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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.


Raman spectra of PTFO films and LAO substrate: (a) Raman intensity I under 442 nm excitation. (b) I for 325 nm excitation. The dashed black line indicates a two-Lorentzian fit to the PTFO-200 spectra. (c) Raman intensity under 442 nm excitation after subtracting the substrate's contribution. The dashed black line is the model for PTFO-200 as described in the text and Table 2, where black arrows indicate individual oscillators. The lengths of the arrows represent the oscillator strengths, while the widths of the arrow heads denote the widths Γ. The thin back lines (bottom) are the data of Sun et al.22 for x = 0 and x = 0.1.
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f6: Raman spectra of PTFO films and LAO substrate: (a) Raman intensity I under 442 nm excitation. (b) I for 325 nm excitation. The dashed black line indicates a two-Lorentzian fit to the PTFO-200 spectra. (c) Raman intensity under 442 nm excitation after subtracting the substrate's contribution. The dashed black line is the model for PTFO-200 as described in the text and Table 2, where black arrows indicate individual oscillators. The lengths of the arrows represent the oscillator strengths, while the widths of the arrow heads denote the widths Γ. The thin back lines (bottom) are the data of Sun et al.22 for x = 0 and x = 0.1.

Mentions: Raw Raman spectra for the PTFO samples and a (001)-oriented LaAlO3 reference sample obtained under 442 nm (2.81 eV) excitation are presented in Fig. 6(a). As the films are not strongly absorbing at this wavelength, there is a strong component from the LaAlO3 substrate (black line). In contrast, using 325 nm (3.82 eV) excitation, where the film absorbs strongly, yields a dominant Raman signal from the PTFO films [coloured lines in Figure 6(b)], but over a more limited spectral range (see Methods). For the data obtained at 442 nm the subtraction of the substrate's contribution43 permits the Raman spectra of the PTFO films to be seen [coloured lines in Figure 6(c)]. The narrow gaps correspond to the sharp Raman active modes of the substrate, at 15.3 meV, 18.9 meV, 25.4 meV, 57.5 meV and 60.3 meV, corresponding well to previous reports4445.


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)

Raman spectra of PTFO films and LAO substrate: (a) Raman intensity I under 442 nm excitation. (b) I for 325 nm excitation. The dashed black line indicates a two-Lorentzian fit to the PTFO-200 spectra. (c) Raman intensity under 442 nm excitation after subtracting the substrate's contribution. The dashed black line is the model for PTFO-200 as described in the text and Table 2, where black arrows indicate individual oscillators. The lengths of the arrows represent the oscillator strengths, while the widths of the arrow heads denote the widths Γ. The thin back lines (bottom) are the data of Sun et al.22 for x = 0 and x = 0.1.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Raman spectra of PTFO films and LAO substrate: (a) Raman intensity I under 442 nm excitation. (b) I for 325 nm excitation. The dashed black line indicates a two-Lorentzian fit to the PTFO-200 spectra. (c) Raman intensity under 442 nm excitation after subtracting the substrate's contribution. The dashed black line is the model for PTFO-200 as described in the text and Table 2, where black arrows indicate individual oscillators. The lengths of the arrows represent the oscillator strengths, while the widths of the arrow heads denote the widths Γ. The thin back lines (bottom) are the data of Sun et al.22 for x = 0 and x = 0.1.
Mentions: Raw Raman spectra for the PTFO samples and a (001)-oriented LaAlO3 reference sample obtained under 442 nm (2.81 eV) excitation are presented in Fig. 6(a). As the films are not strongly absorbing at this wavelength, there is a strong component from the LaAlO3 substrate (black line). In contrast, using 325 nm (3.82 eV) excitation, where the film absorbs strongly, yields a dominant Raman signal from the PTFO films [coloured lines in Figure 6(b)], but over a more limited spectral range (see Methods). For the data obtained at 442 nm the subtraction of the substrate's contribution43 permits the Raman spectra of the PTFO films to be seen [coloured lines in Figure 6(c)]. The narrow gaps correspond to the sharp Raman active modes of the substrate, at 15.3 meV, 18.9 meV, 25.4 meV, 57.5 meV and 60.3 meV, corresponding well to previous reports4445.

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.