540 Chemie und zugeordnete Wissenschaften
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Herein, the high-pressure/high-temperature synthesis (11 GPa, 650 °C) of Tb3B10O17(OH)5 in a modified Walker-type multianvil device is presented. The structure of this rare-earth borate was determined by single-crystal X-ray diffraction methods and was found to crystallize orthorhombically in the space group Pmn21 (no. 31) with the unit cell parameters a = 16.2527(4), b = 4.4373(1), and c = 8.8174(2) Å. The new compound was further characterized using infrared spectroscopy, energy-dispersive X-ray spectroscopy, second harmonic generation (SHG) measurements, and temperature-dependent X-ray powder diffraction. Tb3B10O17(OH)5 decomposes to β-Tb(BO2)3 at temperatures higher than 460 °C. With increasing temperatures, the formation of μ-TbBO3 was observed, which transforms to π-TbBO3 upon cooling.
High-pressure/high-temperature synthesis of the new boron-rich terbium hydroxyborate Tb3B12O19(OH)7
(2023)
Monoclinic Tb3B12O19(OH)7 was obtained by multianvil high-pressure/high-temperature syntheses at 6 GPa and 650 °C. The crystal structure was investigated by single-crystal X-ray diffraction methods and space group C2 (no. 5) with the unit cell parameters a = 24.2299(5) Å, b = 4.4667(1) Å, c = 7.0964(2) Å, β = 94.58(1)°, and two formula units per cell were revealed. Powder X-ray diffraction, infrared spectroscopy and the investigation of its second harmonic generation properties support the proposed structural model.
CrB4O6N crystallizes in the non-centrosymmetric space group P63mc (no. 186) with the lattice parameters a=5.1036(1), c=8.3519(3) Å, and a volume of 188.40(1) Å3. It was synthesized in a high-pressure/high-temperature experiment at 7 GPa and 1673 K and represents the first high-pressure oxonitridoborate. It is built up of starlike-shaped entities of four BO3N tetrahedra, connected via one common nitrogen atom that resembles the fourfold-coordinated nitrogen atoms in the homeotypic nitridosilicates MYbSi4N7 (M=Sr, Ba). Building up a network with channels that contain the Cr3+ ions, CrB4O6N contains for the first time a tetrahedral building unit in contrast to trigonal planar B(O/N)3 entities in all other known oxonitridoborates. The structural relations as well as the results of spectroscopic measurements and calculations on the chromium oxonitridoborate are discussed.
Transition metal nitrides, carbides and borides have a high potential for industrial applications as they not only have a high melting point but are generally harder and less compressible than the pure metals. Here we summarize recent advances in the synthesis of binary transition metal nitrides, carbides and borides focusing on the reaction of the elements at extreme conditions generated within the laser-heated diamond anvil cell. The current knowledge of their structures and high-pressure properties like high-(p; T) stability, compressibility and hardness is described as obtained from experiments.