Evolution of defect signatures at ferroelectric domain walls in Mg-doped LiNbO₃

Abstract

The domain structure of uniaxial ferroelectric lithium niobate single crystals is investigated using Raman spectroscopy mapping. The influence of doping with magnesium and poling at room temperature is studied by analysing frequency shifts at domain walls and their variations with dopant concentration and annealing conditions. It is shown that defects are stabilized at domain walls and that changes in the defect structures with Mg concentration can be probed by the shift of Raman modes. We show that the signatures of polar defects in the bulk and at the domain walls differ.

Imaging of 180∘ ferroelectric domain walls in uniaxial ferroelectrics by confocal Raman spectroscopy: Unraveling the contrast mechanism

“…To analyze DW spectra at y-incident geometry, locations of domain walls need to be identified. Most Raman investigations were performed in z incident though [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Therefore, domain-structure-sensitive phonons have to be identified first.…”

“…In the last decade, Raman microscopy has been applied to visualize and analyze ferroelectric domain structures in numerous materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. A relation between the phonon spectra and ferroelectric domain walls (DW) was first noted by Dierolf et al in 2004 [1] performing luminescence microscopy on periodically poled, Er-doped lithium niobate.…”

“…The resolution of diffraction limited microscopy (≈500 nm) is not sufficient to analyze the scale of the ferroelectric DW transition itself, which is supposed to be a few unit cells (≈1 nm) [17][18][19][20][21]. However, Raman spectroscopy is sensitive to other effects as well, such as crystallographic defects [7,16,22], stoichiometry [22,23], strains [24][25][26], or E fields [27]. The understanding of those effects and their interaction with domain structures is particular important in technological relevant systems, such as periodically poled waveguide structures [2,8,74].…”

Raman signatures of ferroic domain walls captured by principal component analysis

“…Ferroelectric DWs in lithium niobate with congruent [19,20,[22][23][24] or stoichiometric [20,22,25] compositions have been extensively studied by Raman spectroscopy [19,20,[22][23][24][25]. The usual measurement consists of point-by-point mapping across a DW.…”

“…Only two domain states are possible, both with polarization along the rhombohedral c-axis, and therefore only 180°-domain walls are observed. Interesting anomalies are observed in the vicinity of these DWs: unexpected optical contrast [17], strain on length scales of micrometers [18], anomalies in the Raman [19][20][21][22][23][24][25] and dielectric [26] spectra and photo-induced conduction [14,15]. These observations are usually discussed in term of variations in defect concentrations but the precise underlying mechanisms remain unclear and are debated in literature [19][20][21].…”