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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 polarization part (εp”) versus frequency in (a) BFO, (b) La doped BFO and (c) Nd doped BFO. The insets show the distance of relaxation shift from 300 K to 673 K. The arrows represent the shift direction of relaxation peak with increasing temperature.
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f2: The polarization part (εp”) versus frequency in (a) BFO, (b) La doped BFO and (c) Nd doped BFO. The insets show the distance of relaxation shift from 300 K to 673 K. The arrows represent the shift direction of relaxation peak with increasing temperature.

Mentions: The imaginary permittivity consists of conduction part (εc”) and polarization part (εp”). According to the conductivity (Fig. S2), the frequency dependence of εc” is acquired (Fig. S3). The εc” of La/Nd doped BFO is bigger than that of BFO due to the abrupt rise of the conductivity above ~460 and ~480 K, respectively (Fig. S2). The electron hopping plays an important part in the great increase of conductivity2122. The εp” of all samples versus frequency from 300 to 673 K are shown in Fig. 2. After subtracting εc” from imaginary permittivity, the dielectric relaxation is obviously observed in the εp” of all samples. It is noted that two relaxations (relaxation A and relaxation B) appear in BFO, which are located respectively at ~9.6 GHz and ~11.8 GHz, hardly shift with increasing temperature. For La/Nd doped BFO, however, only one relaxation appears in the frequency range, and shifts to low frequency with increasing temperature (the whole data in Fig. S4). The relaxation of La doped BFO shifts 1.1 GHz and the relaxation of Nd doped BFO shifts 0.2 GHz (inset in Fig. 3b,c).


Thermal frequency shift and tunable microwave absorption in BiFeO3 family.

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

The polarization part (εp”) versus frequency in (a) BFO, (b) La doped BFO and (c) Nd doped BFO. The insets show the distance of relaxation shift from 300 K to 673 K. The arrows represent the shift direction of relaxation peak with increasing temperature.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: The polarization part (εp”) versus frequency in (a) BFO, (b) La doped BFO and (c) Nd doped BFO. The insets show the distance of relaxation shift from 300 K to 673 K. The arrows represent the shift direction of relaxation peak with increasing temperature.
Mentions: The imaginary permittivity consists of conduction part (εc”) and polarization part (εp”). According to the conductivity (Fig. S2), the frequency dependence of εc” is acquired (Fig. S3). The εc” of La/Nd doped BFO is bigger than that of BFO due to the abrupt rise of the conductivity above ~460 and ~480 K, respectively (Fig. S2). The electron hopping plays an important part in the great increase of conductivity2122. The εp” of all samples versus frequency from 300 to 673 K are shown in Fig. 2. After subtracting εc” from imaginary permittivity, the dielectric relaxation is obviously observed in the εp” of all samples. It is noted that two relaxations (relaxation A and relaxation B) appear in BFO, which are located respectively at ~9.6 GHz and ~11.8 GHz, hardly shift with increasing temperature. For La/Nd doped BFO, however, only one relaxation appears in the frequency range, and shifts to low frequency with increasing temperature (the whole data in Fig. S4). The relaxation of La doped BFO shifts 1.1 GHz and the relaxation of Nd doped BFO shifts 0.2 GHz (inset in Fig. 3b,c).

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.