High-pressure x-ray diffraction study of YBO3/Eu3+, GdBO3, and EuBO3: Pressure-induced amorphization in GdBO3

Abstract

Angle-dispersive synchrotron X-ray diffraction measurements were performed on vaterite-type YBO3/Eu3+, GdBO3, and EuBO3, respectively, up to 41 GPa at room temperature using a diamond-anvil cell. Pressure-induced amorphization was observed in hexagonal GdBO3 with a significant compression along the c-axis. Compared to the ions of the distorted GdBO3 phase, its anions may lose their long-range order prior to the cations at high pressures. Based on the experimental pressure-volume data, the obtained bulk moduli of YBO3/Eu3+ and GdBO3 are 329 and 321 GPa, respectively, which are more than 90% larger than that of EuBO3 (167 GPa) and are presumably attributed to Gd3+ and Y3+ with a high density of d valence electrons.

GdBO3 and YBO3 crystals under compression

“…[11] to be 326 GPa, which the authors allege supports the earlier reported value of 321 GPa by Wang et al in Ref. [12]. In our previous work, Ref.…”

“…(The data of Wang et al Ref. [12] are included in Fig. 3(a) for comparison, a detailed discussion of which is available in Ref.…”

“…The experimental results of Ref. [12] pertaining to GdBO 3 attracted close criticism from Ref. [14], which provided ab initio calculations and arguments based on the systematics of isomorphic borates to suggest that the actual isothermal bulk modulus of GdBO 3 is in fact closer to 135 GPa.…”

“…[13], we commented on the reliability of the bulk modulus alleged in Ref. [12] pertaining to the isomorphic borate YBO 3 , and the reader is referred there for more details. The focus of the current article is the reported bulk moduli of GdBO3, although nanocrystal YBO3 samples were investigated in parallel for comparison.…”

Pressure-induced phase transitions in acentric BaHf(BO3)2

“…Surprisingly, such studies are relatively rare for borates, due probably to high mechanical stability of these compounds. For instance, YBO 3 :Eu 3 þ and EuBO 3 are stable up to 41 GPa [16]. However, Li 2 B 4 O 7 and GdBO 3 amorphize under high pressure conditions [16,17] whereas FeBO 3 and LiB 3 O 5 show presence of pressure-induced phase transitions at 22.7 and 5 GPa, respectively [18,19].…”