A. Levstik’s research while affiliated with Jožef Stefan Institute and other places

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Publications (190)


Polaron conductivity mechanism in potassium acid phthalate crystal: AC-conductivity investigation
  • Article

August 2016

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18 Reads

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1 Citation

Japanese Journal of Applied Physics

Cene Filipič

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Iva Levstik

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Adrijan Levstik

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Dušan Hadži

The complex dielectric constant, epsilon*(v, T), of potassium acid phthalate monocrystal (KAP) was investigated over the broad frequency and temperature range. While the imaginary part of dielectric constant epsilon"(v) increases rapidly with increasing temperature in the studied temperature range, the real part of dielectric constant epsilon'(v) increases only at high temperatures; there is almost no change of epsilon'(v) below 200 K. Both values of epsilon' and epsilon" are frequency dependent; the values increase with decreasing frequencies. At temperatures below 450K the ac electrical conductivity and dielectric constant follow simultaneously the universal dielectric response ( UDR). The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that this mechanism governs the charge transport in KAP crystal in the studied temperature range. (C) 2016 The Japan Society of Applied Physics


Dielectric relaxation in pure and Co-doped Bi12GeO20 single crystals
  • Article
  • Full-text available

August 2015

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79 Reads

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3 Citations

C. Filipič

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A. Klos

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[...]

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A. Levstik

We report the results of investigation of dielectric spectroscopy study of single crystals of Bi12GeO20 and Bi12GeO20 doped with Co nanoparticles. The complex dielectric constant was measured in the temperature interval from 5 to 450 K and frequencies from 1 Hz to 1 MHz. The electrical conductivity of both samples was thermally activated with potential barriers of 0.55 eV and 0.59 eV, respectively. Doped samples had bigger complex dielectric constants and σ′ exhibited slightly steeper temperature dependence than in the pure sample. The dielectric relaxation was observed in pure and doped single crystals and relaxation frequencies showed similar activation energies as electrical conductivities.

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Table 1 . Polaron parameters of samples. 
Fig. 5. Temperature dependence of the UDR parameter s, for Pb 5 Cr 3 F 19 , determined from the simultaneous fits of the experimental 0 ðÞ and " 0 ðÞ data (as presented in Fig. 4). The solid line is the fit to a model for small polaron tunneling [Eqs. (1) and (2)]. 
Fig. 6. (Color online) M 00 versus M 0 at four temperatures in Pb 5 Cr 3 F 19. The solid lines serve as a guide for the eye. M 1 is extrapolated by the red straight line at high frequencies. 
Femtosecond tunneling of polarons in Pb5Cr3F19

July 2014

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70 Reads

The complex dielectric constant/ac electrical conductivity was investigated as a function of frequency and temperature in Pb5Cr3F19. The system undergoes a ferroelectric phase transition at higher temperatures. At lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response (UDR) σ′ ∝ νs, typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in Pb5Cr3F19. The value of the inverse attempt frequency τ0 indicates the femtosecond tunneling of polarons in the system similar to the Büttiker–Landauer transversal time.


Polaronic behavior of La0.8Te0.2MnO3

December 2013

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17 Reads

We have analyzed recently published data of the ac electrical conductivity and dielectric constant in La0.8Te0.2MnO3 (LTMO), and at temperatures below 500 K both quantities follow the universal dielectric response (UDR) typical of hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 500 K, this mechanism governs the charge transport in LTMO system.


Polarons in crystalline perfluorotetradecanoic acid monohydrate

May 2013

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10 Reads

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1 Citation

The ac electrical conductivity and dielectric constant of perfluorotetradecanoic acid monohydrate (PFTDA) were investigated in the frequency range from 1 Hz to 1 MHz and the temperature range from 5 K to 300 K. At temperatures below 300 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR) typical of hopping or tunneling of localized charge carriers. The analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for small polarons revealed that below 300 K this mechanism governs the charge transport in PFTDA.


Polarons in Magnetoelectric Fluorides

January 2013

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18 Reads

Ferroelectrics

The complex dielectric constant/ac electrical conductivity was investigated as a function of the frequency and temperature in four fluorides systems, K3Fe5F15, K3Fe2Cr3F15, (NH4)2FeF6, and Pb5Cr3F19. All studied fluorides systems undergo ferroelectric (or antiferroelectric) phase transition at higher temperatures, and ferromagnetic (or antiferromagnetic) transition at low temperatures. At lower temperatures, in all studied systems, the real part of the complex ac electric conductivity was found to follow the universal dielectric response σ′ ∝ ν s, being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in all studied fluoride systems.


Polaronic behavior of MnO doped LiI-AgI-B2O3 glass

October 2012

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154 Reads

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23 Citations

The ac electrical conductivity and dielectric constant of LiI-AgI-B2O3 glass doped with 0.1 mol. % MnO were investigated in the frequency range from 1 Hz to 1 MHz and the temperature range from 5 K to 450 K. At temperatures below 450 K, an ac conductivity and dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, below 450 K, this mechanism governs the charge transport in this glass. The comparison of the values of characteristic coefficients W∞ and Eac determined by two different methods confirms the polaronic behavior of this system.


Polarons in boron doped iron phosphate glasses

October 2012

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39 Reads

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3 Citations

Journal of Non-Crystalline Solids

The electrical conductivity and dielectric properties of xB2O3–(40 − x)Fe2O3–60P2O5 (x = 6–20, mol%) glasses were investigated in the frequency range from 0.01 Hz to 1 MHz and the temperature range from 303 K to 523 K. At temperatures below 523 K an ac conductivity and the dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 523 K this mechanism governs the charge transport in these glasses. The comparison of the values of characteristic coefficients W∞ and α determined by two different methods confirms the polaronic behavior of boron doped iron phosphate glasses.


Polarons in low temperature phase of (NH4)3FeF6

November 2011

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55 Reads

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1 Citation

The frequency and temperature dependence of the dielectric constant and the ac electrical conductivity in (NH4)3FeF6 was investigated. The temperature dependence of the dielectric constant reveals the phase transition from tetragonal to cubic phase at 270 K. At temperatures below 225 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 225 K this mechanism governs the charge transport in this fluoride system.



Citations (71)


... This indicates that, at a set temperature, the crystal structure of bulk and thin-film PLZT with identical composition could differ. Even though several studies [10, 24,25] have concentrated on understanding the phase transitions of bulk PLZT ceramics in the range between −125 and 125°C, the ferroelectricparaelectric phase transition in PLZT ceramics in general is still not fully understood. As mentioned in Section 1, this phase transition might affect the temperature coefficient of the refractive index of ferroelectric materials in general [11][12][13]. ...

Reference:

Investigation of relaxor PLZT thin films as resonant optical waveguides and the temperature dependence of their refractive index
Relaxor freezing and electric-field–induced ferroelectric transition in a lanthanum lead zirconate titanate ceramics

... It was predicted that in the high temperature region such as 300-390 K, the experimental data can be fitted with r V while below the room temperature region by r T . This prediction was well verified in MoS 2 system [49] and TiO 2 system [50]. ...

Fluctuation-induced tunneling in TiO[sub 2]-derived nanotube pellets
  • Citing Article
  • April 2007

... Recently, many research groups have examined the temperature changes in the physical properties of BMO, which occur in the range of 'moderately high' temperatures (300 K < T < 600 K) [4][5][6][7][8]. The appropriate information is important for evaluating thermal stability of the physical properties of BMO and studying possible thermally induced effects in it. ...

Dielectric relaxation in pure and Co-doped Bi12GeO20 single crystals

... Now-a-days functional electroactive polymers/ copolymers are intensively investigated by many researchers for having potential applications in several fields such as pressure sensor, vibration measurement, ultrasonic imaging in medical instruments, and most importantly energy harvesting [1][2][3]. Ferroelectric polymers such as poly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-co-trifluoroethylene-chlorofluoroethylene)(P(VDF-TrFE-CFE)) have great potential for converting mechanical energy into electrical energy [4]. However, due to low coupling between electrical and mechanical properties it is highly desirable to substantially improve the dielectric response of such polymers [4,5]. ...

Relaxor Ferroelectric Polymers
  • Citing Article
  • September 2006

Ferroelectrics

... It has been shown [3] that a proton transfer between the O\ \H acid group and the short hydrogen bonded water molecules at 17°C, occurs at ms time-scale. The ac conductivity in the α-POX crystals as a function of the temperature and the applied frequency has also been investigated [4]. One of the conclusions of that work is that at temperatures below 200 K, proton polarons are involved in the conductivity. ...

Polaron conductivity mechanism in oxalic acid dihydrate: ac conductivity experiment
  • Citing Article
  • October 2006

Physical review. B, Condensed matter

... Understanding nonlinear effects allowed decisive breakthrough in condensed matter physics. Spin glasses[1, 2, 3, 4, 5, 6], ferroelectric, freezing, or dipolar glass transitions[7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19], isotropic-liquid crystal transition [20, 21] or binary mixtures [22, 23], superconductivity[24, 25, 26, 27, 28, 29], field[30, 31, 32, 33, 34] or heating[35, 36, 37, 38, 39, 40] effects in electrical transport, heating due to electric field excitation of supercooled liquids[41, 42] are a few among many topics where non linear measurements have proven to be a precious tool. ...

Glassy dynamics in an electron-irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer system
  • Citing Article
  • March 2003

Physical review. B, Condensed matter

... Within the intermediate range of ω, σ ac varied sub-linearly, following the relationship σ ac ∝ ω s , where s is the UDR exponent (always < 1). Figure 18 illustrates isotherms of log σ ac vs log ω drawn in the range of temperatures 20-140 °C for all three glasses. The value of s, deduced from the slopes of these plots, showed a decreasing tendency with temperature (inset of Fig. 18), indicating that the conduction is impacted by the tunnelling behaviour of polarons [47]. Comparison LGSCr glass and the minimum for LGSMo glass ( Table 3), implying that the free volume space available for charge carriers to diffuse is maximal in the LGSMo glass network [47]. ...

Polaronic behavior of MnO doped LiI-AgI-B2O3 glass

... We have detected additional relaxation at low temperatures below 30 K (Figure 3). Most probably, the origin of this relaxation in the nominally pure KTaO 3 crystal, [31] as proposed by Bidault et al. [37] and Levstik et al. [38] and observed by us, lies in the localization of polarons on defects. Figure 4 shows the temperature dependences of the of the linear, x 0 1 , (Figure 4(a)) and the nonlinear,x 0 2 , (Figure 4(b)), x 0 3 , (Figure 4(c)), electric susceptibility and the scaled non-linear susceptibility, a 3 , (Figure 4(d)), for the four frequencies of the ac probing electric field: 37, 111, 317 and 1000 Hz at ZFH after ZFC regime. ...

Frequency and temperature dependence of the electrical conductivity of KTaO3; Li and PbTiO3; La, Cu: Indication of a low temperature polaron mechanism
  • Citing Article
  • October 2008

Physica B Condensed Matter

... Impedance spectroscopy of the samples has been done in "Novocontrol Alpha High Resolution Dielectric Analyzer" device at the temperature ranges of 100 K-400 K and at the alternating current (AC ~ 1V). During the measurements, storage accuracy of temperature in any degree was 10 − 2 K and this accuracy was obtained by the bridge method [36,37]. ...

Contributions of distinctive dynamic processes to dielectric response of a relaxorlike reduced poly(vinylidene fluoride-trifluoroethylene) copolymer

Physical Review B

... Such behavior is in agreement with that predicted by the Correlated Barrier Hopping (CBH) model (Elliott, 1987). In other words, the hopping of charge carriers over the potential barrier may be considered as the conduction mechanism for the studied glasses (Ahlawat et al., 2016;Filipic et al., 2012;Pal et al., 2011). ...

Polarons in boron doped iron phosphate glasses

Journal of Non-Crystalline Solids