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The trigonal polymorph of strontium tetraborate, β-SrB4O7

Acta Cryst. (2010). E66, i48 (

[Framework of SrB4O7] The framework of linked BO3 triangles and BO4 tetrahedra with channels filled with the Sr2+ ions.

The trigonal phase of strontium tetraborate, β-SrB4O7, arises as the metastable crystal and possesses a greater structural correspondence with a glass in the process of its crystallization. The proportion of the four-coordinated boron ions is 50% in this phase while this proportion in a glass is 30–50% and in the stable rhombohedral phase, α-SrB4O7, is 100%. Crystals of the β-phase have noncentrosymmetric structure and show interesting nonlinear optical properties.

A.D. Vasiliev, A.V. Cherepakhin and A.I. Zaitsev