The antiferroelectric incommensurate phase in Pb(Co1/2W1/2)O3 is incommensurate in both wavelength and direction of the wave vector characterizing the modulation. In this study, the crystallographic features of the incommensurate and commensurate phases in Pb(Co1/2W1/2)O3 have been investigated by transmission electron microscopy to elucidate the details of commensuration to the commensurate phase. The wave vector of the modulation in the incommensurate phase was found to be k1=[1-δI 1-δI Δ1] with δI≈0 and ΔI≈0, while the wave vector in the commensurate phase is given by kc=[1/2 1/2 0]. The important features of the incommensurate and commensurate phases are that the modulation modes with k1 and kc1 are transverse atomic displacements of the Pb ions associated with the Σ3 irreducible representation of the C2v point group, and that another modulation with kc2= takes place in the commensurate phase. The kc2 modulation is associated with the X10 representation corresponding to the antiparallel displacement of the Pb ions. The appearance of the kc2 modulation is accompanied by that of a pseudoperiodic array of antiphase boundaries with a phase shift of π, and thus the commensurate phase is a nearly commensurate phase. That is, commensuration of both wavelength and direction of the incommensurate modulation takes place via the introduction of the X10 displacement with the antiphase boundaries, If the antiphase boundary is regarded as a discommensuration, the commensuration process of the antiferroelectric incommensurate phase to the commensurate phase is therefore characterized by the appearance of a discommensuration, not by its annihilation.
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||Published - 2002 2 1|
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