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Thermal expansion of Ba silicates with tetrahedrally coordinated Si atoms in the temperature range of 25–1100 °C had been studied by high-temperature X-ray powder diffraction. The volume thermal expansion coefficients (TECs) are in the range 41–50×10 −6 °C −1 with an average value of 〈 α V 〉 = 45 × 10 − 6 ° C − 1 . In the structures with chain and layered silicate anions, thermal expansion is anisotropic: the direction of maximal TEC is parallel to the extension of the zweier chains of silicate tetrahedra, which are strained owing to the interactions with Ba 2+ . The strain is released during thermal expansion due to the increasing effective size of Ba 2+ induced by thermal vibrations. Information-theoretic analysis of the structural and topological complexities of Ba silicates indicates that their structural complexity is a function of the topological complexity of their silicate anions. The latter displays a non-linear behaviour with increasing SiO 2 content (=the increasing degree of polymerization and increasing dimensionality): it starts from simple topologies, reaches a maximum at topologies of intermediate complexity, and ends up at simple topologies again. The specificity of the interactions of Ba 2+ with the silicate anions results in higher complexity of high-temperature α -BaSi 2 O 5 compared to that of low-temperature β -BaSi 2 O 5 . This uncommon behaviour may be explained by the vibrational advantages provided by flatter and more complex silicate layers in the α -phase, which overcome negative differences in configurational entropies of the two modifications apparent in the differences of their structural Shannon information. [ABSTRACT FROM AUTHOR]