Search results for "Thermal"
showing 10 items of 3576 documents
Magnetic field dependent thermal conductance in La0.67Ca0.33MnO3
2015
Abstract Using the differential 3 ω technique we measured the low-temperature out-of-plane thermal conductance of heteroepitaxial thin film La0.67Ca0.33MnO3 (LCMO). The magnetic field dependence of the thermal conductance reached values of up to 23%. The effect was observed to be largest in the vicinity of the metal–insulator transition, since the enhancement in thermal conductance is triggered by the colossal magnetoresistance effect increasing the electronic contribution to the thermal conductance. The point of the maximal change was adjusted by post-annealing the samples in an oxygen atmosphere. Samples with a higher transition temperature and lower epitaxial strain displayed a lower mag…
Morphology and properties of poly(methyl methacrylate) (PMMA) filled with mesoporous silica (MCM-41) prepared by melt compounding
2016
This paper reports on the morphologies of poly(methyl methacrylate) (PMMA)/mesoporous silica (MCM-41) composites prepared by melt compounding with various MCM-41 contents in the range of 0.1–5 wt%, the interactions between the polymer and filler in these composites, and their thermomechanical, mechanical and thermal degradation properties. The composites formed transparent films at low filler loadings (\0.5 wt%) because of well-dispersed, unagglomerated particles. The presence of polymer did not alter the pore dimensions in the MCM-41 structure and it maintained its hexagonal structure, even though the polymer chains partially penetrated the pores during composite preparation. The PMMA inte…
Photoinduced charge transfer from Carbon Dots to Graphene in solid composite
2019
Abstract The emission in solid phase of Carbon Dots (CDs) deposited by drop-casting technique is investigated by means of micro-photoluminescence. Graphene and SiO2 are used as substrates, and the influence of their different nature – conductive or insulating – on the emission of CDs is highlighed. In particular, a systematic loss of efficiency in the emission of CDs on graphene is found, suggesting a CD-graphene interaction possibly due to a photoinduced electron transfer between the surface states of CDs and the conduction band of graphene. Finally, thanks to the negligible influence on CDs emission, SiO2 substrate is used as support to perform thermal processing of CDs in solid phase, sh…
Interaction of Lamb modes with two-level systems in amorphous nanoscopic membranes
2007
Using a generalized model of interaction between a two-level system (TLS) and an arbitrary deformation of the material, we calculate the interaction of Lamb modes with TLSs in amorphous nanoscopic membranes. We compare the mean free paths of the Lamb modes with different symmetries and calculate the heat conductivity $\kappa$. In the limit of an infinitely wide membrane, the heat conductivity is divergent. Nevertheless, the finite size of the membrane imposes a lower cut-off for the phonons frequencies, which leads to the temperature dependence $\kappa\propto T(a+b\ln T)$. This temperature dependence is a hallmark of the TLS-limited heat conductance at low temperature.
Structural properties ofSi1−xGexalloys: A Monte Carlo simulation with the Stillinger-Weber potential
1995
The structural properties of binary silicon-germanium alloys are investigated by means of large-scale constant-pressure Monte Carlo simulations of the Stillinger-Weber model. At low temperatures, the binary-mixture phase separates into Si-rich and Ge-rich phases. The two-phase coexistence region is terminated by a critical point that belongs to the mean-field universality class. We also studied the structural properties of pure Si and Ge as well as the binary mixture. In particular, we found that the linear thermal expansions for both Si and Ge are in agreement with experiments, and that V\'egard's law is valid at temperatures above the critical point. Finally, we compare the bond-length an…
Thermal irreversibility in optically labeled low-temperature glasses.
1989
We present an investigation of irreversible features of thermal broadening of persistent spectral holes. The investigation is based on temperature-cycling hole-burning experiments performed with a variety of organic glasses doped with rather different probe molecules. The results show a rich temperature dependence. They can, however, be interpreted in terms of the well-known spectral diffusion models, in which we introduced a freezing condition to account for thermal irreversiblity. There is a tunneling regime for low temperatures and an activated regime for high temperatures. In the tunneling regime the broadening is linear in T; in the activated regime it increases with ${T}^{3/2}$ and lo…
2021
Controlling thermal transport at the nanoscale is vital for many applications. Previously, it has been shown that this control can be achieved with periodically nanostructured two-dimensional phononic crystals for the case of suspended devices. Here, we show that thermal conductance can also be controlled with three-dimensional phononic crystals, allowing the engineering of the thermal contact of more varied devices without the need for suspension in the future. We show the experimental results obtained at sub-Kelvin temperatures for two different period three-dimensional crystals and for a bulk control structure. The results show that the conductance can be enhanced with the phononic cryst…
Influence of Structure Ordering, Defects and External Conditions on Properties of Ferroelectric Perovskites
2000
Results of comprehensive studies of the (A’A“)(B’B”)O3-ferroelectric perovskites are reported. Examined compositions include Pb1-xLax(Zr0.65Ti0.35)1-x/4O3(PLZT), PbSc0.5Nb0.5O3(PSN), PbSc0.5Ta0.5O3(PST), and PMNT, PSNT and PLuNT pseudo-binary systems exhibiting pronounced dielectric, electrooptical, and electromechanical properties. Degree of ordering in the materials has been varied by chemical composition (modification, isomorphic ion substitution), by variation of technology (hot-pressing, specific thermal treatment, thin films), and by irradiation of different kind and intensity (γ-rays, electrons, neutrons).