C. Filipic’s research while affiliated with Jožef Stefan Institute and other places

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Publications (140)


Figure 1. Typical relaxor-like diffuse frequency-dependent peaks of the real part of the dielectric permittivity ε in BZT40.
Figure 6. Temperature-frequency plots representing the temperature evolution of various segments of the distribution of the relaxation times, measured by the reduced dielectric permittivity  top to Figure 6. Temperature-frequency plots representing the temperature evolution of various segments of the distribution of the relaxation times, measured by the reduced dielectric permittivity δ top to bottom, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 0.95, 0.98. The temperature evolution of each relaxation spectrum segment denoted by δ was fitted to a VF ansatz (solid lines).
The fitting parameters for the fitting curves shown in the inset of Figure 4.
The fitting parameters for the relaxation spectrum cut-off frequencies f 1 and f 2 for BZT40 and BZT50 ceramics.
Glassy Properties of the Lead-Free Isovalent Relaxor BaZr0.4Ti0.6O3
  • Article
  • Full-text available

August 2023

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63 Reads

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1 Citation

Crystals

Cene Filipič

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Raša Pirc

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Glassy dielectric properties were investigated in lead-free BaZr0.4Ti0.6O3 (BZT40) ceramic samples using dielectric spectroscopy in the frequency range of 0.003 Hz–1 MHz and at temperatures of 10 K < T < 300 K. Measurements of the quasistatic dielectric polarization in bias electric fields up to ~28 kV/cm suggested that a ferroelectric state could not be induced, in contrast to the case of canonical relaxors such as PMN. The quasistatic dielectric and freezing dynamics results for the above field amplitudes showed that BZT40 effectively behaves as a dipolar glass. The relaxation spectrum was analyzed employing a frequency–temperature plot, which showed that the longest relaxation time obeyed the Vogel–Fulcher relation τ=τ0expE0/T−T0, with a freezing temperature of 76.7 K. The shortest relaxation time, in contrast, was characterized by a freezing temperature value close to 0 K, implying an Arrhenius-type behavior. The higher value of the polarization and the nonlinear third-order dielectric coefficient ε3 indicated a shift from a pseudospin glass behavior observed for BaZr0.5Ti0.5O3 (BZT50) toward a classical relaxor ferroelectric state.

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

August 2016

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18 Reads

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1 Citation

Japanese Journal of Applied Physics

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


BaZr 0.5 Ti 0.5 O 3 : Lead-free relaxor ferroelectric or dipolar glass

June 2016

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81 Reads

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32 Citations

C. Filipič

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[...]

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Glassy freezing dynamics was investigated in BaZr0.5Ti0.5O3 (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz–1 MHz at temperatures 10<T<300 K. From measurements of the quasistatic dielectric polarization in bias electric fields up to ∼28 kV/cm it has been found that a ferroelectric state cannot be induced, in contrast to the case of typical relaxors. This suggests that—at least for the above field amplitudes—BZT50 effectively behaves as a dipolar glass, which can be characterized by a negative value of the static third order nonlinear permittivity. The relaxation spectrum has been analyzed by means of the frequency-temperature plot, which shows that the longest relaxation time obeys the Vogel-Fulcher relation τ=τ0exp[E0/(T−T0)] with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is ∼0 K, implying an Arrhenius type behavior. By applying a standard expression for the static linear permittivity of dipolar glasses and/or relaxors the value of the Edwards-Anderson order parameter q(T) has been evaluated. It is further shown that q(T) can be described by the spherical random bond-random field model of relaxors.


A multicaloric material as a link between electrocaloric and magnetocaloric refrigeration

May 2016

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301 Reads

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33 Citations

The existence and feasibility of the multicaloric, polycrystalline material 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3, exhibiting magnetocaloric and electrocaloric properties, are demonstrated. Both the electrocaloric and magnetocaloric effects are observed over a broad temperature range below room temperature. The maximum magnetocaloric temperature change of ~0.26 K is obtained with a magnetic-field amplitude of 70 kOe at a temperature of 5 K, while the maximum electrocaloric temperature change of ~0.25 K is obtained with an electric-field amplitude of 60 kV/cm at a temperature of 180 K. The material allows a multicaloric cooling mode or a separate caloric-modes operation depending on the origin of the external field and the temperature at which the field is applied.



Dielectric relaxation in pure and Co-doped Bi12GeO20 single crystals

August 2015

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79 Reads

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3 Citations

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.


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.


Citations (68)


... 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]. ...

Reference:

Scaling description of non-ohmic direct current conduction in disordered systems
Fluctuation-induced tunneling in TiO[sub 2]-derived nanotube pellets
  • Citing Article
  • April 2007

... For instance, in the temperature range T ER-FE < T < T B , two anomalies have been observed: the first is the maxima at low-temperature T mLT = − 22.3 • C and the second occurred at high-temperature T mHT = 33.8 • C. It is worth noting that these two maxima have been observed in PMN annealed at T = 400 • C for 28 h with slow cooling to room temperature for 12 h [35]. Note also that these two anomalies have different positions and intensities, which depend on electric dipoles and other defective (random field source) features as well as single dipole dynamic parameters [36]. ...

BaZr 0.5 Ti 0.5 O 3 : Lead-free relaxor ferroelectric or dipolar glass
  • Citing Article
  • June 2016

... Beyond heat-pump cooling and heating applications, chip-scale cooling has been demonstrated [24], cooling of batteries, seats other parts of electric vehicles discussed in [25], and electrocaloric energy harvesting was demonstrated [26]. Electrocalorics might be combined with other field effects, such as in multicaloric materials [27]. ...

A multicaloric material as a link between electrocaloric and magnetocaloric refrigeration
  • Citing Article
  • May 2016

... The MOSFET's fast switching time of <10 ns allows monitoring of the switching processes inside the material in the form of a transient current flowing in and out of the sample. Similar approaches to investigating switching behaviour have been used in the past [19,[25][26][27][28]. By examining the discharge transient from HV to ground rather than the charge transient from ground to HV the frequency response of the high voltage source does not affect the transient behaviour of the sample. ...

Switching kinetics in thick film and bulk lead lanthanum zirconate titanate ceramics
  • Citing Article
  • May 1997

... 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

... 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

... 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