High-Pressure Syntheses, Crystal Structures, And Thermal Behaviour Of β-Re(Bo₂)₃ (Re = Nd, Sm, Gd)

Abstract

The compounds β -RE(BO 2 ) 3 [RE = Nd (neodymium meta-borate), Sm (samarium meta-borate) and Gd (gadolinium meta-borate)] were synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 3.5 GPa (Nd), 7.5 GPa (Sm, Gd) and 1050 • C. The crystal structures were determined by single crystal X-ray diffraction data collected at r. t. (Sm, Gd) and at −73 • C (Nd), respectively. The structures are isotypic with the already known ambient-pressure phases β -RE(BO 2 ) 3 (RE = (Tb, Dy) and the high-pressure phases β -RE(BO 2 ) 3 (RE = Ho-Lu).

Ambient‐Pressure Stabilization of β‐GdB3O6 by Doping with Bi3+ and Color‐Tunable Emissions by Co‐Doping with Tb3+ and Eu3+: The First Photoluminescence Study of a High‐Pressure Polymorph

“…β‐TbB 3 O 6 is the first member of the β‐ RE B 3 O 6 ( RE =Nd‐Lu, except Pm) series. Although it was obtained under normal pressure in a molten salt that contained Tb, Tb 4 O 7 , TbCl 3 , and B 2 O 3 at 950 °C for three weeks, β‐GdB 3 O 6 , the target compound of this work, was previously prepared at 7.5 GPa and 1050 °C . Herein, β‐GdB 3 O 6 could be realized by Bi 3+ doping (2 atom %) at 820 °C and ambient pressure.…”

“…Figure shows XRD patterns for β‐Gd 0.75− x Bi 0.25 Tb x B 3 O 6 (0≤ x ≤0.75), β‐Gd 0.75− y Bi 0.25 Eu y B 3 O 6 (0≤ y ≤0.75), and β‐Gd 0.50− z Bi 0.25 Tb 0.25 Eu z B 3 O 6 (0≤ z ≤0.05). All samples share the same characteristic pattern as that calculated based on the structure of β‐GdB 3 O 6 , and no impurity peaks were observed. First, this proves the successful formation of β‐ RE B 3 O 6 at ambient pressure; second, the diffraction peaks for samples with different dopant concentrations do not show an obvious peak shift, which is due to the comparable cationic radii of Gd 3+ (1.053 Å for eight coordination), Tb 3+ (1.04 Å), and Eu 3+ (1.066 Å) .…”

New Aspects of Borate Chemistry under High-Pressure

“…β-MB 4 O 7 (M = Ca [2], Zn [3], Hg [4]), χ-REBO 3 (RE = Dy, Er) [5], and ν-DyBO 3 [6] were discovered. Furthermore, in the field of rare-earth meta-oxoborates we were able to add two new modifications γ-RE(BO 2 ) 3 (RE = La-Nd) [7,8] and δ-RE(BO 2 ) 3 [9,10] (RE = La, Ce) to the already existing modifications αand β-RE(BO 2 ) 3 [11,12]. These investigations led to fundamental insights into the structural behaviour of oxoborates under high-pressure conditions.…”

Phase stabilities of monoclinic oxoborates LaB3O6 and GdB3O6 in C121 and I12/a1 phase—Energetics and chemical bonds derived from first-principles calculations

“…We note that the experimental I12/a1 structures for Ln ¼ Dy-Lu are still missing, which may be supported by the distinct electronic structures of the monoclinic I12/a1 a-LnB 3 O 6 between Ln ¼ La-Tb and Ln ¼ Dy-Lu as the consequence of the down-shifting energetic levels of Ln p states relative to O 2p states. However, the experience based on the calculated electronic structures of I12/a1 a-LnB 3 O 6 needs to be reconsidered with great care in cases of other polymorphs of LnB 3 O 6 , for example, the orthorhombic Pnma b-LnB 3 O 6 with both Ln ¼ Nd, Sm and Gd [24] and Ln ¼ Tb-Lu [25,26].…”

“…The starting of the monoclinic series of a-LnB 3 O 6 with the centrosymmetric space group I12/a1 is marked by LaB 3 O 6 (a ¼ 6.509 Å , b ¼ 8.172 Å , c ¼ 7.983 Å , b ¼ 93.431) [17] and terminated at TbB 3 O 6 (a ¼ 6.215 Å , b ¼ 8.023 Å , c ¼ 7.811 Å , b ¼ 93.441) [18] through Ce [19], Pr [20], Nd [21], Sm [22], Eu [23] and Gd [22]. The lanthanide elements entering into the orthorhombic series of the centrosymmetric space group Pnma include Nd, Sm and Gd [24] as well as those smaller ones from Tb to Lu [25,26], which makes the b-LnB 3 O 6 series. The second orthorhombic polymorphs with the noncentrosymmetric symmetry Pca2 1 , called g-LnB 3 O 6 , have been also grown under the high pressure for LnB 3 O 6 containing the lighter lanthanide elements for La, Ce, Pr and Nd [27,28].…”