Europium-activated phosphor Ba3Lu2B6O15: Influence of isomorphic substitution on photoluminescence properties

This work demonstrates the luminescent properties of Ba₃Lu₂B₆O₁₅ phosphors doped with Eu³⁺ ions for the first time. The Ba₃(Lu_1–xEu_x)₂B₆O₁₅ (x = 0.01–0.375) phosphors have been prepared using a multi-step high-temperature solid-state synthesis. X-ray diffraction measurements verify the successful isomorphic substitution of the Lu³⁺ sites by the Eu³⁺ ions. The luminescence properties and its dependence on the crystal structure of Ba₃(Lu_1–xEu_x)₂B₆O₁₅ have been reported in this work. There are two nonequivalent sites in this crystal structures occupied by lutetium, both of them can be consistently substituted by the Eu³⁺ ions. The highest emission intensity with quantum yield of 17% was demonstrated by Ba₃(Lu_0.82Eu_0.18)₂B₆O₁₅ powder. Increase of Eu³⁺ doping concentration leads to gradual change of chromaticity from violet to red. It was expected that Ba₃(Lu_1–xEu_x)₂B₆O₁₅ phosphors can be used as a phosphor with predicted chromaticity under LED excitation.     

Sintering behavior and microwave dielectric characteristics of BaO–Sm2O3–4TiO2 ceramics with B2O3 and BaB2O4 addition

We studied the low temperature sintering and the reaction in BaO–Sm₂O₃–4TiO₂ ceramics with boron-based additives for the application to microwave dielectric devices. The amount of the boride glasses of B₂O₃ and BaB₂O₄ was varied from 1 to 10 wt.% and the green compacts were sintered in the temperature range of 900–1200 °C for 2 h. When B₂O₃ was added, second phases of Sm₂Ti₂O₇, BaTi(BO₃)₂, Ba₂Ti₉O₂₀, and TiO₂ were formed, while BaB₂O₄ addition resulted in the formation of BaSm₂Ti₄O₁₂ single phase without second phases. On the basis of these results, it is regarded that the B₂O₃ is a reactive glass and the BaB₂O₄ is a non-reactive glass. The second-phase development, sintering behavior and microwave dielectric characteristics of BaO–Sm₂O₃–4TiO₂ ceramics were examined.     

Subsolidus Phase Relations of the BaO–Y2O3–MnO2 System in Air

The subsolidus phase relations of the BaO–Y₂O₃–MnO₂ system have been investigated in air. There are eight binary compounds, a new ternary compound and 11 three‐phase regions in this system. The ternary compound with the BaO:YO_1.5:MnO₂ molar ratio of 8:2:5 was indexed by a rhombohedral lattice with a = 5.7929 (6) and c = 28.586 (4) Å. The synthesized compounds were determined to be stoichiometric except for the Ba_1?xY_xMnO₃ phase (x ≤ 0.01).     

Effect of magnesium source on the fabrication of kotoite Mg3B2O6 ceramic

The effect of magnesium source on the fabrication of kotoite, Mg₃B₂O₆, ceramic has been investigated by high temperature solid‐state reaction route based on the calcination of different magnesium sources, containing magnesium oxide, magnesium carbonate, magnesium sulfate, and magnesium nitrate with boric acid. The X‐ray powder diffraction results showed that single‐phase kotoite, Mg₃B₂O₆, was synthesized using MgNO₃.6H₂O and 5 wt.% excess of H₃BO₃ powders as starting materials at 900°C for 48 hours. Mg₃B₂O₆ obtained, is well crystallized, in orhorhombic crystal structure with lattice parameters of a = 5.399(9), b = 8.424(6), and c = 4.506(5) Å. Jana2006 refinement of this product shows excellent fit of the experimental data with software data, GOF= 1.33. The crystallite size of the product was calculated as 40.50 nm using Debye‐Scherrer's equation. The existence of BO₃ triangles were detected by FTIR measurements of Mg₃B₂O₆. The thermal properties were studied in the temperature range of 20°C to 1400°C by TG/DTA. The results showed that thermal stability of Mg₃B₂O₆ is detected about 1380°C. Scanning electron microscopy was employed for observation of microstructure. The microstucture of obtained ceramic samples strongly depended on the magnesium source on the fabrication of Mg₃B₂O₆ ceramic.     

Local Structure Evolution in Ba‐Substituted Pb(Fe1/2Nb1/2)O3 Ceramics

Evolution of crystal structure in Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ ceramics has been investigated by X‐ray diffraction and Raman spectra analysis together with the dielectric characterization. The crystal structure for all compositions is cubic and the cell volume indicates a sudden change at x = 0.075. Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ ceramics with x > 0.075 are paraelectric, whereas those for x < 0.075 are ferroelectric at room temperature. The evolution of phonon modes indicates that the ferroelectricity of Pb_1‐xBa_x(Fe_1/2Nb_1/2)O₃ solid solution ceramics is caused by the off‐center Nb⁵⁺ in BO₆ octahedron. The ferroelectric‐related distortion is still observed in paraelectric solid solutions with x > 0.075.     

Synthesis,crystal structure,photoluminescence of Ba3Y2(BO3)4:Er3+ and thermal expansion of Ba3Y2(BO3)4

The Ba₃Y_2–xEr_x(BO₃)₄ (х = 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) phosphors were obtained by crystallization from a melt. The Ba₃Y₂(BO₃)₄ crystal structure was refined from single crystal X-ray diffraction data to R = 0.037. Its anisotropic atomic displacement parameters for all atoms were refined for the first time. The borate crystallizes in the orthorhombic crystal system, space group Pnma with unit cell parameters a = 7.673(1), b = 16.44(1), c = 8.977(2) Å, V = 1132.3(3) ų, Z = 4. These phosphors are isotypical to those of the A₃M₂(BO₃)₄ (A = Ca, Sr, Ba, M = Ln, Y, Bi) family. The crystal structure contains the isolated BO₃ triangles, two general and a special one independent crystallographic sites for large cations, which are disordered over sites. Thermal behavior of Ba₃Y₂(BO₃)₄ was investigated by high-temperature X-ray powder diffraction and thermal expansion coefficients are calculated in a wide temperature range. An inflections of temperature dependencies of the unit cell parameters is observed in a range 600–740 °C. Luminescence spectra, excitation and kinetic curves of the Ba₃Y₂(BO₃)₄:Er³⁺ series are reported. A maximum luminescence intensity is observed for the x = 0.1 sample. According to vibrational spectroscopy data no structural changes upon activation of the Ba₃Y₂(BO₃)₄ matrix with the Er ions are observed.     

Design and preparation of BaO–Al2O3–SiO2–B2O3/Quartz LTCC composites with tailored coefficient of thermal expansion

In this work, by focusing on widespread problem of thermal mismatch caused by different coefficients of thermal expansion (CTE) in electronic packaging materials, low-temperature co-fired ceramic (LTCC) materials with tunable CTE values were designed. By substituting Ba²⁺ with Sr²⁺ and replacing quartz with alumina and zirconia, respectively, BaO–Al₂O₃–SiO₂–B₂O₃/quartz LTCC composites with CTE of 7.05–9.52 × 10^?6/°C were developed. Results show that major crystalline phases of LTCC composite materials are quartz and hexacelsian. By replacing quartz with alumina or zirconia, sintering behavior and subsequently thermal expansion and dielectric properties were modulated. On the other hand, substituting Ba²⁺ with Sr²⁺ can be beneficial to the densification of composite materials. The introduction of Sr²⁺ triggered mixed alkali effect and hindered the crystallization of hexacelsian phase, which can further improve mechanical properties. Finally, sandwich structure module of BaO–Al₂O₃–SiO₂–B₂O₃/quartz with gradient CTE values was obtained, which showed potential for electronic packaging with sustained thermal compatibility under cyclic temperatures.     

Optical properties of Eu3+/Pr3+ doped Zn4O(BO2)6 synthesized by solid-state reaction

Zn₄O(BO₂)₆ based on the [B₂₄O₄₈] sodalite-cage structure fixed by the inside [Zn₄O₁₃] clusters is expected to be a new class of solid-state lighting material with perfect thermal and mechanical stability. Herein, in the current work, we have respectively introduced non-equivalent rare-earth cations Eu³⁺ and Pr³⁺ into Zn₄O(BO₂)₆ host to design white and green emission materials by a novel solid-phase sintering method at lower temperatures. Zn₂B₆O₁₁ replacing B₂O₃ or H₃BO₃ as raw materials can effectively avoid the impure products caused by the uncontrollable volatilization of B₂O₃ or H₃BO_3. The newly designed light-emitting materials of Zn_4(1-x)O(BO₂)₆: xRe³⁺ (ReEu or Pr), including Zn₄O(BO₂)₆ host, have good absorption capacity in the ultraviolet region. Under ultraviolet irradiation, Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ emit the blue, white and green lights, respectively. In addition, all these materials can effectively degrade methylene blue, in which Zn_4(1-x)O(BO₂)₆: xPr³⁺ has the highest efficiency. The luminescence and degradation mechanisms of Zn₄O(BO₂)₆, Zn_4(1-x)O(BO₂)₆: xEu³⁺and Zn_4(1-x)O(BO₂)₆: xPr³⁺ have been adequately explained by their electronic structures based on the first principle calculations. The current study confirms that the doping of Eu³⁺/Pr³⁺ in Zn₄O(BO₂)₆ can broaden its applications as photoluminescent and photocatalytic materials.     

The evolution of the mold flux melt structure during the process of fluorine replacement by B2O3

This study presented the melt structure evolution of mold flux during the substitution of fluorine by B₂O₃, and a computational model for the degree of polymerization (DOP) for borosilicate structure was developed. The results showed that the reduction of fluorine content would promote the replacement of F in [SiF₆]-octahedral unit by the dissociative free oxygen ions (O²⁻), and release F⁻ ions into the melt to compensate the reduction of F⁻ ions. With the 2 mass% addition of B₂O₃, the original Si–O–Si bond would be disrupted, and connect with [BO₃]-trihedral to form boroxol ring structure containing [BO₂O⁻]-trihedral and [BO₃]-trihedral structural units. Then, the Si–O–B bond that [BO₃]-trihedral links [SiO₄]-tetrahedral in boroxol ring was destroyed with the further addition of B₂O₃, and then the [BO₃]-trihedral could link with the dissociative Q¹(Si) and Q⁰(Si) structural units to transform into [BO₄]-tetrahedral and form a borosilicate long chain. Finally, with 6 mass% addition of B₂O₃, the borosilicate chain would combine with simple borate and borosilicate structures, and a complex borosilicate structure containing boroxol ring with certain symmetry was formed ultimately. Besides, the calculated result of DOP suggested that the DOP of the melt structure improved during the process of fluorine replacement by B₂O₃.     

Optical Investigation of Ce3+‐Activated Borogermanate Glass Induced by Substitution of BaF2 for BaO

Transparent and colorless CeO₂‐activated borogermanate glasses, with the nominal molar composition of 25B₂O₃–40GeO₂–14Gd₂O₃–1CeO₂–(20?x) BaO–xBaF₂ (x = 0, 2.5, 5, 10, 15 and 20), were synthesized by a melt‐quenching method in air. Their optical investigation on the transmittance, photoluminescence (excitation and emission spectra), the luminescence decay curves, as well as the temperature‐dependent Ce³⁺ emission are studied systematically with the gradual substitution of BaF₂ for BaO. The room‐temperature photoluminescence results reveal that the emission intensity can be improved by about 2.5 times with the full substitution of BaF₂ for BaO. The blue shift of the cut‐off edge, excitation and emission spectra of Ce³⁺‐activated borogermanate glass, and the emission intensity of Ce³⁺ ions as a function of temperature range in 80–500 K are also discussed.     

Effect of properties and crystallization behavior of BaO–ZnO–B2O3–SiO2 glass on the electrical conductivity of Cu paste

The extensive application of multilayer ceramic capacitors provides an attractive development for terminal electrode pastes. However, the growing requirement for advanced glass materials used in terminal electrode pastes is substantiated. Therefore, to advance the development of electrode pastes, better development and deeper exploration of glass powder are required. Here, a series of BaO–ZnO–B₂O₃–SiO₂ (BZBS) glasses were prepared by melt-quenching technique, which are used to investigate the effect of the introduction of BaO on structure and properties of the ZnO–B₂O₃–SiO₂ (ZBS) glass. With the introduction of BaO, the relative amount of [BO₄] was much less, which made the glass network structure loosen, decreased the glass transition temperature (T_g) and increased the coefficient of thermal expansion of the glass. The decreasing contact angle was observed on the surface of a barium titanate (BaTiO₃) substrate. When the BaO content was around 3–7 mol%, the stability of ZBS glass frit could be strengthened by inhibiting the precipitation of Zn₂SiO₄ crystal. In addition, to further characterize the effect of glass on terminal electrode paste, BZBS glass powder was adopted to prepare copper electrode paste, which was printed on the BaTiO₃ substrate and subsequently fired at 800°C for 10 min. With the related copper paste containing ZBS glass doped with 7 mol% BaO, the optimum value of acid resistance and sheet resistance (1.99 mΩ) were exhibited, at which the coated copper paste formed a dense conducting layer.     

Influence of B2O3 on viscosity and structure of the CaO–Al2O3-waste electrolyte (WE) based melt

The fluorides contained waste electrolyte (WE) from the electrolytic aluminum industry can be used as a substitution of fluorite (CaF₂) in the newly designed mold flux. In this study, the influence of B₂O₃ on viscosity and structure of CaO–Al₂O₃-WE based melt was investigated. Results show that the viscosity of mold flux melt decreases with both increasing temperature and B₂O₃ content. The apparent activation energy (E_a) also reduces from 78.96 ± 1.75 to 55.26 ± 2.79 kJ/mol with the addition of B₂O₃ from 0 to 7 wt%. The analyses of fourier transform infrared (FTIR) and Raman spectroscopies suggest that the lower symmetry of the original aluminate and silicate structure due to the insertion of [BO₄]-tetrahedral and [BO₃]-triangular, and the formation of more non-bridging oxygen (O⁻) and 2D structural units in the network with the addition of B₂O₃, deceases the viscosity and E_a of the CaO–Al₂O₃-WE Based Melt.     

Fabrication of Sr0.5Ba0.5Nb2O6 Nanocrystallite‐Precipitated Transparent Phosphate Glass‐Ceramics

Transparent (Sr_0.5Ba_0.5)Nb₂O₆ (SBN50) nanocrystallite‐precipitated phosphate glass‐ceramics were prepared by a conventional glass‐ceramic process. x(SrO–BaO–2Nb₂O₅) ? (100–4x)P₂O₅ (xSBNP) glasses with a refractive index of 1.9–2.0 exhibited high water resistance owing to the presence of Q⁰ and Q¹ phosphate units. Both bulk and surface crystallization of the SBN50 phase were observed in 20SBNP and 21SBNP glass‐ceramics. Although the nominal content of SBN50 crystals in the 21SBNP glass was larger than that in the 20SBNP glass, the latter exhibited better crystallinity of SBN50 and a higher number density of precipitated SBN nanocrystallites. By tuning the two‐step heat‐treatment and the chemical composition, transparent SBN50‐precipitated glass‐ceramics were successfully obtained. Given that no remarkable increase of the relative dielectric constants was observed after crystallization of the SBN50 nanocrystallites, it is postulated that the relative dielectric constant of the bulk is mainly governed by the amorphous phosphate region, and that the contribution of precipitation of the SBN50 nanocrystallites to the dielectric constant is not very significant in this system.     

Electrical Conductivity Improvement of Nd2Ce2O7 Ceramic Co‐doped with Gd2O3 and ZrO2

(Nd_1–xGd_x)₂(Ce_1–xZr_x)₂O₇ (0 ≤ x ≤ 0.5) ceramic powders synthesised by the chemical‐coprecipitation and calcination method were pressureless‐sintered at 1,973 K for 10 h in air. The structure and electrical conductivity of (Nd_1–xGd_x)₂(Ce_1–xZr_x)₂O₇ ceramics were investigated by the X‐ray diffraction and impedance spectroscopy measurements. (Nd_1–xGd_x)₂(Ce_1–xZr_x)₂O₇ (0 ≤ x ≤ 0.5) ceramics exhibit a single phase of defect fluorite‐type structure. The electrical conductivity of (Nd_1–xGd_x)₂(Ce_1–xZr_x)₂O₇ ceramics increases with temperature in the range 623–1,173 K following an Arrhenius law. At identical temperature levels, the measured electrical conductivity of (Nd_1–xGd_x)₂(Ce_1–xZr_x)₂O₇ ceramics varies with doping different Gd₂O₃ and ZrO₂ contents and exhibits a maximum at x = 0.1.     

Low-loss and temperature stable (1-x)Ba3P2O8-xMg2B2O5 composite ceramics with low sintering temperature

In this study, the Ba₃P₂O₈ and Mg₂B₂O₅ were fabricated by the solid-state reaction method separately, and the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ (x = 0.2–0.4) low-temperature co-fired ceramic (LTCC) materials were obtained in the sintering temperature range of 880–960 °C. The phase compositions, microstructures, elemental compositions, and microwave dielectric properties of the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and TE_01δ mode dielectric resonator method, respectively. The results revealed that the Mg₂B₂O₅ phase and Ba₃P₂O₈ phase could coexist well in the (1-x)Ba₃P₂O₈-xMg₂B₂O₅ composite ceramics without formation of any new phases. The abnormal grain growth of Ba₃P₂O₈ grains was inhibited by the addition of Mg₂B₂O₅. In addition, through composition of Ba₃P₂O₈ and Mg₂B₂O₅, the temperature coefficient of resonant frequency (τ_f) and quality factor (Q×f) were effectively optimized, and the sintering temperature was reduced to 880–960 °C. The optimal performance of 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic was achieved at a sintering temperature of 920 °C, τ_{f =} ?1.9 ppm/°C, Q×f = 61,250 GHz, and a low permittivity ε_r = 10.7. The chemical compatibility test demonstrated that the composite ceramic could coexist well with silver, which indicated that the 0.8Ba₃P₂O₈-0.2Mg₂B₂O₅ composite ceramic is a candidate LTCC material with wide application prospects.     

Effect of temperature and stoichiometry on the long-range 1:2 cation order in BaZn1/3Ta2/3O3

We report on the compositional stability range, the degree of atomic order and Raman and optical spectra of the off-stoichiometric BaZn_1/3Ta_2/3O₃ (BZT) within the BaO–ZnO–Ta₂O₅ ternary diagram. Almost all off-stoichiometric BZT compositions equilibrated at 1200?°C show significant degree of the long-range 1:2 cation order ranging from 60% to 80%. Ceramics equilibrated at 1550?°C and annealed at 1450?°C show strong effect of composition on the 1:2 order. The regions where an 1:2 atomic order is robust to the deviation from stoichiometry include the off-stoichiometric compositions along the BZT–Ba₄Ta₂O₉, BZT–Ba₃Ta₂O₈, BZT–BaTa₂O₆, BZT–Ta₂O₅, BZT–ZnTa₂O₆ and BZT–Zn₄Ta₂O₉ (pseudo) tie lines. At the same time ceramics formulated along the BZT–BaO, BZT–ZnO, BZT–BaZnO₂, BZT–Ba₂ZnO₃ tie lines and BZT–‘Ba₃ZnO₄’ pseudo tie line show complete disorder. There is a very close correlation between the degree of the 1:2 order on one hand and the unit cell volume and lattice distortion on the other hand. The ordered BZT show contraction of the unit cell whereas disordered ceramics show expansion of the unit cell in the off-stoichiometric region. The pronounced signatures of the order-disorder phase transition in the Raman and optical spectra are discussed.     

Correlation between crystal structure and dielectric response for orthorhombic tungsten bronze ceramics Ba4(Nd1-xSmx)28/3(Ti0.95Zr0.05)18O54

Ba₄(Nd_1-xSm_x)_28/3(Ti_0,95Zr_0,05)₁₈O₅₄ ceramics with (x = 0; 0.2; 0.4; 0.8 and 1) were synthesized by solid method at 1250 °C for 10 h. The effects of Nd/Sm ratio on the structure and dielectric behavior were studied by changing the value of x. The study of Ba/RE order with (RE = Nd and Sm) in the solid solution Ba₄(Nd_1-xSm_x)_28/3(Ti_0,95Zr_0,05)₁₈O₅₄ was realized by X-ray diffraction. The crystal structure of these phases belongs to the tungsten bronze type, which is constructed on the basis of the (3x3) Ti/ZrO₆ octahedron more than (2x2) (orthorhombic symmetry, space group Pnma, a ≈22.3 Å, b ≈ 7.67 Å, c ≈ 12.1 Å). A structural model has been established, corresponding to an order within the structure. The model of formula [Ba₄]_A2[Ba_2-a(Nd_1-xSm_x)_1.33+b□_c]_A1'[(Nd_1-xSm_x)_8-d□_d]_A1(Ti_0.95Zr_0.05)₁₈O₅₄, corresponds to a model associated to infinite perovskite rows parallels to the Oy axis, constructed on the basis of the octahedron (3x3) Ti/ZrO₆. Scanning electron microscopy (SEM) has showed that Ba₄(Nd_1-xSm_x)_28/3(Ti_0,95Zr_0,05)₁₈O₅₄ ceramics have a typical columnar grain, which indicates that the phase structure of tungsten bronze exists in the x range and all samples show a dense microstructure. The average grain size ranges from 1.179 to 0.912 μm. The dielectric properties were studied by complex impedance spectroscopy in the temperature range from 30 °C to 800 °C where an anomaly was observed in a few compositions characterized by a maximum of the dielectric permittivity that shifts with increasing frequency at higher temperatures. The presence of a strong dispersion over a wide range of temperatures, is probably related to cationic disorder within the Ba₄(Nd_1-xSm_x)_28/3(Ti_0,95Zr_0,05)₁₈O₅₄ structure.     

Partial cation substitution of tunable blue-cyan-emitting Ba2B2O5:Ce3+ for near-UV white LEDs

In this study, Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ ions act to tune the emission band to the blue-cyan region in Ba_xSr_yB₂O₅:Ce³⁺ (BSBO), Ba_xCa_zB₂O₅:Ce³⁺ (BCBO), Ba_xZn_uB₂O₅:Ce³⁺ (BZBO), and Ba_xMg_vB₂O₅:Ce³⁺ (BMBO) phosphors. A red shift occurs with the increase of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ concentration, and a blue shift occurs when the concentrations of Sr²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ exceed the critical value. The emission color can be tuned from deep blue (0.15, 0.12) to cyan (0.16, 0.27) upon 365 nm UV lamp excitation due to the crystal field splitting and centroid shifts. The excitation band shift to long wavelength by introducing ions, so that the synthesized phosphor can be better matched with the n-UV chip. The emission intensity slowly decreases with the temperature increasing. Therefore, the BMBO:Ce³⁺, BZBO:Ce³⁺, BCBO:Ce³⁺, and BSBO:Ce³⁺ phosphors with relatively good thermal stability were synthesized, which could have potential applications in the n-UV white LEDs.     

Formation of Mixed Bond‐Angle Linkages in Zinc Boromolybdate Glasses

The short and medium range structure of glassy MoO₃–ZnO–B₂O₃ has been studied by neutron diffraction and reverse Monte Carlo simulation. The partial atomic pair correlation functions and coordination numbers are presented that are not yet reported for this system. We have established that the first neighbor distances do not depend on concentration within limit of error, the actual values are r_B‐O = 1.38 Å, r_Mo‐O = 1.72 Å, and r_Zn‐O = 1.97 Å. It is found that ZnO takes part in the glassy structure as network former, as ZnO₄ tetrahedral are linked both to MoO₄ and to BO₃ and BO₄ groups. It is revealed that BO₄/BO₃ increases with increasing B₂O₃ content. We have found that only small amount of boroxol ring is present, BO₃ and BO₄ groups are organized into superstructure units, and a small part is in isolated BO₃ triangles. The BO₃ and BO₄ units are linked to MoO₄ or ZnO₄ forming mixed ^[4]Mo‐O‐^[3]B, ^[4]Mo‐O‐^[4]B, ^[4]Mo‐O‐^[4]Zn, ^[3]B‐O‐^[4]Zn, ^[4]B‐O‐^[4]Zn bond linkages.     

Synthesis and Crystal Structure of Na2Ba9Si20O50—An Intermediate Phase Along the Join Na2Si2O5‐BaSi2O5

Single crystals of Na₂Ba₉Si₂₀O₅₀ were obtained from solid state reactions performed along the join Na₂Si₂O₅‐BaSi₂O₅. The crystal structure has been determined from a data set collected at ambient temperatures and subsequently refined to a residual of R(|F|) = 0.0328 for 2211 independent reflections. The compound belongs to the group of phyllosilicates and adopts the monoclinic space group C2/m with the following lattice parameters: a = 39.111(3) Å, b = 7.6566(6) Å, c = 8.2055(6) Å, β = 97.319(6)°, V = 2437.2(3) Å³, Z = 2. Furthermore, weak one‐dimensional diffuse streaks running parallel to a* as well as a very small number of low intensity reflections at b*/3, indicating the presence of a superstructure, were observed. Basic buiding units are silicate layers parallel to (40‐1) which can be obtained from the condensation of single chains with a periodicity of four running along [010]. The sheets can be partitioned into two kinds of consecutive strips containing (i) a sequence of four‐ and eight‐membered rings and (ii) a four‐ring wide “zig‐zag shaped” unit consisting of exclusively six‐membered rings. The sodium and barium cations—distributed among six crystallographically independent positions—are sandwiched between subsequent layers and are linked to seven to nine nearest oxygen neighbors. The structure of Na₂Ba₉Si₂₀O₅₀ is closely related to that of K₂Ba₅Si₁₂O₃₀ and K₂Ba₇Si₁₆O₄₀, respectively. There are strong arguments that the previously claimed phase Na₄Ba₈Si₂₀O₅₀ is actually misinterpreted Na₂Ba₉Si₂₀O₅₀ and that the composition of the intermediate phase along the join Na₂Si₂O₅–BaSi₂O₅ is slightly different from that described in the literature.