Comment on “High-pressure x-ray diffraction study of YBO3/Eu3+, GdBO3, and EuBO3: Pressure-induced amorphization in GdBO3” [J. Appl. Phys. 115, 043507 (2014)]

Abstract

High-pressure x-ray diffraction studies on vaterite-type borates were reported on the above paper and their room-temperature P-V equation of state (EOS) determined. YBO3/Eu3+ and GdBO3 were found to have bulk moduli around 320 GPa, 90% larger than the bulk modulus obtained for EuBO3. Consequently, it was stated that vaterite-type borates are as incompressible as cubic BN. Such a different compressional behavior of isomorphic borates contradicts the known systematic of related borates. Here, we show that the conclusions reported on the above article could be hindered by experimental errors and artifacts. Ab initio calculations support our criticism giving similar bulk moduli (130–141 GPa) in the three compounds. Based upon these arguments, we conclude that the high-pressure behavior of vaterite-type borates should be revised using accurate experimental techniques. Finally, a methodological critic on EOS fits and to structural refinements is also presented.

High-pressure powder x-ray diffraction study of EuVO4

“…It is well known that the use of different PTM could induce different deviatoric stresses within the pressure chamber of the DAC leading to conditions that range from quasi-hydrostatic to nonhydrostatic. This could strongly influence the HP structural sequence of the materials even at low pressures [34,43,44]. This influence is prevalent in scheelite-type oxides [45,46].…”

High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4

“…19 Special care was taken during sample loading to occupy only a small fraction on the pressure chamber with the loaded sample to reduce the possibility of sample bridging between the diamond anvils. 20,21 In situ HP XRD measurements at RT were carried out at the Materials Science and Powder Diffraction beamline (BL04-MSPD) of ALBA Synchrotron Light Source 22 . The incident monochromatic beam of wavelength 0.4246 Å was focused down to a 10 µm × 15 µm spot using 6 Kirkpatrick-Baez mirrors.…”

Cobalt ferrite nanoparticles under high pressure

“…20 Special attention was paid during sample loading into the DAC to avoid sample overloading, which leads to sample bridging under compression affecting the measurements. 16 The experiments were performed in the angle-dispersive configuration with a monochromatic beam with wavelength of 0.620231(5) Å . The images were collected using a CCD Rayonix 165.…”

“…Additionally, the reported resistivity experiments 12 could have been affected by the experimental method: two contact resistivity measurements 38 and no use of PTM. 16 Both things are highly not recommendable for high-pressure studies and could hinder the conclusions extracted from the experiments.…”

“…14 In addition to particle size, there are other facts that could influence the HP behavior of nanocrystals; one is the selection of the pressure-transmitting medium (PTM) used in high-pressure experiments, which may have a strong influence on the physical state of the studied sample. [15][16][17] Therefore, to compare with the most recent HP XRD study, 7 we performed our experiments using the same PTM. However, to compare with the previous studies on CoFe 2 O 4 nanoparticles 11 and to reduce the influence of non hydrostaticity, we limit the maximum pressure to 17 GPa.…”