Structure variations within RSi2 and R2TSi3 silicides. Part I. Structure overview.

Here, structural parameters of various structure reports on RSi2 and R2TSi3 compounds [where R is an alkaline earth metal, a rare earth metal (i.e. an element of the Sc group or a lathanide), or an actinide and T is a transition metal] are summarized. The parameters comprising composition, lattice parameters a and c, ratio c/a, formula unit per unit cell and structure type are tabulated. The relationships between the underlying structure types are presented within a group-subgroup scheme (Bärnighausen diagram). Additionally, unexpectedly missing compounds within the R2TSi3 compounds were examined with density functional theory and compounds that are promising candidates for synthesis are listed. Furthermore, a correlation was detected between the orthorhombic AlB2-like lattices of, for example, Ca2AgSi3 and the divalence of R and the monovalence of T. Finally, a potential tetragonal structure with ordered Si/T sites is proposed.

Structure variations within RSi2 and R2Si3 silicides. Part II. Structure driving factors.

To gain an overview of the various structure reports on RSi2 and R2TSi3 compounds (R is a member of the Sc group, an alkaline earth, lanthanide or actinide metal, T is a transition metal), compositions, lattice parameters a and c, ratios c/a, formula units per unit cell, and structure types are summarized in extensive tables and the variations of these properties when varying the R or T elements are analyzed. Following the structural systematization given in Part I, Part II focuses on revealing the driving factors for certain structure types, in particular, the electronic structure. Here, concepts of different complexity are presented, including molecular orbital theory, the principle of hard and soft acids and bases, and a Bader analysis based on Density Functional Theory calculations for representatives of the reported structure types. The potential Si/T ordering in different structures is discussed. Additionally, the influences from intrinsic and extrinsic properties (e.g. elemental size and electronics as well as lattice parameters and structure type) are investigated on each other using correlation plots. Thermal treatment is identified as an important factor for the ordering of Si/T atoms.

Structural stability and thermoelectric performance of high quality synthetic and natural pyrites (FeS2).

Synthetic bulk and natural pyrite from the hydrothermal mine in Schönbrunn (Saxony, Germany) are confirmed to be stoichiometric FeS2 compounds and stable (for thermoelectric applications) up to ∼600 K by combined thermal, chemical, spectroscopic and X-ray diffraction analyses. Natural pyrite with a small amount (<0.6 wt%) of well-defined transition metal carbonates revealed characteristics of a nondegenerate semiconductor and is suitable as a model system for the investigation of thermoelectric performance. In the temperature range 50-600 K both natural and synthetic high quality bulk FeS2 samples show electrical resistivity and Seebeck coefficients varying within 220-5 × 10-3 Ω m and 4 - (-450) µV K-1, respectively. The large thermal conductivity (∼40 W m-1 K-1 at 300 K) is exclusively due to phononic contribution, showing a well pronounced maximum centered at ∼75 K for natural pyrite (grain size ≤5 mm). It becomes almost completely suppressed in the sintered bulk samples due to the increase of point defect concentration and additional scattering on the grain boundaries (grain size ≤100 µm). The thermoelectric performance of pure pyrite with ZT ∼ 10-6 at 600 K is indeed by a factor of ∼1000 worse than those reported earlier for some minerals and synthetic samples.

Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1-xCrx(SO4)2 × 6H2O crystals by metal ion substitution.

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric (ME) interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH2(CH3)2Al1-x Cr x (SO4)2 × 6H2O. Doing so we are able to induce and even tune a sign of the ME interactions, in the paramagnetic ferroelectric (FE) state. Both studied samples with x = 0.065 and x = 0.2 become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature (T c ) increases nonlinearly, with the shift being larger for the 6.5% of Cr. A magnetic field applied along the polar c axis increases ferroelectricity for the x = 0.065 sample and shifts T c to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient αME = 1.7 ns/m found for a crystal with Cr content of x = 0.2 is among the highest reported up to now. The observed sign change of αME with a small change in Cr content paves the way for ME coupling engineering.

Optical Writing of Magnetic Properties by Remanent Photostriction.

We present an optically induced remanent photostriction in BiFeO_{3}, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO_{3}/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO_{3}. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

Intermetallic germanides with non-centrosymmetric structures derived from the Yb3Rh4Sn13 type.

New germanides with composition RE3Pt4Ge13 (RE = Y, Pr, Sm, Gd, Tb, Tm) have been prepared by high-pressure, high-temperature synthesis. Their crystal structures have been refined, and the relationship of this new rhombohedral and monoclinic structure types with the primitive cubic Yb3Rh4Sn13 prototype is discussed. Band structure calculations within density functional theory confirm the distorted rhombohedral and monoclinic structural arrangements to be energetically more favorable than the simple cubic one. X-ray absorption spectroscopy and magnetic susceptibility measurements indicate that the RE-atoms are in the +3 oxidation state in all studied compounds.

Structural transformation with "negative volume expansion": chemical bonding and physical behavior of TiGePt.

The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.

Charge-doping-driven evolution of magnetism and non-Fermi-liquid behavior in the filled skutterudite CePt4Ge(12-x)Sb(x).

The filled skutterudite compound CePt(4)Ge(12) is situated close to the border between the intermediate valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and, ultimately, upon further increasing the Sb concentration, an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.

Physical properties and valence state of cerium in the filled skutterudite CePt4Ge12.

Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt4Ge12 are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium L(III) edge demonstrate that CePt4Ge12 in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax D 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient γ = 105 mJ mol⁻¹ K⁻², deduced from specific heat, indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt4Ge12] framework.

Superfluid density and energy gap function of superconducting PrPt4Ge12.

The filled skutterudite superconductor PrPt4Ge12 was studied in muon-spin rotation (muSR), specific heat, and electrical resistivity experiments. The continuous increase of the superfluid density with decreasing temperature and the dependence of the magnetic penetration depth lambda on the magnetic field obtained by means of muSR, as well as the observation of a T3 dependence of the electronic specific heat indicate the presence of pointlike nodes in the superconducting energy gap. The gap and the specific heat are found to be well described by two models with point nodes, similar to results obtained for the unconventional heavy fermion skutterudite superconductor PrOs4Sb12.

Electronic structure and thermodynamic properties of CeRh(2)Sn(4) and LaRh(2)Sn(4).

The electronic structure and thermodynamic properties of CeRh(2)Sn(4) and LaRh(2)Sn(4) are reported. The crystal structure of CeRh(2)Sn(4) has been determined from single-crystal diffraction experiments. The Ce core-level x-ray photoemission spectra and Ce L(III) x-ray absorption data unanimously indicate a stable trivalent state of the Ce ions in CeRh(2)Sn(4), consistent with static magnetic susceptibility. Thermodynamic measurements for CeRh(2)Sn(4) show a noncollinear antiferromagnetic ordering with a ferromagnetic component at T(N)≈3.2 K. There is evidence for spin fluctuations in both CeRh(2)Sn(4) and LaRh(2)Sn(4). A Fermi surface analysis reveals sections, which could generate 'nesting' instabilities and be responsible for the spin fluctuation effects. Both CeRh(2)Sn(4) and LaRh(2)Sn(4) exhibit slight homogeneity ranges and can be described by RE(1+x)Rh(2)Sn(4-x), where [Formula: see text] for Ce and [Formula: see text] in the case of La. Implantation of additional Ce atoms into the CeRh(2)Sn(4) structure leads to a distinct lowering of T(N) and the weakening of the ferromagnetic component of the magnetic ground state, whereas for the La-based systems the alloying reduces the strong diamagnetism.

Superconductivity in the platinum germanides MPt4Ge12 (M = rare-earth or alkaline-earth metal) with filled skutterudite structure.

New germanium-platinum compounds with the filled-skutterudite crystal structure were synthesized. The crystal structure and composition were investigated by x-ray diffraction and microprobe analysis. Magnetic susceptibility, specific heat, and electrical resistivity measurements evidence superconductivity in LaPt4Ge12 and PrPt4Ge12 below 8.3 K. The parameters of the normal and superconducting states were established. Strong coupling and a crystal electric field singlet ground state is found for the Pr compound. Electronic structure calculations show a large density of states at the Fermi level. Similar behavior with lower Tc was observed for SrPt4Ge12 and BaPt4Ge12.

5S rRNA gene hybridizes to human chromosome 1 at two sites (1q42.11-->q42.13 and 1q43).

Hybridization of a loach (Misgurnus fossilis) oocyte 5S rRNA gene repeat with human chromosomes was carried out to refine the localization of the 5S RNA gene in the human genome. Preliminary in situ hybridization analysis showed that this repeat hybridized with human chromosome region 1q42-->q43, the same location previously reported for the human 5S rRNA gene. High-resolution banding revealed the presence of two sites of hybridization, with a main peak in chromosome region 1q42.1 and a second peak in 1q43. These results are consistent with our data on the existence in the human genome of different 5S rRNA gene clusters specified by BamHI and HindIII restriction sites in spacer DNA (Timofeeva et al., 1993) and suggest a multicluster organization of the human 5S rRNA genes.

[Positive and negative regulation of replication in hybrid cells]. / Pozitivnaia i negativnaia reguliatsiia replikatsii v gibridnykh kletkakh.

DNA replication blockage in various differentiated cells was investigated on the model of heterokaryons. Two distinct types of DNA synthesis regulation in heterokaryons "differentiated cell + proliferating cell" were revealed: I. Neutrophils and nucleated erythrocytes efficiently prevented the entry of non-malignant proliferating cells nuclei into the S-period but usually failed to substantially inhibit the replication in malignant cells nuclei. Both "mortal" and immortalized proliferating cells activated the DNA synthesis in neutrophil and chicken erythrocyte nuclei. II. Macrophages did not influence the DNA synthesis in the nuclei of non-malignant cells in heterokaryons but drastically inhibited that in the nuclei of malignant cells. Only immortalized cells reactivated DNA synthesis in the nuclei of macrophages. These data show that the mechanisms maintaining differentiated cells in non-proliferating state are not uniform. Nucleated erythrocytes were shown to suppress the duplication of centrioles in partner cells. The possibility of the blockage of DNA replication upon the fusion of two proliferating cells (fibroblast + leukemia cell) was demonstrated for the first time in the present work. The influence of various oncogenes upon the regulation of DNA synthesis in heterokaryons was investigated in detail. New modifications of the methods of cell fusion, enucleation and heterokaryon identification were proposed.

[The nature of a proliferation block in differentiated cells with heterokaryons as a model: various types of absence of proliferation in cells in terminal differentiation]. / Issledovanie prirody bloka proliferatsii v differentsirovannykh kletkakh na modeli geterokarionov: razlichnye tipy otsutstviia proliferatsii v kletkakh pri terminal'noi differentsirovke.

Heterokaryons obtained by fusion of proliferating and terminally differentiated cells were studied. The data obtained suggest that mechanisms of proliferation arrest are different in macrophages on one hand and nucleate erythrocytes and polymorph leukocytes on the other. Macrophages appeared to be devoid of factors preventing replication in nontransformed and spontaneously immortalized cells. Inhibition of proliferation was probably due to certain modifications of macrophage genome which arise during differentiation and can be compensated by the effect of "immortalizing" oncogenes. On the contrary, nucleate erythrocytes and polymorphs evidently contain some factors mediating negative control of proliferation. For reactivation of DNA synthesis in these cell types after fusion with other cells the latter did not have to be immortalized. After cell fusion macrophages specifically inhibit DNA synthesis in cells containing active oncogenes.

Resident macrophages specifically inhibit DNA synthesis in the nuclei of transformed cells in heterokaryons.

DNA synthesis in heterokaryons of mouse peritoneal macrophages and various proliferating cultured cells was analyzed. Macrophages did not inhibit replication in the nuclei of non-immortalized and spontaneously immortalized cells (rat fibroblasts and macrophages, mouse pre-macrophages, NIH3T3 cells). On the contrary, the percentage of DNA-synthesizing nuclei of malignant HeLa cells was drastically reduced in heterokaryons. The transformation of NIH3T3 cells with c-Ki-ras oncogene and that of rat chondrocytes with p53 oncogene made these cells sensitive to the replication-inhibiting activity of macrophages in heterokaryons. Our observation represents a kind of "intracellular" cytotoxic activity of macrophages directed against transformed cells.

Immortalized phenotype and the presence of active oncogenes correlate with the capacity of culture cells to induce reactivation of DNA synthesis in macrophage nuclei in heterokaryons.

Several types of culture cells with limited life span (rat embryo fibroblasts, rat chondrocytes and mouse premacrophages) were found to be unable to induce the reactivation of DNA synthesis in the nuclei of non-dividing differentiated cells (mouse peritoneal resident macrophages) in heterokaryons. By contrast, malignant HeLa cells have this ability. In heterokaryons formed by fusion of mouse macrophages with HE239 cells (Syrian hamster fibroblasts transformed with a ts mutant of the SV40 virus), DNA synthesis in macrophage nuclei is reactivated only at the permissive temperature (33 degrees C), at which viral T antigen is stable. Immortalization of rat chondrocytes by transfection with p53 gene enables to induce DNA synthesis in macrophage nuclei upon fusion. All the evidence indicates that the function of immortalizing oncogenes is necessary for the resumption of the DNA synthesis in macrophage nuclei in heterokaryons.