Two new ternary germanides Tb _2 Pt _1.2 Ge _2.8 , Dy _2 Pt _1.15 Ge _2.85 and one already known germanium Ho _2 Pt _1.1 Ge _2.9. were synthesized using an arc melting technique. The obtained samples were investigated by powder x-ray diffraction, which indicated that all of them crystallized in a hexagonal structure with P 6/ mmm (no. 191) space group. This structure is a disordered variant of the AlB _2 aristotype that favors the formation of a spin-glass-like state. The physical properties were examined by measuring magnetic susceptibility, heat capacity and electrical resistance. Experiments indicated that all of the compounds can be classified as cluster-spin-glasses with the freezing temperature of T _f = 12.0 K, T _f = 6.0 K and T _f = 2.9 K for Tb _2 Pt _1.2 Ge _2.8 , Dy _2 Pt _1.15 Ge _2.85 and Ho _2 Pt _1.1 Ge _2.9 respectively.

The intermetallic germanide Gd2Pt1.1Ge2.9 was synthesized using an arc-melting method. The crystal structure was characterized using powder x-ray diffraction, revealing a disordered ternary AlB2-type structure (space group P6/mmm, No. 191) with lattice parameters a = 4.2092(1) angstrom and c = 4.0546(2) angstrom. Physical properties were investigated by magnetic susceptibility and heat capacity measurements, which indicated onset of antiferromagnetic order at Tt = 8 K. The obtained properties were compared with the ones reported for other members of the AlB2-type Gd2TGe3 (T = Ni, Cu, and Pd) family. The magnetic ordering in these compounds was discussed in terms of their crystal structure and the influence of Gd ions.

Users expect reliable operation of the surge arrester during overvoltages, which may originate from a switching process or a lightning discharge. The necessary conditions to guarantee these expectations are: appropriate construction of the surge arrester, its production being maintained in accordance with technical standards, and a positive results of the type test (as well routine and acceptance tests). The recipient, especially when purchasing large quantities of the product, can check the final quality of the product through selective testing of samples from the market in order to find the best supplier. This manuscript specifies the basic parameters of low-voltage (LV) surge arresters of four manufacturers. Basic electrical parameters, i.e. leakage current and varistor voltage ( $\text{U}_{\mathrm {1mA}}$ ) before and after the nominal discharge current ( $\text{I}_{\mathrm {n}}$ ) of $8~\mu \text{s}$ /20 $\mu \text{s}$ , were determined for 10 randomly selected surge arresters of each manufacturer. Moreover one sample of each varistor batches was aged by fifty 8 $\mu \text{s}$ /20 $\mu \text{s}$ current impulses with $\text{I}_{\mathrm {n}}$ . The obtained results of structural analysis indicate that the crystal structure of the varistor materials changes after ageing process, affecting its electrical properties. The proposed research methodology can be employed as a basis for forecasting the stability of the arrester parameters under operating conditions.

In the present study we report a successful synthesis of the new intermetallic compound Nd2PtGe3 by an arcmelting method. The powder X-ray diffraction analysis indicates that this compound crystallizes in an disordered variant of the AlB2-type structure (space group P6/mmm, no. 191) with lattice parameters a = 4.2455 angstrom and c = 4. 1933 angstrom. The compound exhibits a cluster-glass transition below T-f = 2.9 K, characterized through ac and dc magnetic susceptibility and heat capacity measurements.

Recently conical magnetic order induced by Sc3+ doping has been reported in ferrimagnetic M-type hexagonal ferrite single-and polycrystals resulting in multiferroic properties of spin origin in bulk material. We were interested in Sc-induced modifications of superexchange interactions in M-hexaferrite nanocrystals since a reduction in size is usually accompanied by degradation in properties important for applications. Nd-stabilized, Sc-doped M-type strontium hexaferrite nanocrystalline powder was obtained by citric sol-gel method. Crystal-and microstructure of Sr0.95Nd0.05Fe12-xSCxO19 (x = 0.60, 0.84, 1.08 1.56) were controlled by X-ray diffraction and scanning electron microscopy. Temperature variation in magnetic hysteresis loops and temperature dependences of magnetization in zero field cooling-field heating experiments were measured from 10 K to 300 K in various magnetic fields. The analysis shows a conical magnetic ordering at low temperatures, below T-cone and enabled us to construct the (T-cone H, x) phase diagram. Though the effect is similar to that induced by selectively substituted Sc3+ in the place of ferric ions at the 4f(2) and 12k Wyckoff positions in the hexagonal lattice of single and polycrystals the temperatures T-cone, in nanocrystalline, single domain particles are considerably lower.

Responding to the rapidly increasing demand for efficient energy usage and increased speed and functionality of electronic and spintronic devices, multiferroic oxides have recently emerged as key materials capable of tackling this multifaceted challenge. In this paper, we describe the development of single-site manganese-based multiferroic perovskite materials with modest amounts of nonmagnetic Ti substituted at the magnetic Mn site in Sr1- x Ba x Mn1- y Ti y O3 (SBMTO). Significantly enhanced properties were achieved with ferroelectric-type structural transition temperatures boosted to ∼430K. Ferroelectric distortions with large spontaneous polarization values of ∼30μC/cm2, derived from a point charge model, are similar in magnitude to those of the prototypical nonmagnetic BaTiO3. Temperature dependence of the system's properties was investigated by synchrotron x-ray powder diffraction and neutron powder diffraction at ambient and high pressures. Various relationships were determined between the structural and magnetic properties, Ba and Ti contents, and T N and T C. Most importantly, our results demonstrate the large coupling between the magnetic and ferroelectric order parameters and the wide tunability of this coupling by slight variations of the material's stoichiometry.

Kamal Chapagain ,1,* Dennis E. Brown,1 Stanislaw Kolesnik,1 Saul Lapidus,2 Bianca Haberl,3 Jamie Molaison,3 Chuanlong Lin,4,† Curtis Kenney-Benson,5 Changyong Park,5 Jaroslaw Pietosa,6 Ewa Markiewicz,7 Bartlomiej Andrzejewski,7 Jeffrey W. Lynn,8 Stephan Rosenkranz,9 Bogdan Dabrowski,6 and Omar Chmaissem1,9 1Department of Physics, Northern Illinois University, DeKalb, Illinois 60115, USA 2X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA 3Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA 4Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA 5HPCAT, X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA 6Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland 7Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, PL-60179 Poznań, Poland 8NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-6102, USA 9Materials Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA

Lithium manganese oxide nanopowders doped with Ce ions are synthesized using modified sol-gel method and the effect of annealing atmosphere (air vs. nitrogen) on the structure, morphology, and phase composition is studied thoroughly. Electrochemical testing is conducted to evaluate the effect of annealing atmosphere on electrochemical performance. The X-ray diffraction indicates the cubic spinel structure for all the obtained samples. The lattice parameter is observed to slightly decrease with increasing concentration of Ce3+ ions substituting Mn3+ ions from 8.230 to 8.228 Ẵ and from 8.227 to 8.224 Ẵ for air annealing and for nitrogen-air annealing, respectively. A limited solubility of cerium in LiMn2O4 is also observed, as small amounts of cerium dioxide is detected on the surface of LiMn2-xCexO4 grains and confirmed by XPS analysis of cerium which shows only the spectrum of Ce4+ ions. Electrochemical testing is conducted to evaluate the effect of annealing atmosphere on electrochemical performance. It is shown that annealing in nitrogen and then in air results in excellent capacity retention with minimal, 4–8% capacity loss after 150 cycles. LiMn1.99Ce0.01O4 samples prepared that way display better high rate performance in comparison with pristine LiMn2O4.

Agglomerated single-phase Sr0.95Nd0.05Fe12-xAlxO19 nanocrystallites with 0.36 <= x <= 1.08 were synthesized hydrothermally and their properties were studied. Ferrimagnetic hysteresis loops were observed in the range 10-300K and the analysis of doping-induced changes in magnetization shows that Al3+ ions substitute the ferric ions in 4f(2), 12k and 2a Wyckoff sites. The substitution in 4f(2) and 12k sites induces electric dipoles in trigonal bipyramids and results in two relaxation processes apparent in the dielectric and electric response. Zero field cooling/field heating experiments in H = 100Oe have pointed to a coexistence of noncollinear and uniaxial magnetic moments in doped nanocrystalline hexaferrites and yield the (T-1-x) phase diagram.

Magnetic and dielectric properties of hexagonal ferrites important for applications in microwave absorbers are strongly determined by the processing conditions. We studied dielectric and magnetic response of Sr1-xNdxFe12O19 (x = 0, 0.03, 0.05, 0.07, 0.09) solid solutions obtained by coprecipitation method. The structure of the samples was controlled by X-ray diffraction and scanning electron microscope images revealed that the powder is a mixture of small nanograins and crystallites of 500 nm(-1) mu m in size. Nd3+ doping was found to result in an increase in the coercive field which we would like to relate to the domain wall pinning. The doping-induced changes are monotonous with x up to 0.07. The observed dispersion of permittivity was found to be correlated with the frequency behaviour of electric conductivity of the samples.

Single-phase BiFeO3 powder consisting of ball-like aggregates resembling nanoflowers with petals, the thickness of which can be controlled by polyethylene glycol addition, was synthesized by microwave hydrothermal method. The powder was characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy studies revealed that the mean thickness of petals is equal to 78 nm for the synthesis without PEG2000 and increases to 524 nm when the concentration of the PEG2000 reaches 10 wt.%, Variation in the petal thickness was found to enhance the magnetic properties of the nanopowder. The room temperature remnant magnetization of BiFeO3 with mean thickness of 524 nm was found to be comparable to the bulk value (0.006 Am-2 kg(-1)), whereas for powder with thinnest petals it increases considerably to 0.15 Am-2 kg(-1). The changes in the magnetic properties were related both to the size effect and to uncompensated surface spins of Fe3+/Fe2+ ions. (C) 2016 Elsevier Ltd. All rights reserved.

In this work, we present the spectral investigation of the interactions between the coverage with alginic acid (AA) and nanoparticles for three different composites containing 74, 80, and 88wt% of magnetite. These results show that the Fe3O4 nanoparticles are coated with the AA and indicate that there is an interaction between them. Moreover, we have investigated the thermal and magnetic properties of all investigated compounds. We show that bonding of alginic acid to the surface of magnetite results in better thermal stability of the polymer and in higher temperature of AA chains degradation. We find that for dense assembly of magnetite nanoparticles, at low temperatures, the intergranular coupling becomes much stronger than between nanoparticles dispersed in composites.

BiFeO3 powder which formed ball-like structures resembling flowers was obtained by microwave hydrothermal synthesis. The flowers were of a dozen or so mm in diameter and the thickness of the crystallites forming petals could be controlled. The material was characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. Dielectric response of ceramics obtained from the powder contained three extrinsic contributions, which could be correlated with the differences in temperature variation of the ac conductivity. The dielectric relaxation between 150 K and 300 K was related to reorientations of Fe3+-Fe2+ dipoles and characterized by an activation energy of 0.4 eV, which was independent of the petal thickness. The dielectric and electric response in the range 300 K divided by 450 K usually ascribed to the grain boundary and interfacial polarization effect was diffused and could not be characterized. Above 450 K the activation energy of dc conductivity was 1.73 eV and 1.52 eV for ceramics consisting of crystallites of mean thickness of 160 nm and 260 nm, respectively. The energies, which are considerably higher than those reported earlier for BFO nanoceramics, were discussed considering the interactions between oxygen vacancies and size scaled ferroelectric domain walls, which in BiFeO3 are associated with electrostatic potential steps. (C) 2016 Elsevier B.V. All rights reserved.

ABSTRACT Bi1 − xLaxFeO3 single-phase solid solution with 0 ≤ x ≤ 0.3 was obtained by mechanochemical synthesis and characterized by X-ray diffraction, FT NIR Raman spectroscopy and magnetic studies. The nanocrystalline powders of rhombohedrally distorted perovskite structure R3c were studied ‘as synthesized’ by mechanosynthesis and after annealing at 500 °C for 1 h. The annealing, which resulted in recrystallization of the amorphous shell of the nanograins, was found to modify the external lattice modes of Bi1−xLaxFeO3 and resulted in changes in the temperature variation of the magnetization.

Nanocomposites of hard magnetic SrFe12O19 hexaferrite and soft magnetic CoFe2O4 spinel with exchange spring interaction were obtained by simple solid state reaction during 8 h and 14 hat 1050 degrees C. The structure and morphology of the composites was characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Dielectric and electric response of the composites were found to be similar to the behavior of other ferrites and can be well described within the Koops model of the ceramic consisting of highly conducting grains separated by poorly conducting grain boundaries. Single-phase magnetic hysteresis loops obtained for SrFe12O19/CoFe2O4 composites with weight ratio 4:1 containing similar to 1 wt.% hematite. The difference in magnetization below the temperature of irreversibility, measured in field cooling and zero field cooling experiments in fields exceeding doubled coercivity, was found to be greater for composites synthesized during 4-14 h than that obtained for 22 h. (C) 2016 Elsevier B.V. All rights reserved.

Multiferroic (Bi1-x La x FeO3)0.5(PbTiO3)0.5 ceramics with x = 0, 0.1, 0.2, 0.3 and 0.5 was prepared from mechanochemically synthesized nanopowders. The XRD studies revealed the tetragonal structure for x ≤ 0.2 and rhombohedral for x = 0.5 with mean grain sizes from 15 to 28 nm. Dielectric response of the compounds in the temperature range 125–525 K was found to contain two anomalies: at ~400 K attributed to the presence of oxygen vacancies and that below 300 K characteristic of ferroelectric relaxors; the Curie point anomaly was apparent at 500 K only for samples with x = 0.5. Analysis of the low-temperature response enabled us to characterize the relaxor state of the solid solution and to yield information on the decrease in the activation energy of dipole moment flipping in polar nanoregions. Magnetic studies revealed two contributions to the magnetization of the nanoceramics pointing to a coexistence of weak ferromagnetic and antiferromagnetic orderings in the range 4 ÷300 K. Low temperature variation of the magnetization in field-cooling and zero-field–cooling conditions revealed spin glass behavior which in (Bi1-xLaxFeO3)0.5(PbTiO3)0.5 is dependent on x. Moreover, a sharp step in magnetization at ~250 K was found to be dependent on the La content and related to the A-site distortion leading to a modification of Fe-O-Fe angles and antiferromagnetic coupling between magnetic Fe3+ moments.