11. ferroelectric⇔paraelectric
Experimentally observed temperature dependence of lattice constants
for BaTiO3. There are three first-order phase transitions. the cubic to
tetragonal phase transition is nearly second-order one. After [H. E. Kay
and P. Vousden: Philos. Mag. 40, 1019 (1949)].
23. その他に必要な第一原理計算
格子定数、弾性定数を求める計算
フォノンの分散関係の計算(線形応答で)
より正確にはフォノンの dynamical matrix D(k) で
はなく、原子の質量で割る前の interatomic force
constant matrix Φ(k)を計算し、その固有値から擬
スピン間の相互作用を見積もる
With four parameters I can fit an elephant,
and with five I can make him wiggle his trunk.
-- John von Neumann
25個ものパラメータを第一原理計算
だけで決めるのはわりとしんどい
-- 西松毅
http://www.lanl.gov/history/atomicbomb/images/NeumannL.GIF
27. Only with long-range
dipole-dipole interactions
Only with long-range
dipole-dipole
interactions, the
minimum is at
M-point (antiferro).
Adding short-rang
interactions, the
minimum
goes to
Γ-point.
M
long-rang interactions
+ short-range interactions
Γ
BaTiO3
42. PbTiO3の90°ドメイン(2)
HAADF-STEM image around edge dislocations with an a-domain.
After [T. Kiguchi et al.: Sci. Technol. Adv. Mater. 12 (2011) 034413].
600℃成膜時ミスフィット大→室温a軸はミスフィット小→転移→aドメイン