Pressure-Induced Phase Transformations of Quasi-2D Sr₃Hf₂O₇

Author(s)

Barbosa, M. C. B. ; da Silva, E. Lora ; Lekshmi, P. Neenu ; Marcondes, M. L. ; Assali, L. V. C. ; Petrilli, H. M. ; Lopes, A. M. L. ; Araujo, J. P.

• Document type: Journal article
• Source: Journal of Physical Chemistry C; v. 127, n. 31, p. 8-pg., 2023-08-01.

Abstract

We present an abinitio study of the quasi-2D layeredperovskiteSr(3)Hf(2)O(7) compound, performed withinthe framework of the density functional theory and lattice dynamicsanalysis. At high temperatures, this compound takes a I4/mmm centrosymmetric structure (S.G. n. 139); as the temperature is lowered,the symmetry is broken into other intermediate polymorphs before reachingthe ground-state structure, which is the Cmc2(1) ferroelectric phase (S.G. n. 36). One of these intermediatepolymorphs is the Ccce structural phase (S.G. n.68). Additionally, we have probed the C2/c system(S.G n. 15), which was obtained by following the atomic displacementscorresponding to the eigenvectors of the imaginary frequency modelocalized at the & UGamma;-point of the Ccce phase.By observing the enthalpies at low pressures, we found that the Cmc2(1) phase is thermodynamically the most stable.Our results show that the I4/mmm and C2/c phases never stabilize in the 0-20 GPa range of pressurevalues. On the other hand, the Ccce phase becomesenergetically more stable at around 17 GPa, surpassing the Cmc2(1) structure. By considering the effect ofentropy and the constant-volume free energies, we observe that the Cmc2(1) polymorph is energetically the most stablephase at low temperature; however, at 350 K, the Ccce system becomes the most stable. By probing the volume-dependentfree energies at 19 GPa, we see that Ccce is alwaysthe most stable phase between the two structures and also throughoutthe studied temperature range. When analyzing the phonon dispersionfrequencies, we conclude that the Ccce system becomesdynamically stable only around 19-20 GPa and that the Cmc2(1) phase is metastable up to 30 GPa. (AU)

• FAPESP's process: 19/07661-9 - Functional lattice instabilities in naturally layered perovskites
• Grantee: Michel Lacerda Marcondes dos Santos
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/07760-4 - Functional lattice instabilities in naturally layered perovskites
• Grantee: Helena Maria Petrilli
• Support Opportunities: Regular Research Grants