Oxyde β-Ga 2O 3: Champ de force, dilatation thermique, et rigidité anisotropes

Abstract

The thermal expansion tensor of the gallium oxide β-Ga 2O 3 was determined from low temperature X-ray diffraction. At T = 250 K the principal directions of the tensor ( α 3 ⋍ α a = 2 × 10 −6 K −1, α 2 = α b = 5.9 × 10 −6 K −1, α 1 ⋍ α c = 5 × 10 −6 K −1 ) are close to the mean directions associated with the various chemical bonds of the monoclinic structure. The components α a, α b, and α c are directly linked to the thermal bond expansions. These can be estimated from values of stretching force constants available in a previous vibrational study. The structure may be described in terms of an infinite set of rigid blocks weakly bound to each other along the c direction. The Debye temperature ( Θ D ⋍ 730 K ) can be calculated using the Debye model. This value leads to an estimate of the mean force constant (1.75 mdyne/Å) close to that obtained by spectroscopic data. Through these numerical values, one can evaluate the compressibility (0.5 × 10 −11 Pa −1) and the Grüneisen constant (∼0.96). These parameters, characteristic of the compound and of its crystal structure, were obtained from structural data. In addition, previous mechanical and morphological properties are also interpreted and correlated with disorder effects.