High-pressure Syntheses and Crystal Structures of Monoclinic B-Ho₂O₃ and Orthorhombic HoGaO₃

Abstract

Monoclinic holmium sesquioxide B-Ho 2 O 3 and orthorhombic holmium orthogallate HoGaO 3 were synthesized in a Walker-type multianvil apparatus under high-pressure / high-temperature conditions of 11.5 GPa / 1250 • C and 7.5 GPa / 1250 • C, respectively. Both crystal structures could be determined by single-crystal X-ray diffraction data, collected at r. t. The monoclinic holmium oxide crystallizes in the space group C2/m (Z = 6) with the parameters a = 1394.7(3), b = 350.83 (7), c = 865.6(2) pm, β = 100.23(3) • , R1 = 0.0517, wR2 = 0.1130 (all data), and the orthorhombic compound HoGaO 3 in Pnma (Z = 4) with the parameters a = 553.0(2), b = 753.6(2), c = 525.4(2) pm, R1 = 0.0222, and wR2 = 0.0303 (all data). Experimental Section SynthesesOur original intention was to synthesize rare-earth gallates with new compositions. We started with a stoichiometric ratio of C-Ho 2 O 3 : β -Ga 2 O 3 = 6 : 1. Starting materials were fine powders of cubic Ho 2 O 3 (Alfa Aesar, Emmerich, Germany, 99.995 %) and β -Ga 2 O 3 (Fluka, Seelze, Germany, 99.99 %), which were ground, mixed, and filled into a boron nitride crucible (Henze BNP GmbH, HeBoSint R S10, Kempten, Germany).

New High-Pressure Gallium Borate Ga2B3O7(OH) with Photocatalytic Activity

“…Thus, the BB1 is not straight-lined but buckled inward with an O4–O5–O2 angle of 166.05(4)° instead of even 180°. The Ga–O distances in Ga 2 B 3 O 7 (OH) with a range from 190.9(2) to 211.6(2) pm and an average value of 198.6 pm accord well with data from the literature. − Extended tables for interatomic distances, angles, atomic coordinates, isotropic/anisotropic displacement parameters, Wyckoff positions, and detailed information about the hydrogen bonds can be found in the SI.…”

Pressure-Induced Structural Transition Trends in Nanocrystalline Rare-Earth Sesquioxides: A Raman Investigation

“…In B-type, RE atoms are located in three different 4i positions. The 18 oxygen atoms of the unit cell occupy five different crystallographic sites: four in 4i ( m or C s symmetry) = O (1), O (2), O (3), O (4), that is, 16 O in 4i, and one in 2b (2 /m or C 2 h symmetry) = O (5), that is, two O in 2b. ,, Hence, the irreducible representation according to group theory gives 21 Raman-active modes among, which 14 are A g modes and 7 are B g modes; however, all of the modes are rarely observed in practice.…”

Raman scattering of rare earth sesquioxide Ho2O3: A pressure and temperature dependent study

“…The crystal lattice has three different cation sites and five different anion sites which bond to four, five, or six metal ions. 20 16,20,22 Hence, the irreducible representation according to group theory gives 21 Raman active modes which include 14A g and 7B g modes. Gouteron et al 17 also predicted 21 Raman active modes, i.e., 14A g þ 7B g , from the factor group analysis for B-type crystals, although fewer modes are observed in practice.…”