Metal Borate Research Articles

Exploiting Deep‐Ultraviolet Nonlinear Optical Material Rb2ScB3O6F2 Originated from Congruously Oriented [B3O6] Groups

AbstractThe exploration and research for deep‐ultraviolet (UV) nonlinear optical (NLO) crystals are of great significance for all‐solid‐state lasers. This work is based on the excellent structural [B3O6] units which manipulate the excellent performances of famous commercial NLO crystal β‐BaB2O4 (β‐BBO) to explore new alternatives of deep‐UV NLO materials. A deep‐UV rare‐earth metal borate fluoride Rb2ScB3O6F2 (RSBF) is successfully designed by combining the heterovalent ions substitution strategy, and fluorination strategy. Expectedly, RSBF exhibits an extremely short cutoff edge below 175 nm (189 nm for β‐BBO), and a moderate birefringence of 0.088 at 1064 nm. The shortest phase‐matching (PM) wavelength of RSBF (λPM=182 nm) is shortened by 23 nm compared with β‐BBO (λPM=205 nm) due to the improvements in the chromatic dispersion and cutoff edge, and an experimental frequency‐doubling effect 1.4×KH2PO4 (KDP) further suggests that RSBF can output a deep‐UV harmonic laser. This work provides new sights from the original influencing factors for the rational and purposeful design of deep‐UV NLO materials.

Exploiting Deep-Ultraviolet Nonlinear OpticalMaterial Rb2ScB3O6F2 Originated from Congruously Oriented [B3O6] Groups.

The exploration and research for deep-ultraviolet (UV) nonlinear optical (NLO) crystals are of great significance for all-solid-state lasers. This work is based on the excellent structural [B3O6] units which manipulate the excellent performances of famous commercial NLO crystal β-BaB2O4 (β-BBO) to explore new alternatives of deep-UV NLO materials. A deep-UV rare-earth metal borate fluoride Rb2ScB3O6F2 (RSBF) is successfully designed by combining the heterovalent ions substitution strategy, and fluorination strategy. Expectedly, RSBF exhibits an extremely short cutoff edge below 175 nm (189 nm for β-BBO), and a moderate birefringence of 0.088 at 1064 nm. The shortest phase-matching (PM) wavelength of RSBF (λPM=182 nm) is shortened by 23 nm compared with β-BBO (λPM=205 nm) due to the improvements in the chromatic dispersion and cutoff edge, and an experimental frequency-doubling effect 1.4×KH2PO4 (KDP) further suggests that RSBF can output a deep-UV harmonic laser. This work provides new sights from the original influencing factors for the rational and purposeful design of deep-UV NLO materials.

(Ga1-xAlx)4B2O9: controlled surface acid-base properties and catalytic behavior towards the Strecker reaction.

Solid bases are valuable catalysts for industrial syntheses. However, controlling the basicity of these catalysts remains a challenge. Ga4B2O9, due to μ3-O within its structure, could behave as a special solid base catalyst exhibiting intrinsic Lewis basicity. In this work, a sol-gel method was proposed to obtain continuously adjustable acidity and basicity of the metal borate catalyst (AlxGa1-x)4B2O9. According to the results of NH3-TPD, CO2-TPD, and the systematic experimental design, Lewis basic sites originating from GaO5 groups in (AlxGa1-x)4B2O9 boost the Strecker reaction rather than the Lewis acid sites related to unsaturated Al. This work illustrates the possible application of bulk-type solid solutions with simultaneous Lewis acid and base sites for the first time. A reaction mechanism has also been proposed based on the catalytic reaction results.

Optimization of structural, optical, and shielding properties of Ni2⁺/Ni³⁺-doped heavy metal borate glasses via La³⁺ doping

This study investigates the impact of structural modifications induced by rare earth ions, specifically La3+, on the ligand field, optical properties, and radiation shielding capabilities of heavy metal glasses doped with Ni2+/Ni3+ ions. FT-IR spectra and density measurements confirmed the entry of La3+ cations as network modifiers, resulting in network compressibility resulting from increased sample density as well as increased non-bridging oxygen content resulting from conversion of BO4 to BO3 units. The structural modifications in turn effectively narrowed the band gap and increased the structural disorder as inferred from the gradual increase of the Urbach energy. In addition, the increase in electronic polarization and optical basicity with La₂O₃ additions led to higher linear and nonlinear refractive indices. The optical absorption bands confirmed that Ni2⁺/Ni³⁺ ions occupied octahedral and/or tetrahedral sites, while the Ni2+ tend to occupy more octahedral sites with increasing La₂O₃ content. The crystal field strength around Ni2⁺ ions increased with increasing La³⁺ concentration, along with a decrease in the nephelauxetic ratio, indicating the covalent bonding nature of Ni2⁺ ions with neighboring ions. In addition, several radiation shielding parameters were evaluated and compared with those of common shielding materials, and it was found that samples with higher La3+ ion concentration pave the way for the possibility of obtaining low-thickness glass materials for use as highly efficient radiation shielding materials, especially in the range of energies below 1 MeV.

High-pressure synthesis and crystal structure of the mixed-cation borate V5−x Co x Co y [B12O26−z (OH) z

Abstract A mixed transition metal borate Co5–x VxCoy[B12O26–z (OH) z ] was synthesized in a Walker-type module using the high-pressure/high-temperature approach at 12 GPa and 1,300 °C. The product crystallizes in the space group I41/acd. It is isotypic to other 3d metal cation borates of the M 5[B12O25(OH)]–M 5 M[B12O22(OH)4] solid solution series. The title compound features three different metal cation positions; one octahedral site contains a mixture of V and Co, another octahedral site is fully occupied with Co, and a cuboctahedral position that is partially occupied with Co. It is the first compound within this structure type to contain Co, increasing the range of elements that can be incorporated and thus illustrating the adaptability and structural diversity of this anionic borate network.

Influence of La3+ ions on the structural, elastic, optical, and radiation shielding properties of Cr2O3-Doped heavy metal glasses

This study investigates the effect of La³⁺ rare earth ions on the structural, elastic, optical, and radiation shielding features of heavy metal borate glass (B₂O₃-PbO) doped with Cr₂O₃. Density measurements and FT-IR spectra analysis revealed the role of La3+ ions as a network modifier, where successive additions of La2O3 content led to a gradual increase in the density and an increase in the non-bridging oxygen content resulting from the structural transformation between the BO4 and BO3 units. The significant improvement in the elastic modulus and microhardness factor moduli was confirmed by calculating the change in ultrasonic velocities through the glassy system. The structural modifications induced by La³⁺ ions narrowed the band gap and increased the Urbach energy, indicating higher disorder within the glass network. The linear refractive indices increased due to increased optical basicity and electronic polarization. Optical absorption results showed that Cr⁶⁺/Cr³⁺ ions occupy octahedral/tetrahedral sites, with the tendency for Cr³⁺ cations to occupy more octahedral sites with increasing La₂O₃ content. The produced samples showed a greenish-yellow color caused by the absorption band centered at ∼415 nm associated with the electronic transition ⁴A₂g(F)→2Eg(G). The ligand field effect highlighted the significance of La³⁺ cations in increasing the crystalline field intensity surrounding Cr³⁺ cations and reducing the nephelauxetic ratio, signifying enhanced covalent character between Cr³⁺ cations and neighboring ions. Moreover, the radiation shielding capabilities of the glassy system were analyzed and compared with standard shielding materials, confirming superior shielding performance in samples with the highest La₂O₃ content.

Simple generic self-assembly fabrication of transition metal borates on polyaminophenylboric acid modified foam nickel for highly-efficient overall water splitting

Water electrocatalysis for hydrogen production as a prospect strategy to store renewable energy and reduce carbon emissions has attracted great attention, and exploring water electrolysis catalysts has become a research hotspot for widespread industrial water electrolysis application. Very recently, transition metal borates have been demonstrated great potential for electrocatalytic hydrogen or oxygen evolution in alkaline media. However, a generic method for fabricating transition metal borates as bifunctional oxygen catalysts are still challenging. Herein, through a two-step process including poly-aminophenylboronic acid electrodeposition and subsequent electrostatic self-assembly of transitional metal ions, for the first time, to our best knowledge, a simple and generic approach to fabricate polyaminophenylborate transition metal salt modified nickel foam electrodes (PAB-M/NF, M represents transition metal element) was developed for highly efficient water splitting. As a proof of concept, the obtained PAB-Ru/NF exhibited remarkable bifunctional HER and OER catalytic activities and stability in alkaline medium. To drive the HER and OER with a current density of 10 mA cm−2 in 1 M KOH electrolyte, PAB-Ru/NF only required an overpotential of 14 mV and 301 mV, respectively. Moreover, even at a great current density of 250 mA cm−2, PAB-Ru/NF can exhibit very favorable long-term stability for over 35 h. When assembled into an electrolyzer with PAB-Ru/NF as both the anode and cathode, a current density of 10 mA cm−2 can be achieved at a very low cell voltage of 1.50 V. In addition, the other PAB-M/NF catalysts (M including but not limited to Fe, Co and Ni) prepared by the same way also show excellent bifunctional HER and OER catalytic activities and durability. This study provides a prospective and economically feasible generic approach for developing practical bifunctional catalysts for industrial water electrolysis.

Metal vacancies and self-reconstruction of high entropy metal borates to boost the oxygen evolution reaction

Exploring highly efficient oxygen evolution reaction (OER) electrocatalysts is important for industrial water electrolysis. Herein, a new high entropy material was reported, i.e., an amorphous high entropy metal borate (CrMnCoNiFe)0.2BOx was synthesized by a new simple solvothermal method. The key of this new synthesis method was to obtain (CrMnCoNiFe)0.2BOx with a high specific surface area (446 m2/g) and porous structure, being expected to promote OER reaction. (CrMnCoNiFe)0.2BOx provided a low overpotential of 236 mV at 10 mA cm−2, a reduced Tafel slope of 64 mV dec–1, and good stability. The outstanding OER performance of (CrMnCoNiFe)0.2BOx was attributed to the high entropy structure, generation of metal vacancies, and self-reconstruction during OER. The Cr vacancies generated during the OER process have been demonstrated by Cr 2P XPS and EPR experiments. Various in situ and Ex-situ analyses such as In situ Raman, XPS, and TEM were used to investigate the self-reconstruction of the (CrMnCoNiFe)0.2BOx during the OER. The resulting metal (oxy)hydroxide was believed to be the true active center for OER. The DFT calculation showed the high entropy structure can reduce the adsorption and conversion energy barriers of oxygen-containing intermediates, matching well with the catalytic performance results. This study provided a new simple strategy to construct high entropy metal borate (CrMnCoNiFe)0.2BOx and would inspire the design of high-performance OER catalysts.

Environmental influences of La3+ ions on the structural, ligand field, and optical characteristics of Mn2+/Mn3+ ions inside heavy metal borate glass

In this work, the heavy metal borate glass system (B2O3-PbO) was doped with a hybrid of transition metal and rare earth ions via a fixed ratio of MnO2 and a variable La2O3 ratio. X-ray diffraction spectra confirmed the amorphous nature of the manufactured glassy system. The effect of La2O3 ions in causing modifications to the internal structure was examined through density measurements and Fourier-transform infrared spectroscopy. According to structural studies, the density increases gradually with increasing La2O3/B2O3 concentrations, in addition to an increase in the ratio of non-bridging oxygen resulting from structural transformations between the BO4 and BO3 units. The optical absorption bands were deconvoluted and studied, where the samples acquired a light brown color resulting from the absorption band at ∼466 nm and the electronic transition 6A1 g(S) → 4A1 g(G). The detected absorption bands verified the existence of Mn2+/Mn3+ in octahedral/tetrahedral sites. However, photoluminescence spectra indicated the tendency of Mn2+ ions to occupy more octahedral coordination. The shift of the fundamental absorption edges to lower energy with La2O3 addition confirmed the successive narrowing of the optical band gap. In addition, the entry of La3+ ions improved the optical basicity and electronic polarization, raising linear/nonlinear refractive indices. The ligand field effect showed the role of La3+ ions in reducing the crystal field intensity around Mn2+ ions and increasing the nephelauxetic ratio, indicating a gradual increase in the ionic bonding nature between the Mn2+ cations and the adjacent ions.

Synthesis, Characterization and Optical Properties of Two Novel Metal Borates

AbstractTwo novel metal borates, namely, Ag7B9O16(OH)2 (1) and AgCa2B7O11(OH)4 (2) were obtained under hydrothermal conditions. Ag7B9O16(OH)2 crystallizes into the centrosymmetric space group of C2/c in the monoclinic crystal system and displays a unique three‐dimensional (3D) framework built by 1D double borate chains further connected by Ag cations. AgCa2B7O11(OH)4 also belongs to monoclinic space group C2/c and it features borate chains with B8O8 8‐membered rings along the c axis which are further coordinated via AgO3 into 2D layers. These layers are bridged via CaO8 polyhedron into the final 3D framework. Two compounds were further characterized through thermogravimetric and optical analysis and density functional theory calculation have also been carried out, addressing their electronic structures.

Expansion and adaptation of the M 5B12O25(OH) structure type to incorporate di- and trivalent transition metal cations

Abstract Five transition metal borates were synthesized in a Walker-type module under high-pressure/high-temperature conditions of 8–9 GPa and 800–1200 °C. They all exhibit the same interpenetrating, anionic borate network B12O26 16−, crystallizing in the space group I41/acd, and therefore show high similarities to the borates Ti5B12O26 and Ga5B12O25(OH). Cr5B12O25(OH) and V5B12O25(OH) are isotypic to Ga5B12O25(OH), whereas Mn5Mn0.83B12O26 and Fe5Fe0.14B12O24.3(OH)1.7 feature the partial occupation of an additional, cuboctahedral cavity in the structure. This is due to a partial reduction of the cations to the oxidation state +2, as presented with the novel compound Mn5MnB12O22(OH)4, which only features Mn2+ for charge compensation. These structures feature a twelvefold coordination of manganese and iron.

Galloborates as ultraviolet nonlinear optical crystals: advances and perspectives.

Metal borates are excellent source materials for exploring short-wavelength nonlinear optical (NLO) crystals. Galloborates show rich structural chemistry with various coordination configurations of Ga cation and B-O anionic units and are suitable candidates as ultraviolet NLO crystals. Up to now, the shortest cut-off edge of galloborates was reported to be down to 190 nm in KCs2Ga(B5O10)(OH), while the largest second harmonic generation (SHG) effect of galloborates was reported to be up to 4.6 times that of KH2PO4 (KDP) in Na5Ga[B7O12(OH)]2·2B(OH)3. Herein, we give a detailed summary of the recent progress in NLO inorganic galloborates, where these galloborates are grouped into two types in terms of their compositions: (1) alkali/alkaline earth metal galloborates and (2) alkali/alkaline earth metal galloborate halides. We discuss their structural features, band gaps, and SHG intensities. Finally, we give future perspectives in this field.

Rb3MgB5O10 and LiBaAl(BO3)2: covalent tetrahedra MO4-containing borates with deep-ultraviolet cutoff edges.

Borates are favored by materials scientists and chemists because of the significant electronegativity difference between B and O atoms and their flexible assembly modes resulting in abundant structures and excellent properties. For the design of deep-ultraviolet (DUV) optical crystals with excellent macroscopic performance, it is crucial to choose appropriate cations and anionic groups and microscopically reasonable assembly patterns. Herein, by introducing covalent tetrahedra ([MO4], M = Mg, Al), two new mixed alkali metal and alkaline earth metal borates, Rb3MgB5O10 and LiBaAl(BO3)2, were synthesized using the melt method and high-temperature solution method. They contain M-B-O two-dimensional (2D) layers (2∞[MgB5O10] and 2∞[Al(BO3)2], respectively) composed of isolated B-O groups ([B5O10]5- and [BO3]3-, respectively) and metal-centered tetrahedral connectors ([MgO4]6- and [AlO4]5-, respectively). Combining experiments and theoretical calculations shows that the two compounds have short cutoff edges (<200 nm) and moderate birefringences. Further analysis manifests that the isolated [MO4] covalent tetrahedra can optimize the arrangement of anion groups, guarantee the balanced optical properties of materials, and point out the direction for further exploration of novel borate structures.

Prediction of ultraviolet optical materials in the K2O-B2O3 system.

Ultraviolet (UV) birefringent crystals play a crucial role in various fields, such as laser technologies, optical telecommunications, and advanced scientific instrumentation. Alkali metal borates, with their diverse structures and remarkable ultraviolet optical properties, have garnered significant attention in recent years. In this study, employing the evolutionary crystal structure prediction algorithm USPEX, in conjunction with ionic substitutions and first-principles calculations, we systematically explored the pseudo-binary K2O-B2O3 system and predicted two stable structures (oP56-K3BO3 and mC44-K4B2O5) previously unreported, and twelve metastable structures in the K2O-B2O3 system. A comprehensive analysis of their structural, electronic and optical properties is conducted. The coplanar arrangement of BO3 and B3O6 groups is found to enhance optical anisotropy, thereby increasing the birefringence. In the K2O-B2O3 system, six structures with wide band gaps and high birefringence (mP28-1-K3BO3, tR72-KBO2, oP112-1-KB5O8, oP112-2-KB5O8, mC220-K5B19O31, and hR21-K3BO3) are found to be possible candidates for UV optical materials. Importantly, hR21-K3BO3, the only non-centrosymmetric structure in this system, exhibits a significant frequency doubling coefficient (about 4.6 KDP) and a moderate birefringence index (0.056@1064 nm), marking it a promising UV nonlinear optical material.

Evaluation of the Standard Entropy of Crystalline Alkali Metal Borates

A composition–property relationship has been developed that makes it possible to select the optimal values of the standard entropy of alkali metal borates, for which available experimental and reference data vary in wide ranges. This relationship allows one to estimate the standard entropy of unstudied alkali metal borates with sufficient validity. To ensure the reliability of the relationship, a critical analysis of the initial data borrowed from reference books and original experimental works has been carried out. Experimental measurements of low-temperature heat capacity were processed to verify the reliability of the standard entropy values of alkali metal borates presented in the literature.

Speciation and Phase Equilibria of Aqueous Boric Acid and Alkali Metal Borates from Ambient to Hydrothermal Conditions: A Comprehensive Thermodynamic Model

Speciation and Phase Equilibria of Aqueous Boric Acid and Alkali Metal Borates from Ambient to Hydrothermal Conditions: A Comprehensive Thermodynamic Model

Computationally-driven discovery of second harmonic generation in EuBa3(B3O6)3 through inversion symmetry breaking

Nonlinear optical (NLO) crystals with superior properties are significant for advancing laser technologies and applications. Introducing rare earth metals to borates is a promising and effective way to modify the electronic structure of a crystal to improve its optical properties in the visible and ultraviolet range. In this work, we computationally discover inversion symmetry breaking in EuBa3(B3O6)3, which was previously identified as centric, and demonstrate noncentrosymmetry via synthesizing single crystals for the first time by the floating zone method. We determine the correct space group to be P6¯. The material has a large direct bandgap of 5.56 eV and is transparent down to 250 nm. The complete anisotropic linear and nonlinear optical properties were also investigated with a d11 of ∼0.52 pm/V for optical second harmonic generation. Further, it is Type I and Type II phase matchable. This work suggests that rare earth metal borates are an excellent crystal family for exploring future deep ultraviolet (DUV) NLO crystals. It also highlights how first principles computations combined with experiments can be used to identify noncentrosymmetric materials that have been wrongly assigned to be centrosymmetric.

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.

Enhancing photocatalytic degradation of potassium butyl xanthate in mineral processing wastewater: Novel VO2+-doped LiZnBO3 nanosheets under visible light

Metal borates have attracted significant scientific attention due to their remarkable functional properties, making them versatile materials for applications in photocatalysis and energy storage. For the current investigation, three different concentration (1, 3, and 5 mol %) of vanadyl ions doped LiZnBO3 nanosheets (VO2+-doped LZB) were synthesized by an in-situ hydrothermal method. To better understand the properties of these prepared samples, a thorough characterization has been carried out, utilizing a range of structural and optical spectroscopy techniques. This study investigated the photocatalytic performance of the synthesized materials in the context of removing the mineral pollutant potassium butyl xanthate (PBX). Remarkably, at a 3 mol % concentration, the LZB-VO3 nanocomposite displayed significantly higher photocatalytic activity, achieving an impressive PBX degradation rate of 96.58 % within a short duration of 70 min. In contrast, the pure LZB material exhibited a more modest degradation efficiency of only 30.58 % when exposed to visible light. The optimized catalyst demonstrated a maximum rate constant of 0.0392 min−1, representing a remarkable enhancement of approximately 7.13 times compared to pure LZB. These findings underscore the remarkable potential of vanadyl ion doping, as it improves the absorption of the visible light spectrum and facilitates the efficient detachment of photoinduced charges, thereby significantly enhancing overall photocatalytic activity.

Ba3.75MgB7O14F2.5: A Mixed Alkaline-Earth Metal Borate Fluoride with Short Ultraviolet Cutoff Edge and Large Birefringence.

Fluorine-containing borate crystal materials are particularly attractive due to their rich structural chemistry and excellent properties for optical applications. In this work, a new compound Ba3.75MgB7O14F2.5 has been synthesized through the high-temperature solution method. In the crystal structure of Ba3.75MgB7O14F2.5, the [B7O14] basic building unit and the [MgO3F3] octahedra are interconnected to create a complex three-dimensional network. The structural feature of the less commonly observed [B7O14] units is discussed, and it has been found that such units in Ba3.75MgB7O14F2.5 are most conducive to achieving large birefringence. In addition, Ba3.75MgB7O14F2.5 exhibits good thermal stability, a short ultraviolet cutoff of 203 nm, and large birefringence (0.081@546 nm), indicating its potential as a new UV birefringent crystal.