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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]

The novel red-emitting phosphors Ba 3 Lu 1– x Eu x B 9 O 18 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.85) belonging to the Ba 3 REE B 9 O 18 (REE – Y, Pr–Lu) family were successfully obtained by a multistep solid-phase synthesis. X-ray diffraction experiments revealed no phase transitions caused by the Eu3+ → Lu3+ isomorphic substitution in this series of solid solutions. An increase in the Eu3+ content leads to an expectable increase of hexagonal unit cell parameters and volume. Optical properties of the Ba 3 Lu 1– x Eu x B 9 O 18 (x = 0–0.85) phosphors were investigated. The highest emission intensity was demonstrated by Ba 3 Lu 0.6 Eu 0.4 B 9 O 18. The concentration quenching of luminescence was revealed for the x (Eu3+) > 0.4 samples. Concentration quenching, quantum yield and structural data were compared between three red-emitting Ba–Lu borates-phosphors (BLBO:Eu3+) containing independent crystallographic sites for the REE ions (n = 1–3) in crystal structure. It was revealed that the higher the number of nonequivalent cationic REE sites suitable for the Eu3+ → Lu3+ substitution, the higher the quantum yield taking into account practically equal amount of an optimal concentration of the activator-ion. Such an observation could be useful for a crystal chemical design of novel phosphors. [Display omitted] • Novel red-emitting phosphors Ba 3 LuB 9 O 18 :Eu3+ are synthesized. • Optical properties of the phosphors are studied. • Luminescence and structural data of three Ba–Lu borates-phosphors are compared. • Dependence of quantum yield on number of nonequivalent REE cationic sites is discussed. [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]

This paper reports an investigation of the chemistry, crystal structure refinement and thermal behavior (80–1650 K) of ludwigite from the Iten'yurginskoe deposit (Eastern Chukotka, Russia). Its chemical composition was determined by electron microprobe analysis, giving an empirical formula (Mg1.70Fe2+0.29Mn0.01)Σ2.00(Fe3+0.90Al0.08Mg0.02)Σ1.00O2(BO3). A refinement of the crystal structure from single‐crystal X‐ray diffraction data (SCXRD) was provided for the first time for ludwigite from this deposit (R = 0.047). The structure can be described as a framework composed of [MO6]n− octahedra and isolated [BO3]3− triangles located in triangular interstices of the framework. Based on a comprehensive analysis of SCXRD and Mössbauer spectroscopy data, the M1 site is occupied by Mg, M2 and M3 by Mg and Fe2+, M4 by Fe3+, Mg and Al. There are also oxo‐centered [O4M4]n+ and [O2M5]n+ polyhedra building up a framework with the [BO3]3− triangles located in its hexagonal interstices. No indications of magnetic ordering are found in the temperature range investigated. The Fe2+ → Fe3+ oxidation occurs above 600 K, and is accompanied by a decrease of the unit‐cell parameters and subsequent incomplete solid‐phase decomposition with the formation of hematite, warwickite and magnetite. The mineral melts at temperatures above 1582 K. The thermal expansion of ludwigite is slightly anisotropic, which is explained by a dense packing of the [MO6]n− octahedra as well as a virtually perpendicular orientation of the oxo‐centered double chains to each other. At room temperature, maximum expansion is along the c axis (αc = 9.1 × 10−6 K−1) and minimum expansion is in the ab plane (αa = 8.6 × 10−6, αb = 7.6 × 10−6 K−1), which is due to the preferred orientation of the [BO3]3− triangles. A comparison of the thermal behavior of three oxoborates of the ludwigite group, namely azoproite (Mg,Fe2+)2(Fe3+,Ti,Mg,Al)O2(BO3), vonsenite (Fe2+,Mg)2(Fe3+,Mn2+,Sn,Al)O2(BO3) and ludwigite (Mg,Fe2+,Mn)2(Fe3+,Al,Mg)O2(BO3), is provided. [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]

This work is devoted to an investigation of the magnetic properties and thermal behaviour of the natural oxoborates vonsenite and hulsite in the temperature range 5–500 K. The local environment, the oxidation states of the Fe and Sn atoms, and the charge distribution were determined using Mössbauer spectroscopy and are in accordance with a refinement of the crystal structure of hulsite from single‐crystal X‐ray diffraction data (SCXRD) in anisotropic approximation for the first time. The magnetic properties were studied by vibrating sample magnetometry (VSM) (5 ≤ T ≤ 400 K) and are reported for the first time for iron‐rich hulsite. Both oxoborates show a very complex magnetic behaviour. Cascades of magnetic transitions are revealed and the critical temperatures were determined. The sequences of magnetic transitions in both vonsenite and hulsite with increasing temperature were found to be as follows: magnetically ordered state → partial magnetic ordering → paramagnetic state. According to X‐ray diffraction data (93 ≤ T ≤ 500 K), these processes are accompanied by anomalies in the unit‐cell parameters and thermal expansion of the oxoborates at critical temperatures. A strong negative volume thermal expansion is observed for both oxoborates at temperatures below ∼120 K. [ABSTRACT FROM AUTHOR]

The first bismuth borate oxyiodide, Bi4BO7I, has been prepared by solid‐state reaction in evacuated silica ampoules. Its crystal structure [space group Immm(00γ)000] comprises litharge‐related layers of edge‐sharing OBi4 tetrahedra; the interlayer space is filled by I− and [BO3]3− anions. The wavevector, q = 0.242 (3)c*, is very close to the rational value of c*/4, yet refinement based on commensurate modulation faces serious problems indicating the incommensurate nature of the modulation. The I‐/[BO3]3− anions are ordered in a complex sequence along [001], i.e. –<–BO3–BO3–I–I–>n = 28–I–I–I–<–BO3–BO3–I–I–>n = 28–BO3–BO3–BO3–, leading to a structural modulation. The principal feature of the latter is the presence of –I–I–I– and –BO3–BO3–BO3– sequences that cannot be accounted for in the a × b × 4c supercell. The thermal expansion of Bi4BO7I is weakly anisotropic (αa = 8, αb = 15 and αc = 17 × 10−6 K−1 at 500 K) which is caused by preferential orientation of the borate groups. [ABSTRACT FROM AUTHOR]

A brief review is presented of the structure hierarchy, main fundamental building blocks (FBBs) and some thermal characteristics of crystalline alkali and alkaline earth borosilicates. Low-dimensional borosilicate anions are typical for borosilicates with considerable contents of non-tetrahedrally coordinated cations. There are only six types of borosilicate anions containing boron in BO3 triangles, which are almost never connected to silicon tetrahedra. The lower the ratio "non-tetrahedral/tetrahedral cation", the higher the dimension of the layered and framework anions that form. Most Si-dominant borosilicates (B/Si_1) with a low content of non-tetrahedrally coordinated cations have 3D-framework structures formed by boron and silicon atoms in tetrahedral coordination only. As with aluminosilicates, 3D-borosilicate structures contain a great variety of rings of tetrahedra, which are the main FBBs of borosilicate structures. The most common rings of tetrahedra are 4-, 6- and 8-membered. An ordered distribution of Si and B is typical for borosilicates. There are many OH-containing borosilicates, especially among the structures with 0D-, 1D- and 2D-anions; conversely, they almost never have H2O molecules in the crystal structure. OH-groups are often involved in the coordination of boron. Non-tetrahedral alkali and alkaline earth cations are coordinated by oxygen or hydroxyl groups with usual coordination numbers: lithium is 4-coordinated, sodium is mostly 6-coordinated, and 8-coordination is typical for calcium. Other large cations have irregular coordinations with more than eight oxygen atoms. Thermal expansion coefficients (TECs) determined for 31 natural and synthetic compounds have relatively low values independent of the dimensionality of the structure. The linear TECs of crystals are slightly higher than those of glasses of corresponding composition; the average values are 10×10-6 and 8×10-6°C-1 for crystals and glasses, respectively. [ABSTRACT FROM AUTHOR]

Single crystals of Lu5Ba6B9O27 were obtained by cooling from a melt and polycrystals of the borate were prepared using a multi‐step solid‐state synthesis. The crystal structure was determined from single‐crystal X‐ray diffraction data. The borate crystallizes in a new structure type in the monoclinic crystal system in space group C2/c, with cell parameters a = 13.0927 (3), b = 9.9970 (2) and c = 20.4884 (4) Å, β = 106.827 (1)°, V = 2566.86 (9) Å3 and Z = 4. It is described as a framework composed of rings consisting of vertex‐sharing [BO3] triangles and [LuO6] octahedra. The Ba atoms are in the cavities of the framework. The structure is disordered: one of the B atoms is surrounded by six O atoms with partial occupancies of 0.5. The thermal properties of Lu5Ba6B9O27 were investigated by thermal analysis and high‐temperature X‐ray powder diffraction. Its thermal expansion is highly anisotropic. The negative expansion (contraction) is along the b axis, i.e. parallel to the planes of the largest number of [BO3] triangles. The coefficient of negative linear expansion ranges from −1.42 (at 20°C) to −5.57 × 10–6 °C–1 (at 1000°C). Thermal deformation of the ac plane is described in terms of the theory of shear deformation of monoclinic crystals. The Lu5Ba6B9O27 sample melts at 1170°C. [ABSTRACT FROM AUTHOR]

The first silver bismuth borate, AgBi2B5O11 (silver dibismuth pentaborate), has been prepared via glass crystallization in the Ag2O–Bi2O3–B2O3 system and characterized by single‐crystal X‐ray diffraction. Its structure is derived from that of centrosymmetric Bi3B5O12 by ordered substitution of one Bi3+ ion for Ag+, which results in the disappearance of the mirror plane and inversion centre. Second harmonic generation (SHG) measurements confirm the acentric crystal structure. It is formed by [Bi2B5O11]∞ layers stretched along c and comprised of vertex‐sharing B5O10 and BiO3 groups which incorporate the Ag+ cations. The new compound was characterized by thermal analysis, high‐temperature powder X‐ray diffraction, and vibrational and UV–Vis–NIR (near infrared) spectroscopy. Its thermal expansion is strongly anisotropic due to the presence of rigid B5O10 groups aligned in a parallel manner. The minimal value is observed along their axis [parallel to c, αc = 3.1 (1) × 10−6 K−1], while maximal values are observed in the ab plane [αa = 20.4 (2) and αb = 7.8 (2) × 10−6 K−1]. Upon heating, AgBi2B5O11 starts to decay above 684 K due to partial reduction of silver; incongruent melting is observed at 861 K. According to density functional theory (DFT) band‐structure calculations, the new compound is a semiconductor with an indirect energy gap of 3.57 eV, which agrees with the experimental data (absorption onset at 380 nm). [ABSTRACT FROM AUTHOR]

New cation-deficient solid solutions of Ca 3–1.5 x Yb x □ 0.5 x B 2 SiO 8 ( x  = 0–0.4) based on Ca 3 B 2 SiO 8 borosilicate were synthesized. It was found that solid solutions in the range 0 ≤  x  < 0.125 are structurally similar to the low-temperature monoclinic β-Ca 3 B 2 SiO 8 , whereas those of the range 0.187 <  x  < 0.4 are similar to the high-temperature orthorhombic α-Ca 3 B 2 SiO 8 . The crystal structures of solid solutions with x  = 0.2 and 0.3 were determined from single crystal X-ray diffraction data and refined in the orthorhombic space group Pnma to R obs  = 0.051 and 0.057, respectively. Thermal expansion of the samples with x  = 0.1, 0.3 was investigated using powder high-temperature X-ray diffraction in the temperature range of 20–800 °C. Photoluminescence spectra of Ca 3–1.5 x Yb x □ 0.5 x B 2 SiO 8 consist of the intra-configurational 2 F 5/2 – 2 F 7/2 transitions inside of Yb 3+ ions with a maximum at 975 nm. [ABSTRACT FROM AUTHOR]

The low-temperature polymorph β-Ca11B2Si4O22 crystallizes as a monoclinic structure [space group is P21/c, a=14.059(9), b=6.834(5), c=10.597(7) Å, β=100.735(8)°]. The crystal investigated by single-crystal X-ray diffraction was a twin composed of six individuals. The crystal structure is similar to that of mineral spurrite, Ca5(SiO4)2CO3, and can be described as a framework of [CaO5] and [CaO6] polyhedra, the cavities of which are filled with [SiO4] and [BO3] groups. The orientation relationship of twin domains was investigated by electron backscatter diffraction (EBSD). Thermal expansion was studied by high-temperature X-ray powder diffraction. It is slightly anisotropic: α11=10, α22=16, α33=12×10−6°C−1 at 200°C. [ABSTRACT FROM AUTHOR]

Crystal structures of γ-, β- and α-Sr2B2O5 polymorphs resulting from the γ ↔ (at 565 K) β ↔ (at 637 K) α′ ↔ (at 651 K) α sequence of reversible first-order phase transitions are studied by high-temperature single-crystal X-ray diffraction, high-temperature X-ray powder diffraction, differential scanning calorimetry and impedance spectroscopy. Out of these phases, the structure of γ-Sr2B2O5 was already known whereas the structures of β- and α-Sr2B2O5 were determined for the first time. The sequence of phase transitions is associated with an unusual change of symmetry, with triclinic intermediate β-Sr2B2O5 phase and monoclinic low-temperature γ-Sr2B2O5 as well as high-temperature α-Sr2B2O5 phase. Taking the α-Sr2B2O5 phase with space group P21/ c as a parent structure, the γ-Sr2B2O5 phase was refined as a twofold superstructure with symmetry P21/ c, whereas the β-Sr2B2O5 phase was a sixfold superstructure with symmetry P. To construct a unified structure model for all Sr2B2O5 modifications, phases of γ- and β-Sr2B2O5 were also refined as commensurately modulated structures using the basic unit cell of the parent α-Sr2B2O5. The phase transitions are related to the orientational order-disorder arrangement of B2O5 pyroborate groups, where the degree of disorder grows towards the high-temperature phase. Thermal expansion is strongly anisotropic and dictated by preferable orientations of BO3 triangles in the structure. The intermediate phase α′-Sr2B2O5, stable over a narrow temperature range (637-651 K), features the largest anisotropy of expansion for the known borates: α11 = 205, α22 = 57, α33 = −81 × 10−6 K−1. [ABSTRACT FROM AUTHOR]

In the present study the thermal structure evolution is reviewed for known nonlinear optical borates such as β-BaB2O4, LiB3O5, CsLiB6O10, Li2B4O7, K2Al2B2O7, and α-BiB3O6, based on single-crystal and powder X-ray diffraction data collected over wide temperature ranges. Temperature-dependent measurements of further borates are presented for the first time: α-BaB2O4 (295-673 K), β-BaB2O4 (98-693 K), LiB3O5 (98-650 K) and K2Al2B2O7 (98-348 K). In addition to the established criteria for nonlinear optical (NLO) properties of crystals, here the role of the anisotropy and anharmonicity of the thermal vibrations of atoms is analysed as well as changes in their coordination spheres and the anisotropy of the thermal expansion of the crystal structure. Non-centrosymmetric borates, especially those that have NLO properties, often show distinct anisotropies for each cation in comparison to centrosymmetric borates. All considered NLO borates contain BO3 triangles, which are the principal cause of the strong anisotropy of the thermal expansion. [ABSTRACT FROM AUTHOR]

Thermal expansion of Ba silicates with tetrahedrally coordinated Si atoms in the temperature range of 25–1100 °C had been studied by high-temperature X-ray powder diffraction. The volume thermal expansion coefficients (TECs) are in the range 41–50×10 −6 °C −1 with an average value of 〈 α V 〉 = 45 × 10 − 6 ° C − 1 . In the structures with chain and layered silicate anions, thermal expansion is anisotropic: the direction of maximal TEC is parallel to the extension of the zweier chains of silicate tetrahedra, which are strained owing to the interactions with Ba 2+ . The strain is released during thermal expansion due to the increasing effective size of Ba 2+ induced by thermal vibrations. Information-theoretic analysis of the structural and topological complexities of Ba silicates indicates that their structural complexity is a function of the topological complexity of their silicate anions. The latter displays a non-linear behaviour with increasing SiO 2 content (=the increasing degree of polymerization and increasing dimensionality): it starts from simple topologies, reaches a maximum at topologies of intermediate complexity, and ends up at simple topologies again. The specificity of the interactions of Ba 2+ with the silicate anions results in higher complexity of high-temperature α -BaSi 2 O 5 compared to that of low-temperature β -BaSi 2 O 5 . This uncommon behaviour may be explained by the vibrational advantages provided by flatter and more complex silicate layers in the α -phase, which overcome negative differences in configurational entropies of the two modifications apparent in the differences of their structural Shannon information. [ABSTRACT FROM AUTHOR]

Crystal structures of Sr3B2 + xSi1 − xO8 − x/2 solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0βγ)000(0γ)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P21/ n(0βγ). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content. [ABSTRACT FROM AUTHOR]

The structural behavior of the non-linear optical, nanoporous compound CsLiB6O10 was studied in a wide temperature range. Both the highly anisotropic thermal expansion of the borate with temperature variation and the deterioration of its crystals were investigated. The electron density distribution was analyzed in detail. A reversible, partial transition to a new modification, β-CsLiB6O10, was observed during cooling crystalline and moist samples of CsLiB6O10 to -25 °C. The crystal structure of the new phase is described. [ABSTRACT FROM AUTHOR]

A new lithium borate, Li3B11O18, was synthesized by crystallization from glass, containing an excess of B2O3. The compound crystallizes monoclinic, P21/ a, Z=4, a=9.766(5) Å, b=7.849(5) Å, c=17.899(9) Å, β=100.96(5)°, V=1347.0(13) Å3 (R=0.06, wR=0.12). The structure is based upon two interpenetrating frameworks formed by triborate and pentaborate groups. The thermal behaviour of Li3B11O18 was studied using DTA, DSC, and high-temperature XRD. Highly anisotropic thermal expansion and a new high-temperature phase were observed. [ABSTRACT FROM AUTHOR]

Single crystals of Cs2[(UO2)2(CrO4)3] ( 1) were obtained by hydrothermal synthesis. The structure of 1 is based upon 2-dimensional uranyl chromate layers with the composition [(UO2)2(CrO4)3]2-. The cesium atoms are located in the interlayer under 'bulbs' centered at the Cr(2)O4 tetrahedra. The thermal behavior of 1 was studied in air. The diffraction maxima of 1 gradually disappear at approximately 450 °C. At this temperature, peaks of Cs2[(UO2)2(Cr2O8)] ( 2) appear indicating reduction of Cr6+ to Cr5+. Thermal expansion of 1 and 2 is anisotropic. Thermal expansion of the crystal structure of 1 in the [001] direction is greater than that in the other directions, while thermal expansion in the ab plane is uniform. Thermal expansion of 2 is strongly anisotropic as well with the higher expansion along the direction approximately perpendicular to the layers (along the a axis). The high-temperature study demonstrates that stable uranyl compounds with Cr5+ may form not only from hydrothermal aqueous solutions, but also as a result of high-temperature solid-state reactions. [ABSTRACT FROM AUTHOR]

Single crystals of novel metastable borate Ba3Bi2(BO3)4, were obtained from melt with stoichiometric composition. The compound is structurally related to the A3Ln2(BO3)4 family of luminescent borates (A = Ca, Sr, Ba; Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). The crystal structure was solved by direct methods and refined to R = 0.041 (wR = 0.045), orthorhombic, Pnma, a = 7.9508(5), b = 17.399(1), c = 8.9791(5) A˚ , V = 1242.1(1) A˚ 3, Z = 4. The structure contains isolated BO3 triangles linked through Ba2+and Bi3+ cations distributed among three cation sites, M1, M2 and M3. The mixture of the Ba3Bi2(BO3)4 and BaBiBO4 phases in the ~1 : 1 ratio was investigated by means of high-temperature X-ray powder diffraction in air. Ba3Bi2(BO3)4 demonstrates an anisotropic thermal expansion with the following coefficients: aa = 16, ab = 11, ac = 11, aV = 38 x 10-6 K-1 at 25 ºC. The anisotropy increases on heating: aa = 32, ab=-2, ac = 7, aV = 37 x 10-6 K-1 at 700 ºC. The reason for the strong anisotropy of thermal expansion is the preferable orientation of the BO3 triangles. [ABSTRACT FROM AUTHOR]

Single crystals of novel metastable borate Ba3Bi2(BO3)4, were obtained from melt with stoichiometric composition. The compound is structurally related to the A3Ln2(BO3)4 family of luminescent borates (A = Ca, Sr, Ba; Ln = Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). The crystal structure was solved by direct methods and refined to R = 0.041 (wR = 0.045), orthorhombic, Pnma, a = 7.9508(5), b = 17.399(1), c = 8.9791(5) A˚ , V = 1242.1(1) A˚ 3, Z = 4. The structure contains isolated BO3 triangles linked through Ba2+and Bi3+ cations distributed among three cation sites, M1, M2 and M3. The mixture of the Ba3Bi2(BO3)4 and BaBiBO4 phases in the ~1 : 1 ratio was investigated by means of high-temperature X-ray powder diffraction in air. Ba3Bi2(BO3)4 demonstrates an anisotropic thermal expansion with the following coefficients: aa = 16, ab = 11, ac = 11, aV = 38 x 10-6 K-1 at 25 ºC. The anisotropy increases on heating: aa = 32, ab=-2, ac = 7, aV = 37 x 10-6 K-1 at 700 ºC. The reason for the strong anisotropy of thermal expansion is the preferable orientation of the BO3 triangles. [ABSTRACT FROM AUTHOR]

Li2B4O7 crystal structure was studied at elevated temperatures and refined in anharmonic approximation: 20 °C, a = 9.475(3), c = 10.283(6) Å, 883 F(h k l), R = 0.015; 200 °C, a = 9.501(3), c = 10.275(6) Å, 826 F(h k l), R = 0.021; 400 °C, a = 9.535(3), c = 10.295(8) Å, 809 F(h k l), R = 0.022; and 500 °C, a = 9.550(3), c = 10.295(6) Å, 779 F(h k l), R = 0.029. B—O bond lengths were corrected in a view of O and B atomic vibrations. Refinement of anharmonic components of atomic temperature factors has revealed high asymmetry of Li thermal vibrations. The behaviour of tetraborate groups was studied. A stability of rigid B—O groups configuration was indicated, as in the case of β—CsB5O8, LiB3O5 and β-Na2B8O13, studied by us earlier. The boron–oxygen framework expands as a three-dimensional hinge; B—O—B and O—B—O angles inside tetraborate groups practically do not change, while B1—O1—B2 angles between the groups increase to 1.6° on heating up to 500 °C due to O1 atoms shifts letting Li atom to fall through oxygen atoms along c-axis causing the contraction in this direction. [Copyright &y& Elsevier]

• Crystal structure of CaBi 2 B 2 O 7 was refined in space group Pnma. • Its thermal expansion is negative along [0 0 1] at 30–700 °C. • All members of the M Bi 2 B 2 O 7 , M = Ca, Sr, Ba family can be obtained from the hypothetical hexagonal aristotype. The single crystal of CaBi 2 B 2 O 7 was obtained by recrystallization in solid-state and studied by single-crystal X-ray diffraction. Its crystal structure was refined in the centrosymmetric orthorhombic space group Pnma with a = 8.5556(8) Å, b = 5.1569(5) Å, c = 9.6677(7) Å, Z = 4. The structure is based upon parallel (0 1 0) {CaBi 2 B 2 O 7 } ∞ layers from BO 3 triangles, ψ -tetrahedral BiO 3 groups, and CaO 6 triangular prisms connected each to other via long and weak Bi–O bonds. This borate is representative of M Bi 2 B 2 O 7 family (M = Ca, Sr, Ba), where all members can be obtained from the hypothetical hexagonal aristotype. Thermal expansion is studied by high-temperature X-ray powder diffraction, its strongly anisotropic and negative along [0 0 1]: α a = 11.8(1) × 10−6 °C−1, α b = 34.2(3) × 10−6 °C−1, α c = –25.7(4) × 10−6 °C−1 at 600 °C. As a result, a / c cell parameters ratio tends to ideal √3 value, corresponding to the hexagonal aristotype. [ABSTRACT FROM AUTHOR]

Two novel strontium barium borates, Ba 2 Sr 3 B 4 O 11 and Ba 3 Sr 3 B 4 O 12 have been synthesized and their crystal structures were characterized by a single-crystal X-ray diffraction. Ba 2 Sr 3 B 4 O 11 is monoclinic, sp.gr. C 2/ c and based on isolated BO 3 triangles and B 2 O 5 pyroborate groups in relation of 1:2. The crystal structure of Ba 2 Sr 3 B 4 O 11 has no structural analogues and belongs to a new structural type. Ba 3 Sr 3 B 4 O 12 is tetragonal, sp.gr. I 4/ mcm and based on isolated BO 3 triangles oriented in a non-parallel manner. Ba 3 Sr 3 B 4 O 12 is a member of the "anti-zeolite" borate family, and structurally close to the Ba 3 B 2 O 6 borate. Sr and Ba cations are ordered in Ba 2 Sr 3 B 4 O 11 and partially disordered in Ba 3 Sr 3 B 4 O 12. The structure of Ba 3 Sr 3 B 4 O 12 contains BO 3 triangles orientationally disordered over the 4 and 8 orientations, while the structure of Ba 2 Sr 3 B 4 O 11 contains B 2 O 5 pyroborate groups orientationally disordered over the 2 orientations. Ba 2 Sr 3 B 4 O 11 and Ba 3 Sr 3 B 4 O 12 exhibit a short cut-off edge lower than 210 and 206 nm, respectively. Thermal behaviour of these borates including Ba 5 B 4 O 11 was studied by high-temperature X-ray powder diffraction in the 20–800°С temperature range. Thermal expansion is strongly anisotropic for monoclinic Ba 2 Sr 3 B 4 O 11 (α 11 = 2.8(3), α 22 = 5.6(1), α 33 = 38.0(5) × 10−6 °С−1 at 200°С), less anisotropic for orthorhombic Ba 5 B 4 O 11 (α 11 = 9.9(2), α 22 = 11.7(3), α 33 = 20.1(2) × 10−6 °С−1 at 200°С) and close to the isotropic for tetragonal Ba 3 Sr 3 B 4 O 12 (α 11 = α 22 = 12.8(2), α 33 = 20.0(1) × 10−6 °С−1 at 200°С). The new compounds were also characterized by thermal analysis, vibrational and UV–Vis–NIR spectroscopy and Ba 2 Sr 3 B 4 O 11 was characterized by DFT calculations. Image 1 [ABSTRACT FROM AUTHOR]

The first silver bismuth borate, AgBi2B5O11 (silver dibismuth pentaborate), has been prepared via glass crystallization in the Ag2O–Bi2O3–B2O3 system and characterized by single‐crystal X‐ray diffraction. Its structure is derived from that of centrosymmetric Bi3B5O12 by ordered substitution of one Bi3+ ion for Ag+, which results in the disappearance of the mirror plane and inversion centre. Second harmonic generation (SHG) measurements confirm the acentric crystal structure. It is formed by [Bi2B5O11]∞ layers stretched along c and comprised of vertex‐sharing B5O10 and BiO3 groups which incorporate the Ag+ cations. The new compound was characterized by thermal analysis, high‐temperature powder X‐ray diffraction, and vibrational and UV–Vis–NIR (near infrared) spectroscopy. Its thermal expansion is strongly anisotropic due to the presence of rigid B5O10 groups aligned in a parallel manner. The minimal value is observed along their axis [parallel to c, αc = 3.1 (1) × 10−6 K−1], while maximal values are observed in the ab plane [αa = 20.4 (2) and αb = 7.8 (2) × 10−6 K−1]. Upon heating, AgBi2B5O11 starts to decay above 684 K due to partial reduction of silver; incongruent melting is observed at 861 K. According to density functional theory (DFT) band‐structure calculations, the new compound is a semiconductor with an indirect energy gap of 3.57 eV, which agrees with the experimental data (absorption onset at 380 nm). [ABSTRACT FROM AUTHOR]

Crystals of the first new organo–inorganic hybrid borate based on potassium crown ether complex, [K(C12H24O6)B5O6(OH)4](H2O) (1), have been produced from aqueous solutions and characterized by single-crystal X-ray diffraction. 1 crystalizes is orthorhombic system, Pnma, a = 10.1684(3) Å, b = 11.6289(3) Å, c = 21.2247(6) Å, V = 2509.76(12) Å3, Robs = 0.059. The structure of 1 consists of molecular [K(C12H24O6)B5O6(OH)4]0 complexes, common for crown ether complexes but yet not among borates, with a very rare monodentate coordination of the common pentaborate anion(1-). The molecular complexes are linked into weak chains via hydrogen bonding to outer-sphere water molecules. Hirshfeld surfaces analysis and complexity measurement of 1 were performed. Perspectives of borate structures containing crown ether complexes as templates are briefly outlined. [ABSTRACT FROM AUTHOR]

A sequence of reversible phase transitions γ ↔ β′ (at 511°С) ↔ α (at 587°С) was found in Ca 2 B 2 O 5 by high-temperature X-ray powder diffraction, DSC and in the high-temperature Raman spectroscopy. The crystal structure of high-temperature modification, α-Ca 2 B 2 O 5 , was refined by the Rietveld method at 600°С. It is isostructural to the α-Sr 2 B 2 O 5 and shows the orientational disorder of isolated B 2 O 5 pyroborate groups. Thermal expansion is strongly anisotropic (α 11 = 25, α 22 = 7, α 33 = 2 × 10−6 °C−1 at 400 °C) and dictated by preferential orientations of BO 3 triangles in the structure. [Display omitted] • Ca 2 B 2 O 5 shows γ ↔ β ′ (at 511°С) ↔ α (at 587°С) reversible phase transitions. • Thermal expansion of all modifications is strong anisotropic. • High-temperature phase of Ca 2 B 2 O 5 is isostructural to those of Sr 2 B 2 O 5. [ABSTRACT FROM AUTHOR]

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi3B5O12. The Bi3B5O12 single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi3B5O12 was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) A˚, V=937.2(5) A˚3, Z=4, R=3.45%. Bi3+ atoms have irregular coordination polyhedra, Bi(1)O6 (d(B–O)=2.09–2.75 A˚) and Bi(2)O7 (d(B–O)=2.108–2.804 A˚). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O3 (2.09–2.20 A˚) and tetragonal Bi(2)O4 (2.108–2.331 A˚) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO4 polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B2IVB3IIIO11]7− through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi–O chains. The Bi3B5O12 thermal expansion is sharply anisotropic (α11&ap;α22=12, α33=3×10−6 °C−1) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains. [Copyright &y& Elsevier]

Dobrovolskyite, Na4Ca(SO4)3, is a new sulfate mineral from the Great Tolbachik fissure eruption, Kamchatka peninsula, Russia. It occurs as aggregates of tabular crystals up to 1–2 mm in maximum dimension, with abundant gas inclusions. The empirical formula calculated on the basis of O = 12 is (Na3.90K0.10)Σ4(Ca0.45Mg0.16Cu0.12Na0.10)Σ0.83S3.08O12. The crystal structure of dobrovolskyite was determined using single-crystal X-ray diffraction data as: trigonal, R3, a = 15.7223(2), c = 22.0160(5) Å, V = 4713.1(2) Å3, Z = 18 and R1 = 0.072. The Mohs' hardness is 3.5. The mineral is uniaxial (+), with ω = 1.489(2) and ɛ = 1.491(2) (λ = 589 nm). The seven strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 11.58(40)(101); 5.79(22)(202); 4.54(18)(030); 3.86(88)(033); 3.67(32)(006); 2.855(50)(306); and 2.682(100)(330). The mineral is named in honour of Prof. Dr. Vladimir Vitalievich Dolivo-Dobrovolsky (1927–2009), one of the leading Russian scientists in the field of petrology, crystal optics and crystal chemistry. The crystal structure of dobrovolskyite can be described as composed of three symmetrically independent rods running parallel to the c axis. The rods consist of six octahedral–tetrahedral [Na(SO4)6]11– or [Ca(SO4)6]10– clusters of central octahedra sharing common corners with six adjacent SO4 tetrahedra. Alternatively, the crystal structure of the mineral can be described as a 12-layer ABACABACABAC eutactic array of Na+ and Ca2+ cations, and vacancies with disordered (SO4) tetrahedra in interstices. Dobrovolskyite and similar minerals probably formed upon cooling of a high-temperature phase with disordered cation and anion arrangements. [ABSTRACT FROM AUTHOR]

In this work, we present a new borate, Ag 3 B 6 O 10 Br, as well as thermal properties of two recently reported members of M 3 B 6 O 10 X family, Ag 3 B 6 O 10 (NO 3) and Na 3 B 6 O 10 I. The structure of Ag 3 B 6 O 10 Br is non-centrosymmetric, Pnm 2 1 , and exhibits a new version of packing the ionic Ag–Br and covalent B–O frameworks. The non-centrosymmetry is induced by alternation of disordered and ordered borate "layers" normal to a. The Ag–Br sublattice is also strongly disordered and exhibits pronounced ahnarmonicity of thermal vibrations modeled using the Gram – Charlier series. Thermal behavior of Ag 3 B 6 O 10 Br, Ag 3 B 6 O 10 (NO 3) and Na 3 B 6 O 10 I was characterized using variable-temperature powder X-ray diffraction and thermal analysis. The thermal behavior of Ag 3 B 6 O 10 Br (α a = −0.5, α b = −7.4, α c = 41.5 at 200°С), Ag 3 B 6 O 10 (NO 3) (α a = 4.5, α b = 4.8, α c = 31.8 at 200°С), and Na 3 B 6 O 10 I (α a = 9.4, α b = −1.2, α c = 48.3 at 200°С) is strongly anisotropic due to the alignment of the hexaborate B 6 O 13 groups in the structure. [Display omitted] • A new non-centrosymmetric borate, Ag 3 B 6 O 10 Br was prepared. • Cationic [Ag 3 Br]3+sublattice shows strongly anharmonic displacement parameters. • Thermal expansion of Ag 3 B 6 O 10 X, X = Br, NO 3 , and Na 3 B 6 O 10 I is anisotropic. [ABSTRACT FROM AUTHOR]

Belomarinaite, ideally KNaSO4, is a new sulfate mineral discovered in the Toludskoe lava field, formed during the 2012–2013 Tolbachik Fissure eruption. The mineral occurs as arborescent aggregates of tabular crystals (1 mm × 0.3 mm × 0.1 mm) comprising hematite impurities. The average size of the aggregates is 0.5–0.7 mm. The empirical formula is (K0.95Na0.92Cu0.04)Σ1.91S1.01O4. The crystal structure of belomarinaite was determined using single-crystal X-ray diffraction data; the space group is P 3 m 1, a = 5.6072(3), c = 7.1781(4) Å, V = 195.45(2) Å3, Z = 2 and R 1 = 2.6%. In the crystal structure of belomarinaite, there are six cation sites: the [4] S 1 and [4] S 2 sites are occupied by S, the [6]Na and [12]K sites are occupied by Na and K, respectively, giving Na0.5K0.5 apfu and the [10] M 1 and [10] M 2 sites are occupied by Na0.78K0.22 and K0.78Na0.22 apfu, respectively. The crystal structure is a framework of SO4 tetrahedra, Na octahedra and K, M 1 and M 2 polyhedra. Belomarinaite is isostructural with the synthetic compound KNaSO4. In belomarinaite, Na and K are disordered over M 1 and M 2 sites; in its synthetic analogue, Na and K are ordered over M 1 and M 2 sites, respectively. The Mohs' hardness is 2–3. The mineral is uniaxial (+), with ω = 1.485(3) and ε = 1.488(3) (λ = 589 nm). The strongest lines of the powder X-ray diffraction pattern [ d , Å (I , %) (hkl)] are: 4.022(31)(101); 3.591(26)(002); 2.884(74)(102); 2.800(100)(110); 2.391(16)(003); 2.296(8)201; 2.008(38)(022); and 1.634(10)(212). The mineral was named in honour of Russian volcanologist Marina Gennadievna Belousova (b. 1960) for her significant contributions to the monitoring of the Tolbachik Fissure eruption. [ABSTRACT FROM AUTHOR]

Abstract New solid solutions of Li x Na 1 –x KZnP 2 O 7, belonging to the MM' ZnP 2 O 7 structural family (M = Li+, Na+, Zn2+; M' = Na+, K+), were prepared and phase equilibria along the LiKZnP 2 O 7 –NaKZnP 2 O 7 section were reported. These solid solutions were investigated single-crystal X-ray diffraction, high-temperature X-ray powder diffraction (HTXRD), differential scanning calorimetry, and impedance spectroscopy. A miscibility gap was found within the range of 0.8 < x < 1.0, and a binodal curve was constructed using HTXRD data. The similarity of the thermal and compositional deformation of Li x Na 1 –x KZnP 2 O 7 solid solutions is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 31 °C. The Li/Na↔Zn cation exchange lead to an increase in conductivity above 300 °C. The alkali mixed effect in activation energy occurs for Li x Na 1– x KZnP 2 O 7 solid solutions near x = 0.5. The phase with the 2 a ×2 b × c superstructure ordering was observed as a result of the solid solution melting. Graphical abstract Schematic illustration of the possible Na+/Li+/Zn2+-cation migration path in the structure of Li x Na 1– x KZnP 2 O 7 solid solution with x = 0.5. fx1 Highlights • Synthesis of Li x Na 1 –x KZnP 2 O 7 diphosphate and its relation to the MM' ZnP 2 O 7 family. • Its crystal structure and thermal expansion. • Study of the Li/Na↔Zn cation exchange in Li x Na 1 –x KZnP 2 O 7 solid solutions. [ABSTRACT FROM AUTHOR]

The structural behavior of the non-linear optical, nanoporous compound CsLiB6O10 was studied in a wide temperature range. Both the highly anisotropic thermal expansion of the borate with temperature variation and the deterioration of its crystals were investigated. The electron density distribution was analyzed in detail. A reversible, partial transition to a new modification, β-CsLiB6O10, was observed during cooling crystalline and moist samples of CsLiB6O10 to -25 °C. The crystal structure of the new phase is described. [ABSTRACT FROM AUTHOR]

The novel polycrystalline phosphors BaBi 2- x Eu x B 2 O 7 (x ​= ​0, 0.05, 0.10, 0.15, 0.20, 0.30, 0.40) were obtained by crystallization from glass-ceramics. Single-crystal X-ray diffraction experiments were provided for the x ​= ​0.10, 0.20 and 0.40 samples in order to investigate a distribution of the Eu3+ ions over cation sites. It is shown that the Eu3+ ions substitute the Bi3+ ones in the M 1 and M 2 sites. Luminescent properties of the BaBi 2- x Eu x B 2 O 7 phosphors were investigated for the first time. The optimal concentration of the Eu3+ ions was revealed for the sample with x ​= ​0.40, after that an immiscibility of the BaBi 2- x Eu x B 2 O 7 solid solutions occurs, which is of a structure-dependent nature. Increase of the Eu3+ content leads to a gradual change of chromaticity from light red to orange-red/red. It is expected that the BaBi 2 B 2 O 7 :Eu3+ phosphors can be used as red-emitting ones under LED excitation. CIE chromaticity coordinates and glass ceramics sample of BaBi 2 B 2 O 7 :Eu3+. [Display omitted] • Novel red-emitting color-tunable phosphors BaBi 2 B 2 O 7 :Eu3+ are prepared. • The optimum doping concentration of BaBi 2 B 2 O 7 :Eu3+ was determined to be 20 ​at.%. • Chromaticity of BaBi 2 B 2 O 7 :Eu3+ phosphors emission depends on the Eu3+ concentration. [ABSTRACT FROM AUTHOR]

A new triclinic layered borate, |Ag 4 Br|@[B 7 O 12 ], has been prepared by glass crystallization and slow cooling stoichiometric melts in evacuated silica ampoules. The structure is based upon a layered borate anion 7:∞2 [(4: 2Δ + 2 T) + (3: 2Δ + T)] with an architecture yet not observed among inorganic borates. The layers consist of two parts comprised of tri- and tetraborate groups; it is ∼7 Å thick and oriented parallel to (001). The interlayer space is filled by the cationic [Ag 4 Br]3+sublattice exhibiting disorder and anharmonicity at the silver sites. The new compound was characterized by thermal analysis, high-temperature powder X-ray diffraction, vibrational and UV–Vis–NIR spectroscopy, as well as DFT calculations. For the triclinic unit cell, the eigenvalues of the thermal expansion tensor and the orientation of the thermal expansion tensor relative to the crystallographic axes are determined. The thermal expansion of the new borate bromide is strongly anisotropic, being marginal in the plane of the B–O layers (α 11 = 8.2 (1), α 22 = 4.71 (3) × 10−6 °С−1) while quite large in the normal direction (α 33 = 38.2 (3) × 10−6). [Display omitted] • A new triclinic layered borate,.|Ag 4 Br|@[B 7 O 12 ] was studied • Crystal structure is based upon a new layered borate anion. • Cationic [Ag 4 Br]3+sublattice shows strongly anharmonic vibrations. • Thermal expansion is strongly anisotropic. [ABSTRACT FROM AUTHOR]

Single crystals of Cs2[(UO2)2(CrO4)3] ( 1) were obtained by hydrothermal synthesis. The structure of 1 is based upon 2-dimensional uranyl chromate layers with the composition [(UO2)2(CrO4)3]2-. The cesium atoms are located in the interlayer under 'bulbs' centered at the Cr(2)O4 tetrahedra. The thermal behavior of 1 was studied in air. The diffraction maxima of 1 gradually disappear at approximately 450 °C. At this temperature, peaks of Cs2[(UO2)2(Cr2O8)] ( 2) appear indicating reduction of Cr6+ to Cr5+. Thermal expansion of 1 and 2 is anisotropic. Thermal expansion of the crystal structure of 1 in the [001] direction is greater than that in the other directions, while thermal expansion in the ab plane is uniform. Thermal expansion of 2 is strongly anisotropic as well with the higher expansion along the direction approximately perpendicular to the layers (along the a axis). The high-temperature study demonstrates that stable uranyl compounds with Cr5+ may form not only from hydrothermal aqueous solutions, but also as a result of high-temperature solid-state reactions. [ABSTRACT FROM AUTHOR]

Three series of Sr 3–1.5 x Eu x B 2+ y Si 1– y O 8– y /2 (x Eu3+ = 0.01–0.51; y = 0, 0.28, 0.53) solid solutions were prepared by crystallization of the melt. The crystal structures of solid solutions with x = 0.2, y = 0; x = 0.06, y = 0.28; x = 0.23, y = 0.28; x = 0.46, y = 0.28; x = 0.06, y = 0.53 and x = 0.51, y = 0.53 were determined on the basis of single-crystal X-ray diffraction data (XRD) and refined in the orthorhombic space group Pnma to R obs = 0.029, 0.054, 0.030, 0.029, 0.042 and 0.025, respectively. Heterovalent substitution scheme 3Sr2+ → 2Eu3+ + □ is assumed from the single-crystal XRD data. In the phases with x Eu3+≥ 0.2 the substitution leads to a split of the Sr/Eu positions. According to the results of powder and single crystal study, the critical concentration of europium in the structure reaches about 17 at. %. The Eu-doped borosilicates are thermally stable upon heating in air up to at least 800 °C, but decompose at above 900 °C forming a mixture of borates and silicates of Sr and Eu. Ceteris paribus, fluorescence intensity of the borosilicates with y = 0 and 0.28 shows a similar high level of fluorescence while that of the series enriched in boron (y = 0.53) is reduced. The measured quantum yield of the promising red phosphors (x Eu3+ ≥ 0.4) demonstrates high values from 44 up to 79% depending on Sr/B/Si ratio. Image 1 • Sr 3 B 2+ y Si 1– y O 8– y /2 (x Eu 3 + ≤ 0.51, y = 0, 0.28, 0.53) solutions were synthesized from the melt. • The crystal structures are characterized by single crystal and powder XRD. • The position Sr/Eu is split in the structures with high Eu3+ content. • For x Eu3+ ≥ 0.4 the measured quantum yield is between 44 and 79% depending on Sr/B/Si ratio. • Homogeneous solutions crystallise up to x Eu = 0.4; they are stable on heating to at least 800 °C. [ABSTRACT FROM AUTHOR]