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Dielectric characterization of a nonlinear optical material.

Lunkenheimer P, Krohns S, Gemander F, Schmahl WW, Loidl A - Sci Rep (2014)

Bottom Line: No evidence for ferro- or antiferroelectric polarization is found.As the second-harmonic generation observed in batisite points to a non-centrosymmetric structure, this material is piezoelectric, but most likely not ferroelectric.In addition, we found evidence for hopping charge transport of localized charge carriers and a relaxational process at low temperatures.

View Article: PubMed Central - PubMed

Affiliation: Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany.

ABSTRACT
Batisite was reported to be a nonlinear optical material showing second harmonic generation. Using dielectric spectroscopy and polarization measurements, we provide a thorough investigation of the dielectric and charge-transport properties of this material. Batisite shows the typical characteristics of a linear lossy dielectric. No evidence for ferro- or antiferroelectric polarization is found. As the second-harmonic generation observed in batisite points to a non-centrosymmetric structure, this material is piezoelectric, but most likely not ferroelectric. In addition, we found evidence for hopping charge transport of localized charge carriers and a relaxational process at low temperatures.

No MeSH data available.


Related in: MedlinePlus

Frequency dependence of the dielectric loss of batisite.The spectra were measured at various temperatures (from top to bottom: 349 K, 322 K, 300 K, 276 K, 250 K, 226 K, 200 K, 174 K, 150 K, 110 K, 62 K; to keep Fig. 1 readable, only part of these temperatures were shown there). The inset shows the temperature dependence of the relaxation times calculated from the loss-peak frequencies in an Arrhenius representation. The red line is a linear fit demonstrating thermally activated behaviour with an energy barrier of 0.52 eV. The blue line shows a fit with the VFT law (τ0 = 1.1 × 10−11 s, B = 2100 K, TVF = 78 K).
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f3: Frequency dependence of the dielectric loss of batisite.The spectra were measured at various temperatures (from top to bottom: 349 K, 322 K, 300 K, 276 K, 250 K, 226 K, 200 K, 174 K, 150 K, 110 K, 62 K; to keep Fig. 1 readable, only part of these temperatures were shown there). The inset shows the temperature dependence of the relaxation times calculated from the loss-peak frequencies in an Arrhenius representation. The red line is a linear fit demonstrating thermally activated behaviour with an energy barrier of 0.52 eV. The blue line shows a fit with the VFT law (τ0 = 1.1 × 10−11 s, B = 2100 K, TVF = 78 K).

Mentions: Just as for the temperature dependence, relaxation processes should lead to peaks in the frequency dependence of ε″, too910. Already in Fig. 2(b) such behaviour can be suspected for the lower temperatures (open symbols) and it becomes clearly obvious in the magnified view of this region provided by Fig. 3. The detected loss peaks strongly shift to lower frequencies with decreasing temperature, finally dropping out of the investigated frequency window. This mirrors the continuous slowing down of the relaxational dynamics. Via the relation τ ≈ 1/(2πνp), the relaxation time τ, characterizing the mobility of the relaxing entities, can be estimated from the peak frequencies νp9. The inset of Fig. 3 shows the obtained temperature dependence of τ in Arrhenius representation. The found nearly linear increase of log[τ(1/T)] corresponds to thermally activated behaviour, τ ∝ exp(E/kBT). From the slope of the linear fit curve (red line in the inset of Fig. 3) we deduce a hindering barrier E = 0.52 eV. However, a close inspection of the inset of Fig. 3 reveals a small but systematic deviation of log[τ(1/T)] from linear behaviour. The blue line is a fit with the empirical Vogel-Fulcher-Tammann (VFT) law, τ = τ0 exp[B/(T − TVF)]171819, which leads so somewhat better agreement with the experimental data. In analogy to the interpretation of the commonly found VFT behaviour of supercooled liquids10202122, this finding seems to indicate an increasing cooperativity of the relaxational motions at low temperatures.


Dielectric characterization of a nonlinear optical material.

Lunkenheimer P, Krohns S, Gemander F, Schmahl WW, Loidl A - Sci Rep (2014)

Frequency dependence of the dielectric loss of batisite.The spectra were measured at various temperatures (from top to bottom: 349 K, 322 K, 300 K, 276 K, 250 K, 226 K, 200 K, 174 K, 150 K, 110 K, 62 K; to keep Fig. 1 readable, only part of these temperatures were shown there). The inset shows the temperature dependence of the relaxation times calculated from the loss-peak frequencies in an Arrhenius representation. The red line is a linear fit demonstrating thermally activated behaviour with an energy barrier of 0.52 eV. The blue line shows a fit with the VFT law (τ0 = 1.1 × 10−11 s, B = 2100 K, TVF = 78 K).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4127497&req=5

f3: Frequency dependence of the dielectric loss of batisite.The spectra were measured at various temperatures (from top to bottom: 349 K, 322 K, 300 K, 276 K, 250 K, 226 K, 200 K, 174 K, 150 K, 110 K, 62 K; to keep Fig. 1 readable, only part of these temperatures were shown there). The inset shows the temperature dependence of the relaxation times calculated from the loss-peak frequencies in an Arrhenius representation. The red line is a linear fit demonstrating thermally activated behaviour with an energy barrier of 0.52 eV. The blue line shows a fit with the VFT law (τ0 = 1.1 × 10−11 s, B = 2100 K, TVF = 78 K).
Mentions: Just as for the temperature dependence, relaxation processes should lead to peaks in the frequency dependence of ε″, too910. Already in Fig. 2(b) such behaviour can be suspected for the lower temperatures (open symbols) and it becomes clearly obvious in the magnified view of this region provided by Fig. 3. The detected loss peaks strongly shift to lower frequencies with decreasing temperature, finally dropping out of the investigated frequency window. This mirrors the continuous slowing down of the relaxational dynamics. Via the relation τ ≈ 1/(2πνp), the relaxation time τ, characterizing the mobility of the relaxing entities, can be estimated from the peak frequencies νp9. The inset of Fig. 3 shows the obtained temperature dependence of τ in Arrhenius representation. The found nearly linear increase of log[τ(1/T)] corresponds to thermally activated behaviour, τ ∝ exp(E/kBT). From the slope of the linear fit curve (red line in the inset of Fig. 3) we deduce a hindering barrier E = 0.52 eV. However, a close inspection of the inset of Fig. 3 reveals a small but systematic deviation of log[τ(1/T)] from linear behaviour. The blue line is a fit with the empirical Vogel-Fulcher-Tammann (VFT) law, τ = τ0 exp[B/(T − TVF)]171819, which leads so somewhat better agreement with the experimental data. In analogy to the interpretation of the commonly found VFT behaviour of supercooled liquids10202122, this finding seems to indicate an increasing cooperativity of the relaxational motions at low temperatures.

Bottom Line: No evidence for ferro- or antiferroelectric polarization is found.As the second-harmonic generation observed in batisite points to a non-centrosymmetric structure, this material is piezoelectric, but most likely not ferroelectric.In addition, we found evidence for hopping charge transport of localized charge carriers and a relaxational process at low temperatures.

View Article: PubMed Central - PubMed

Affiliation: Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany.

ABSTRACT
Batisite was reported to be a nonlinear optical material showing second harmonic generation. Using dielectric spectroscopy and polarization measurements, we provide a thorough investigation of the dielectric and charge-transport properties of this material. Batisite shows the typical characteristics of a linear lossy dielectric. No evidence for ferro- or antiferroelectric polarization is found. As the second-harmonic generation observed in batisite points to a non-centrosymmetric structure, this material is piezoelectric, but most likely not ferroelectric. In addition, we found evidence for hopping charge transport of localized charge carriers and a relaxational process at low temperatures.

No MeSH data available.


Related in: MedlinePlus