Precise measurement of the lattice parameters of α‐Al 2 O 3 in the temperature range 4.5–250 K using the Mössbauer wavelength standard

The lattice parameters of α‐Al 2 O 3 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 λ M = 86.025474 (16) pm of the nuclear resonance radiation of 57 Fe (Shvyd'ko et al. , 2000), which has previously been applied successfully to measure the lattice parameters of α‐Al 2 O 3 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.