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During high-pressure torsion (HPT) the dynamic equilibrium establishes with a certain steady-state composition of the solid solution along with the grain refinement by a factor of more than thousand. The formation of such HPT steady-state in copper alloys with Co, Ag and In has been studied. If precipitates of a second phase were present in the sample before HPT, their dissolution led to the enrichment in the (Cu) matrix solid solution. If precipitates of a second phase were absent, the HPT led to the depletion in the (Cu) matrix due to the segregation in newly formed defects like grain boundaries.

Permanent magnets based on neodymium-iron-boron (Nd-Fe-B) alloys provide the highest performance and energy density, finding usage in many high-tech applications. Their magnetic performance relies on the intrinsic properties of the hard-magnetic Nd$_2$Fe$_{14}$B phase combined with control over the microstructure during production. In this study, a novel magnetic hardening mechanism is described in such materials based on a solid-state phase transformation. Using modified Nd-Fe-B alloys of the type Nd$_{16}$Fe$_{bal-x-y-z}$Co$_x$Mo$_y$Cu$_z$B$_7$ for the first time it is revealed how the microstructural transformation from the metastable Nd$_2$Fe$_{17}$B$_x$ phase to the hard-magnetic Nd$_2$Fe$_{14}$B phase can be thermally controlled, leading to an astonishing increase in coercivity from ≈200 kAm$^{−1}$ to almost 700 kAm$^{−1}$. Furthermore, after thermally treating a quenched sample of Nd$_{16}$Fe$_{56}$Co$_{20}$Mo$_2$Cu$_2$B$_7$, the presence of Mo leads to the formation of fine FeMo$_2$B$_2$ precipitates, in the range from micrometers down to a few nanometers. These precipitates are responsible for the refinement of the Nd$_2$Fe$_{14}$B grains and so for the high coercivity. This mechanism can be incorporated into existing manufacturing processes and can prove to be applicable to novel fabrication routes for Nd-Fe-B magnets, such as additive manufacturing

The influence of high pressure torsion (HPT) on the formation and decomposition of solid solutions in the copper–silver system has been studied. The investigated Cu-8 wt.% Ag alloy was annealed at two different temperatures, 500 and 650°C, and quenched. The samples consisted of (Cu) solid solution in the matrix with (Ag) precipitates. During HPT a steady-state value of torsion torque was reached after about 1.5 anvil rotations. After HPT (5 anvil rotations) the composition of the (Cu) solid solution in both samples had become equal. In other words, the concentration of silver in the (Cu) matrix annealed at 650°C decreased and in the sample annealed at 500°C increased. Moreover, a similar process took place in (Ag) precipitates as well. The concentration of copper in (Ag) particles in the sample annealed at 650°C decreased and in the sample annealed at 500°C increased. Thus, the composition of (Cu) and (Ag) solid solutions reached at steady-state during HPT does not depend on that before HPT. The composition of the (Cu) and (Ag) solid solutions after HPT is as high as if the samples were annealed at a certain intermediate temperature about 600 ± 20°C.

The structural and spectroscopic features of the EuAl3(BO3)4 individual skeletal microcrystals synthesized by a melt solution method have been studied. Their infrared spectra taken from the as-grown microcrystal surfaces mainly contain the lines of the rhombohedral modification of EuAl3(BO3)4 and additional peaks of its monoclinic modification. TEM and X-ray diffraction studies confirm that these additional peaks in the IR spectra belong to the monoclinic C2/c polytype of the EuAl3(BO3)4 compound. We are the first to demonstrate the presence of coherent monoclinic domains in rhombohedral EuAl3(BO3)4 crystals by TEM. Cathodoluminance spectroscopy shows that the microcrystals generate strong emission lines in the range 580–630 nm, and their intensities are strongly influenced by the crystal orientation.

Fully-dense bulk CoCrFeMnNi high entropy alloy (HEA) has been obtained by high-pressure torsion (HPT) deformation. Elemental, micrometer sized powders were successively mixed in equimolar proportions, consolidated and deformed at 5 GPa using imposed shear strain equivalent up to 100 rotations. Transmission electron microscopy, X-ray diffraction and 3D atom probe tomography were performed to study the microstructure evolution resulting from HPT-induced mechanical alloying. Single-phase, nanocrystalline (grain size of 50 nm) alloy with smaller chromium oxide precipitates (of 7–10 nm) exhibited a hardness of 6700 MPa, which is the highest one reported for as-processed bulk CoCrFeMnNi alloys to our best knowledge.

The effects of High Pressure Torsion (HPT) deformation on the microstructure and mechanical properties of a corrosion-resistant, low modulus Zr-Ti-Nb alloy, obtained by vacuum sintering of cold pressed powder are studied. It is shown that HPT treatment leads to the following effects: elimination of the residual chemical heterogeneity of the alloy, significant reduction of the porosity of the material and the pore size and improvement of mechanical properties. The phase composition of the alloy does not change during processing. The results show the potential of the HPT method for the production of alloys with a favorable combination of properties.

In this work we present a comprehensive study of the domain structure of a nickel oxide single crystal grown by floating zone melting and suggest a correlation between point defects and the observed domain structure. The properties and structure of domains dictate the dynamics of resistive switching, water splitting and gas sensing, to name but a few. Investigating the correlation between point defects and domain structure can provide a deeper understanding of their formation and structure, which potentially allows one to tailor domain structure and the dynamics of the aforementioned applications. A range of inhomogeneities are observed by diffraction and microscopy techniques. X-ray and low-energy electron diffraction reveal domains on the submicron- and nanometer-scales, respectively. In turn, these domains are visualised by atomic force and scanning tunneling microscopy (STM), respectively. A comprehensive transmission electron microscopy (TEM) study reveals inhomogeneities ranging from domains of varying size, misorientation of domains, variation of the lattice constant and bending of lattice planes. X-ray photoelectron spectroscopy and electron energy-loss spectroscopy indicate the crystal is Ni deficient. Density functional theory calculations-considering the spatial and electronic disturbance induced by the favourable nickel vacancy-reveal a nanoscale distortion comparable to STM and TEM observations. The different inhomogeneities are understood in terms of the structural relaxation induced by ordering of nickel vacancies, which is predicted to be favourable. Funding Agencies|Russian Science FoundationRussian Science Foundation (RSF) [18-12-00492]; RFBRRussian Foundation for Basic Research (RFBR) [19-29-03021]; Research Facility Center at the ISSP of RAS; Erasmus Plus mobility Grants [2016-1-IE02-KA107-000479, 2017-1-IE02-KA107-000538 2018-1-IE02-KA107-000589]; Ministry of Science and Higher Education of the Russian Federation [K2-2019-001, 211]; Swedish Research Council (VR)Swedish Research Council [2019-05600]; Swedish Government Strategic Research Areas in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Irish Research Council Laureate AwardIrish Research Council for Science, Engineering and Technology [IRCLA/2019/171]

Improving the interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is a vital step toward the development of high-performance solid-state batteries (SSBs). One of the challenges plaguing this field is an economical and scalable approach to fabricate high-quality protective coatings on the CAM particles. A new wet-coating strategy based on preformed nanoparticles is presented herein. Nonagglomerated nanoparticles of the coating material (≤5 nm, exemplified for ZrO$_{2}$) are prepared by solvothermal synthesis, and after surface functionalization, applied to a layered Ni-rich oxide CAM, LiNi$_{0.85}$Co$_{0.10}$Mn$_{0.05}$O$_{2}$ (NCM85), producing a uniform surface layer with a unique structure. Remarkably, when used in pelletized SSBs with argyrodite Li$_{6}$PS$_{5}$Cl as SE, the coated NCM85 is found to exhibit superior lithium-storage properties (q$_{dis}$ ≈ 204 mAh g$_{NCM85}$$^{-1}$ at 0.1 C rate and 45 °C) and good rate capability. The key to the observed improvement lies in the homogeneity of coating, suppressing interfacial side reactions while simultaneously limiting gas evolution during operation. Moreover, this strategy is proven to have a similar effect in liquid electrolyte-based Li-ion batteries and can potentially be used for the application of other, even more favorable, nanoparticle coatings.

International audience; Herein, a study on radiation‐induced defect structures in a reactor Fe–14Cr–1W (wt%) steel with grain sizes of 5 μm and 110 nm is presented. Self‐ion irradiation of the steel in both states is conducted with a damage dose of 10 dpa. Microstructure characterization shows that the density of intragranular radiation‐induced dislocations is significantly lower in case of the nanostructured material. From the results obtained, it follows that microstructure refinement to a grain size of about 100 nm can be effectively used to approach a problem of higher defect production rate in Fe–Cr steels driven by irradiation and to produce alloys with significantly enhanced mechanical performance as well as radiation tolerance.

Titania aerogels are synthesized using various solvents for sol preparation. The morphology, the optical transmittance, the phase composition and the specific surface area of samples are determined. The sample prepared from isopropanol is found to be white and light-tight and to consist of fibers about 17 nm wide. The fibers are crystalline and have an anatase structure. The specific surface area of the sample is 150 m2/g. The samples prepared from methoxy- or etoxyethanol are transparent yellowish monoliths. They are X-ray amorphous and consist of spherical nanoparticles 1.5–3.5 nm. The specific surface area of these samples is more than 500 m2/g. Transparent titania aerogels are prepared in all-solution approach for the first time.

High-pressure torsion of a laminate consisting of a layer of monocrystalline molybdenum sandwiched between two layers of copper was investigated. Computed tomography showed that at sufficiently large angles of rotation of the anvils the molybdenum layer loses planarity. It develops periodic folds and vortices, leading to ruptures. EBSD analysis revealed the formation of a blocky substructure in the molybdenum layer and a pronounced fragmentation of copper sheets, with the formation of a significant proportion of high-angle grain boundaries. The proposed mathematical model of the process accounts for the observed phenomena qualitatively. It is based on the gradient plasticity theory and predicts the loss of stability of the harder molybdenum layer when the shear strain in the laminate exceeds a critical value.

Europium alumoborate EuAl3(BO3)4 microcrystals have been synthesized by the flux method at a temperature of 1050°C. The obtained crystals have different morphologies: both plane-faced and skeletal microcrystals have been observed. Infrared spectroscopy, cathodeluminescence, and transmission electron microscopy investigations of individual microcrystals showed that the spectral and structural characteristics of these morphological forms coincide. The obtained crystals are characterized by the rhombohedral symmetry (sp. gr. R32) with the inclusions of C2/c monoclinic phase domains.

The microstructure of Nd–Fe–B-based liquid-phase sintered alloy has been studied. The Nd2Fe14B/Nd2Fe14B GBs can be pseudo-incompletely (or pseudo-partially) wetted by the Nd-rich melt. Such GBs form the non-zero contact angle with the melt in the triple junctions and contain the uniformly thin (7-10 nm) Nd-rich layer. Such GBs are different from the completely wetted as well as from partially wetted GBs. Most probably, such thin Nd-rich GB layers are responsible for the excellent magnetic properties of the NdFeB-base permanent magnets because these GB layers ensure the magnetic isolation between the Nd2Fe14B grains needed for the high coercivity.

Phase transitions in α'-Ti martensite driven by high pressure torsion (HPT) as well as α' → ω transformations in Ti–Fe alloys were observed for the first time. The as cast alloys transformed into α'-Ti martensite after annealing in the β-(Ti,Fe) solid solution region and subsequent quenching. Lattice parameters of α'-Ti martensite decreased with increasing iron content, similar to the lattice parameter of β-Ti. During HPT, α'-Ti martensite transformed partly into ω-Ti. At the same time, the lattice parameters of remaining α'-Ti phase increased towards those for iron-free α-Ti. These processes included an increased mass transfer of iron atoms out of α'-Ti.

Metastable W/WO 3 interface has been formed at the surface of a tungsten metal bar using a solid state redox reaction of W with powdered WO 3 . Superconductivity at 35 ≤ T ≤ 75 K in the W/WO 3 interfacial layer has been observed by means of the ac magnetic susceptibility and electrical resistance measurements. Comparative analysis of the experimental results infers that the W/WO 3 interfacial layer consists of weakly linked superconducting regions.

Novel functionally graded hardmetals comprise a low-Co hard surface layer and a tough core region containing lots of Co. They are fabricated by self-assembly during liquid-phase sintering due to Co drifts from the surface layer having a high carbon content towards the core region with a low carbon content. A new mechanism of the self-assembly of the functionally graded hardmetals is proposed and their superior properties are explained by examining WC-WC grain boundaries on the nano-level.

The important class of grain boundary (GB) complexions includes the few nanometer thick layers having composition which strongly differs from that of the abutting grains. Such GB complexions are frequently called intergranular films (IGFs) and can be observed close to the lines of wetting, prewetting and premelting complexion transitions in the bulk phase diagrams. In the majority of systems, the direct transition between complete and partial GB wetting takes place (by changing temperature, pressure, etc.). However, in certain conditions the so-called pseudopartial (or pseudoincomplete, or frustrated complete) GB wetting appears in a phase diagram between complete and partial wetting. In case of pseudopartial GB wetting, the thin GB layer of a complexion (IGF or 2-D interfacial phase) can coexist with large droplets (or particles) of the wetting phase with a non-zero dihedral (contact) angle. Thus, such IGFs can be observed in the two-phase (or multiphase) fields of bulk phase diagrams, in the broad intervals of concentrations, temperature and/or pressure. The IGFs driven by the pseudopartial GB wetting can drastically modify the properties of polycrystals. In this review, we discuss this phenomenon for the technologically important Fe–Nd–B-based hard magnetic alloys, WC–Co cemented carbides and Al-based light alloys.

Metastable superconductivity at T c ≈ 65 K has been observed in Al foil subjected to special oxidation process, according to the ac magnetic susceptibility and electrical resistance measurements. Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial granular layer formed during the oxidation process between metallic aluminum and its oxide.

A new method named High Pressure Torsion Extrusion (HPTE) is proposed based on a modification of the conventional high pressure torsion technique of severe plastic deformation. During HPTE, a specimen is extruded through sectional containers rotating relative to each other. The specimen is subjected to shear deformation in the area where the containers meet each other. One of the main advantages of the HPTE process is that already after a single extrusion pass a high accumulated strain can be achieved in the specimen. Furthermore, the presence of a strong velocity gradient in the specimen cross-section during HPTE provides the possibility to process hybrid materials or composite parts with helical architecture of functional elements. The HPTE method is evaluated theoretically by using finite element methods (FEM) and experimentally by using HPTE for processing copper specimen and the results are presented and discussed.

The transition from incomplete to complete grain boundary wetting in copper alloys with 2.2 and 4.9 wt % Co has been studied. These alloys with peritectic phase diagrams differ from previously studied systems with eutectic transformation by the fact that the melt layer separating grains from each other is not enriched, but is depleted by the second component (cobalt in this case). The fraction of completely wetted grain boundaries increases with temperature, as in eutectic systems, from zero at a temperature of 1098°C to ~80% at 1096°C. For symmetric twin boundaries, the temperature dependence of the contact angle with melt drops is constructed. As in the eutectic systems, the contact angle decreases with increasing temperature (although not to zero due to the extremely low energy of symmetric twin boundaries).

A reason for the presence or absence of thin Co layers on a surface of WC–Co hardmetal articles after sintering has been a riddle for a long time. Such shiny Co layers are sometimes present on the surface of sintered WC–Co articles and their formation is referred to as “Co capping” in literature. Here we propose a detailed mechanism explaining the presence or absence of such thin cobalt layers on hardmetal articles after sintering. The proposed mechanism is based on considering wetting phenomena of WC by liquid Co in hardmetal surface layers and capillarity pressures acting on the liquid Co in narrow channels between WC grains in the surface layers. The mechanism explains all the phenomena of the Co layer formation during sintering of various hardmetal grades followed by either fast or slow cooling.

Functionally graded cemented carbides obtained on the basis of capillarity phenomena can be very important for numerous applications and are expected to substitute conventional WC–Co cemented carbides. Drifts of liquid Co-based binders in couples of model WC–Co alloys with different WC mean grain sizes sintered together were examined. Noticeable Co drifts occur from coarse-grain into fine-grain regions of the model alloys due to different capillary forces. The Co drifts become more pronounced when the difference between WC mean grains sizes of the coarse-grain region and fine-grain region increases.

High pressure torsion (HPT) has been used for the severe plastic deformation (SPD) treatment of molten Fe–12.3 at% Nd–7.6 at% B alloy (5 GPa, 1 rpm, 5 rot, room temperature). After HPT the microstructure contained the nanograins of the ferromagnetic Nd 2 Fe 14 B phase embedded in the amorphous matrix with uniform composition. It is different to the commercial multicomponent FeNdB-based alloy where two different amorphous phases appeared after HPT (B.B. Straumal, A.R. Kilmametov, A.A. Mazilkin, S.G. Protasova, K.I. Kolesnikova, P.B. Straumal, B. Baretzky, Mater. Lett., 2015, 145, pp. 63–66). The SPD-treatment at room temperature T SPD =30 °C is frequently equivalent to the heat treatment at a certain elevated temperature T eff >30 °C. The composition of phases in the studied NdFeB-based alloy after HPT corresponds to the state at T eff ~1140 °C.

The complex research of the structure and electronic properties of defects occurring on the bonding border of twist misfit Si(001) wafers of n-type conductivity was carried out by the methods of transmission electron microscopy, deep level transient spectroscopy (DLTS), and photoluminescence. The revealed defects main are two types of dislocation structure: the orthogonal dislocation network composed of two screw dislocation families and zigzag mixed dislocations. The dislocation structures observed are the sources of intense luminescence, whose spectrum differ considerably from the standard dislocation luminescence spectrum at all investigated misfit angles of bonded Si wafers. It is shown that an increase of the misfit angle results in a strong transformation of the dislocation luminescence spectra consisting in the changes of the spectra form and a decrease in the integral luminescence intensity. In the studied samples, by means of the deep level transient spectroscopy method, the presence of deep centers whose concentration increases with an increase of the misfit angle of the bonded wafers is revealed. It is established that the deep centers are related to the dislocation structures observed by means of transmission electron microscopy.

The excellent properties of heavy tungsten-based alloys are based on the combination of hardness of W grains, as well on the toughness and ductility of the binder with low melting temperature (usually containing nickel, iron, or copper). The topology (and resulting properties) of binder network are controlled by the complete and incomplete wetting of W/W grain boundaries (GBs) and GB triple junctions (TJ). We observed for the first time that pseudoincomplete (or pseudopartial, or frustrated complete) GB wetting by Ni layers is also present in W–Ni alloys. Namely, the channel of a Ni-rich solid solution in GB TJ forms the non-zero dihedral contact angle not only with “dry” W/W GBs (incomplete GB wetting), but also with W/W GBs containing the uniformly thin (3 nm) Ni-rich layer (pseudoincomplete GB wetting).

Present work is dedicated to the investigation of grain boundary (GB) wetting phase transition on different types of grain boundaries in the Cu–Ag system. The character of GBs in the samples was determined by the electron backscattering diffraction. GB character distribution was based on the coincidence site lattice (CSL) model and on the values of the misorientation angle of GBs. Experimental results show that only the low angle GBs and the Σ3 CSL GBs do not reach complete wetting by the melt. Random high misorientation angle (HA) GBs reach complete wetting at 895 °C. Only Σ11, Σ5 and Σ13 CSL GBs have a higher wetting temperature than the HA GBs, so their GB energy should be lower than the energy of HA GBs.

Metastable superconducting-like behavior of rhombohedral Bi samples exposed to surface oxidation under special conditions has been observed below the critical temperature range of 15–35 K. The ac magnetic susceptibility and electrical resistance measurements imply that the superconductivity appears in the Bi/Bi2O3 interfacial layer formed at the surface of the samples.

International audience

Model Fe-Cr alloys with and without W were nanostructured by severe plastic deformation at 350˚C. Transmission electron microscopy observations of the microstructure indicate that the addition of 1 wt% of W led to a reduction of the mean grain size from 129 to 110 nm. Atom probe analyses show that only Cr and Si segregate at grain boundaries during deformation while W remains homogeneously distributed. This solid solution leads to higher mechanical strength and plasticity as compared to Fe-Cr. The origin of the beneficial effect of W on the mechanical performance is discussed.

During severe plastic deformation (SPD), a steady-state is usually reached after a certain value of strain (i. e. number of passes during equal-channel pressing or number of rotations during high pressure torsion). The structure and properties of a material in a steady state (including composition of phases) do not depend on those in the starting state before SPD. In other words they are equifinal, and the production of lattice defects is in dynamic equilibrium with defect elimination. Moreover, the SPD-treatment at ambient temperature T SP D = 300 K is frequently equivalent to the heat treatment at a certain elevated temperature T eff > 300 K. For example, the composition of phases in Cu–Ni, Co–Cu and Nd–Fe–B-based alloys after high pressure torsion corresponds to the states at 200, 890 and 1 170 °C, respectively, and is rather insensitive to the high pressure torsion rate (between 0.2 and 2 rpm) and pressure (between 3 and 8 GPa).

The Ti–Fe alloys are quite important among various Ti-based alloys doped with β-stabilisers. Severe plastic deformation by the high pressure torsion (HPT) leads to the strong grain refinement in Ti–Fe alloys. The high-pressure ωTi-phase appears during HPT of the Ti–1 wt.% Fe alloy. However, the ωTi does not appear after uniaxial compression at the same pressure, without torsion. ωTi remains quenched after pressure release and disappears by heating around 140–150 °C. However, the further alloying with iron suppresses the formation of ωTi-phase. As a result, ωTi does not appear after HPT in the Ti–10 wt.% Fe alloy.

WC–Co cemented carbides are metal–ceramic composites consisting of a ceramic phase, tungsten carbide, and a cobalt binder. The key to the exceptional properties of cemented carbides is the optimal combination of hardness and wear-resistance of WC grains, and toughness and ductility of the Co-based matrix. However, only the minority of WC/WC GBs are completely wetted by Co melt during the liquid phase sintering. We observed for the first time that other WC/WC GBs are not partially wetted and, therefore, “dry”. They are pseudopartially wetted, namely they have the high contact angle with cobalt binder and, nevertheless, contain the 2–3 nm thin uniform Co-rich layer.

The high pressure torsion (HPT) has been used for the severe plastic deformation (SPD) treatment of liquid-phase sintered hard magnetic NdFeB-based alloy (5 GPa, 1 rpm, 5 torsions, ambient temperature). The amorphization of the crystalline alloy under the action of HPT has been observed. HPT permitted to obtain for the first time the mixture of two different amorphous phases with embedded grains of the ferromagnetic Nd2Fe14B phase. The SPD-treatment at ambient temperature TSPD=300 K is frequently equivalent to the heat treatment at a certain elevated temperature Teff>300 K. The composition of phases in the studied NdFeB-based alloy after HPT corresponds to the state at Teff~1170 °C.

High-pressure torsion of six homogenized Cu–In alloys (2.3 to 13.5 at. % In) with negative mixing enthalpy has been studied. The torsion torque reached a steady-state after 1–2 anvil rotations. Differently to the alloys with positive mixing enthalpy, the Cu(In) solid solution did not decompose. Moreover, the precipitates of δ-phase in the Cu–13.5 at. % In alloy partially dissolved and additionally enriched the Cu(In) solid solution.

The architecture of novel metallic mesostructures obtained via self-organization of growing nanowires has been investigated. Seashell, fungus and lotus leafshaped structures are reproducibly formed by programmable pulse current electrodeposition on porous membranes. The samples several millimeters in size are obtained. SEM investigation has revealed that the frame of the metallic seashell presents a hierarchical system with elements of fractal selfsimilarity at the nano- and microlevels. The frame is a volumetric multilayer net with conical bundles of nanowires as building blocks. The Pd-Ni nanowires have V-like branches and periodic bulges . TEM study showed that the nanowires consist of nanocrystallites dispersed in an amorphous matrix. Their sizes range from 4 to 15 nm. Local inhomogeneity of PdNi solid solution was observed. In perspective, the proposed technique can be used as a 3D printer for the purposeful synthesis of novel materials with complex quantum nano-architecture., Comment: 11 pages, 9 figures

For conventional structural and tool materials, in particular WC-Co cemented carbides, hardness and wear-resistance can usually be increased only at the expense of toughness and strength. For the first time we have achieved a dramatically increased combination of hardness, wear-resistance, fracture toughness and strength as a result of precipitation of extremely fine nanoparticles in the cobalt binder of cemented carbides. These nanoparticles are similar to 3 nm in size, coherent with the Co matrix and consist of a metastable phase. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In ultra-fine grained Al–Zn alloys after high pressure torsion Al/Al grain boundaries (GBs) completely, partially or pseudopartially wetted by Zn in the solid state have been observed using analytical and high resolution electron microscopy. In the latter case the solid Zn particles in the triple joints form a non-zero contact angle θ = 80–160° with Al/Al GBs. Simultaneously, a 2–10 nm thick uniform Zn-rich layer is present in the Al/Al GBs.

The influence of the grain boundary (GB) specific area sGB on the appearance of ferromagnetism in Fe-doped ZnO has been analysed. A review of numerous research contributions from the literature on the origin of the ferromagnetic behaviour of Fe-doped ZnO is given. An empirical correlation has been found that the value of the specific grain boundary area sGB is the main factor controlling such behaviour. The Fe-doped ZnO becomes ferromagnetic only if it contains enough GBs, i.e., if sGB is higher than a certain threshold value sth = 5 × 104 m2/m3. It corresponds to the effective grain size of about 40 μm assuming a full, dense material and equiaxial grains. Magnetic properties of ZnO dense nanograined thin films doped with iron (0 to 40 atom %) have been investigated. The films were deposited by using the wet chemistry “liquid ceramics” method. The samples demonstrate ferromagnetic behaviour with Js up to 0.10 emu/g (0.025 μB/f.u.ZnO) and coercivity Hc ≈ 0.03 T. Saturation magnetisation depends nonmonotonically on the Fe concentration. The dependence on Fe content can be explained by the changes in the structure and contiguity of a ferromagnetic “grain boundary foam” responsible for the magnetic properties of pure and doped ZnO.

The microstructure and magnetic properties of binary Cu–Co alloys are studied. The investigations have been carried out using samples in two structural states, i.e. as-cast and after severe plastic deformation by the high-pressure torsion (HPT) carried out at the ambient temperature and pressure of 6 GPa. The grain size after HPT is in the nanometer range. HPT allows one to control the ratio between ferromagnetic and superparamagnetic precipitates in the diamagnetic matrix.

The influence of the grain boundary (GB) specific area s GB on the appearance of ferromagnetism in Co-doped ZnO has been analysed based on a review of numerous research contributions from the literature on the origin of the ferromagnetic behaviour of Co-doped ZnO. An empirical correlation has been found that the value of the specific grain boundary area s GB is the main factor controlling such behaviour. The Co-doped ZnO becomes ferromagnetic only if it contains enough GBs, i.e., if s GB is higher than a certain threshold value s th = 1.5 × 106 m2/m3. It corresponds to the effective grain size of about 1 µm assuming a full dense material and equiaxial grains. The magnetic properties of Co-doped (0 to 42 at. %) ZnO dense nanograined thin films have been investigated. The films were deposited using the wet chemistry “liquid ceramics” method. The samples demonstrate ferromagnetic behaviour with J s up to 0.12 emu/g and coercivity H c ∼ 0.01 T. Saturation magnetization non-monotonically depends on the Co conc...

The paper presents a review of the causes of the occurrence of ferromagnetic properties in zinc oxide. It is shown that ferromagnetism only occurs in polycrystals at a fairly high density of grain boundaries. The critical grain size is about 20 nm for pure ZnO and over 1000 nm for zinc oxide doped with manganese. The solubility of manganese and cobalt in zinc oxide increases considerably with diminishing grain size. Even at the critical grain size, the ferromagnetic properties depend significantly on the film texture and the struc� ture of intercrystalline amorphous layers.

The possibility to attain ferromagnetic properties in transparent semiconductor oxides such as ZnO is very promising for future spintronic applications. We demonstrate in this review that ferromagnetism is not an intrinsic property of the ZnO crystalline lattice but is that of ZnO/ZnO grain boundaries. If a ZnO polycrystal contains enough grain boundaries, it can transform into the ferromagnetic state even without doping with “magnetic atoms” such as Mn, Co, Fe or Ni. However, such doping facilitates the appearance of ferromagnetism in ZnO. It increases the saturation magnetisation and decreases the critical amount of grain boundaries needed for FM. A drastic increase of the total solubility of dopants in ZnO with decreasing grain size has been also observed. It is explained by the multilayer grain boundary segregation.

Zr–Nb alloys play the important role in the energy production of being the main material for the cladding of nuclear fuel in the nuclear power plants. Severe plastic deformation by high‐pressure torsion (HPT) leads to the strong grain refinement in Zr–Nb alloys. HPT leads also to formation of the high-pressure ωZr phase. It remains quenched at the ambient pressure and disappears by heating only above 400 °C. The diffusion-controlled αZr + βNb↔αZr + βZr↔βZr transformations are observed only in the as-cast alloy Zr–2.5 mass% Nb. Transformation αZr↔βZr in as-cast alloy Zr–8 mass% Nb occurs as martensitic. Phase transformations occurring in alloys of both compositions after HPT on heating are martensitic. The effective temperature during HPT has been determined as Teff = 700 °C at 5 GPa.

The nanograined thin films of undoped ZnO were synthesized by the wet chemistry method. Films consist of the equiaxial nanograins, and possess ferromagnetic properties. Structural investigations by the XRD and HREM reveal that the crystalline wurtzite grains do not contact each other and are completely surrounded by a layer of amorphous phase. It forms a kind of continuous foam-like network, where the amorphous intergranular phase amount could be increased by the synthesis parameters. Simultaneously, the saturation magnetization increases as well.

The structures of palladium and palladium alloys thin films deposited from organic electrolytes onto metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 microm thick films with high adhesive strength to the substrate surface. EDX, XRD, SEM and TEM methods were used to determine the composition and structure of alloy coatings of the following binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed.