First-principles lattice dynamics and thermodynamic properties of pre-perovskite PbTiO3. (1st June 2019)

• Record Type: Journal Article
• Authors: Zhou, Meng-Jun; Wang, Yi; Ji, Yanzhou; Liu, Zi-Kui; Chen, Long-Qing; Nan, Ce-Wen
• Is Part Of: Acta materialia. Volume 171(2019)
• Page Start: 146
• Page End: 153
• Publication Date: 2019-06-01
• Subjects: Pre-perovskite PbTiO3 (PP-PTO) -- First-principles calculations -- Lattice dynamics -- Phase diagram; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2019.04.008
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: It was recently found that nanowires of PbTiO3 synthesized through an intermediate pre-perovskite phase exhibit enhanced spontaneous polarization. Here we investigated the pre-perovskite PbTiO3 (PP-PTO) nanowire phase at finite temperatures employing first-principles quasiharmonic calculations. We calculated its band gap, phonon dispersions, phonon density of states, Debye temperature, and thermodynamic properties. The corresponding calculations for cubic and tetragonal PbTiO3 were also carried out for comparison. In the current calculations, the amount of imaginary frequencies associated with the ideal cubic PTO structure, i.e., a cubic cell shape with ion positions at the ideal cubic perovskite lattice sites, was decreased to a negligible level by employing a constrained cubic structure, a structure with the same cubic cell shape as the ideal cubic PTO structure but allowing the ion positions to relax to thermodynamically more stable tetragonal positions at 0 K. In contrast to the general observation that a higher volume phase would have relatively higher entropy, it is found that the PP-PTO phase possesses the lowest entropy while having the largest volume compared to cubic and tetragonal PbTiO3 phases. Furthermore, the temperature-pressure phase diagram for the three PbTiO3 phases was obtained, which demonstrates that PP-PTO could be stabilized under a large volume or a negative pressure. This study provides insights to experimentally synthesizing the PP-PTO phase and to better understanding its phase transition into the converted tetragonal PbTiO3 nanowires with enhanced piezoelectric and ferroelectric properties. Graphical abstract: Image 1