High-pressure Synthesis and Characterization of the Rare-earth Borate La₄B₁₀O₂₁

Abstract

The lanthanum(III)-decaborate La 4 B 10 O 21 was synthesized under high-pressure/high-temperature conditions of 2.6 GPa and 750 • C in a Walker-type multianvil apparatus. The single-crystal structure determination revealed that La 4 B 10 O 21 is isotypic to Pr 4 B 10 O 21 . La 4 B 10 O 21 crystallizes monoclinically with four formula units in the space group P2 1 /n with the lattice parameters a = 716.7(2), b = 1971.5(4), c = 958.3(2) pm, and β = 93.7(1) • . The three-dimensional boron-oxygen framework consists of [BO 4 ] 5− tetrahedra and trigonal-planar [BO 3 ] 3− groups. The structure contains four crystallographically different lanthanum ions. Two of the ions are surrounded by 10, one by 11, and the fourth one by 12 oxygen anions. In addition to IR-spectroscopic investigations, DFT calculations were performed to support the assignment of vibrational bands.

The synthesis of novel lanthanum hydroxyborate at extreme conditions

“…The comparison of the bond distances for La-O and B-O (in trigonal planar orientation) from publications (Böhlhoff et al, 1971;Lin et al, 1996;Emme et al, 2004;Hinteregger et al, 2012) Frontiers in Chemistry frontiersin.org situation with coaxial BO 3 arrangement is slightly different. The value for optical anisotropy depends not only on BO 3 pattern, but also on the detailed orientation and spatial density of the planar BO 3 groups (Jiang et al, 2015).…”

“…FIGURE 6The comparison of the bond distances for La-O and B-O (in trigonal planar orientation) from publications(Böhlhoff et al, 1971;Lin et al, 1996;Emme et al, 2004;Hinteregger et al, 2012) and for La 2 B 2 O 5 (OH) 2 (present work). The ranges from the literature are shown in grey bars, the red squares are corresponding to the smallest value of the bond length of the La 2 B 2 O 5 (OH) 2 , while the black dots are representing the biggest value.…”

“…Along with alkali and transition metals borates, rare-earth (RE) borates (and lanthanum borates in particular) have raised significant interest due to their stable physical and chemical properties, wide bandwidth, and good light transmittance. The system La-B-O is represented by several compositionally different borates: λ-LaBO 3 ( Sari et al, 2017 ), high-temperature modification H-LaBO 3 , LaB 3 O 6 (ambient pressure), and its two high-pressure modifications γ-LaB 3 O 6 ( Emme et al, 2004 ) and δ-LaB 3 O 6 ( Heymann et al, 2006 ), La 4 B 14 O 27 ( Nikelski et al, 2008 ), La 26 O 27 (BO 3 ) 8 ( Lin et al, 1996 ), La 4 B 10 O 21 (isotypic to Pr 4 B 10 O 21 ) ( Hinteregger et al, 2012 ) and La 2 B 8 O 15 (isotypic to Ce 2 B 8 O 15 ) ( Glätzle et al, 2016 ). Except for the high-pressure modifications (γ-LaB 3 O 6 , δ-LaB 3 O 6, and La 4 B 10 O 21 ), all known lanthanum borates are synthesized by heating stoichiometric mixtures of La 2 O 3 and B 2 O 3 under ambient pressure conditions.…”

“…There is a common trend in high-pressure borates where the boron atoms tend to prefer four-fold coordination as pressure increases. Typically, trigonal-planar BO 3 groups transform into tetrahedral BO 4 groups beyond 10 GPa pressure ( Hinteregger et al, 2012 ). However, a few compounds are known to contain trigonal-planar BO 3 groups beyond this pressure threshold, for example, in Ho 31 O 27 (BO 3 ) 3 (BO 4 ) 6 ( Hering et al, 2010 ).…”