## 抄録

A model of lead phosphate which describes its rhombohedral-monoclinic improper ferroelastic phase transition is proposed. It contains a reduced number of degrees of freedom but it is constructed consistently with symmetry changes at the phase transition. Potential parameters of the model are derived from available, experimental data. The crystallites of 25 × 25 × 25 and 121 × 121 × 25 unit cells have been simulated by the molecular-dynamics technique. The results determine the phase transition at the L point of reciprocal space, the order parameter, and the temperature behavior of monoclinic lattice parameters. In the rhombohedral phase the calculated dynamical structure factor shows inelastic peaks from which a soft branch of underdamped phonons has been established. The model has been used to calculate a diffuse scattering function which shows above Tc a maximum at an incommensurate wave vector located along the L -F line of the Brillouin zone. The mentioned line is parallel to the ternary symmetry axis. On the basis of the above results we were able to vizualize the nature of the dynamical monoclinic microdomains persisting in the high-temperature rhombohedral phase. It has been shown that above T_{c} the fluctuations can be treated as temporary orientational monoclinic microdomains. Each type of microdomains always contains an irregular sequence of antiphase domains.

本文言語 | English |
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ページ（範囲） | 153-175 |

ページ数 | 23 |

ジャーナル | Journal de Physique II |

巻 | 7 |

号 | 1 |

出版ステータス | Published - 1997 12月 1 |

## ASJC Scopus subject areas

- 原子分子物理学および光学
- 工学（全般）
- 物理学および天文学（その他）