Extended Data Fig. 1: Crystallographic structures of different phases in the phase diagram of P(VDF-TrFE) copolymers.
From: Ferroelectric polymers exhibiting behaviour reminiscent of a morphotropic phase boundary
a, b, Side (a) and top (b) view of the trans-planar phase. c, d, Side (c) and top (d) view of the 3/1-helical phase. e, Side view of the gauche dihedral angle ϕ in the 3/1-helical phase. f, Top view of the regular 3/1-helical phase (ϕ = 60°). g, Top view of the (pseudo-)disordered 3/1-helical phase (ϕ1, ϕ2 ≠ 60°). Intramolecular disorder occurs in the (pseudo-)disordered 3/1-helical phase in terms of random departure from the gauche dihedral angle of 60° in the regular form (f). The 3/1-helical phase becomes energetically more stable than the trans-planar phase as the VDF content decreases in the vicinity of 50 mol% (Fig. 4a). Moreover, intramolecular disorder develops mainly in the 3/1-helical phase at the critical VDF content of 55 mol%, while the fraction of the regular trans-planar phase decreases. With further decrease of the VDF content (49 mol% ≤ CVDF ≤ 55 mol%), the fraction of the disordered 3/1-helical phase increases substantially and strongly competes with the trans-planar phase (we call this phase coexistence of the pseudo-disordered and ordered phases, or a morphotropic phase in the phase diagram). Here the morphotropic phase (49 mol% ≤ CVDF ≤ 55 mol%) differs from the disordered paraelectric phase owing to the existence of a phase transition (Fig. 3). As the VDF content decreases below 49 mol%, only the disordered 3/1-helical phase (namely, the pseudo-disordered phase) is energetically preferred. In this case, the pseudo-disordered phase has nearly the same structure as the disordered paraelectric phase owing to the absence of a phase transition (Fig. 3), and differs from both the morphotropic and the VDF-rich compositions. We note that we use the structure of PVDF to simplify this discussion. For the case of P(VDF-TrFE), the substitution of some H atoms by some F atoms leads to different chain tacticities of P(VDF-TrFE) (Fig. 1a), which requires a slight generalization of the above description.
