Thermal Expansion of Bismuth Triborate

Anisotropic thermal expansion and electronic transitions in the Co3BO5 ludwigite

The investigations of the crystal structure, magnetic and electronic properties of Co₃BO₅ at high temperatures were carried out using powder X-ray diffraction, magnetic susceptibility, electrical resistivity, and thermopower measurements. The orthorhombic symmetry (Sp.gr. Pbam) was observed at 300 K and no evidence of structural phase transitions was found up to 1000 K. The compound shows a strong anisotropy of the thermal expansion. A large negative thermal expansion along the a-axis is observed over a wide temperature range (T = 300-600 K) with α_a = -35 M K^-1 at T = 500 K with simultaneous expansion along the b- and c-axes with α_b = 70 M K^-1 and α_c = 110 M K^-1, respectively. The mechanisms of thermal expansion are explored by structural analysis. The activation energy of the conductivity decreases significantly above 700 K. Electronic transport was found to be a dominant conduction mechanism in the entire temperature range. The correlations between the thermal expansion, electrical resistivity, and effective magnetic moment were revealed and attributed to the evolution of the spin state of Co³⁺ ions towards the spin crossover and gradual charge-ordering transition.

Research and Development of Zincoborates: Crystal Growth, Structural Chemistry and Physicochemical Properties

Borates have been regarded as a rich source of functional materials due to their diverse structures and wide applications. Therein, zincobrates have aroused intensive interest owing to the effective structural and functional regulation effects of the strong-bonded zinc cations. In recent decades, numerous zincoborates with special crystal structures were obtained, such as Cs₃Zn₆B₉O₂₁ and AZn₂BO₃X₂ (A = Na, K, Rb, NH₄; X = Cl, Br) series with KBe₂BO₃F₂-type layered structures were designed via substituting Be with Zn atoms, providing a feasible strategy to design promising non-linear optical materials; KZnB₃O₆ and Ba₄Na₂Zn₄(B₃O₆)₂(B₁₂O₂₄) with novel edge-sharing [BO₄]^5- tetrahedra were obtained under atmospheric pressure conditions, indicating that extreme conditions such as high pressure are not essential to obtain edge-sharing [BO₄]^5--containing borates; Ba₄K₂Zn₅(B₃O₆)₃(B₉O₁₉) and Ba₂KZn₃(B₃O₆)(B₆O₁₃) comprise two kinds of isolated polyborate anionic groups in one borate structure, which is rarely found in borates. Besides, many zincoborates emerged with particular physicochemical properties; for instance, Bi₂ZnOB₂O₆ and BaZnBO₃F are promising non-linear optical (NLO) materials; Zn₄B₆O₁₃ and KZnB₃O₆ possess anomalous thermal expansion properties, etc. In this review, the synthesis, crystal structure features and properties of representative zincoborates are summarized, which could provide significant guidance for the exploration and design of new zincoborates with special structures and excellent performance.

Li4Na2CsB7O14: a new edge-sharing [BO4]5− tetrahedra containing borate with high anisotropic thermal expansion

Li₄Na₂CsB₇O₁₄, a new edge-sharing [BO₄]⁵⁻ tetrahedra containing borate with high anisotropic thermal expansion, was obtained under the atmospheric pressure conditions.

Area negative thermal expansion in a beryllium borate LiBeBO3with edge sharing tetrahedra

A very rare area negative thermal expansion phenomenon is observed in LiBeBO₃, attributed to its abnormal structural features.

X-ray diffraction study of the piezoelectric properties of BiB3O6 single crystals

We have determined all eight components of the piezoelectric tensor of a monoclinic crystal, BiB3O6, by means of synchrotron X-ray diffraction technique. The experiments have been performed on a four circle goniometer using the ω-scan method introduced by Graafsma [1] which is universal in the choice of appropriate reflections. The determined values of the piezoelectric tensor are in good agreement with those obtained earlier for BiB3O6 with the use of an optical Michelson interferometer.

Temperature-dependent X-ray and neutron diffraction study of BiB3O6

The structure of bismuth triborate has been analyzed by the combination of neutron and X-ray diffraction on powder and on single-crystalline samples. Bismuth triborate exhibits a distinct anisotropic thermal expansion with the coefficient along a being negative over the wide temperature range studied, 20 to 800 K. The remarkable crystal structure of bismuth triborate with a netlike linkage of rigid borate units [BO3] and [BO4], is found to generate the uncommon thermal expansion behavior. Our investigations gave no evidence for a structural phase transition in bismuth triborate between 3.5 and 999 K at ambient pressure.

Computational investigation of the Bi lone-pairs in monoclinic bismuth triborate BiB3O6

The Bi-O interactions and the Bi lone-pairs in monoclinic BiB3O6 are investigated with gradient-corrected hybrid B3PW density functional theory within the Gaussian-orbital-based CO-LCAO scheme. The Bi 6s and O 2p orbitals contribute to both bonding and antibonding interactions below the Fermi level. The stereochemical activity of the Bi lone-pairs was found to have a major origination from the primary interaction for the Bi 6s-O 2p antibonding orbital. The Bi 6p orbitals are not critically responsible for the non-spherical shape of the Bi lone-pairs, although they indeed participate into the secondary interaction with the Bi 6s-O 2p antibonding states. It is also suggested that O 2p components within the Bi lone-pairs are dominantly significant for the optical responses of BiB3O6 over the Bi 6s components.