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Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-x Fex)nO(3n+1)-δ Ruddlesden-Popper superstructures.

Doig KI, Peters JJ, Nawaz S, Walker D, Walker M, Lees MR, Beanland R, Sanchez AM, McConville CF, Palkar VR, Lloyd-Hughes J - Sci Rep (2015)

Bottom Line: No evidence of macroscopic ferromagnetism was found in SQUID magnetometry.The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales.An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.

ABSTRACT
Bulk crystals and thin films of PbTi(1-x)FexO3(-δ) (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti(1-x)Fex)nO3(n+1)-δ forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n ≃ 8 and x ≃ 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti0.5Fe0.5)nO3(n+1)-δ, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

No MeSH data available.


X-ray characterisation of Pbn+1(Ti0.5Fe0.5)nO3n+1−δ films: (a) 2θ scans around the LaAlO3 substrate's (002) peak for PTFO-100, -200 and -300 films (solid lines). The asterisk marks the PTFO's Bragg peak corresponding to . The dashed line is the model described in the text. (b) Wide angle 2θ scan for PTFO-100. (c) Shallow angle x-ray reflectivity for PTFO-100 from experiment (solid line) and simulation (dashed line). (d) A symmetric 2θ − ω scan for PTFO-100 around the (003) substrate peak, at ϕ = 0. (e), (f) Reciprocal space maps for PTFO-100 around the (103) and (113) LaAlO3 substrate peaks (indicated by the dashed lines), respectively. qx, q∥ and qz denote the scattering wavevectors in the [100], [110] and [001] directions of the substrate.
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f1: X-ray characterisation of Pbn+1(Ti0.5Fe0.5)nO3n+1−δ films: (a) 2θ scans around the LaAlO3 substrate's (002) peak for PTFO-100, -200 and -300 films (solid lines). The asterisk marks the PTFO's Bragg peak corresponding to . The dashed line is the model described in the text. (b) Wide angle 2θ scan for PTFO-100. (c) Shallow angle x-ray reflectivity for PTFO-100 from experiment (solid line) and simulation (dashed line). (d) A symmetric 2θ − ω scan for PTFO-100 around the (003) substrate peak, at ϕ = 0. (e), (f) Reciprocal space maps for PTFO-100 around the (103) and (113) LaAlO3 substrate peaks (indicated by the dashed lines), respectively. qx, q∥ and qz denote the scattering wavevectors in the [100], [110] and [001] directions of the substrate.

Mentions: Thin films of PTFO with nominal thicknesses of 100 nm, 200 nm and 300 nm were deposited on (001) LaAlO3 (LAO) by pulsed laser deposition (see Methods), and are referred to herein as PTFO-100, PTFO-200 and PTFO-300. High-resolution 2θ − ω X-ray diffraction scans were taken to examine the crystal structure of the films. In Figure 1a the pseudocubic (002) peak of the LaAlO3 substrate (space group , a = 3.789Å, α = 90.12°)26 is visible at 2θ = 48°. For each film a sequence of diffraction peaks at lower 2θ (larger c) than the substrate peak is evident. The wider range 2θ − ω scan in Figure 1b indicates diffraction peaks up to the substrate's (004) peak for the PTFO-100 sample. While the (002) film peaks are at lower 2θ than the LAO peak, those for (001) straddle the substrate peak (23.5°) with one of the four at a higher angle. The data resemble the diffraction pattern of a superlattice owing to their regular spacing in 2θ.


Structural, optical and vibrational properties of self-assembled Pbn+1(Ti1-x Fex)nO(3n+1)-δ Ruddlesden-Popper superstructures.

Doig KI, Peters JJ, Nawaz S, Walker D, Walker M, Lees MR, Beanland R, Sanchez AM, McConville CF, Palkar VR, Lloyd-Hughes J - Sci Rep (2015)

X-ray characterisation of Pbn+1(Ti0.5Fe0.5)nO3n+1−δ films: (a) 2θ scans around the LaAlO3 substrate's (002) peak for PTFO-100, -200 and -300 films (solid lines). The asterisk marks the PTFO's Bragg peak corresponding to . The dashed line is the model described in the text. (b) Wide angle 2θ scan for PTFO-100. (c) Shallow angle x-ray reflectivity for PTFO-100 from experiment (solid line) and simulation (dashed line). (d) A symmetric 2θ − ω scan for PTFO-100 around the (003) substrate peak, at ϕ = 0. (e), (f) Reciprocal space maps for PTFO-100 around the (103) and (113) LaAlO3 substrate peaks (indicated by the dashed lines), respectively. qx, q∥ and qz denote the scattering wavevectors in the [100], [110] and [001] directions of the substrate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296293&req=5

f1: X-ray characterisation of Pbn+1(Ti0.5Fe0.5)nO3n+1−δ films: (a) 2θ scans around the LaAlO3 substrate's (002) peak for PTFO-100, -200 and -300 films (solid lines). The asterisk marks the PTFO's Bragg peak corresponding to . The dashed line is the model described in the text. (b) Wide angle 2θ scan for PTFO-100. (c) Shallow angle x-ray reflectivity for PTFO-100 from experiment (solid line) and simulation (dashed line). (d) A symmetric 2θ − ω scan for PTFO-100 around the (003) substrate peak, at ϕ = 0. (e), (f) Reciprocal space maps for PTFO-100 around the (103) and (113) LaAlO3 substrate peaks (indicated by the dashed lines), respectively. qx, q∥ and qz denote the scattering wavevectors in the [100], [110] and [001] directions of the substrate.
Mentions: Thin films of PTFO with nominal thicknesses of 100 nm, 200 nm and 300 nm were deposited on (001) LaAlO3 (LAO) by pulsed laser deposition (see Methods), and are referred to herein as PTFO-100, PTFO-200 and PTFO-300. High-resolution 2θ − ω X-ray diffraction scans were taken to examine the crystal structure of the films. In Figure 1a the pseudocubic (002) peak of the LaAlO3 substrate (space group , a = 3.789Å, α = 90.12°)26 is visible at 2θ = 48°. For each film a sequence of diffraction peaks at lower 2θ (larger c) than the substrate peak is evident. The wider range 2θ − ω scan in Figure 1b indicates diffraction peaks up to the substrate's (004) peak for the PTFO-100 sample. While the (002) film peaks are at lower 2θ than the LAO peak, those for (001) straddle the substrate peak (23.5°) with one of the four at a higher angle. The data resemble the diffraction pattern of a superlattice owing to their regular spacing in 2θ.

Bottom Line: No evidence of macroscopic ferromagnetism was found in SQUID magnetometry.The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales.An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

View Article: PubMed Central - PubMed

Affiliation: University of Oxford, Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom.

ABSTRACT
Bulk crystals and thin films of PbTi(1-x)FexO3(-δ) (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pbn+1(Ti(1-x)Fex)nO3(n+1)-δ forms spontaneously during pulsed laser deposition of PTFO on LaAlO3 substrates. High-resolution transmission electron microscopy, x-ray diffraction and x-ray photoemission spectroscopy were utilised to perform a structural and compositional analysis, demonstrating that n ≃ 8 and x ≃ 0.5. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes and the observation of second harmonic generation establishes a non-centrosymmetric point group for Pbn+1(Ti0.5Fe0.5)nO3(n+1)-δ, a prerequisite for (but not proof of) ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO3 and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

No MeSH data available.