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.