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New high T(c) multiferroics KBiFe₂O₅ with narrow band gap and promising photovoltaic effect.

Zhang G, Wu H, Li G, Huang Q, Yang C, Huang F, Liao F, Lin J - Sci Rep (2013)

Bottom Line: Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties.Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities.The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P.R. China.

ABSTRACT
Intrinsic polarization of ferroelectrics (FE) helps separate photon-generated charge carriers thus enhances photovoltaic effects. However, traditional FE with transition-metal cations (M) of d⁰ electron in MO₆ network typically has a band gap (E(g)) exceeding 3.0 eV. Although a smaller E(g) (2.6 eV) can be obtained in multiferroic BiFeO₃, the value is still too high for optimal solar energy applications. Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties. Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities. The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃. This finding may open a new avenue to discovering and designing optimal FE compounds for solar energy applications.

No MeSH data available.


Related in: MedlinePlus

Magnetic structure and weak ferromagnetism of KBiFe2O5.(a) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 300 K. Vertical bars indicate calculated positions of Bragg peaks from the nuclear phase (upper) and the magnetic phase (lower). λ = 1.5403 Å. Space group P21cn, No. 33, a = 7.9855(1) Å, b = 11.8225(1) Å, c = 5.7396(1) Å, V = 541.87(1) Å3; Rwp = 0.0373, Rp = 0.0316, χ2 = 1.230. Magnetic symmetry of Shubnikov group: P21′cn′ with Fe moment of 3.77(2) μB along c-axis direction. (Inset: Refinement with nuclear phase only. Difference profile shows reflections from magnetic phase). (b) Magnetic and crystal structure of KBiFe2O5 (P21cn cell). (c) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 4 K under 6 T magnetic field. Vertical bars indicate the calculated positions of Bragg peaks from the nuclear phase P21cn (upper), from the G-type antiferromagnetic phase P21′cn′ (lower), and from the ferromagnetic phase P21c′n′ at 6 T (bottom). λ = 1.5403 Å. Rwp = 0.0619, Rp = 0.0490, χ2 = 1.348. (d) Temperature dependence of the magnetic (110) reflection indicative of a magnetic phase transition at ~560 K. (e) Magnetization (M) measured at three fields showing near coincidence of ZFC and FC data except at the lowest temperature at 1 kOe and 2 kOe. Magnetic transition at 2 kOe occurs at about 550 K. (f) Magnetization-field (H) curves at 3 K, 30 K and 300 K.
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f3: Magnetic structure and weak ferromagnetism of KBiFe2O5.(a) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 300 K. Vertical bars indicate calculated positions of Bragg peaks from the nuclear phase (upper) and the magnetic phase (lower). λ = 1.5403 Å. Space group P21cn, No. 33, a = 7.9855(1) Å, b = 11.8225(1) Å, c = 5.7396(1) Å, V = 541.87(1) Å3; Rwp = 0.0373, Rp = 0.0316, χ2 = 1.230. Magnetic symmetry of Shubnikov group: P21′cn′ with Fe moment of 3.77(2) μB along c-axis direction. (Inset: Refinement with nuclear phase only. Difference profile shows reflections from magnetic phase). (b) Magnetic and crystal structure of KBiFe2O5 (P21cn cell). (c) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 4 K under 6 T magnetic field. Vertical bars indicate the calculated positions of Bragg peaks from the nuclear phase P21cn (upper), from the G-type antiferromagnetic phase P21′cn′ (lower), and from the ferromagnetic phase P21c′n′ at 6 T (bottom). λ = 1.5403 Å. Rwp = 0.0619, Rp = 0.0490, χ2 = 1.348. (d) Temperature dependence of the magnetic (110) reflection indicative of a magnetic phase transition at ~560 K. (e) Magnetization (M) measured at three fields showing near coincidence of ZFC and FC data except at the lowest temperature at 1 kOe and 2 kOe. Magnetic transition at 2 kOe occurs at about 550 K. (f) Magnetization-field (H) curves at 3 K, 30 K and 300 K.

Mentions: Neutron powder diffraction (NPD) experiments from 4 K to 863 K (Fig. 3 and Supplementary Fig. S7–9 and Table S4–7) were conducted to delineate any structural transition and to clarify magnetic structure. According to the NPD data refinement, there is no structural transition from 4 K to 698 K, although high temperature XRD (Supplementary Fig. S10) did reveal a gradual distortion manifest as some peak splitting culminating in a cell-doubling at about 773 K (space group Pnna), which is reminiscent of antiferroelectric structures2728. Finally, above ~848 K KBiFe2O5 irreversibly transforms to a monoclinic structure (space group P2/c) according to both NPD at 863 K (Supplementary Fig. S9) and XRD at 933 K (Supplementary Fig. S10). Such irreversible transition implies that the orthorhombic structure is metastable (no evidence of decomposition was observed from the thermogravimetric analysis given in Supplementary Fig. S11). A similarly irreversible structural transition has been reported in a multiferroic perovskite in which both A site and B site are shared by In and Fe29.


New high T(c) multiferroics KBiFe₂O₅ with narrow band gap and promising photovoltaic effect.

Zhang G, Wu H, Li G, Huang Q, Yang C, Huang F, Liao F, Lin J - Sci Rep (2013)

Magnetic structure and weak ferromagnetism of KBiFe2O5.(a) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 300 K. Vertical bars indicate calculated positions of Bragg peaks from the nuclear phase (upper) and the magnetic phase (lower). λ = 1.5403 Å. Space group P21cn, No. 33, a = 7.9855(1) Å, b = 11.8225(1) Å, c = 5.7396(1) Å, V = 541.87(1) Å3; Rwp = 0.0373, Rp = 0.0316, χ2 = 1.230. Magnetic symmetry of Shubnikov group: P21′cn′ with Fe moment of 3.77(2) μB along c-axis direction. (Inset: Refinement with nuclear phase only. Difference profile shows reflections from magnetic phase). (b) Magnetic and crystal structure of KBiFe2O5 (P21cn cell). (c) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 4 K under 6 T magnetic field. Vertical bars indicate the calculated positions of Bragg peaks from the nuclear phase P21cn (upper), from the G-type antiferromagnetic phase P21′cn′ (lower), and from the ferromagnetic phase P21c′n′ at 6 T (bottom). λ = 1.5403 Å. Rwp = 0.0619, Rp = 0.0490, χ2 = 1.348. (d) Temperature dependence of the magnetic (110) reflection indicative of a magnetic phase transition at ~560 K. (e) Magnetization (M) measured at three fields showing near coincidence of ZFC and FC data except at the lowest temperature at 1 kOe and 2 kOe. Magnetic transition at 2 kOe occurs at about 550 K. (f) Magnetization-field (H) curves at 3 K, 30 K and 300 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3569630&req=5

f3: Magnetic structure and weak ferromagnetism of KBiFe2O5.(a) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 300 K. Vertical bars indicate calculated positions of Bragg peaks from the nuclear phase (upper) and the magnetic phase (lower). λ = 1.5403 Å. Space group P21cn, No. 33, a = 7.9855(1) Å, b = 11.8225(1) Å, c = 5.7396(1) Å, V = 541.87(1) Å3; Rwp = 0.0373, Rp = 0.0316, χ2 = 1.230. Magnetic symmetry of Shubnikov group: P21′cn′ with Fe moment of 3.77(2) μB along c-axis direction. (Inset: Refinement with nuclear phase only. Difference profile shows reflections from magnetic phase). (b) Magnetic and crystal structure of KBiFe2O5 (P21cn cell). (c) Experimental (circles), calculated (line), and difference (“noise” at bottom) NPD profiles for KBiFe2O5 at 4 K under 6 T magnetic field. Vertical bars indicate the calculated positions of Bragg peaks from the nuclear phase P21cn (upper), from the G-type antiferromagnetic phase P21′cn′ (lower), and from the ferromagnetic phase P21c′n′ at 6 T (bottom). λ = 1.5403 Å. Rwp = 0.0619, Rp = 0.0490, χ2 = 1.348. (d) Temperature dependence of the magnetic (110) reflection indicative of a magnetic phase transition at ~560 K. (e) Magnetization (M) measured at three fields showing near coincidence of ZFC and FC data except at the lowest temperature at 1 kOe and 2 kOe. Magnetic transition at 2 kOe occurs at about 550 K. (f) Magnetization-field (H) curves at 3 K, 30 K and 300 K.
Mentions: Neutron powder diffraction (NPD) experiments from 4 K to 863 K (Fig. 3 and Supplementary Fig. S7–9 and Table S4–7) were conducted to delineate any structural transition and to clarify magnetic structure. According to the NPD data refinement, there is no structural transition from 4 K to 698 K, although high temperature XRD (Supplementary Fig. S10) did reveal a gradual distortion manifest as some peak splitting culminating in a cell-doubling at about 773 K (space group Pnna), which is reminiscent of antiferroelectric structures2728. Finally, above ~848 K KBiFe2O5 irreversibly transforms to a monoclinic structure (space group P2/c) according to both NPD at 863 K (Supplementary Fig. S9) and XRD at 933 K (Supplementary Fig. S10). Such irreversible transition implies that the orthorhombic structure is metastable (no evidence of decomposition was observed from the thermogravimetric analysis given in Supplementary Fig. S11). A similarly irreversible structural transition has been reported in a multiferroic perovskite in which both A site and B site are shared by In and Fe29.

Bottom Line: Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties.Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities.The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P.R. China.

ABSTRACT
Intrinsic polarization of ferroelectrics (FE) helps separate photon-generated charge carriers thus enhances photovoltaic effects. However, traditional FE with transition-metal cations (M) of d⁰ electron in MO₆ network typically has a band gap (E(g)) exceeding 3.0 eV. Although a smaller E(g) (2.6 eV) can be obtained in multiferroic BiFeO₃, the value is still too high for optimal solar energy applications. Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties. Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities. The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃. This finding may open a new avenue to discovering and designing optimal FE compounds for solar energy applications.

No MeSH data available.


Related in: MedlinePlus