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An x-ray diffraction analysis of the compound EuBa2Cu3O7−δ is carried out in the temperature range 20–300K. At all temperatures of measurement the structure is described in the orthorhombic system. Nonmonotonic growth of the crystal lattice parameter c with decreasing temperature is observed in the interval 150–20K, and substantial features of the temperature dependence of the coefficient of linear thermal expansion appear below the Debye temperature. The results of the experiment are in complete agreement with the conclusions of a microscopic treatment of the vibrations of the atoms of the BaO and europium layers and also the Cu–O chains.

Variation of crystal‐lattice parameters with temperature was studied by means of X‐ray diffraction technique on the perovskite‐like structures with Ba‐ substitution for light rare earth. Anisotropic negative thermal expansion was observed and explained within the “membrane effect” model proving its lattice origin.