Borates — Crystal Structures of Prospective Nonlinear Optical Materials: High Anisotropy of the Thermal Expansion Caused by Anharmonic Atomic Vibrations

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

Borates—Crystal Structures of Prospective Nonlinear Optical Materials: High Anisotropy of the Thermal Expansion Caused by Anharmonic Atomic Vibrations

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

Novel Non-Centrosymmetric NdSr₄O(BO₃)₃ Borate and Nd(Ca_1−<i>x</i>Sr<i>_x</i>)₄O(BO₃)₃ Solid Solutions: Preparation, Crystal Structures, Thermal Expansion and Optical Properties

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

Structural Evolution from 0D Units to 3D Frameworks in Pb Oxyhalides: Unexpected Strongly Corrugated Layers in Pb 7 O 6 Br 2

International audienc

Investigation of thermal behavior of mixed-valent iron borates vonsenite and hulsite containing [OM4]n+ and [OM5]n+ oxocentred polyhedra by in situ high-temperature Mossbauer spectroscopy, X-ray diffraction and thermal analysis Mixed-valent iron borates vonsenite and hulsite

The investigation of elemental composition, crystal structure and thermal behavior of vonsenite and hulsite from the Titovskoe boron deposit in Russia is reported. The structures of the borates are described in terms of cation-centered and oxocentred polyhedra. There are different sequences of double chains and layers consisting of oxocentred [ОM4]^n+ tetrahedra and [OM4]^n+ tetragonal pyramids forming a framework. Elemental composition was determined by energy-dispersive X-ray spectroscopy (EDX). Oxidation states and coordina?tion sites of iron and tin in the oxoborates are determined using Mossbauer spectroscopy and compared with EDX and X-ray diffraction data (XRD). According to results obtained from high-temperature Mossbauer spectroscopy, the Fe2+ to Fe3+ oxidation in vonsenite and hulsite occurs at approximately 500 and 600 K, respectively. According to the high -temperature XRD data, this process is accompanied by an assumed deformation of crystal structures and subsequent solid-phase decomposition to hematite and warwickite. It is seen as a monotonic decrease of volume thermal expansion coefficients with an increase in temperature. A partial magnetic ordering in hulsite is observed for the first time with Tc ~ 383 K. Near this temperature, an unusual change of thermal expansion coefficients is revealed. Vonsenite starts to melt at 1571 К and hulsite starts to melt at 1504 K. Eigenvalues of thermal expansion tensor are calculated for the oxoborates as well as the tensor of anisotropy of the expansion is described in comparison with their crystal structures.1-1

Synthesis and Characterization of the High-Pressure Nickel Borate γ-NiB4O7

gamma-NiB4O7 was synthesized in a high-pressure/high-temperature experiment at 5 GPa and 900 degrees C. The, single-crystal structure analysis yielded the following, results: space group P6(5)22 (No. 179), a = 425.6(2), c = 3490.5(2) pm, V = 0.545(2). nm(3), Z = 6, and Flack parameter x = -0.010(5). Second harmonic generation Measurements confirmed the acentric crystal structure. Furthermore, gamma-NiB4O7 was characterized via vibrational as well as single-crystal electronic absorption spectroscopy, magnetic measurements, high-temperature diffraction, differential scanning calorimetry, and thermogravimetry. Density functional theory-based calculations were performed to facilitate band assignments to vibrational modes and to evaluate the elastic properties and phase stability of gamma-NiB4O7