Influence of Sintering Temperature on Pore Structure and Electrical properties of Technologically Modified MgO-Al2O3 Ceramics

Technologically modified spinel ceramics are prepared from Al2O3 and 4MgCO3×Mg(OH)2×5H2O powders at 1200, 1300 and 1400 oC. The influence of sintering temperature on porous structure and exploitation properties of obtained humidity-sensitive MgO-Al2O3 ceramics are studied. It is shown that increasing of preparing temperature from 1200 to 1400 oC result in transformation of pore size distribution in ceramics from tri- to bi-modal including the open macro- and mesopores with sizes from tem to hundreds nm and nanopores until to a few nm. The studied ceramic elements with electrical resistances ~ 10-2-102 MОhm are high humidity sensitive in the region of 30-95 % with minimal hysteresis in adsorption-desorption cycles. It is established that increasing of humidity sensitivity in ceramics are related to achievement near to optimum pore size distribution and quantity of pores in the all regions. Prolonged degradation transformation in ceramics at higher temperature and relative humidity result in lose sensitivity up to 40-50 %.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5189</p

Integrated thick-film nanostructures based on spinel ceramics

Integrated temperature-humidity-sensitive thick-film structures based on spinel-type semiconducting ceramics of different chemical compositions and magnesium aluminate ceramics were prepared and studied. It is shown that temperature-sensitive thick-film structures possess good electrophysical characteristics in the region from 298 to 358 K. The change of electrical resistance in integrated thick-film structures is 1 order, but these elements are stable in time and can be successfully used for sensor applications

Effect of high-energy mechanical milling on the medium-range ordering in glassy As-Se

International audienceEffect of high-energy mechanical milling on glassy AsxSe100 - x (5 <= x <= 75) is recognized with X-ray powder diffraction analysis applied to their diffuse halos ascribed to intermediate-and extended-range structural ordering, which are revealed respectively in the first sharp diffraction peak (FSDP) and principal diffraction peak (PDP). Straightforward interpretation of the results is developed within modified microcrystalline approach, treating diffuse halos as superposition of broadened Bragg-diffraction reflexes from remnants of inter-planar correlations, supplemented by inter-atomic Ehrenfest-diffraction reflexes from most prominent inter-atomic and inter-molecular correlations between cage-like molecules (such As4Se4 and/or As4Se3). Milling is shown to be ineffective in glassy arsenoselenides near Se (x < 20), while causing increase in the FSDP width for glasses with 20 <= x <= 40 due to destroyed inter-planar ordering. Remnants of cage-like molecules in over-stoichiometric As-rich AsxSe100 - x glasses (40 <= x <= 75) disappear under milling, promoting formation of higher polymerized structural network. This milling-driven reamorphization results in a drastic increase in the FSDP position and fragmentation impact on the correlation length of the FSDP-responsible entities. Breakdown in intermediate-range ordering in these glasses is accompanied by changes in their extended-range ordering revealed in high-angular shift and broadening of the PDP. This effect is concomitant with the disappearance of distant inter-atomic correlations between quasi-crystalline planes in the milled arsenoselenide glasses at a cost of prolonged correlations dominating in their extended-range ordering

High-Energy Mechanical Milling-Driven Reamorphization in Glassy Arsenic Monoselenide: On the Path of Tailoring Special Molecular-Network Glasses

International audienceThe impact of high-energy milling on glassy arsenic monoselenide g-AsSe is studied with X-ray diffraction applied to diffuse peak-halos proper to intermediate- and extended-range ordering revealed in first and second sharp diffraction peaks (FSDP and SSDP). A straightforward interpretation of this effect is developed within the modified microcrystalline approach, treating &quot;amorphous&quot; halos as a superposition of the broadened Bragg diffraction reflexes from remnants of some inter-planar correlations, supplemented by the Ehrenfest diffraction reflexes from most prominent inter-molecular and inter-atomic correlations belonging to these quasi-crystalline remnants. Under nanomilling, the cage-like As(4)Se(4) molecules are merely destroyed in g-AsSe, facilitating a more polymerized chain-like network. The effect of nanomilling-driven molecular-to-network reamorphization results in a fragmentation impact on the correlation length of FSDP-responsible entities (due to an increase in the FSDP width and position). A breakdown in intermediate-range ordering is accompanied by changes in extended-range ordering due to the high-angular shift and broadening of the SSDP. A breakdown in the intermediate-range order is revealed in the destruction of most distant inter-atomic correlations, which belong to remnants of some quasi-crystalline planes, whereas the longer correlations dominate in the extended-range order. The microstructure scenarios of milling-driven reamorphization originated from the As(4)Se(4) molecule, and its network derivatives are identified with an ab initio quantum-chemical cluster modeling code (CINCA)

Femtosecond filamentation in chalcogenide glasses limited by two-photon absorption

Filamentation of 800 nm femtosecond laser pulses in the conditions of strong two-photon absorption was first directly observed in As4Ge30S66 chalcogenide glass, this effect being accompanied by increase in the pulse spectrum width from 8.5 to 11 nm and its modulation indicating the pulse temporal splitting. In contrast, there was no filamentation and pulse spectrum widening in stoichiometric As2S3 glass. The nonlinear figure of merit was shown to be as high as 0.5 and only similar to 0.1 in glassy As4Ge30S66 and As2S3, respectively