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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

Electric polarization and phase transition of KBiFe2O5.(a) Dielectric constant of KBiFe2O5 as a function of temperature measured at 101–4 Hz, using amplitude of 1 V. (b) Corresponding dielectric loss tangent as a function of temperature. (c) Polarized optical images of KBiFe2O5 single crystal from room temperature to 773 K showing polarizing light decreasing with temperature and disappearing at 773 K. The transition temperature of 773 K roughly coincides with the cell-doubling transition at 773 K determined by XRD. (d) Topography image (top left) and the corresponding PFM image (top right) along with local piezoelectric response hysteresis loop (bottom) of KBiFe2O5 single crystal. (e) P-E hysteresis loops measured at room temperature at increasing scan field ranges.
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f4: Electric polarization and phase transition of KBiFe2O5.(a) Dielectric constant of KBiFe2O5 as a function of temperature measured at 101–4 Hz, using amplitude of 1 V. (b) Corresponding dielectric loss tangent as a function of temperature. (c) Polarized optical images of KBiFe2O5 single crystal from room temperature to 773 K showing polarizing light decreasing with temperature and disappearing at 773 K. The transition temperature of 773 K roughly coincides with the cell-doubling transition at 773 K determined by XRD. (d) Topography image (top left) and the corresponding PFM image (top right) along with local piezoelectric response hysteresis loop (bottom) of KBiFe2O5 single crystal. (e) P-E hysteresis loops measured at room temperature at increasing scan field ranges.

Mentions: Inspired by the noncentrosymmetric structure and calculated polarization, we further investigated polarization-related properties. However, it should be noted that, because of the anticipated small bandgap (Eg) of this material, the activation of electronic conduction (with an activation energy Eg/2) will intervene complicating the interpretation of the data. First, the temperature and frequency dependence of dielectric constant (ε) and loss tangent (tan δ) was investigated using ceramic sample. The limiting high-frequency (104 Hz) dielectric constant at room temperature is 9 suggesting little intrinsic polarizability, yet the temperature dependence of ε and tan δ (Fig. 4a and 4b) is rather rich showing a strong dispersion in that their values decrease sharply with increasing frequency. Below 850 K they may be deconvoluted into two broad intermediate-temperature peaks. (a) A low temperature ε peak at ~640 K (the tan δ rise starting at 500 K). This feature could indicate relaxation of structural polarization (antiferroelectric or antiferromagnetic), onset of Maxwell-Wagner relaxation associated with the onset of electronic conduction divided by insulating internal boundaries, or residual oxygen vacancies similarly reported in other perovskite ferrites32. (b) A high temperature peak in ε at 780 K, which roughly coincides with the orthorhombic-to-orthorhombic cell-doubling temperature that is antiferroelectric-like3334. Above 850 K, both ε and tan δ rapidly increase which is most likely due to the (irreversible) phase transition to the monoclinic phase, which may also have increased conductivity. Evidence for the antiferroelectric-like transition was also observed by differential scanning calorimetry (Supplementary Fig. S14), but more direct evidence for a polarization transition was provided by polarized optical microscopy in Fig. 4c, which shows disappearance of polarized light above 780 K. Lastly, when the stable monoclinic phase formed by heating above 850 K was subsequently cooled, it showed no dielectric anomaly during cooling and reheating between 900 K and room temperature (Supplementary Fig. S15). This indicates that it is paraelectric unlike the low temperature orthorhombic polymorphs, and it is not associated with the antiferroelectric-paraelectric transition. Future work is required to more firmly establish the relation between polarization transition and dielectric spectra.


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)

Electric polarization and phase transition of KBiFe2O5.(a) Dielectric constant of KBiFe2O5 as a function of temperature measured at 101–4 Hz, using amplitude of 1 V. (b) Corresponding dielectric loss tangent as a function of temperature. (c) Polarized optical images of KBiFe2O5 single crystal from room temperature to 773 K showing polarizing light decreasing with temperature and disappearing at 773 K. The transition temperature of 773 K roughly coincides with the cell-doubling transition at 773 K determined by XRD. (d) Topography image (top left) and the corresponding PFM image (top right) along with local piezoelectric response hysteresis loop (bottom) of KBiFe2O5 single crystal. (e) P-E hysteresis loops measured at room temperature at increasing scan field ranges.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Electric polarization and phase transition of KBiFe2O5.(a) Dielectric constant of KBiFe2O5 as a function of temperature measured at 101–4 Hz, using amplitude of 1 V. (b) Corresponding dielectric loss tangent as a function of temperature. (c) Polarized optical images of KBiFe2O5 single crystal from room temperature to 773 K showing polarizing light decreasing with temperature and disappearing at 773 K. The transition temperature of 773 K roughly coincides with the cell-doubling transition at 773 K determined by XRD. (d) Topography image (top left) and the corresponding PFM image (top right) along with local piezoelectric response hysteresis loop (bottom) of KBiFe2O5 single crystal. (e) P-E hysteresis loops measured at room temperature at increasing scan field ranges.
Mentions: Inspired by the noncentrosymmetric structure and calculated polarization, we further investigated polarization-related properties. However, it should be noted that, because of the anticipated small bandgap (Eg) of this material, the activation of electronic conduction (with an activation energy Eg/2) will intervene complicating the interpretation of the data. First, the temperature and frequency dependence of dielectric constant (ε) and loss tangent (tan δ) was investigated using ceramic sample. The limiting high-frequency (104 Hz) dielectric constant at room temperature is 9 suggesting little intrinsic polarizability, yet the temperature dependence of ε and tan δ (Fig. 4a and 4b) is rather rich showing a strong dispersion in that their values decrease sharply with increasing frequency. Below 850 K they may be deconvoluted into two broad intermediate-temperature peaks. (a) A low temperature ε peak at ~640 K (the tan δ rise starting at 500 K). This feature could indicate relaxation of structural polarization (antiferroelectric or antiferromagnetic), onset of Maxwell-Wagner relaxation associated with the onset of electronic conduction divided by insulating internal boundaries, or residual oxygen vacancies similarly reported in other perovskite ferrites32. (b) A high temperature peak in ε at 780 K, which roughly coincides with the orthorhombic-to-orthorhombic cell-doubling temperature that is antiferroelectric-like3334. Above 850 K, both ε and tan δ rapidly increase which is most likely due to the (irreversible) phase transition to the monoclinic phase, which may also have increased conductivity. Evidence for the antiferroelectric-like transition was also observed by differential scanning calorimetry (Supplementary Fig. S14), but more direct evidence for a polarization transition was provided by polarized optical microscopy in Fig. 4c, which shows disappearance of polarized light above 780 K. Lastly, when the stable monoclinic phase formed by heating above 850 K was subsequently cooled, it showed no dielectric anomaly during cooling and reheating between 900 K and room temperature (Supplementary Fig. S15). This indicates that it is paraelectric unlike the low temperature orthorhombic polymorphs, and it is not associated with the antiferroelectric-paraelectric transition. Future work is required to more firmly establish the relation between polarization transition and dielectric spectra.

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