Structural phase transitions and electronic phenomena at 180-degree domain walls in rhombohedral BaTiO3

Abstract

The structure and electronic phenomena at the 180-degree domain wall in the rhombohedral phase of BaTiO 3 are described using Landau-Ginzburg-Devonshire theory. Dependent on the wall orientation, two types of domain wall behaviors are identified. The low-energy "achiral" phase occurs in the vicinity of the {110} orientation and has odd polarization profile invariant with respect to inversion about the wall center. The "chiral" phase occurs around {211} wall orientations and corresponds to mixed parity domain walls. The temperature-induced transformation between the phases is abrupt and is accompanied with 20%-30% change of the domain wall thickness. This process gives rise to the significant changes of the electronic structure of the wall. Depending on the temperature and flexoelectric coupling strength, relative conductivity of the wall becomes at least one order of magnitude higher than in the single-domain region. The possible strategies for exploring these transitions based on direct measurements of domain wall width and conductive atomic force microscopy are discussed.

Fundamentals of flexoelectricity in solids

“…This is illustrated in figure 7(b), where the normalized variation of the free-carrier concentration is plotted as a function of the tilt angle θ (after [85], for the material parameters of PbZr 0.2 Ti 0.8 O 3 ). Eliseev et al [90] have shown that the internal structure of ferroelectric DWs may be strongly correlated with current atomic force microscope (AFM) contrast, suggesting the use of current AFM for detecting phase transitions in DW structure.…”

180° Ferroelectric Stripe Nanodomains in BiFeO3 Thin Films

“…This is particularly disappointing since the 180° domain walls have been predicted to exhibit the largest band gap reduction and magnetization out of the three possible domain wall variants in BiFeO3. 12,20 Moreover, the structure and properties of 180° ferroelectric domain walls have been extensively studied theoretically in recent years; 20,21 and a non-Ising character of the 180° domain wall, arising from flexoelectric effects, has been proposed. 22 Therefore, experimental verification of the existence of periodic 180° stripe domains in BiFeO3 is important for better understanding the domain formation mechanism, domain wall structure, and its contributions to magnetic and electric properties in this multiferroic material.…”

Bistability of ferroelectric domain walls: Morphotropic boundary and strain effects

“…[5][6][7][8] The results from Ref. 8 suggest that the approximation neglecting flexoelectricity, which is used in the present paper, provides an acceptable accuracy for the description of the structure of the walls.…”

“…Equations (11) possess a certain symmetry. One can note that if the polarization profile {P 1 (z),P 2 (z)} satisfies the system (11), then {P 1 (z), − P 2 (z)} will also be a solution, and these two solutions are energetically equivalent, because (8) does not contain odd powers of P 2 . This implies that the Bloch walls are bistable.…”

“…This feature makes Bloch walls interesting objects from the point of view of dense memory applications. To the best of our knowledge the only material where Bloch walls are predicted is the rhombohedral phase of BaTiO 3 , [5][6][7][8] and this is done by numerical simulations, based on LandauGinsburg-Devonshire (LGD) theory and ab initio calculations. However, such domain walls may have limited applications because of difficulties, associated with cryogenic temperatures needed to obtain this phase in the material.…”