Delocalization transition in low energy excitation modes of vector spin glasses

We study the energy minima of the fully-connected mm-components vector spin glass model at zero temperature in an external magnetic field for m\ge 3m≥3. The model has a zero temperature transition from a paramagnetic phase at high field to a spin glass phase at low field. We study the eigenvalues and eigenvectors of the Hessian in the minima of the Hamiltonian. The spectrum is gapless both in the paramagnetic and in the spin glass phase, with a pseudo-gap behaving as \lambda^{m-1}λm−1 in the paramagnetic phase and as \sqrt{\lambda}λ at criticality and in the spin glass phase. Despite the long-range nature of the model, the eigenstates close to the edge of the spectrum display quasi-localization properties. We show that the paramagnetic to spin glass transition corresponds to delocalization of the edge eigenvectors. We solve the model by the cavity method in the thermodynamic limit. We also perform numerical minimization of the Hamiltonian for N\le 2048N≤2048 and compute the spectral properties, that show very strong corrections to the asymptotic scaling approaching the critical point.

Sorption Properties of ZrO2-Analcime Composites in Relation to Cs(I) and Sr(II)

Composite zeolite sorbents based on analcime with inclusions of hydrated zirconium dioxide (ZrO2-analcime) have been obtained by hydrothermal treatment of coal fly ash cenospheres with a high glass phase content in the presence of a zirconium compound and an alkaline activating agent at 150 °C and different stirring modes of the reaction mixture. The synthesis products were characterized by XRD, SEM-EDS, STA and low-temperature nitrogen adsorption; their sorption properties with respect to Cs+ and Sr2+ were studied in the pH range of 2–10. It was found that the ZrO2-analcime compositions surpass unmodified analcime by 2–5 times in terms of sorption of Cs+ and Sr2+ and by two orders of magnitude in terms of the distribution coefficient value (KD ~106 ml/g). The process of high-temperature solid-phase transformation of Cs+/Sr2+-exchanged forms of the compositions was studied, which simulates the process of conversion of water-soluble forms of Cs‑137 and Sr‑90 radionuclides into a mineral-like form. It was shown that at 1000 °C the ZrO2-analcime compositions with sorbed Cs+ and Sr2+ undergo the phase transformation resulting in polyphase systems of similar composition based on nepheline, tetragonal ZrO2, and glass phase

Analysis of quality parameters of fused cast AZS refractories for glass-making furnaces

A comprehensive analysis of the quality parameters of fused-cast aluminum-zirconium-silicate (AZS) refractories for glass furnaces has been carried out. It is shown that the assessment of the quality of AZS refractories by the content of ZrO2 and density in them does not give an objective idea of their operational properties. Of fundamental importance are the chemical composition and behavior of the glass phase, which determine the volume and temperature of the onset of exudation. Among the most important conditions for obtaining high-quality AZS refractories, characterized by a melting volume of 2‒3 % of the glass phase and a melting start temperature above 1400 °C, include the oxidative melting technology and the content of impurities in the chemical composition of the refractory no more than 0,25‒0,30 %. The conditions for the service of AZS refractories in the melting basin and the working space of glass-melting furnaces are formulated. Their influence on the course of the exudation process, the corrosion resistance of refractories and the formation of defects in glass is shown. Ill. 2. Ref. 30. Tab. 4.

Vortex Dynamics and Superconducting Phase Diagrams in Ta x Ge 1-x / Ge Multilayers with Coplanar Defects

<p>The superconducting phase diagrams of amorphous multilayered Ta x Ge 1-x / Ge thin films have been studied over a large range of temperatures and magnetic fields by means of dc electrical transport measurements. These superconducting films belong to the class of extremely type-II superconductors, for which a multitude of superconducting phases has been predicted and experimentally verified. A thorough understanding of these phase diagrams is indispensable for future successful applications of high-temperature superconductors since some of the observed phases severely limit the zero-resistance current-carrying capacity of these materials. The Ta x Ge 1-x / Ge films in this study were prepared by vapour deposition under high vacuum conditions. The Ta-content varied between x = 0.31 and 0.37 and individual layer thicknesses ranged from about 3 to 15 nm. Tilting the sample substrates during the deposition resulted in coplanar defects with variable orientation and structure depending on the tilting angle. This way it was possible to study the interplay between magnetic flux lines and the material structure and defect morphology, respectively. Films with thin insulating Ge layers and thus strong interlayer coupling showed three dimensional behaviour over the complete range of fields and temperatures. The coplanar defect structure was able to extend the zero-resistance phase to significantly higher fields and temperatures for magnetic fields co-aligned with the defects. Strong support for the existence of a low-temperature glass phase was found in the case of aligned and misaligned magnetic fields. Increasing the insulating layer thickness lead to a cross-over to 2D behaviour depending on temperature and field as well as field orientation with respect to the defects. In the 2D phase regions the low-temperature zero-resistance glass phase may have disappeared entirely. Current-voltage characteristics measured in the low-temperature glass phases showed significant differences between the strongly and weakly coupled films. However the detailed temperature and field dependence of these current-voltage curves at low temperatures cannot be explained satisfactorily with existing theoretical models.</p>

Vortex Dynamics and Superconducting Phase Diagrams in Ta x Ge 1-x / Ge Multilayers with Coplanar Defects

<p>The superconducting phase diagrams of amorphous multilayered Ta x Ge 1-x / Ge thin films have been studied over a large range of temperatures and magnetic fields by means of dc electrical transport measurements. These superconducting films belong to the class of extremely type-II superconductors, for which a multitude of superconducting phases has been predicted and experimentally verified. A thorough understanding of these phase diagrams is indispensable for future successful applications of high-temperature superconductors since some of the observed phases severely limit the zero-resistance current-carrying capacity of these materials. The Ta x Ge 1-x / Ge films in this study were prepared by vapour deposition under high vacuum conditions. The Ta-content varied between x = 0.31 and 0.37 and individual layer thicknesses ranged from about 3 to 15 nm. Tilting the sample substrates during the deposition resulted in coplanar defects with variable orientation and structure depending on the tilting angle. This way it was possible to study the interplay between magnetic flux lines and the material structure and defect morphology, respectively. Films with thin insulating Ge layers and thus strong interlayer coupling showed three dimensional behaviour over the complete range of fields and temperatures. The coplanar defect structure was able to extend the zero-resistance phase to significantly higher fields and temperatures for magnetic fields co-aligned with the defects. Strong support for the existence of a low-temperature glass phase was found in the case of aligned and misaligned magnetic fields. Increasing the insulating layer thickness lead to a cross-over to 2D behaviour depending on temperature and field as well as field orientation with respect to the defects. In the 2D phase regions the low-temperature zero-resistance glass phase may have disappeared entirely. Current-voltage characteristics measured in the low-temperature glass phases showed significant differences between the strongly and weakly coupled films. However the detailed temperature and field dependence of these current-voltage curves at low temperatures cannot be explained satisfactorily with existing theoretical models.</p>

Influence of microstructure and crystalline phases on impedance spectra of sodium conducting glass ceramics produced from glass powder

Crystallization of highly ionic conductive N5 (Na5YSi4O12) phase from melted Na3+3x-1Y1-xPySi3-yO9 parent glass provides an attractive pathway for cost-effective manufacturing of Na-ion conducting thin electrolyte substrates. The temperature-dependent crystallization of parent glass results in several crystalline phases in the microstructure (N3 (Na3YSi2O7), N5 and N8 (Na8.1Y Si6O18) phases) as well as in rest glass phase with temperature dependent viscosity. The electrical properties of dense parent glass and of compositions densified and crystallized at 700 °C, 800 °C, 900 °C, 1000 °C, and 1100 °C are investigated by impedance spectroscopy and linked to their microstructure and crystalline phase content determined by Rietveld refinement. The parent glass has high isolation resistance and predominantly electrons as charge carriers. For sintering at ≥ 900 °C, sufficient N5 phase content is formed to exceed the percolation limit and form ion-conducting pathways. At the same time, the highest content of crystalline phase and the lowest grain boundary resistance are observed. Further increase of the sintering temperature leads to a decrease of the grain resistance and an increase of grain boundary resistance. The grain boundary resistance increases remarkably for samples sintered at 1100 °C due to softening of the residual glass phase and wetting of the grain boundaries. The conductivity of fully crystallized N5 phase (grain conductivity) is calculated from thorough impedance spectra analysis using its volume content estimated from Rietveld analysis, density measurements and assuming reasonable tortuosity to 2.8 10−3 S cm−1 at room temperature. The excellent conductivity and easy processing demonstrate the great potential for the use of this phase in the preparation of solid-state sodium electrolytes.

Recovery of Hydrothermal Wustite-Magnetite Spherules from the Central Indian Ridge, Indian Ocean.

Not many studies have reported the hydrothermal-related origin of the magnetite-bearing spherules, and hardly any literature discusses the hydrothermal-related origin of wustite-magnetite-bearing spherules. A sediment sample with high abundance (19 spherules in ~85 g) of spherules is recovered from Central Indian Ridge (CIR) segment S2 (70°54′E, 25°14′S to 70°50′E, 24°41′S), ~85 km north of Rodrigues triple junction (RTJ). On the external surface of the spherules, magnetite appears as crystals, whereas wustite mostly appears as a homogenous glass phase. These spherules are composed of wustite and magnetite hosting Mn, unlike micrometeorites which essentially hosts Ni. Mn is more heterogeneously distributed with a relatively higher concentration in the wustite phase than the magnetite, suggesting hydrothermal origin. Furthermore, the presence of sulfide nano-particles in the wustite phase and a minor quantity of Pb and S in the ferrihydrite matrix points to the fact that CIR spherules are of hydrothermal origin. We propose that the CIR spherules originated by the interaction of the reduced hydrothermal fluids with the ultramafic/basaltic rocks or silica-undersaturated magmatic melts. The finding of Mn hosting wustite-magnetite assemblage suggests an active hydrothermal system in the near vicinity and can be considered as an additional proxy for locating hydrothermal vents.

Felsite in Ceramic Materials Production

This project is devoted to the study of the felsite properties for the purpose of its application in the production of various types of fine ceramics: ceramic tiles, acid-resistant tiles, aluminosilicate proppants, etc. Felsite is a mixture of quartz (about 40%) and feldspars. In the compositions of ceramic masses, felsite can play the role of both nonplastic due to the quartz content, and flux due to the content of feldspars, that reduces the amount of mixture components. When felsite is fired, the melt appears at a temperature above 950°C. The felsite has a sintering effect when fired at a temperature of 1000°C. Glass phase enriched with SiO2 ensures the absence of material deformation after firing. Also, glassy phase provides high-acid and chemical resistance of materials based on it. In addition, after firing above 1150°C, felsite has a light color, which is a great advantage in comparing it as a melt with other iron-alkali-containing materials. Ceramics based on felsite does not require the use of opacified glazes.