RbMT3 (BO3 )2 O3 (M=Ba, Sr; T=Al, Ga): New Double-Layered Oxyborates Constructed from [BO3 ] Triangles and [TO4 ] Tetrahedra

KNa2Lu(BO3)2: A Rare-Earth Borate Crystal Characterized by an Enhanced Birefringence and Wide Ultraviolet Transparency Range

Borate materials are of significant interest due to their versatile structural configuration and competitive ultraviolet (UV) transparency range. In this study, we present a novel rare-earth borate crystal, KNa2Lu(BO3)2, synthesized for the first time through a facile spontaneous crystallization method. It adopts the centrosymmetric space group Pnma (no. 62) and yields a unique three-dimensional (3D) structural network formed by isolated [BO3] plane triangles and distorted [LuO7] polyhedra. This compound displays excellent thermal stability up to ∼990 °C, demonstrating a favorable congruent melting nature. Moreover, KNa2Lu(BO3)2 achieves a notably short UV absorption cutoff at approximately 204 nm, yielding a large band gap of 5.58 eV. Remarkably, it showcases an enlarged birefringence of 0.044 at 1064 nm, implying its potential as a birefringent material. Moreover, density functional theory calculations demonstrate that the optical characteristics are predominantly influenced by fundamental building blocks [BO3] triangles and distorted [LuO7] polyhedra. Our findings demonstrate the potential of KNa2Lu(BO3)2 in the development of a birefringent candidate and enrich the structural chemistry of rare-earth-based borates.

Tailored Synthesis of Two Metal Borates KSrM3B2O9 (M = Al and Ga) Exhibiting Wide Ultraviolet Transparency

Borate materials continue to command considerable attention due to their remarkable capacity for applications in deep ultraviolet (UV) wavelengths. Herein, two new metal borates KSrM3B2O9 (M = Al and Ga) were extracted via the application of flux techniques. These two crystals adopt a centrosymmetric space group P21/c (no. 14), showcasing a layered structural configuration composed of isolated [BO3] plane triangles and [AlO4]/[GaO4] tetrahedra. Thermal analysis revealed that KSrM3B2O9 (M = Al and Ga) exhibits an incongruent nature and possesses good thermal stability up to 1083 and 983 °C, respectively. Notably, these compounds display a short UV-transmission cutoff edge, approximately around 194 and 200 nm, accompanied by band gaps of 5.47 and 4.83 eV, respectively. Furthermore, KSrM3B2O9 (M = Al and Ga) demonstrates a moderate optical birefringence of 0.026 and 0.025, respectively. Additionally, first-principles calculations were employed to shed light on the intricate interplay between the structure and properties of these compounds.

Structural Motif Cosubstitution Strategy for Designing Fluoroaluminoborate with the Sr2Be2B2O7-Type Double-Layered Structure

The cosubstitution strategy often was applied to design borate optical crystal materials. Revealingly, a fluoroaluminoborate Sr₂Al_2.18B_5.82O₁₃F₂ with Sr₂Be₂B₂O₇ (SBBO) double-layered like configuration has been rationally designed and successfully synthesized based on structural motif cosubstitution strategy via the high-temperature solution method. In Sr₂Al_2.18B_5.82O₁₃F₂, a structural motif, the [Al₂B₆O₁₄F₄] unit, with edge-sharing [AlO₄F₂] octahedra was filled in interlamination of double-layer structure. The research indicates that Sr₂Al_2.18B_5.82O₁₃F₂ features a short ultraviolet cutoff edge (<200 nm) and moderate birefringence (∼0.058 @ 1064 nm). As the first reported linker in the interlamination of double-layer structures, the [Al₂B₆O₁₄F₄] unit enlightens the synthesis and discovery of new layered structures in borates.

From β-Na2 B6 O10 to Na3 AlB8 O15 and Na3 Al2 B7 O15 : Structural Tuning of Anionic-Group Architectures by Substitution of [BO4 ] by [AlO4 ] Covalent Tetrahedra

Two new sodium aluminum borates, Na₃ AlB₈ O₁₅ and Na₃ Al₂ B₇ O₁₅ , have been successfully synthesized by the high-temperature solution method. They crystallize in the different space groups, P2₁ /c and P2/c, respectively. The B-O configurations of β-Na₂ B₆ O₁₀ , Na₃ AlB₈ O₁₅ and Na₃ Al₂ B₇ O₁₅ are compared to feature complicated different dimensional open-framework structures caused by the substitution of [BO₄ ] by [AlO₄ ] covalent tetrahedra. Moreover, the experimental results indicate that Na₃ AlB₈ O₁₅ and Na₃ Al₂ B₇ O₁₅ have short ultraviolet (UV) cutoff edges (<187 nm). The first-principles calculations show that Na₃ AlB₈ O₁₅ and Na₃ Al₂ B₇ O₁₅ have moderate birefringence (0.075 and 0.041@1064 nm, respectively).

M(B(SeO3)3)H2O (M = Al, Ga): the first boroselenites with a unique sandwich like double-layer structure

Exploration of new types of borates is important because of their promising applications in diverse fields. Two new boroselenites, namely, M(B(SeO₃)₃)H₂O (M = Al, Ga), which represent the first IIIA metal boroselenite, were synthesized by hydrothermal reactions. M(B(SeO₃)₃)H₂O (M = Al, Ga) possesses a unique sandwich like double-layer structure formed by two 2D [MSe₂O₈]^5- layers interconnected by 1D [BSeO₅]^3- chains. More interestingly, both compounds display large band gaps (4.86/4.79 eV) and moderate birefringences (Δn = 0.063/0.064 at 1064 nm) based on density functional theory (DFT) calculations.

Identical in Formula but Not Isotypic in Configuration: Discovery of a New Highly Polymerized [B12O24] Cluster in Cs3AlB6O12

The discovery of new borates with unique structures has always been a growing part of solid-state chemistry, especially for polyborates. Herein, a new aluminoborate, Cs₃AlB₆O₁₂, has been discovered by a high-temperature solution in a vacuum system. The highly polymerized [B₁₂O₂₄] cluster, unlike the annular configuration in previously reported polyborates, is found in Cs₃AlB₆O₁₂ for the first time. The different linkage reflected by the local symmetry in cluster makes these borates not isotypic, although the formula of [B₁₂O₂₄] is identical. Experimental measurement performed on Cs₃AlB₆O₁₂ powder reveals the deep-ultraviolet transparent spectral feature.