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Thermal frequency shift and tunable microwave absorption in BiFeO3 family.

Li Y, Fang X, Cao M - Sci Rep (2016)

Bottom Line: It exhibits an unexpected result: the relaxation shifts to lower frequency with increasing temperature.The microwave absorption of La/Nd doped BFO surpasses -20 dB at 673 K, and the minimum reflection loss of La doped BFO reaches -39 dB.These results open a new pathway to develop BFO-based materials in electromagnetic functional materials and devices for tunable frequency, stealth and thermal imaging at long wavelength.

View Article: PubMed Central - PubMed

Affiliation: School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081, China.

ABSTRACT
Tunable frequency is highly sought-after task of researcher, because of the potential for applications in selecting frequency, absorber, imaging and biomedical diagnosis. Here, we report the original observation of thermal frequency shift of dielectric relaxation in La/Nd doped BiFeO3 (BFO) in X-band from 300 to 673 K. It exhibits an unexpected result: the relaxation shifts to lower frequency with increasing temperature. The relaxation maximally shifts about a quarter of X-band. The nonlinear term of lattice vibration plays an important role in the frequency shift. The frequency shift leads to tuning microwave absorption, which almost covers the whole X-band by changing temperature. Meanwhile, the great increase of dielectric loss of La/Nd doped BFO due to thermal excited electron hopping enhances microwave absorption above ~460 and ~480 K, respectively. The microwave absorption of La/Nd doped BFO surpasses -20 dB at 673 K, and the minimum reflection loss of La doped BFO reaches -39 dB. These results open a new pathway to develop BFO-based materials in electromagnetic functional materials and devices for tunable frequency, stealth and thermal imaging at long wavelength.

No MeSH data available.


The reflection loss of (a) BFO, (b) La doped BFO and (c) Nd doped BFO. (d) The minimum reflection loss of BFO and La/Nd doped BFO at different temperature. (e) The reflection loss of BFO and La/Nd doped BFO versus frequency at 673 K.
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f4: The reflection loss of (a) BFO, (b) La doped BFO and (c) Nd doped BFO. (d) The minimum reflection loss of BFO and La/Nd doped BFO at different temperature. (e) The reflection loss of BFO and La/Nd doped BFO versus frequency at 673 K.

Mentions: where c is the light velocity, f the electromagnetic wave frequency, d the thickness of the absorber, εr the complex permittivity, and μr the complex permeability. Figure 4a–c show the RL of all samples with thickness (d) of 1.8 mm at 300–673 K. With increasing temperature, the absorption peak shifts to low frequency. The absorption peak of BFO shifts ~1.6 GHz from 300 K to 673 K. The absorption peak of La doped BFO and Nd doped BFO shifts ~3.2 GHz and ~2.8 GHz, respectively. This indicates that La/Nd doped BFO can tune absorption frequency in much wider frequency range by thermal driving. The tunable feature of microwave absorption is attributed to the shift of the relaxation by varying the temperature. With increasing temperature, the RL of all samples increases. Compared with BFO, La/Nd doped BFO possesses stronger microwave absorption at high temperature. The minimum (Min.) RL of La doped BFO reaches −39 dB at 673 K, which is 2 times higher than that of BFO (Fig. 4d). The Min. RL of Nd doped BFO surpasses −20 dB at 673 K (Fig. 4e). The increase of microwave absorption for La/Nd doped BFO at high temperature is attributed to the increase of imaginary permittivity. It is found that the εc” increases respectively above ~460 and ~480 K due to the increase of hopping conduction, which plays an important role in the increase of imaginary permittivity (Fig. S10). Therefore, the ability of varying temperature to tune absorption frequency and enhanced microwave absorption indicate that La/Nd doped BFO may be high-efficiency and smart absorber.


Thermal frequency shift and tunable microwave absorption in BiFeO3 family.

Li Y, Fang X, Cao M - Sci Rep (2016)

The reflection loss of (a) BFO, (b) La doped BFO and (c) Nd doped BFO. (d) The minimum reflection loss of BFO and La/Nd doped BFO at different temperature. (e) The reflection loss of BFO and La/Nd doped BFO versus frequency at 673 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837409&req=5

f4: The reflection loss of (a) BFO, (b) La doped BFO and (c) Nd doped BFO. (d) The minimum reflection loss of BFO and La/Nd doped BFO at different temperature. (e) The reflection loss of BFO and La/Nd doped BFO versus frequency at 673 K.
Mentions: where c is the light velocity, f the electromagnetic wave frequency, d the thickness of the absorber, εr the complex permittivity, and μr the complex permeability. Figure 4a–c show the RL of all samples with thickness (d) of 1.8 mm at 300–673 K. With increasing temperature, the absorption peak shifts to low frequency. The absorption peak of BFO shifts ~1.6 GHz from 300 K to 673 K. The absorption peak of La doped BFO and Nd doped BFO shifts ~3.2 GHz and ~2.8 GHz, respectively. This indicates that La/Nd doped BFO can tune absorption frequency in much wider frequency range by thermal driving. The tunable feature of microwave absorption is attributed to the shift of the relaxation by varying the temperature. With increasing temperature, the RL of all samples increases. Compared with BFO, La/Nd doped BFO possesses stronger microwave absorption at high temperature. The minimum (Min.) RL of La doped BFO reaches −39 dB at 673 K, which is 2 times higher than that of BFO (Fig. 4d). The Min. RL of Nd doped BFO surpasses −20 dB at 673 K (Fig. 4e). The increase of microwave absorption for La/Nd doped BFO at high temperature is attributed to the increase of imaginary permittivity. It is found that the εc” increases respectively above ~460 and ~480 K due to the increase of hopping conduction, which plays an important role in the increase of imaginary permittivity (Fig. S10). Therefore, the ability of varying temperature to tune absorption frequency and enhanced microwave absorption indicate that La/Nd doped BFO may be high-efficiency and smart absorber.

Bottom Line: It exhibits an unexpected result: the relaxation shifts to lower frequency with increasing temperature.The microwave absorption of La/Nd doped BFO surpasses -20 dB at 673 K, and the minimum reflection loss of La doped BFO reaches -39 dB.These results open a new pathway to develop BFO-based materials in electromagnetic functional materials and devices for tunable frequency, stealth and thermal imaging at long wavelength.

View Article: PubMed Central - PubMed

Affiliation: School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081, China.

ABSTRACT
Tunable frequency is highly sought-after task of researcher, because of the potential for applications in selecting frequency, absorber, imaging and biomedical diagnosis. Here, we report the original observation of thermal frequency shift of dielectric relaxation in La/Nd doped BiFeO3 (BFO) in X-band from 300 to 673 K. It exhibits an unexpected result: the relaxation shifts to lower frequency with increasing temperature. The relaxation maximally shifts about a quarter of X-band. The nonlinear term of lattice vibration plays an important role in the frequency shift. The frequency shift leads to tuning microwave absorption, which almost covers the whole X-band by changing temperature. Meanwhile, the great increase of dielectric loss of La/Nd doped BFO due to thermal excited electron hopping enhances microwave absorption above ~460 and ~480 K, respectively. The microwave absorption of La/Nd doped BFO surpasses -20 dB at 673 K, and the minimum reflection loss of La doped BFO reaches -39 dB. These results open a new pathway to develop BFO-based materials in electromagnetic functional materials and devices for tunable frequency, stealth and thermal imaging at long wavelength.

No MeSH data available.