Structure optimization and frozen phonons in LiNbO3

✍ Scribed by A.V. Postnikov; V. Caciuc; G. Borstel

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 148 KB
• Volume: 61
• Category: Article
• ISSN: 0022-3697
• DOI: 10.1016/s0022-3697(99)00296-6

✦ Synopsis

The equilibrium ground-state structure of LiNbO 3 in the paraelectric and ferroelectric phases is fully optimized in a firstprinciples calculation using the full-potential linearized augmented plane wave method. The equilibrium volume, c=a ratio and all (four, in the ferroelectric phase) internal parameters are found to be in good agreement with the experimental data. Frozen phonon calculations are performed for TO-G phonons corresponding to the A 1 and A 2 irreducible representations of the R3c space group in the ferroelectric phase. The comparison with available experimental frequencies for the A 1 modes is satisfactory (including the 6 Li isotope effect), and the displacement patterns are unambiguously attributed. For the (Raman inactive) A 2 modes, phonon frequencies and eigenvectors are predicted.