On the determination of linear thermal expansion coefficients of tricliniccrystals using X-ray diffraction

The representation of all components of the tensor of linear thermal expans ion by temperature derivatives of lattice parameters a, b, c, alpha, beta, and gamma has been extended to triclinic symmetry. The advantages of this a pproach are elucidated by taking data of alpha-CuMoO4 as an example. The un certainty due to various influences including the approximation of a(T), b( T),... by power series is discussed quantitatively. Thermal expansion coeff icients of triclinic crystals seem to be particularly sensitive to the exac t procedure of their evaluation.