Nanodomains Coupled to Ferroelectric Domains Induced by Lattice Distortion in Self-Doped LuMn_xO_3±δ Hexagonal Ceramics

Abstract

Self-doped h-LuMn x O3±δ multiferroic ceramics with 0.92 ≤ x ≤ 1.12 were studied for the dependence of magnetic properties on x. Interlocking of lattice distortion at the nanoscale with ferroelectric (FE) domains in bulk RMnO3 materials is mostly unknown. Here we report occurrence of nanodomains in transmission electron microscopy (TEM) images with the presence of antiphase boundaries/ferroelectric domain walls separating nano-FE domains. Observed chemical inhomogeneity across the crystalline grains of the ceramics causes distortion in the lattice. Formation of nanostructural domains revealed across particles of Mn deficient or Lu deficient samples includes bands of strained atomic planes, structural antiphase boundaries, and planar defects similar to stacking fault ribbons. Nanotwins exist in the basal plane, the twin boundary representing disorder of the stacking of atomic planes along the [110] direction. Image contrast in high resolution HRTEM images and TEM image simulation confirm the role of planar defects on switching of electrical polarization, which cause topology breaking of sixfold vortices of FE domains in h-RMnO3 oxides. The local orbital arrangements of ions are investigated by EELS spectroscopy of O K-edge supported by theoretical analysis. Irreversibility in magnetization below the Néel temperature of antiferromagnetic ordering of the h-LuMn x O3±δ multiferroic solid solution is found for all ceramics showing dependence on cation vacancy type and nominal content. The main features observed in the irreversibility of magnetization were correlated to defects and inhomogeneity in the nanoscale images of the lattice of ceramics. The interplay of lattice distortion linked to extended defects and magnetic/ferroelectric properties of multiferroic ceramics is further discussed.

Interaction of multiferroic properties and interfaces in hexagonal LuMnO3ceramics

“…The results for the L 3 /L 2 ratio of h-LuMn x O 3± samples with 1 day annealing are from Figure S3(b) of ref. [25]. Although the nature of covalent bonding may result in slight changes of the valence state the present analysis in Figure 4(b) exhibits a rather constant value of the Mn 3+ oxidation state for all measurements, or very close to it [26][27][28][29].…”

“…Although most attention was devoted on exploring the properties of the 6-fold vortices in this family of multiferroic oxides, there are images of topology breaking of 6-fold vortices or structurally distorted cores [31][32][33][34]. The broad microscopy analysis of the FE domains in ceramics of the current study disclosed frequent topology breaking of the 6-fold vortices, also the interaction of the FE polarization and partial edge dislocations and stacking faults in the lattices, of which the effect on the magnetic properties requires more experiments and theoretical calculations via DFT approaches [25].…”

“…Although in the evaluation of FE domains the topological 6-fold vortices were not found in this particle, the large density of the FE domain walls in a particle of less than 3 micron size demonstrates their potential role on modification of properties driven by the interfaces [13,14]. Beside of FE walls, we often captured stacking faults and anti-phase boundaries where the original symmetry of the crystalline lattice of the non-distorted regions is no longer preserved [25].…”

Link of Weak Ferromagnetism to Emergence of Topological Vortices in Bulk Ceramics of h-LuMnxO3 Manganite

“…Plate-like single crystals of ErMnO 3 cooled through T C under applied loads revealed conversion of isotropic distribution of vortices to lengthy stretched stripes linking vortices to antivortices that moved far apart along easy slip directions dragged by forces coming from the intense shear strain gradients of high temperature plasticity . Minute shifts of chemical composition are expected in solid state reacted samples, and it was already shown that planar defects and dislocations can be found in ceramics of this study, but they appeared mostly at submicron scales. , One must assume that wavy stripe-like FE patterns in Figure a from annealing the x = 0.94 sample at 1510 °C is evidence that this temperature stays below the corresponding T C of the material. Observed features are intrinsic and did not originate from mechanical stress/strain fields or fluctuating chemical composition.…”

In Situ Exploration of Thermal-Induced Domain Evolution with Phase Transition in LiNbO3-Modified K0.5Na0.5NbO3 Single Crystal

“…Thus, to better understand and further enhance ferroelectric responses, domain evolution during heating and cooling cycles must be studied. For illustrating domain structure and distribution, many techniques have been employed including transmission electron microscopy (TEM), optical microscopy (OM), , backscattered mode scanning electron microscopy (BM-SEM), ,, and piezoresponse force microscopy (PFM). ,,, The skillful in situ combination with Raman spectra or Raman mapping will make the discussion between domains and crystal structures more fascinating. , …”