Structural Approach to the Problem of Oxygen Content in Alpha Silicon Nitride

Abstract

The crystal structure ofa-Si3N4 was reinvestigated by an X-ray method using a single-crystal specimen prepared by chemical vapor deposition. The oxygen content of the specimen (0.05?0.03%) was determined by 14 MeV neutron activation analysis. The a form crystallizes in the space group P31c with uniteell dimensions a=7.818?0.003 di and c=5.591~0.004 A. The structure was refined by the full-matrix least-squares method using 1143 observed structure factors. The Si-N distances determind ranged from 1.715 to 1.759 di, and the fmal value of R was 0.041. Structural evidences indicated that the a form is essentially pure Si,N,.

Electronic structure of the alkaline-earth silicon nitrides M2Si5N8(M = Ca and Sr) obtained from first-principles calculations and optical reflectance spectra

“…Si 3 N 4 has two modifications (α and β), with the β-form more stable at high temperature [16,25]. Xu and Ching performed band-structure calculations for α-Si 3 N 4 and β-Si 3 N 4 using the selfconsistent orthogonalized linear combination of atomic orbitals (OLCAO) method [26].…”

Quantitative phase analysis of α- and β-silicon nitrides. I. Estimation of errors

“…The unit-cell parameters of the phase reported by Kato et al (1975) are larger than those of Imai et al (1998), by 0.5% in volume, and they induced shifts of the peak positions by À0.18 on average, while the shift was +0.04 for the phase. The resultant shift of weight fraction [case (2)] was small but in the opposite direction to that in cases (1) and (3), although the magnitudes and signs of ÁR jk (2) are similar to those of ÁR jk (1) and ÁR jk (3).…”

“…Means of unit-cell volumes found in the literature (Kato et al, 1975;Gru È n, 1979;Imai et al, 1998) are 292.6 (4) and 145.5 (4) A Ê 3 for the -and -phase samples, respectively (the numbers in parenthesis are the standard uncertainties of the means). The deviation of V 1 /V 2 from 2 is 0.5% and gives ÁD 9 0.005.…”

“…The other three sets, which are given in the form of differences (ÁR jk ) from the values of Gazzara & Messier (1977), were calculated by using equation (2) in the following three cases. In case (1), atomic parameters of -Si 3 N 4 reported by Kato et al (1975), those of -Si 3 N 4 reported by Gru È n (1979), and unit-cell parameters reported by Imai et al (1998) were used. In case (2), the unit-cell parameters (Imai et al, 1998) of both phases in case (1) were replaced with those reported by Kato et al (1975) and Gru È n (1979).…”

“…In case (1), atomic parameters of -Si 3 N 4 reported by Kato et al (1975), those of -Si 3 N 4 reported by Gru È n (1979), and unit-cell parameters reported by Imai et al (1998) were used. In case (2), the unit-cell parameters (Imai et al, 1998) of both phases in case (1) were replaced with those reported by Kato et al (1975) and Gru È n (1979). In case (3), the correction term for polarization from the graphite monochromator (cos 2 2 M ) in equation (2) was omitted.…”