First Brillouin zone-centre phonon frequencies and elastic stiffness of the Ln2Hf2O7 (Ln = La, Nd, Sm and Eu) pyrochlore

Abstract

First Brillouin zone-centre phonon frequencies, elastic stiffness and mechanical properties of the Ln2Hf20 7 [Ln: La, Nd, Sm and Eu] pyrochlore structure were predicted by using an eight parameter bond-bending force constant model. One of the preliminary results of our study is that all the examined compounds are mechanically stable, and the elastic stiffness constants, and bulk and shear moduli decrease in the following sequence: La2Hf2O7 -> Nd2Hf2O7 -> Sm2Hf2O7 -> Eu2Hf2O7. The Poisson's ratio reveals that the interatomic bonding of the studied compounds has an ionic character and their ionicity decreases when one moves from La to Eu. The elastic properties are anisotropic and the anisotropy increases from La to Eu. The Raman and infrared active and inactive modes of the studied materials were calculated. Our findings are in good accordance with the related available data. (C) 2019 Elsevier B.V. All rights reserved.