Transition-metal dichalcogenides (TMDs) are layered compounds that support many electronic phases, including various charge density waves, superconducting, and Mott insulating states. Their intercalation with magnetic ions introduces magnetic sublayers, which strongly influence the coupling between host layers, and feature various magnetic states adjustable by external means. Co$_{1/3}$NbS$_2$ hosts a particularly sensitive magnetic subsystem with the lowest magnetic ordering temperature in the family of magnetically intercalated TMDs, and the only one where the complete suppression of magnetic order under pressure has been recently suggested. By combining the results of several experimental methods, electronic ab initio calculations, and modeling, we develop insights into the mechanisms of electric transport, magnetic ordering, and their interaction in this compound. The elastic neutron scattering is used to directly follow the evolution of the antiferromagnetic order parameter with pressure and temperature. Our results unambiguously disclose the complete suppression of the observed magnetic order around 1.7 GPa. We delve into possible mechanisms of magnetic order suppression under pressure, highlighting the role of magnetic frustrations indicated by magnetic susceptibility measurements and ab-initio calculations. Electronic conduction anisotropy is measured in the wide temperature and pressure range. Here we show that the transport in directions along and perpendicular to layers respond differently to the appearance of magnetic ordering or the application of the hydrostatic pressure. We propose the 'spin-valve' mechanism where the intercalated Co ions act as spin-selective electrical transport bridges between host layers. The mechanism applies to various magnetic states and can be extended to other magnetically intercalated TMDs.

The magnetic properties of an Nd-Fe-B-type permanent magnet depend on the microstructure and the chemistry of the material. To compensate for unfavorable microstructural features, such as micron-sized grains of the hardmagnetic phase, the intrinsic coercivity is often enhanced by the addition of heavy-rare-earth elements, but these additions also reduce the magnetization. In some applications, like electro-mechanical devices, a high intrinsic coercivity is only required in certain regions of a magnet. In such cases, using magnets with locally tailored magnetic properties, i.e., multicomponent magnets, would enhance the magnet-containing device's performance. Here, we propose a spark-plasma-sintering (SPS) approach to the manufacture of multicomponent Nd-Fe-B magnets. By exploiting the SPS-specific processing conditions, namely fast heating rates (100 C/min) and low consolidation temperatures (approximate to 670 C), such magnets can be prepared directly from nanostructured meltspun powders (the one-step SPS approach) or SPS-processed precursor magnets (the two-step SPS approach). Optimizing the SPS processing conditions prevents the grain coarsening related to the pre-existing microstructural inhomogeneities of the powders. The magnetic characterization reveals reliable performance over a wide range of operating temperatures. The high remanent magnetization of a heavy-rare-earth-free powder (Br = 0.82 T) and the high intrinsic coercivity of a powder containing 1.5 at. % Dy (Hci = 2075 kA/m) are preserved in a multicomponent magnet characterized by an abrupt change in magnetic properties close to the interface between the respective magnet parts.

Shaping metals as a foam modulates their physical properties, enabling attractive applications where lightweight, low thermal conductivity, or acoustic isolation are desirable. Adjusting the size of the bubbles in the foams is particularly relevant for targeted applications. Herein, a method with a detailed theoretical understanding of how to tune the size of the bubbles in aluminum melts in situ via acoustic pressure is provided. The description is in full agreement with the high‐rate 3D X‐ray radioscopy of the bubble formation. The study with the intriguing results on the effect of foaming on electrical resistivity, Seebeck coefficient, and thermal conductivity from cryogenic to room temperature is complemented. Compared with bulk materials, the investigated foam shows an enhancement in the thermoelectric figure of merit. These results herald promising application of foaming in thermoelectric materials and devices for conversion of thermal energy.

Selective Laser Melting (SLM) was used to produce 3D-printed net shape NdFeB (Neodymium Iron Boron) permanent magnets that exhibit relatively large internal permanent magnetization structures, without exposure to any external magnetizing field. The macroscopic magnetization, (M) over right arrow((r) over right arrow), does not create a significant mag-netic stray field outside the as-produced sample, and is pole avoiding and solenoidal. The permanent magne-tization can be detected via the stray field that appears after cutting the sample into pieces. From the field measurements it can be concluded that the magnetization is mainly in the 3D-printing planes which are parallel to (M) over right arrow((r) over right arrow). Maximum magnetic flux densities of almost 80 mT are recorded 1 mm above the cut surfaces in the air. Dependencies of the effect on SLM process parameters, as well as on the sample size and shape are discussed. Although a deep understanding is still missing, a possible mechanism that may partly explain the formation of these self-organized macroscopic magnetization structures is proposed. The discovered effect may offer new routes for producing magnetized rare earth-transition metal (RE-TM) permanent magnets without using a magnetizer, and it shows that the SLM 3D-printing process can lead to new material behavior.

Magnetic remanence (B-r) and coercivity (H-c) of hard magnets play a crucial role in electro-mechanical devices like electrical motors or generators. Elevated remanence ensures high efficiency of the device, and large coercivity protects the magnet from demagnetization. Usually, the increase of one comes at the cost of the other, such that the material optimization has a trade-off character. In this work, we demonstrate that in many electrical machines which use permanent magnets, high coercivity is required mainly at the edges of the magnet. This enables us to design a novel form of a permanent magnet, called a multicomponent magnet, where the sides of the magnet have high coercivity, while the central part is characterized by high remanence. Such multicomponent magnets are realized by two independent methods, namely, conventional high-temperature sintering and Spark Plasma Sintering (SPS). The magnetic and mechanical performances are suitable for applications, and simulation results using the magnetic characteristics of the multicomponent geometry predict its benefit on the device functionality. Further tuning of the geometry of the multicomponent permanent magnets opens avenues for promising applications, particularly in electrical motors for electrical vehicles.

Single crystal growth by chemical vapour transport has resulted samples with Fe1.35Ge stoichiometry. Structural study has shown that the large number of vacancies introduces an incommensuately modulated structure. The electrical resistivity is in the 200 mu Omega cm range at room temperature, and although the ferromagnetic transition temperature at 425 K is clearly visible, it hardly varies down to 4.2 K. It is suggested that the large number of vacancies (and the incommensurate modulation) introduce a strong backscattering, and the system is at the brink of a Mooij correlation. The thermal conductivity and Seebeck coefficient carry also the consequences of the high concentration of vacancies. (c) 2019 Elsevier B.V. All rights reserved.

Thermal conductivity ( κ ) plays an essential role in functional devices. It is advantageous to design materials where one can tune κ in a wide range according to its function: single-crystals and nanowires of anatase polymorph of titanium dioxide, broadly used in applications ranging from photovoltaics, reflective coatings to memristors, have been synthesized in large quantities. Here we identify a new, strong diffusion mechanism of heat by polaronic structures due to oxygen vacancies, which considerably influences both the absolute value and the temperature dependence of κ . The additional decrease of κ is achieved in anatase nanowires organized into foam, where porosity and the quasi-one-dimensional size-effect dramatically hinder the propagation of heat, resulting in an extremely low κ = 0.014 W/Km at room-temperature. Doping this anatase foam could herald promising applications, in particular in thermoelectricity.

Techniques that use the layer-by-layer manufacturing concept have triggered novel research topics related to the processing of functional magnetic materials (FMMs). In this article, we focus on four FMM classes due to their technical relevance for energy conversion, harvesting, transmission, and sensing/actuation. Permanent magnets, soft magnetic materials, magnetocaloric compounds, and magnetic shape memory alloys are reviewed in terms of functionality and performance limits. Relationships among printing techniques and/or conditions, microstructure and performance are highlighted. Additively manufactured hard magnets are the closest to commercial/industrial application.

Different grades of Nd-Fe-B permanent magnets are available on the market today and their magnetic properties highly depend on the microstructure, which is controlled by the chemical composition of the alloy and the magnets' manufacturing route. Gas atomization is a rapid solidification technique that is seldom used for the production of Nd-Fe-B magnetic powders due to the cooling rates that are several orders of magnitude lower than those achieved with the melt spinning. In addition, rare-earth-rich powders experience significant loss of hard magnetic properties at high temperatures in air. We prepared a novel type of bulk Nd-Fe-B permanent magnet from gas-atomized powders using the Spark Plasma Sintering (SPS) technique. Samples manufactured from rare-earth-poor material were porous, while high density was achieved with a neodymium-rich powder. The high-temperature instability was effectively overcome with compaction of the atomized material into a dense magnet. The intrinsic coercivity of the latter surpassed the value of the optimally heat-treated spherical powder. The samples' magnetic, as well as the mechanical properties, reflected the unfavourable microstructural characteristics of the initial atomized material. Refinement of the microstructure achieved with sieving increased the coercivity of the heavy-rare-earth-free bulk magnet to similar to 1000 kA/m. (c) 2018 Elsevier B.V. All rights reserved.

We report a detailed spectroscopic study of Ti3+ self-doped TiO2 nanowires prepared by high temperature annealing of the protonated titanate nanowires (TiONW) in hydrogen atmosphere. Hydrogenation causes a color change from white to cyan and a major increase of photocatalytic activity. Combination of synchrotron X-ray diffraction and Rutherford backscattering spectrometry revealed that the bulk of the protonated titanate and Ti3+ self-doped titania is identical. Raman spectroscopy combined with local laser heating indicated the presence of optically active states in the hydrogenated TiO2 nanowires. Using multi-frequency electron paramagnetic resonance spectroscopy (EPR), the presence of Ti3+ surface states on the cyan titania nanowires is confirmed. We argue that these surface point defects are responsible for enhanced visible light absorption and improved their photocatalytic performance. (C) 2016 Elsevier B.V. All rights reserved.

For two decades, NdFeB based magnets have been a critical component in a range of electrical devices engaged in energy production and conversion. The magnet shape and the internal microstructure of the selected NdFeB grade govern their efficiency and size. However, stricter requirements on device efficiency call for better performing magnets preferably with novel functionality not achievable today. Here we use 3D metal printing by Selective Laser Melting to fabricate dense net shape permanent magnets based on NdFeB that exhibit high magnetic performance. Evidence is provided that the internal microstructure, not achievable by traditional manufacturing means, is the origin of the solid magnetic properties. The freedom in magnet body shape and size that ranges from the millimeter to tens of centimeter scale opens up a design freedom that could be a catalyzer for the next generation of electrical devices.

We report the synthesis of single crystals of a novel layered iridate Ba21Ir9O43 and present the crystallographic, transport, and magnetic properties of this material. The compound has a hexagonal structure with two iridium oxide layers stacked along the c direction. One layer consists of a triangular arrangement of Ir2O9 dimers while the other layer comprises two regular octahedra and one triangular pyramid, forming interpenetrated triangular lattices. The resistivity as a function of temperature exhibits an insulating behavior, with a peculiar T-3 behavior. Magnetic susceptibility shows antiferromagnetic Curie-Weiss behavior with Theta(CW) similar or equal to -90 K while a magnetic transition occurs at a substantially lower temperature of 9 K. We discuss possible valence states and effective magnetic moments on Ir ions in different local environments and argue that the Ir ions in a unique triangular-pyramidal configuration likely carry unusually large magnetic moments.

The intrinsic d.c. electrical resistivity (ρ) - measurable on single crystals only - is often the quantity first revealing the properties of a given material. In the case of CH_3NH_3PbI_3 perovskite measuring ρ under white light illumination provides insight into the coexistence of extended and shallow localized states (0.1 eV below the conduction band). The former ones dominate the electrical conduction while the latter, coming from neutral defects, serve as a long-lifetime charge carrier reservoir accessible for charge transport by thermal excitation. Remarkably, in the best crystals the electrical resistivity shows a metallic behaviour under illumination up to room temperature, giving a new dimension to the material in basic physical studies.

Single crystals of WS2 were prepared by chemical vapor transport method using sulfur as a transport agent. Measurements of electrical resistivity, Seebeck coefficient and thermal conductivity as a function of temperature, along the in-plane and the out-of-plane directions reveal distinct trends. In our interpretation these differences are mainly due to the different nature of the chemical bonding in the two directions and to the presence of impurity intercalates in between the planes.

We report resistivity, thermoelectric power and thermal conductivity of MoS2 single crystals prepared by chemical vapour transport (CVT) method using I2, Br2 and TeCl4 as transport agents. The material presents low-lying donor and acceptor levels, which dominate the in-plane charge transport. Intercalates into the Van der Waals gap strongly influence the inter-plane resistivity. Thermoelectric power displays the characteristics of strong electron-phonon interaction. Detailed theoretical model of thermal conductivity reveals the presence of high number of defects in the MoS2 structure. We show that these defects are inherent to CVT growth method, coming mostly from the transport agent molecules inclusion as identified by Total Reflection X-ray Fluorescence analysis (TXRF) and in-beam activation analysis (IBAA).

The novel iridate Ba8Al2IrO14 was prepared as single crystals by self-flux method, thereby providing a rare example of an all-Ir(VI) compound that can be synthesized under ambient pressure conditions. The preparation of all-Ir(6+) iridate without using traditional high-pressure techniques has to our knowledge previously only been reported in Nd2K2IrO7 and Sm2K2IrO7. The monoclinic crystal structure (space group C2/m, No.12) is stable down to 90 K and contains layers of IrO6 octahedra separated by Ba and AlO4 tetrahedra. The material exhibits insulating behavior with a narrow band gap of ∼0.6 eV. The positive Seebeck coefficient indicates hole-like dominant charge carriers. Susceptibility measurement shows antiferromagnetic coupling with no order down to 2 K.

We report on the temperature dependence of thermal conductivity of single crystalline and polycrystalline organometallic perovskite CH3NH3PbI3. The comparable absolute values and temperature dependence of the two samples' morphologies indicate the minor role of the grain boundaries on the heat transport. Theoretical modeling demonstrates the importance of the resonant scattering in both specimens. The interaction between phonon waves and rotational degrees of freedom of CH3NH3(+) sublattice emerges as the dominant mechanism for attenuation of heat transport and for ultralow thermal conductivity of 0.5 W/(Km) at room temperature.

We report a detailed study that compares various composite materials (CM): Ag/ZnO, Ag/SnO2, Ag/C, Ag/WC, Ag/WC–C and Ag/Ni used in high-current dc circuit breaker applications. Their structural, mechanical, electrical and wetting properties were investigated. In parallel, switching operation tests on the same compounds were performed on commercial high-speed circuit breakers under real conditions (30 kA–900 V). A correlation between the microscopic variables and switching performances of the CMs was established. Materials like Ag/WC and Ag/WC–C were found to be unsuitable for the reliable functionality of the device. In contrast, Ag/C and Ag/SnO2 materials with high electrical and high thermal conductivity revealed remarkably good behaviour during switching operation tests.