Abstract The single crystal of CaBi2B2O7 was obtained by recrystallization in solid-state and studied by single-crystal X-ray diffraction. Its crystal structure was refined in the centrosymmetric orthorhombic space group Pnma with a = 8.5556(8) A, b = 5.1569(5) A, c = 9.6677(7) A, Z = 4. The structure is based upon parallel (0 1 0) {CaBi2B2O7}∞ layers from BO3 triangles, ψ-tetrahedral BiO3 groups, and CaO6 triangular prisms connected each to other via long and weak Bi–O bonds. This borate is representative of MBi2B2O7 family (M = Ca, Sr, Ba), where all members can be obtained from the hypothetical hexagonal aristotype. Thermal expansion is studied by high-temperature X-ray powder diffraction, its strongly anisotropic and negative along [0 0 1]: αa = 11.8(1) × 10−6 °C−1, αb = 34.2(3) × 10−6 °C−1, αc = –25.7(4) × 10−6 °C−1 at 600 °C. As a result, a/c cell parameters ratio tends to ideal √3 value, corresponding to the hexagonal aristotype.

中文翻译：

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CaBi2B2O7硼酸盐的晶体结构和强单轴负热膨胀

摘要 通过固态重结晶获得CaBi2B2O7单晶，并通过单晶X射线衍射进行研究。其晶体结构在中心对称正交空间群 Pnma 中被细化，a = 8.5556(8) A, b = 5.1569(5) A, c = 9.6677(7) A, Z = 4。该结构基于平行 (0 1 0) {CaBi2B2O7}∞ 层来自 BO3 三角形、ψ-四面体 BiO3 基团和 CaO6 三棱柱，通过长而弱的 Bi-O 键相互连接。这种硼酸盐是 MBi2B2O7 家族（M = Ca、Sr、Ba）的代表，其中所有成员都可以从假设的六边形马氏体中获得。通过高温 X 射线粉末衍射研究热膨胀，其强烈的各向异性和负沿 [0 0 1]：αa = 11.8(1) × 10−6 °C−1，αb = 34.2(3) × 10− 6 °C−1，αc = –25.7(4) × 10−6 °C−1，600 °C。因此，