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Identification of inversion domains in KTiOPO4 via resonant X-ray diffraction.

Fabrizi F, Thomas PA, Nisbet G, Collins SP - Acta Crystallogr A Found Adv (2015)

Bottom Line: A novel method is presented for the identification of the absolute crystallographic structure in multi-domain polar materials such as ferroelectric KTiOPO4.This allows one to map the spatial domain distribution in a periodically inverted sample, with a resolution of ∼1 µm achieved with a microfocused beam.This non-contact, non-destructive technique is well suited for samples of large dimensions (in contrast with traditional resonant X-ray methods based on diffraction from Friedel pairs), and its potential is particularly relevant in the context of physical phenomena connected with an absence of inversion symmetry, which require characterization of the underlying absolute atomic structure (such as in the case of magnetoelectric coupling and multiferroics).

View Article: PubMed Central - HTML - PubMed

Affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, England.

ABSTRACT
A novel method is presented for the identification of the absolute crystallographic structure in multi-domain polar materials such as ferroelectric KTiOPO4. Resonant (or 'anomalous') X-ray diffraction spectra collected across the absorption K edge of Ti (4.966 keV) on a single Bragg reflection demonstrate a huge intensity ratio above and below the edge, providing a polar domain contrast of ∼270. This allows one to map the spatial domain distribution in a periodically inverted sample, with a resolution of ∼1 µm achieved with a microfocused beam. This non-contact, non-destructive technique is well suited for samples of large dimensions (in contrast with traditional resonant X-ray methods based on diffraction from Friedel pairs), and its potential is particularly relevant in the context of physical phenomena connected with an absence of inversion symmetry, which require characterization of the underlying absolute atomic structure (such as in the case of magnetoelectric coupling and multiferroics).

No MeSH data available.


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High-resolution maps on the periodically domain-inverted region at (a) E = 4.96 keV and (b) E = 5.007 keV (beam spot ∼ 1.2 × 1.5 µm achieved with microfocusing), collected on the same surface of the sample.
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fig3: High-resolution maps on the periodically domain-inverted region at (a) E = 4.96 keV and (b) E = 5.007 keV (beam spot ∼ 1.2 × 1.5 µm achieved with microfocusing), collected on the same surface of the sample.

Mentions: Since the experimental capability to distinguish between the crystallographic domains had been established, we proceeded to identify and map the surface area artificially poled by the electric field. To this end, we have made use of the microfocusing provided by the KB mirrors. The same procedure used in the case of the low-resolution map has been applied, rastering the sample aligned on the reflection (417) at the same energies below and above the edge (E = 4.96 and 5.007 keV). The results are in Fig. 3 ▸, and the alternating pattern of domains is clearly visible (we note that the patterns measured at the two photon energies are shifted slightly due to the microfocused beam not being aligned to the centre of rotation). The orientation of the sample that brings the crystal into diffraction condition determines a beam footprint on the surface of 1.5 µm (along the direction indicated in the figure as translation x) × 1.75 µm (along the direction y). The stability of the microfocused beam has been characterized, resulting in a drift in position which is largely linear and of the order of a few microns per 12 h, roughly corresponding to the time necessary to acquire one map. The drift in position is corrected when extracting the point-by-point ratio between intensities from the two different maps, as part of the overall shift that had to be applied to correct for the centre of rotation. To obtain a quantitative estimate of the purity of the domains induced by the electric poling, we have collected a series of one-dimensional translation scans that cut through the a-poled domains along the direction , for the two energies and for three different positions in the orthogonal direction x. One of these scans is plotted in Fig. 4 ▸(a). The corresponding domain fraction profile has been extracted by comparison with the simulation of the sum of two incoherent diffraction domains ‘A’ and ‘B’ related by inversion, to which end the ratio of intensities between energies below and above the edge has been employed: where F is the domain fraction (from 0 = domain ‘B’ to 1 = domain ‘A’), and are the intensities from the one-dimensional cuts at the two energies, and () and () are the intensities from the simulations for domain ‘A’ (‘B’) at the two energies. The results for this specific scan cutting across the domains (Fig. 4 ▸b) indicate that the fraction of crystallographic domain ‘A’ ranges from ∼0.18 to ∼0.4. This same procedure has been extended to the whole high-resolution map, thus obtaining the complete two-dimensional pattern of domains in Fig. 5 ▸.


Identification of inversion domains in KTiOPO4 via resonant X-ray diffraction.

Fabrizi F, Thomas PA, Nisbet G, Collins SP - Acta Crystallogr A Found Adv (2015)

High-resolution maps on the periodically domain-inverted region at (a) E = 4.96 keV and (b) E = 5.007 keV (beam spot ∼ 1.2 × 1.5 µm achieved with microfocusing), collected on the same surface of the sample.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4487424&req=5

fig3: High-resolution maps on the periodically domain-inverted region at (a) E = 4.96 keV and (b) E = 5.007 keV (beam spot ∼ 1.2 × 1.5 µm achieved with microfocusing), collected on the same surface of the sample.
Mentions: Since the experimental capability to distinguish between the crystallographic domains had been established, we proceeded to identify and map the surface area artificially poled by the electric field. To this end, we have made use of the microfocusing provided by the KB mirrors. The same procedure used in the case of the low-resolution map has been applied, rastering the sample aligned on the reflection (417) at the same energies below and above the edge (E = 4.96 and 5.007 keV). The results are in Fig. 3 ▸, and the alternating pattern of domains is clearly visible (we note that the patterns measured at the two photon energies are shifted slightly due to the microfocused beam not being aligned to the centre of rotation). The orientation of the sample that brings the crystal into diffraction condition determines a beam footprint on the surface of 1.5 µm (along the direction indicated in the figure as translation x) × 1.75 µm (along the direction y). The stability of the microfocused beam has been characterized, resulting in a drift in position which is largely linear and of the order of a few microns per 12 h, roughly corresponding to the time necessary to acquire one map. The drift in position is corrected when extracting the point-by-point ratio between intensities from the two different maps, as part of the overall shift that had to be applied to correct for the centre of rotation. To obtain a quantitative estimate of the purity of the domains induced by the electric poling, we have collected a series of one-dimensional translation scans that cut through the a-poled domains along the direction , for the two energies and for three different positions in the orthogonal direction x. One of these scans is plotted in Fig. 4 ▸(a). The corresponding domain fraction profile has been extracted by comparison with the simulation of the sum of two incoherent diffraction domains ‘A’ and ‘B’ related by inversion, to which end the ratio of intensities between energies below and above the edge has been employed: where F is the domain fraction (from 0 = domain ‘B’ to 1 = domain ‘A’), and are the intensities from the one-dimensional cuts at the two energies, and () and () are the intensities from the simulations for domain ‘A’ (‘B’) at the two energies. The results for this specific scan cutting across the domains (Fig. 4 ▸b) indicate that the fraction of crystallographic domain ‘A’ ranges from ∼0.18 to ∼0.4. This same procedure has been extended to the whole high-resolution map, thus obtaining the complete two-dimensional pattern of domains in Fig. 5 ▸.

Bottom Line: A novel method is presented for the identification of the absolute crystallographic structure in multi-domain polar materials such as ferroelectric KTiOPO4.This allows one to map the spatial domain distribution in a periodically inverted sample, with a resolution of ∼1 µm achieved with a microfocused beam.This non-contact, non-destructive technique is well suited for samples of large dimensions (in contrast with traditional resonant X-ray methods based on diffraction from Friedel pairs), and its potential is particularly relevant in the context of physical phenomena connected with an absence of inversion symmetry, which require characterization of the underlying absolute atomic structure (such as in the case of magnetoelectric coupling and multiferroics).

View Article: PubMed Central - HTML - PubMed

Affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, England.

ABSTRACT
A novel method is presented for the identification of the absolute crystallographic structure in multi-domain polar materials such as ferroelectric KTiOPO4. Resonant (or 'anomalous') X-ray diffraction spectra collected across the absorption K edge of Ti (4.966 keV) on a single Bragg reflection demonstrate a huge intensity ratio above and below the edge, providing a polar domain contrast of ∼270. This allows one to map the spatial domain distribution in a periodically inverted sample, with a resolution of ∼1 µm achieved with a microfocused beam. This non-contact, non-destructive technique is well suited for samples of large dimensions (in contrast with traditional resonant X-ray methods based on diffraction from Friedel pairs), and its potential is particularly relevant in the context of physical phenomena connected with an absence of inversion symmetry, which require characterization of the underlying absolute atomic structure (such as in the case of magnetoelectric coupling and multiferroics).

No MeSH data available.


Related in: MedlinePlus