High-pressure syntheses of α-RE₂B₄O₉(RE = Sm, Ho), with a structure type displaying edge-sharing BO₄tetrahedra

Abstract

The compounds alpha-RE2B4O9, with RE = Sm (disamarium tetraborate) and Ho (diholmium tetraborate), were synthesized under conditions of high pressure and high temperature in a Walker-type multianvil apparatus, at 7.5 GPa and 1323 K for alpha-Sm2B4O9 and at 10 GPa and 1323 K for alpha-Ho2B4O9. The crystal structures were determined from single-crystal X-ray diffraction data collected at room temperature. The structures are isotypic with the already known alpha-RE2B4O9 (RE = Eu-Dy) phases, displaying the new structural motif of edge-sharing BO4 tetrahedra next to the known motif of corner-sharing BO4 tetrahedra. As the end members of this isotypic series, the two title compounds mark the borders of the stability field of the appearance of edge-sharing BO4 tetrahedra.

High-pressure Synthesis and Characterization of the Alkali Metal Borate HP-RbB3O5

“…Even the structural motif of two edge-sharing BO 4 tetrahedra forming a B 2 O 6 group is possible under high-pressure conditions, as first discovered in Dy 4 B 6 O 15 [11]. Meanwhile several other high-pressure phases are known to contain this B 2 O 6 group, e. g. RE 4 B 6 O 15 , (RE = Dy, Ho) [11,12], α-RE 2 B 4 O 9 (RE = Sm, Eu, Gd, Tb, Ho) [13,14] [19]. Besides these high-pressure phases, the recently discovered compound KZnB 3 O 6 [20,21] is the only normal-pressure phase exhibiting the structural element of two edge-sharing BO 4 tetrahedra.…”

Synthesis and Crystal Structure of the New High‐Pressure Phase CdB2O4

“…RE 4 B 6 O 15 (RE = Dy, Ho), [14][15][16] a-RE 2 B 4 O 9 (RE = Sm-Ho), [17][18][19] and the recently found HP-NiB 2 O 4 [20] show, besides new compositions, the new strucural motif of edge-sharing BO 4 -tetrahedra. HPNiB 2 O 4 is the first borate, in which every BO 4 -group shares one common edge with an adjacent BO 4 -tetrahedron.…”

Oxonium Ions Substituting Cesium Ions in the Structure of the New High‐Pressure Borate HP‐Cs1−x(H3O)xB3O5 (x=0.5–0.7)

“…[8,9] Meanwhile, this structural motif was found in several other high-pressure phases, for example, HP-MB 2 O 4 (M = Ni, [10] Co [11] ) and a-(RE) 2 B 4 O 9 (RE = SmHo). [12,13] Until 2009, edge-sharing BO 4 tetrahedra were only observed in borates synthesized under high-pressure conditions, and thus their occurrence was assumed to be restricted to the domain of high-pressure chemistry. However, in 2010 the ambient-pressure phase KZnB 3 O 6 [14,15] was discovered as the first borate synthesized under ambient-pressure conditions that features this structural motif.…”