On the determination of linear expansion coefficients of triclinic crystals using X-ray diffraction

The representation of all components of the tensor of linear thermal expansion by temperature derivatives of lattice parameters a, b, c, alpha , beta , and gamma has been extended to triclinic symmetry. The advantages of this approach are elucidated by taking data of alpha -CuMoO ₄ as an example. The uncertainty due to various influences including the approximation of a(T), b(T), ... by power series is discussed quantitatively. Thermal expansion coefficients of triclinic crystals seem to be particularly sensitive to the exact procedure of their evaluation.