive technologies in this century including large-area electronics, flexible displays, and inexpensive solar cells. All of these technologies rely on the motion of electrical charges within the material and the diffusivity of these charges critically determines their performance. In this respect, it is remarkable that the nature of the charge transport in these materials has puzzled the community for so many years, even for apparently simple systems such as molecular single crystals: some experiments would better fit an interpretation in terms of a localized particle picture, akin to molecular or biological electron transfer, while others are in better agreement with a wave-like interpretation, more akin to band transport in metals.Exciting recent progress in the theory and simulation of charge carrier transport in OSs has now led to a unified understanding of these disparate findings, and this Account will review one of these tools developed in our laboratory in some detail: direct charge carrier propagation by quantum-classical nonadiabatic molecular dynamics. One finds that even in defect-free crystals the charge carrier can either localize on a single molecule or substantially delocalize over a large number of molecules depending on the relative strength of electronic couplings between the molecules, reorganization, or charge trapping energy of the molecule and thermal fluctuations of electronic couplings and site energies, also known as electron–phonon couplings.Our simulations predict that in molecular OSs exhibiting some of the highest measured charge mobilities to date, the charge carrier forms “flickering” polarons, objects that are delocalized over 10–20 molecules on average and that constantly change their shape and extension under the influence of thermal disorder. The flickering polarons propagate through the OS by short (≈10 fs long) bursts of the wave function that lead to an expansion of the polaron to about twice its size, resulting in spatial displacement, carrier diffusion, charge mobility, and electrical conductivity. Arguably best termed “transient delocalization”, this mechanistic scenario is very similar to the one assumed in transient localization theory and supports its assertions. We also review recent applications of our methodology to charge transport in disordered and nanocrystalline samples, which allows us to understand the influence of defects and grain boundaries on the charge propagation.Unfortunately, the energetically favorable packing structures of typical OSs, whether molecular or polymeric, places fundamental constraints on charge mobilities/electronic conductivity compared to inorganic semiconductors, which limits their range of applications. In this Account, we review the design rules that could pave the way for new very high-mobility OS materials and we argue that 2D covalent organic frameworks are one of the most promising candidates to satisfy them.We conclude that our nonadiabatic dynamics method is a powerful approach for predicting charge carrier transport in crystalline and disordered materials. We close with a brief outlook on extensions of the method to exciton transport, dissociation, and recombination. This will bring us a step closer to an understanding of the birth, survival, and annihiliation of charges at interfaces of optoelectronic devices.

Resistometric and calorimetric analysis of phase transformations in AuCu alloys

Abstract The order – disorder transitions in AuCu alloys have been studied by differential scanning calorimetry and resistometric methods. We have collected data with different sets of samples of equiatomic composition, the structure of which was determined by X-ray diffraction. Grain growth occurs mostly below 300 °C either in rolled and nanocrystalline samples. The occurrence of ordering does not depend on the grain size, but ordering is favoured by high defect contents in the alloy. The shape of heat flow traces provide evidence that ordering and disordering transitions are diffusive at low temperature (below 385 °C) being exothermic and endothermic, respectively, in wide temperature ranges. The transition from AuCuI to AuCuII changes the mechanism above 385 °C. The transition from AuCuII to face-centered cubic (fcc) solid solution is of first order. The reverse transition from the fcc structure to AuCuI occurs by nucleation and growth on continuous cooling.

Influence of polymorphic magnetic phases on exchange bias effect in bulk and nanocrystalline La0.375Ca0.625MnO[formula omitted] compound

Magnetic properties and exchange bias effect of the polycrystalline and nanocrystalline La0.375Ca0.625MnO3 compounds have been presented. With reduction of the particle size, uncompensated surface spin induced ferromagnetism is pronounced in nanocrystalline sample. However, at higher magnetic field value, long range charge ordering (associated with antiferromagnetic nature) is predominant even in nanoparticles similar as bulk counterpart. Exchange bias properties of both compounds have been found at low temperature with increasing nature depending on the cooling magnetic field. Significantly large value of the exchange bias effect in this particular bulk compound and modification of it in nanocrystalline sample is addressed considering the disordered polymorphs developed within the charge-orbital ordered phase.

Magnetic and magnetocaloric properties of nanocrystalline sample of a glassy ferromagnetic compound: Modification of short range ordering

The modification of magnetic interactions due to the reduction of particle size has been explored in the case of nanocrystalline Gd0.5Sr0.5MnO3 compound. In contrast to the normal ferromagnetic or antiferromagnetic compounds, the studied nanoparticle exhibits quite different magnetic and magnetocaloric properties. The experimental outcomes are also compared with its bulk counterparts having disordered ferromagnetic ground state. Additionally, at the cryogenic temperature range, the significant magnetocaloric effect in both the samples indicate the applicability as a suitable magnetic refrigerant material. Moreover, the desertion nature of the magnetic hysteresis loop due to the field cycling indicates the superiority of the nanocrystalline compound over its bulk counterpart.

Unravelling the alkali transport properties in nanocrystalline A3OX (A = Li, Na, X = Cl, Br) solid state electrolytes. A theoretical prediction.

Transport properties of the halogeno-alkali oxides A3OX (A = Li, Na, X = Cl, Br) nanocrystalline samples with the presence of ∑3(111) grain boundaries were computed using large-scale molecular dynamic simulations. Results on the diffusion/conduction process show that these nanocrystalline samples are characterized with higher activation energies as compared to previous theoretical studies, but closer to experiment. Such a performance can be attributed to the larger atomic density at the ∑3(111) grain boundary regions within the nanocrystals. Despite a minor deterioration of transport properties of the mixed cation Li2NaOX and Na2LiOX samples, these halogeno-alkali oxides can also be considered as good inorganic solid electrolytes in both Li- and Na-ion batteries.

Heat capacity of nanocrystalline Yb2O3

A study of the structural, Raman scattering and thermodynamic properties of a nanocrystalline ceramic rare earth oxide Yb 2 O 3 and its bulk counterpart is reported. The nanosized sample was obtained by mechanical milling of bulk Yb 2 O 3 (99.998%, high purity powder). The Rietveld analysis of the X-ray diffraction data indicates the presence of nanoparticles with a mean grain size of 12 ± 1 nm after 75 h of milling time. The crystallographic structure within nanoparticles is cubic Ia-3 and the lattice parameter a = 10.455 ± 0.002 Å. The nanocrystalline structure is confirmed by the evaluation of transmission electron microscopy images, showing a size distribution with a mean size D TEM = 8 ± 2 nm. Measurements of the specific heat (2 K–300 K) reveal an excess contribution respect to the unmilled (bulk) compound in the high temperature region above 70 K. At lower temperatures the results are consistent with a drastic change of the antiferromagnetic contribution (ordered below T N = 2.2 K) as a result of the magnetic disorder arising from the size reduction process. The specific heat above T N for the bulk and nanocrystalline samples are explained by the interplay among the phonon contribution, crystalline field and the presence of anharmonic effects. In the nanocrystalline state, broadening and shifts of the contribution of phonon modes to the Raman spectra, and a further reinforcement of the anharmonic contribution are found.

Biodegradable nanocrystalline Mg-Zn-Ca-Ag alloys as suitable materials for orthopedic implants

Magnesium (Mg) based metallic glasses are gaining considerable attention as biodegradable implant materials, owing to their superior strength, elasticity and higher corrosion resistance than their crystalline counterparts. Though Mg-Zn-Ca based glassy alloys are showing improved performance than their crystalline counterparts, ideal corrosion rate about 0.02 mm/year (Song, 2007), for feasible orthopedic implants is yet to be achieved. Also, poor ductility of the glassy samples limits their practical usage as viable orthopedic implants. Hence, the key challenge in developing Mg based viable implant is to improve its corrosion resistance along with enhanced ductility. Nanocrystalline materials open possibilities for auxiliary improvements in strength and ductility. The aim of this work is to elucidate the influence of nanocrystalline structure and silver (Ag) alloying on in-vitro corrosion behaviour and mechanical properties of biodegradable Mg-Zn-Ca alloys. In this study, Mg66Zn30Ca4 and Mg64Zn29Ca5Ag2 glass forming alloy have been chosen based on a thermodynamic model using PHHS parameter with pivotal effects of electron transfer effects, effect of atomic size mismatch and effect of randomness. In-vitro corrosion behaviour of Mg66Zn30Ca4 and Mg64Zn29Ca5Ag25 in Simulated Body Fluid (SBF) solution analyzed using electrochemical studies showed that on a comparable scale, the corrosion resistance of nanocrystalline Mg64Zn29Ca5Ag25 samples was greater than their amorphous Mg66Zn30Ca4 equivalents. Addition of Ag to Mg-Zn-Ca alloy leads to formation of corrosion influencing phases such as MgAg, Zn8Ag5, MgZnAg2 along with oxides and hydroxides of Ag. Such phases contribute to improved corrosion resistance due to the formation of passive layer. The increase in hardness is credited to the lack of free volume in the nanocrystalline sample (Mg64Zn29Ca5Ag2) in comparison to the amorphous sample (Mg66Zn30Ca4). The reported results demonstrate that Mg64Zn29Ca5Ag2 acquiring the proper combination of mechanical properties and corrosion resistance can be further explored on antibacterial and cytocompatible perspectives in order to make them ideal bioimplant materials.

Decoupling the roles of constituent phases in the strengthening of hydrogenated nanocrystalline dual-phase high-entropy alloys

Nanocrystalline (NC) dual-phase Al0.7CoCrFeNi HEAs containing face-centered cubic (FCC) and body-centered cubic (BCC) microstructural phases were fabricated by high-pressure torsion (HPT). The influences of hydrogen on the thermal desorption and nanoindentation responses of NC HEA were compared with the coarse-grained alloy. The plastic zone size and indentation size effects were carefully considered to identify the distinct contributions of the constituent phases to the hardness and its variation with hydrogen charging. Results show that the FCC phase is susceptible to a larger degree of hydrogen-induced hardening than the BCC phase. Such difference is negated in the NC samples. These results are discussed in terms of the distinct responses of FCC and BCC HEA phases to hydrogen and the governing deformation mechanisms in coarse grained and NC samples.

Effect of Preparation Method and Ni2+ Substitution on the Structural, Thermal, and Optical Properties of Nanocrystalline Lanthanum Zirconate Pyrochlore

In order to establish the effective application of materials in a particular area, it is important to first investigate the physical and chemical properties, such as the crystallinity, structure, and the optical and surface properties. The objective of the present study is to fabricate thermally stable pyrochlore oxides, namely, lanthanum zirconate (La2Zr2O7, LZ) and Ni-doped lanthanum zirconate (La2Zr1.5Ni0.5O7, LZN) by the solid-state and sol-gel methods. The effects of the preparation and substitution of Zr4+ by Ni2+ for the resulting nanocrystalline samples were characterized in terms of structure, purity, porosity, the thermal and optical properties, and photoluminescence by different techniques: XRD, FT-IR, BET, EDS, TG-DTG, UV-Vis-DRS, and PL. The XRD results confirm that the pyrochlores prepared via the sol-gel method (LZ-sg and LZN-sg) had a cubic unit-cell lattice, whereas the solid-state method (LZ-s and LZN-s) had impurities of the oxides. The XRD patterns, LZ-sg and LZN-sg, were further treated with the Rietveld technique. The textural measurements reveal that LZ-sg had a higher BET surface area compared to LZN-sg. In addition, the substitution of Zr4+ by the Ni2+ ion provides rational evidence for the improvement in the oxygen mobility, as well as the optical and photoluminescence properties through the lowering of the optical band energy and the electron–hole pairs.

The Influence of Annealing Temperature on the Structure and Magnetic Properties of Nanocrystalline BiFeO3 Prepared by Sol\u2013Gel Method

In this work, BiFeO3 powders were synthesized by a sol–gel method. The influence of annealing temperature on the structure and magnetic properties of the samples has been discussed. X-ray diffraction studies showed that the purest phase was formed in the temperature range of 400 °C to 550 °C and the samples annealed at a temperature below 550 °C were of nanocrystalline character. Mössbauer spectroscopy and magnetization measurements were used as complementary methods to investigate the magnetic state of the samples. In particular, the appearance of weak ferromagnetic properties, significant growth of magnetization, and spin-glass-like behavior were observed along with the drop of average grain size. Mössbauer spectra were fitted by the model assuming cycloidal modulation of spins arrangement and properties of the spin cycloid were determined and analyzed. Most importantly, it was proved that the spin cycloid does not disappear even in the case of the samples with a particle size well below the cycloid modulation period λ = 62 nm. Furthermore, the cycloid becomes more anharmonic as the grain size decreases. The possible origination of weak ferromagnetism of the nanocrystalline samples has also been discussed.

Effect of Alloying Additions on Microstructure, Mechanical and Magnetic Properties of Rapidly Cooled Bulk Fe-B-M-Cu (M = Ti, Mo and Mn) Alloys

The influence of alloying additions on the microstructure, mechanical, and magnetic properties of bulk Fe79B20Cu1, Fe79B16Ti4Cu1, Fe79B16Mo4Cu1 and Fe79B16Mn4Cu1 (at. pct) alloys was investigated. Nanocrystalline samples in the form of 3 mm rods were prepared directly by suction casting without additional heat treatment. Mössbauer spectroscopy, transmission electron microscopy and scanning electron microscopy studies confirmed that the investigated alloys consist α-Fe and Fe2B nanograins embedded in an amorphous matrix. The addition of alloying elements, such as Ti, Mo and Mn to Fe79B20Cu1 alloy increases the amount of amorphous phase and decreases the presence of Fe2B phase in all examined alloys. The mechanical properties of the samples, such as hardness, elastic modulus, and elastic energy ratio, were analysed by an instrumented indentation technique performed on a 12 × 12 nanoindentation grid. These tests allowed to characterise the mechanical properties of the regions observed in the same material. For the Fe79B20Cu1 alloy, the hardness of 1508 and 1999 HV, as well as Young’s modulus of 287 and 308 GPa, were estimated for the amorphous- and nanocrystalline-rich phase, respectively. The addition of Ti, Mo, and Mn atoms leads to a decrease in both hardness and elastic modulus for all regions in the investigated samples. Investigations of thermomagnetic characteristics show the soft magnetic properties of the studied materials. More detailed studies of magnetisation versus magnetic field curves for the Fe79B20−xMxCu1 (where x = 0 or 4; M = Ti, Mo, Mn) alloy, recorded in a wide range of temperatures, followed by the law of approach to magnetic saturation revealed the relationship between microstructure and magneto-mechanical properties.

Highly Conducting Li(Fe1-xMnx)0.88V0.08PO4 Cathode Materials Nanocrystallized from the Glassy State (x = 0.25, 0.5, 0.75).

This study showed that thermal nanocrystallization of glassy analogs of LiFeMnPO (with the addition of vanadium for improvement of glass forming properties) resulted in highly conducting materials that may be used as cathodes for Li-ion batteries. The glasses and nanomaterials were studied with differential thermal analysis, X-ray diffractometry, and impedance spectroscopy. The electrical conductivity of the nanocrystalline samples varied, depending on the composition. For , it exceeded S/cm at room temperature with an activation energy as low as 0.15 eV. The giant and irreversible increase in the conductivity was explained on the basis of Mott’s theory of electron hopping and a core-shell concept. Electrochemical performance of the active material with was also reported.

Crystalline and magnetic properties of CoO nanoparticles locally investigated by using radioactive indium tracer

We herein report a comprehensive investigation on the magnetic, structural, and electric properties of CoO nanoparticles with different sizes by local inspection through hyperfine interactions measured in a wide range of temperatures (10–670 K) by using radioactive ^{111}In(^{111}Cd) tracers with the perturbed angular correlations technique. Small cobalt oxide nanoparticles with the characteristic size of 6.5 nm have been prepared by the wet chemical route that turned out to be essential to incorporate radioactivity tracers during nucleation and growth of the particles. Nanocrystalline samples with 22.1 nm size were obtained by thermal treatments under low pressure of helium at 670 K. The hyperfine data were correlated with X-ray diffraction, ZFC–FC magnetic measurements, and transmission electron microscopy to describe the structure, magnetic properties, size, and shape of samples. An analysis of the temperature evolution of hyperfine parameters revealed that the structural distortion and the magnetic disorder in the core and on the surface layer play an important role in the magnetic behavior of CoO nanoparticles.