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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 measured electrical properties of batisite.The dielectric constant (a), dielectric loss (b) and conductivity (c) are shown as obtained at various temperatures. The lines are fits of the spectra at 501 and 601 K using Eqs. (1) and (2), performed simultaneously for ε′ and σ′ [the lines in (b) were calculated from those in (c)].
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f2: Frequency dependence of the measured electrical properties of batisite.The dielectric constant (a), dielectric loss (b) and conductivity (c) are shown as obtained at various temperatures. The lines are fits of the spectra at 501 and 601 K using Eqs. (1) and (2), performed simultaneously for ε′ and σ′ [the lines in (b) were calculated from those in (c)].

Mentions: Figure 2 shows the frequency dependence of the dielectric permittivity [real and imaginary part; frames (a) and (b), respectively] and the conductivity (c) of batisite measured at various temperatures. While at low temperatures (open symbols) ε′(ν) is only weakly frequency dependent, at higher temperatures (closed symbols) it exhibits a smooth decrease with increasing frequency. Similar behaviour is found for ε″(ν). In σ′(ν), the high-temperature spectra show a plateau at low frequencies before starting to increase with increasing frequency. At lower temperatures a continuous increase is observed throughout the whole frequency range. This overall behaviour of ε′(ν), ε″(ν) and σ′(ν) is typical for hopping conductivity of localized charge carriers, which leads to an approximate power-law increase of the conductivity, σ′ ∝ νs with s < 11115. Such behaviour correspond to the so-called “universal dielectric response” (UDR), observed in various materials16. Taking into account the dc conductivity σdc, one arrives at (σ0 is a prefactor). Via the Kramers-Kronig relation, Eq. (1) leads to a corresponding power law in the imaginary part of the conductivity, namely σ″ = tan(sπ/2)σ0νs (ref. 16). As the dielectric constant is directly related to σ″ via ε′ = σ″/(2πνε0) (with ε0 the permittivity of vacuum), hopping conduction is expected to lead to Here ε∞ was added to account for the high-frequency limit of the dielectric constant arising from the ionic and electronic polarizability. Equation (2) implies a divergence of the dielectric constant for low frequencies, which explains the high values of ε′ revealed in Figs. 1(a) and 2(a)8. To check if hopping conductivity indeed governs the high-temperature dielectric response of batisite, we have fitted the spectra for 501 and 600 K using Eqs. (1) and (2). The fits were simultaneously performed for ε′(ν) and σ′(ν). In ε′(ν) a good agreement of fit and experimental data was obtained. However, in the loss and conductivity only the results at the lower frequencies could be well described by this approach while marked deviations show up at high frequencies. They can be ascribed to the influence of the relaxation process, already mentioned in the above discussion of Fig. 1(b). The fit curves shown as lines in Fig. 2 were thus obtained by disregarding the results at the highest frequencies.


Dielectric characterization of a nonlinear optical material.

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

Frequency dependence of the measured electrical properties of batisite.The dielectric constant (a), dielectric loss (b) and conductivity (c) are shown as obtained at various temperatures. The lines are fits of the spectra at 501 and 601 K using Eqs. (1) and (2), performed simultaneously for ε′ and σ′ [the lines in (b) were calculated from those in (c)].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Frequency dependence of the measured electrical properties of batisite.The dielectric constant (a), dielectric loss (b) and conductivity (c) are shown as obtained at various temperatures. The lines are fits of the spectra at 501 and 601 K using Eqs. (1) and (2), performed simultaneously for ε′ and σ′ [the lines in (b) were calculated from those in (c)].
Mentions: Figure 2 shows the frequency dependence of the dielectric permittivity [real and imaginary part; frames (a) and (b), respectively] and the conductivity (c) of batisite measured at various temperatures. While at low temperatures (open symbols) ε′(ν) is only weakly frequency dependent, at higher temperatures (closed symbols) it exhibits a smooth decrease with increasing frequency. Similar behaviour is found for ε″(ν). In σ′(ν), the high-temperature spectra show a plateau at low frequencies before starting to increase with increasing frequency. At lower temperatures a continuous increase is observed throughout the whole frequency range. This overall behaviour of ε′(ν), ε″(ν) and σ′(ν) is typical for hopping conductivity of localized charge carriers, which leads to an approximate power-law increase of the conductivity, σ′ ∝ νs with s < 11115. Such behaviour correspond to the so-called “universal dielectric response” (UDR), observed in various materials16. Taking into account the dc conductivity σdc, one arrives at (σ0 is a prefactor). Via the Kramers-Kronig relation, Eq. (1) leads to a corresponding power law in the imaginary part of the conductivity, namely σ″ = tan(sπ/2)σ0νs (ref. 16). As the dielectric constant is directly related to σ″ via ε′ = σ″/(2πνε0) (with ε0 the permittivity of vacuum), hopping conduction is expected to lead to Here ε∞ was added to account for the high-frequency limit of the dielectric constant arising from the ionic and electronic polarizability. Equation (2) implies a divergence of the dielectric constant for low frequencies, which explains the high values of ε′ revealed in Figs. 1(a) and 2(a)8. To check if hopping conductivity indeed governs the high-temperature dielectric response of batisite, we have fitted the spectra for 501 and 600 K using Eqs. (1) and (2). The fits were simultaneously performed for ε′(ν) and σ′(ν). In ε′(ν) a good agreement of fit and experimental data was obtained. However, in the loss and conductivity only the results at the lower frequencies could be well described by this approach while marked deviations show up at high frequencies. They can be ascribed to the influence of the relaxation process, already mentioned in the above discussion of Fig. 1(b). The fit curves shown as lines in Fig. 2 were thus obtained by disregarding the results at the highest frequencies.

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