X-ray diffraction studies of thermal properties of the core and surface shell of isolated and sintered SiC nanocrystals (original) (raw)

The effect of the presence of surface strains on the apparent lattice parameters (alp) obtained experimentally for nanocrystalline SiC is discussed. The alp values were determined for two kinds of powders with an average crystallite size of 11 nm and related sintered samples. The measurements were done in a wide range of the diffractions vector up to Q = 12 Å −1 , allowing for evaluation of the internal pressure in the grains. Based on in situ high-temperature measurements, the thermal expansion coefficient and overall temperature factor B T were evaluated. It is shown that while the thermal expansion coefficient changes very little upon sintering, there is a large difference in the amplitude of the atomic oscillations between powders and sintered SiC reflected in a difference between respective Debye temperatures. It is concluded that the overall thermal properties of nanocrystals are determined by two components: thermal properties of the crystallite surface and its interior. The atoms at the surface vibrate much stronger than those in the bulk, and their behavior is strongly affected by the crystallite's environment.