Artículos SCI

Samples of β-SiC/Si ecoceramics with a silicon concentration of ∼21 vol % have been prepared using a series of consecutive procedures (carbonization of sapele wood biocarbon, synthesis of high-porosity biocarbon with channel-type pores, infiltration of molten silicon into empty channels of the biocarbon, formation of β-SiC, and retention of residual silicon in channels of β-SiC). The electrical resistivity ρ and thermal conductivity κ of the β-SiC/Si ecoceramic samples have been measured in the temperature range 5–300 K. The values of ρ Si chan(T) and κ Si chan(T) have been determined for silicon Sichan located in β-SiC channels of the synthesized β-SiC/Si ecoceramics. Based on the performed analysis of the obtained results, the concentration of charge carriers (holes) in Sichan has been estimated as p ∼ 1019 cm−3. The factors that can be responsible for such a high value of p have been discussed. The prospects for practical application of β-SiC/Si ecoceramics have been considered.

High resolution synchrotron powder XRD, 89Y CPMG NMR, and 139La MAS NMR spectroscopy have been applied to eventually draw the phase diagram of the La2Si2O7–Y2Si2O7 system. The diagram presents a solid solubility region of G-(La,Y)2Si2O7, which extends to the La0.9Y1.1Si2O7 composition at any temperature of this study. Compositions richer in Y show two-phase domains, with G + α at T < 1450 °C and G + δ at T > 1450 °C. The Y-rich extreme is more complex, showing two solid solution regions of δ- and γ-(La,Y)2Si2O7 polymorphs which appear with increasing Y content, respectively. It is interesting to note that the La for Y substitution mechanism in the G-(La,Y)2Si2O7 polymorph is not homogeneous, but a preferential occupation of Y for the RE2 site is observed. Finally, the 89Y and 139La isotropic chemical shift values in G-(La,Y)2Si2O7 have been described here for the first time and assigned to the different RE crystallographic sites of the unit cell.