Precise measurement of the lattice parameters of α-Al2O3 in the temperature range 4.5-250 K using the Mössbauer wavelength standard

The lattice parameters of α‐Al2O3 have been measured in a temperature range from 4.5 to 250 K with a relative accuracy of better than 6 × 10−6. The experimental method uses Bragg backscattering and the recently proposed Mössbauer wavelength standard, i.e. the wavelength λM = 86.025474 (16) pm of the nuclear resonance radiation of 57Fe (Shvyd'ko et al., 2000), which has previously been applied successfully to measure the lattice parameters of α‐Al2O3 at temperatures between 286 and 374 K (Shvyd'ko et al., 2002). The experimental data in the range from 4.5 to 374 K are consistent with the Debye model of thermal expansion. At 4.5 K, the thermal expansion coefficient is as low as 1.2 (9) × 10−10 K−1 in the a direction.