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The thermal expansion of four alkaline-earth borates, namely Ca3B2O6 (0D), CaB2O4 (1D), Sr3B14O24 (2D) and CaB4O7 (3D), has been studied by in situ high-temperature powder X-ray diffraction (HTXRD). Strong anisotropy of thermal expansion is observed for the structures of Ca3B2O6 (0D) and CaB2O4 (1D) built up from BO3 triangles only; these borates exhibit maximal expansion perpendicular to the BO3 plane, i.e., along the direction of weaker bonding in the crystal structure. Layered Sr3B14O24 (2D) and framework CaB4O7 (3D) built up from various B–O groups expand less anisotropically. The thermal properties of the studied compounds compared to the other alkaline-earth borates are summarized depending on the selected structural characteristics like anion dimensionality, residual charge per one polyhedron (BO3 BO4), cationic size and charge, and structural complexity. For the first time, these dependencies are established as an average for both types of polyhedra (triangle and tetrahedron) occurring in the same structure at the same time. The most common trends identified from these studies are as follows: (i) melting temperature decreases with the dimensionality of the borate polyanion, and more precisely, as the residual charge per one polyhedron (triangle or tetrahedron) decreases; (ii) volumetric expansion decreases while the degree of anisotropy increases weakly when the residual charge decreases; (iii) both trends (i) and (ii) are most steady within borates built by triangles only, while borates built by both triangles and tetrahedra show more scattered values. [ABSTRACT FROM AUTHOR]

Solvothermal reaction of magnesium nitrate and boron oxide in N,N-dimethylformamide produced a number of particularly complex supramolecular magnesium borates. Five topologically different types of negatively charged {Mg@[B18ϕ34–35]}-clusters, ϕ = O, OH, were observed with the magnesium cation as a core and octadecaborate anions as shells. The clusters assemble via common borate polyhedra forming 1D chains, a 2D mesoporous layer, and 3D mesoporous frameworks with an effective channel width of up to 16 Å. Topological analysis of the clusters in combination with the modular crystallography approach indicates that numerous new functional materials can be obtained by varying their assembly mode. At least one compound containing such clusters exhibits a very strong luminescence. [ABSTRACT FROM AUTHOR]

Belomarinaite KNaSO4 (space group P3m1, a = 5.6072(3), c = 7.1781(4) Å and Z = 2) has been studied by high-temperature single crystal X-ray diffraction. The K and Na atoms are disordered, and M1(1c) and M2(1b) sites merge into an M1(2d)(K50%/Na50%) site with increasing temperature, and novel translationsgleiche phase transition of belomarinaite KNaSO4 (P3m1 → P-3m1) was revealed at 123 °C. Then, the temperature increase leads to phase transition of P 3 ¯ m 1 -polymorph of KNaSO4 to α-KNaSO4 (P63/mmc) at 446 °C, and sodium and potassium atoms in K1(1a) and Na1(1b) sites merged into an M4(2a)(K50%/Na50%) site. Crystal structures of KNaSO4 were refined at 300, 500 and 750 °C to R1 = 0.057, 0.056 and 0.048, respectively. The BVS maps and bond-valence energy landscape (BVEL) have been calculated, and the probability of the Na+ migration has been predicted using structural data for belomarinaite at 25 °C. The Na+ ion migration can occur at 2.14 eV in the ab plane and 2.80 eV along the c axis at 25 °C. [ABSTRACT FROM AUTHOR]

A novel non-centrosymmetric NdSr4O(BO3)3 borate and solid solutions of Nd(Ca1−xSrx)4O(BO3)3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 1.0) were synthesized by solid-state reactions as well as crystallization from a melt. The crystal structures of the Nd(Ca1−xSrx)4O(BO3)3 solid solutions with x = 0.2, 0.5 and 1.0 were determined from single crystal X-ray diffraction data and refined in the monoclinic space group Cm to Robs = 0.028, 0.034 and 0.028, respectively. The thermal expansion of the samples with x = 0, 0.2 and 0.5 was investigated using powder high-temperature X-ray diffraction in the temperature range of 25–1000 °C. A similarity of the thermal and compositional (Ca-Sr substitution) deformations of Nd(Ca1−xSrx)4O(BO3)3 solid solutions is revealed: Heating of Nd(Ca0.5Sr0.5)4O(BO3)3 by 1 °C leads to the same deformations of the crystal structure as increasing the amount of Sr atoms in Nd(Ca0.5Sr0.5)4O(BO3)3 by 0.26 at% Sr. The SHG signal of the series of Nd(Ca1−xSrx)4O(BO3)3 solid solutions has a maximum at approximately x = 0.2. [ABSTRACT FROM AUTHOR]

Novel Ba3Sr3B4O12: Eu3+ phosphors were synthesized by crystallization from a melt. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 (x = 0.03, 0.06, 0.15, 0.20, 0.25) solid solutions were refined from SCXRD data. The crystal structures of Ba3(Sr3−1.5xEux)B4O12 phosphors can be described in terms of the cationic sublattice and belong to the "anti-zeolite" family of borates. Its cationic framework is constructed of Ba and Sr atoms. The Eu3+ ions occupy the Sr(1) extraframework cationic site in the Ba3(Sr3−1.5xEux)B4O12 (x = 0.01–0.20) phosphors. The Ba3Sr2.625Eu0.25B4O12 borate crystallizes in a new structure type (I4/mcm, a = 13.132(3), c = 14.633(4) Å, V = 2523.5(11) Å3, Z = 8, R1 = 0.067). In the Ba3Sr2.625Eu0.25B4O12 crystal structure, the Eu3+ ions occupy Sr(1) and Ba/Sr(1) sites, which leads to changes in the crystal structure. The Wyckoff letter and occupancy of the O(5) site are changed; B–O anion groups contain two BO3 triangles (B(3) and B(4)), orientationally disordered over the four orientations, and two ordered BO3 triangles (B(1) and B(2)) in contrast to Ba3Sr3B4O12, in which these groups are disordered over the 4 and 8 orientations. The emission spectra of Ba3Sr3B4O12: Eu3+ show characteristic lines corresponding to the intraconfigurational 4f-4f transitions of Eu3+ ions. Ba3Sr2.7Eu0.20B4O12 demonstrates the strongest luminescent intensity among Ba3(Sr3−1.5xEux)B4O12 solid solutions. The increase in the Eu3+ content results in a gradual change in chromaticity from light red to orange-red/red. It can be concluded that Ba3Sr3B4O12: Eu3+ is a promising red phosphor. [ABSTRACT FROM AUTHOR]

Data are reported on the incommensurately modulated structures of bismuth oxyhalide borates, Bi4BO7X (X = Cl and Br). Their crystal structure is similar to that of the previously reported oxyiodide and can be described as alternating litharge‐related [Bi4O4]4+ layers of edge‐sharing OBi4 tetrahedra. The X− and BO33− anions fill the interlayer space; they alternate in the following sequence: ...⟨...–BO3–BO3–X–X–...⟩–X–X–X–⟨...–BO3–BO3–X–X–...⟩–BO3–BO3–BO3–..., wherein the ⟨...–BO3–BO3–X–X–...⟩ part of the sequence is maintained for 152 cells for X = Cl and 56 cells for X = Br. The incommensurate structure is deceptively close to the commensurate fourfold a × b × 4c superstructure due to the extreme closeness of the q vector to (0,0,¼). The incommensurate nature of the structure could be revealed from accurate analysis of single‐crystal and Rietveld diffraction data. Fine details of the diffraction pattern are discussed, indicating the incommensurate deviation of the crystal structures. The compound Bi4BO7Br was additionally characterized by thermal analysis and vibrational and UV–Vis–NIR spectroscopy, as well as by density functional theory (DFT) calculations. On the basis of the DFT calculations, it is possible to predict that the a × b × 4c superstructure of Bi4BO7Br is unstable under ambient conditions. [ABSTRACT FROM AUTHOR]

The novel red-emitting BaBi2−xEuxB4O10 (x = 0.05, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6) phosphors were obtained by a crystallization from a glass. Distribution of the Eu3+ ions over cation sites were refined for x = 0.1, 0.3 and 0.4 from single-crystal X-ray diffraction data. Emission and excitation spectra of the Eu3+-doped BaBi2B4O10 phosphors were investigated for the first time, where it was shown that characteristic lines are attributed to the intraconfigurational 4f-4f transitions. The optimal concentration for the BaBi2−xEuxB4O10 phosphors is x = 0.4, after which a luminescence intensity decreases. The CIE chromaticity coordinates for the BaBi2B4O10:Eu3+ (x = 0.4) phosphor (0.65, 0.35) are close to the NTSC standard values (0.67, 0.33) for commercial red phosphor. The obtained results show that the BaBi2B4O10:Eu3+ phosphors are promising candidates for solid state lighting application. [ABSTRACT FROM AUTHOR]

This work is devoted to an investigation of elemental composition, crystal structure and thermal expansion of natural oxoborate azoproite from the Tazheran massif (Siberia, Russia) in the temperature range 5–1650 K. Elemental composition was determined by energy‐dispersive X‐ray spectroscopy (EDX). Its empirical formula based on five oxygen atoms is (Mg1.81Fe2+0.19)∑2.00(Fe3+0.36Ti0.26Mg0.26Al0.12)∑1.00O2(BO3). Local environment, oxidation states and ratio of Fe atoms are determined using Mössbauer spectroscopy and compared with EDX and single‐crystal X‐ray diffraction (SCXRD) data. A refinement of the crystal structure from SCXRD data collected at 293 K was provided for the first time. The structure could be described both in terms of cation‐ and anion‐centered polyhedra. It is composed of vertex‐ and edge‐sharing metal–oxygen [MO6]n− octahedra that form extended zigzag chains along the a axis building up a framework with the [BO3]3− triangles located in its distorted trigonal channels. From the other point of view, there are double chains consisting of oxocentred [OM4]n+ tetrahedra and [OM5]n+ tetragonal pyramids forming six‐membered rings with the triangles in its cavities. Four non‐equivalent Mn+ sites are occupied by cations as follows: M(1) (2a) and M(2) (2d) – Mg, M(3) (4g) – Mg and Fe2+, M(4) (4h) – Fe3+, Ti4+, Mg and Al3+. According to differential scanning calorimetry, low‐ and high‐temperature powder X‐ray diffraction (LT‐ and HT‐XRD) data, Mössbauer spectroscopy and magnetometry data (5 ≤ T ≤ 1650 K), there are no phase transitions obtained in the temperature range investigated. However, some anomalies in temperature dependencies of unit‐cell parameters caused by a partial Fe2+ → Fe3+ oxidation are found in the range 873–1173 K. Azoproite melts at a temperature higher than 1600 K. Eigenvalues of the thermal expansion tensor are calculated for the oxoborate and thermal expansion is described in comparison with its crystal structure. [ABSTRACT FROM AUTHOR]