Triggered incommensurate transition in PbHfO3статья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 11 ноября 2019 г.
Аннотация:We report a type of structural phase transitions in dielectric materials: the triggered incommensurate (IC)
transition. We demonstrate evidence for such a transition in the perovskite antiferroelectric PbHfO3 by means
of single-crystal x-ray diffraction, diffuse, and inelastic-scattering experiments, which we interpret using the
Landau theory of phase transitions. This transition is not driven by an IC soft mode, as is the case for the
majority of IC dielectrics, but by the soft mode associated with a different, coexisting order parameter related to
antiferrodistortive (AFD) tilts of the oxygen octahedra. When cooling from the high-temperature cubic phase
these two order parameters are established simultaneously and discontinuously at TIC ≈ 468 K. Two lattice
instabilities are present in the cubic phase: AFD instability with critical temperature T0 ≈ 441 K and ferroelectric
instability with T0 ≈ 408 K. The IC instability is absent. The analysis of the transition mechanism within the
Landau theory of coupled order parameters indicates that the transition is of triggered character, conditioned
upon the attractive biquadratic coupling between the IC modulation and the AFD octahedral tilts, and is driven
by the AFD soft mode.